GDOT design policy manual : a Georgia Department of Transportation publication

TABLE OF CONTENTS

Chapter

Revision

1. INTRODUCTION................................................................................ 6/11/2010
1.1 Purpose 1.2 Organization 1.3 Contact 1.4 Manual Updates 1.5 Project Review and Submission Requirements 1.6 Acknowledgements
2. DESIGN POLICIES, GUIDELINES, AND STANDARDS............................. 6/11/2010
2.1 General Design Policy Information 2.2 Exceptions to Design Standards 2.3 Context Sensitive Design
3. DESIGN CONTROLS.......................................................................... 4/22/2011
3.1 Functional Classification 3.2 Design Vehicles 3.3 Design Speed 3.4 Highway Capacity 3.5 Establishment of Access Control 3.6 Frontage Roads and Access Roads 3.7 Fencing 3.8 Right-of-Way Controls 3.9 Value Engineering 3.10 Environmental
4. ELEMENTS OF DESIGN....................................................................... 9/3/2010
4.1 Sight Distance 4.2 Horizontal Alignment 4.3 Vertical Alignment 4.4 Combined Horizontal and Vertical Alignments 4.5 Superelevation
5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTIONS..........02/22/2011
5.1 General Considerations 5.2 Rural Shoulders Lateral Offset to Obstruction 5.3 Urban Shoulders Lateral Offset to Obstruction 5.4 Lateral Offsets for Signs 5.5 Lateral Offsets for Light Standards 5.6 Lateral Offsets for Utility Installations 5.7 Lateral Offsets for Signal Poles and Controller Cabinets 5.8 Lateral Offsets to Trees and Shrubs
6. CROSS SECTION ELEMENTS.............................................................07/22/2011
6.1 Lane Width 6.2 Pavement Type Selection 6.3 Cross Slope

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6.4 Pavement Crowns 6.5 Shoulders 6.6 Side Slopes 6.7 Border Area (urban shoulder) 6.8 Bike Lanes 6.9 Curbs 6.10 Sidewalks 6.11 Barriers 6.12 Medians 6.13 Parking Lanes 6.14 Summary of Design Criteria for Cross Section Elements
7. AT GRADE INTERSECTIONS............................................................... 6/11/2010
7.1 Intersection Design Elements 7.2 Intersection Geometrics 7.3 Median Openings 7.4 Driveways 7.5 Signalization 7.6 Highway-Railroad Grade Crossings
8. ROUNDABOUTS.................................................................................6/27/2011
8.1 Introduction 8.2 Roundabout Validation Process 8.3 Design Guidelines 8.4 References 8.5 Definition of Terms
9. BICYCLE AND PEDESTRIAN ACCOMMODATIONS............................... 3/1/2011
9.1 Overview 9.2 Typical Users & Needs 9.3 Bicycle Route Networks 9.4 Warrants for Accommodation 9.5 Facility Design 9.6 Work Zone Accessibility
10. ROADWAY USER COST UNDER DEVELOPMENT.................................. TBD
11. OTHER PROJECT TYPES.................................................................. 7/21/2011
11.1 Preventative Maintenance (PM), 3R, and Reconstruction Guidelines for Federal Aid Projects
11.2 Special Design Considerations for Other Project Types 11.3 Design Elements for Other Project Types
12. STAGE CONSTRUCTION UNDER DEVELOPMENT.................................. TBD
13. TRAFFIC FORECASTING AND ANALYSIS............................................. 5/21/2009
13.1 Traffic Forcasting Process 13.2 Freeway Traffic Analysis and Design 13.3 Arterial Traffic Analysis and Design 13.4 Trip Generation and Assignment for Traffic Impact Studies

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14. LIGHTING......................................................................................... 2/12/2009

14.1 General Considerations 14.2 Types of Lighting Projects 14.3 Illumination Requirements 14.4 Lighting Calculations 14.5 Design Considerations 14.6 Power Service

RESOURCES Glossaries References Implementation

5/21/2007 5/21/2007 5/21/2007

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1. INTRODUCTION
1.1. Purpose
The GDOT Design Policy Manual is the primary resource for design guidelines and standards adopted by the Georgia Department of Transportation (GDOT) for the preparation of roadway construction plans. This manual is intended to provide guidance to the designer involving "controlling criteria" and "non-controlling criteria" recommended and in some cases stipulated by the Georgia Department of Transportation (GDOT), the American Association of State Highway and Transportation Officials (AASHTO), the Federal Highway Administration (FHWA), and various national research organizations involving the design of roadways and related infrastructure. Designers are encouraged to select design criteria that provide a balance among the design vehicle, other users of the facility, and the context of the surrounding environment.
The GDOT Design Policy Manual was created by committee with representatives from GDOT, FHWA, and the consultant community in Georgia. This manual was written primarily for GDOT personnel, local governments, and consulting engineering firms that design roadway construction plans for Federal-Aid projects and State-Aid projects in accordance with the policies and objectives of Titles 23, 40, and 42 of the United States Code, and Title 32 of the Official Code of Georgia Annotated. Every effort has been made to make this manual as complete and error free as possible.
1.2. Organization
The Georgia Department of Transportation improves, constructs, and maintains the state's roads and bridges and provides planning and financial support for other modes of transportation such as mass transit and airports. GDOT also provides administrative support to the State Road and Tollway Authority (SRTA) and the Georgia Regional Transportation Authority (GRTA). GDOT is managed and operated by the Commissioner of the Georgia Department of Transportation with direct oversight by the State Transportation Board. GDOT's Mission statement is:
The Georgia Department of Transportation provides a safe, seamless and sustainable transportation system that supports Georgia's economy and is sensitive to its citizens and environment.
The Georgia Department of Transportation Organization Chart can be found at: http://www.dot.ga.gov/aboutGeorgiadot/Documents/OrgChart.pdf
The GDOT Division of Engineering has the primary role in the roadway design process. The mission of the Division of Engineering is to develop a quality set of right of way plans, construction plans, and bid documents, through a cooperative effort, that results in a project design and implementation that is the best transportation value for the taxpayers of Georgia.
Offices under the umbrella of the Division of Engineering are:
1. Office of Environmental Services 2. Office of Design Policy & Support
Design Policy/Standards/Hydraulic Engineering and ESPCP Tech Support Statewide Location Bureau Engineering Systems Support 3. Office of Roadway Design 4. Office of Bridge and Structural Design 5. Office of Right-of-Way

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1.3. Contact
The GDOT Design Policy Manual is maintained by the Office of Design Policy & Support. To submit questions or comments specific to the GDOT Design Policy Manual and its contents, please send an e-mail to: designmanual@dot.ga.gov
The current GDOT Design Policy Manual is published on the Department's Repository for Online Access to Documentation and Standards (R.O.A.D.S) homepage at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/Pages/default.aspx
1.4. Manual Updates
The GDOT Design Policy Manual will be periodically updated so that it appropriately reflects the Department's current design policies and practices. An entire chapter or any portion of one or more chapters of the manual may be re-written and replaced at any time. Revisions to this manual are summarized in the Table of Contents. The version and latest revision date are listed in the manual's Table of Contents, in the Table of Contents for each chapter, and at the bottom of each page of the manual. Implementation dates may be specified for certain revisions.
Subscribers to the R.O.A.D.S. homepage will receive e-mail notices of updates to the GDOT Design Policy Manual.
1.5. Project Review and Submission Requirements
Project review and submission requirements shall be in accordance with the latest edition of the GDOT Plan Development Process (PDP). The current PDP is published online at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/Pages/default.aspx
The GDOT PDP sets forth the current procedures and steps necessary for GDOT to administer Federal-Aid projects in accordance with the policies and objectives of Titles 23, 40, and 42 United States Code, and to administer State-Aid projects to fulfill the policies and objectives of Title 32, Official Code of Georgia Annotated. The GDOT PDP outlines the current process of project development from project identification through construction award.
All design criteria and design decisions should be documented in a Project Design Data Book, which is to be included with the project files. Procedures and criteria for the Project Design Data Book are provided in the GDOT PDP Chapter 6, Preliminary Design.
1.6. Acknowledgements
The Georgia Department of Transportation Division of Engineering wishes to acknowledge the following for their contribution to the development of the GDOT Design Policy Manual:
GDOT - Brent Story, Eugene Hopkins, Brad Ehrman, Kim Fulbright, Ben Buchan, Darrell Richardson, Darryl Van Meter, Chuck Hasty, Babs Abubakari, Keith Golden, Kathy Bailey, Abby Ebodaghe, Gary Langford, Joel North, Joe Wheeler, Ron Wishon, Del Clippard
FHWA - David Painter and the Georgia Division of FHWA Consultants - Stan Hicks, Bill Pate, Jody Braswell, Jill Hodges, Joe Macrina, Tim Heilmeier, Taylor
Stukes, Julie Doyle, Jeff Dyer, Michael Holt, Mike Reynolds, Harris Robinson, Vern Wilburn

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Chapter 2 Contents

2. Design Policies, Guidelines, and Standards

1

2.1. General Design Policy Information

1

2.1.1. Sources of Design Policy and Practice

2

2.2. Exceptions to Design Standards

4

2.2.1. Design Exception

4

2.2.2. Design Variance

4

2.3. Context Sensitive Design

5

Chapter 2 Index

6

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2. DESIGN POLICIES, GUIDELINES, AND STANDARDS

2.1. General Design Policy Information
Design policy is defined as the basic principles and goals established by GDOT to guide (guidelines) and control (standards) the design of roadways and related infrastructure in Georgia. The intent of design policy is to provide recommended and stipulated values for critical dimensions. Flexibility is permitted to encourage independent design tailored to individual situations. When flexibility is applied to a proposed design, and critical dimensions do not meet GDOT design policy, additional documentation is required to record the decision-making-process.

Criteria within this manual denoted as "standard" or as "controlling criteria" have been identified as a required or mandatory practice with deviation from the controls requiring prior agency approval. All other criteria within this manual are considered to be "non-controlling criteria" and are denoted as "guidelines" intended as recommended practice with deviation allowed if engineering judgment or study indicate the deviation to be appropriate. Designers are encouraged to select design criteria that provide a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment.

Unless stated otherwise, the policies in this manual apply to permanent construction of roadways and related infrastructure. Different criteria may be applicable to temporary facilities. Guidance specific to non-interstate roadway resurfacing, restoration, or rehabilitation (3R) projects is provided in Chapter 11 of this Manual.

The following definitions offer guidance for interpreting policy statements found in this manual:

Standard a required criteria or mandatory practice. Criteria denoted as standard have been identified by the Department as having substantial importance to the operational and safety performance of a roadway such that special agency review and approval (Design Variance or Design Exception) will be required before deviation from the controls can be incorporated into a design. All controlling criteria are denoted as standard. In some cases, GDOT has denoted specific non-controlling criteria as standard.

Controlling Criteria: The FHWA has specifically identified "13 controlling criteria" (listed below) as having substantial importance to the operational and safety performance of a roadway such that special agency attention should be given to the criteria in the design decision making process.

1. Design speed 2. Lane width 3. Shoulder width 4. Bridge width 5. Horizontal alignment 6. Superelevation 7. Vertical alignment

8. Grades 9. Stopping sight distance 10. Cross slope 11. Vertical clearance 12. Lateral offset to obstruction 13. Structural capacity

The conditions of the "13 controlling criteria" are defined by AASHTO and are adopted and

denoted as standard criteria by GDOT. In some cases, GDOT provides more specific and

selective guidelines relating to controlling criteria; however, at a minimum, the conditions defined

by AASHTO control. A decision to use a design value that does not meet the minimum

controlling criteria defined by AASHTO will require the prior approval of a Design Exception from the GDOT Chief Engineer.

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Shall: The use of the word "shall" denotes a required or mandatory condition, and the designer must make every effort to follow the appropriate design criteria or condition.

Guideline recommended practice in typical situations. Deviations from criteria denoted as guidelines are allowed when engineering judgment or study indicates the deviation to be appropriate. Adequate study, justification, and documentation by the GDOT office or consultant responsible for the engineering is required. Decisions to deviate from guidelines are subject to review and scrutiny by GDOT at any time.
Should: The use of the word "should" indicates an advisory condition. Under this condition, it is recommended, although not mandatory, that the designer follow the appropriate design criteria.
May: The use of the word "may" indicates a permissive condition. Under this condition, the designer is encouraged to use sound engineering judgment.
Practical: The use of the word "practical" is intended to indicate that a design decision is effective and applicable with consideration to economic resources; appropriate, adaptable, and balanced.
Where practical: The use of the term "where practical" is intended to indicate that agencies may consider economic resource constraints when making a decision.

2.1.1. Sources of Design Policy and Practice GDOT adopts the AASHTO Green Book, "A Policy on Geometric Design of Highways and Streets," and the AASHTO "A Policy on Design Standards for the Interstate System" as the standard for controlling criteria required and mandatory on State Routes and routes on the National Highway System (NHS) in Georgia.

For additional guidance on the design of roadways and related infrastructure, refer to the most current edition of the following publications, unless a specific version is noted. These publications, including the website addresses (url) for resources available online, are cited in the References section of this Manual:

American Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) A Policy on Design Standards---Interstate System Guide for the Development of Bicycle Facilities Guide for High-Occupancy Vehicle (HOV) Facilities Guide for Park-and-Ride Facilities Guide Specifications for Horizontally Curved Steel Girder Highway Bridges Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400) Highway-Rail Crossing Elimination and Consolidation Roadside Design Guide Roadway Lighting Design Guide Standard Specifications for Highway Bridges

American Railway Engineering and Maintenance of Way Association (AREMA) Manual for Railway Engineering

Federal Highway Administration (FHWA) Americans with Disabilities Act (ADA) and Transportation Enhancements (TE)

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Flexibility in Highway Design Guidance on Traffic Control Devices at Highway-Rail Grade Crossings Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure Manual on Uniform Traffic Control Devices (MUTCD) Roundabouts: An Informational Guide FHWA-RD-00-67 Value Engineering and The Federal Highway Administration (Website) Roadway Lighting Handbook Mitigation Strategies for Design Exceptions
Georgia Department of Transportation (GDOT) Bridge and Structures Policy Manual Environmental Procedures Manual Manual on Drainage Design for Highways Construction Standards and Details Context Sensitive Design Online Manual Pavement Design Manual Pedestrian and Streetscape Guide Plan Development Process (PDP) Plan Presentation Guide Regulations for Driveway and Encroachment Control Standard Specification Book Traffic Analysis and Design Manual Traffic Signal Design Guidelines Utility Accommodation Policy and Standards Manual
Georgia Soil and Water Conservation Commission (GSWCC) Manual for Erosion and Sediment Control in Georgia

Illuminating Engineering Society of North America (IESNA) Guideline for Security Lighting for People, Property and Public Spaces Lighting Handbook, 9th Edition Lighting For Parking Facilities Recommended Lighting for Walkways Recommended Lighting for Walkways and Class 1 Bikeways Roadway Lighting ANSI Approved Roadway Sign Lighting Tunnel Lighting Roundabout Lighting

Institute of Transportation Engineers (ITE)

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Manual of Uniform Transportation Engineering Studies Trip Generation Handbook
National Cooperative Highway Research Program (NCHRP) Modern Roundabout Practices [Synthesis 264] Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504] Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457] Impacts of Access Management Techniques [NCHRP Project 3-52] Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report
350]
National Fire Protection Association (NFPA) National Electrical Code [NFPA-70]
Texas Transportation Institute (TTI) Grade Separations - When Do We Separate? Highway-Rail Crossing Conference
Transportation Research Board (TRB) Highway Capacity Manual
2.2. Exceptions to Design Standards
2.2.1. Design Exception If a design feature of a new construction or reconstruction project does not meet the minimum conditions of one of the "13 controlling criteria" defined in the current edition of the AASHTO Green Book and the AASHTO publication, A Policy on Design Standards - Interstate System, then approval to build or retain the feature is required by formal Design Exception. For projects identified as "Full Oversight" such as interstate projects, the FHWA is the agency that grants Design Exceptions. For all other projects, both federally and state funded, the GDOT Chief Engineer grants Design Exceptions.
The requirement of a Design Exception is not meant to impede design flexibility, but to document a very important design decision that is well scrutinized by the Department in a deliberative and thorough manner. To obtain a Design Exception, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP), and in the FHWA publication, Mitigation Strategies for Design Exceptions.

2.2.2. Design Variance
Whenever a "non-controlling" criteria has been denoted by GDOT as a standard, then the approval of a Design Variance must be obtained by the GDOT Chief Engineer before deviation outside the controls can be incorporated into the design.

The requirement of a Design Variance is not meant to impede design flexibility, but to document a very important design decision that is well scrutinized by the Department in a deliberative and thorough manner. To obtain a Design Variance, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP).

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2.3. Context Sensitive Design
Context Sensitive Design (CSD) is a process for achieving design excellence by developing transportation solutions that require continuous, collaborative communication and consensus among transportation agencies, professionals, and stakeholders. A common goal of CSD projects is to develop a facility that is harmonious with the community, and preserves aesthetics, history and the environmental resources, while integrating these innovative approaches with traditional transportation goals for safety and performance.
Refer to the GDOT Context Sensitive Design Online Manual for additional information on communication strategies, design flexibility, environmental sensitivity, and stakeholder involvement for developing successful context-sensitive solutions.

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Chapter 3 Contents

3. Design Controls

3.1. Functional Classification

3.2. Design Vehicles 3.2.1. Design Vehicle Types 3.2.2. Local Input for Selecting a Design Vehicle
3.3. Design Speed

3.3.1. 3.3.2. 3.3.3. 3.3.4.

General Considerations Intersections Approaching a Stopped Condition Freeway Exit and Entrance Ramps Urban Subdivision Streets

3.4. Highway Capacity

3.5. Establishment of Access Control 3.5.1. Definitions 3.5.2. Access Management
3.6. Frontage Roads and Access Roads

3.7. Fencing

3.7.1 Fencing on State Right-of-Way 3.7.2 Fencing on Private Property

3.8. Right-of-Way Controls

3.8.1. 3.8.2. 3.8.3. 3.8.4.

Rural Areas Urban Areas Special Types of Right-of-Way Accommodating Utilities

3.9. Value Engineering

3.10. Environmental

Chapter 3 Index List of Figures

Figure 3.1 Limit of Access Control Interstate/Freeway Interchange

List of Tables Table 3.1 Minimum Design Vehicles

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1 1 5 5 6 7 7 7 7 8 8 8 8 9 11 12 12 13 14 14 15 15 15 16 16 18
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3. DESIGN CONTROLS
This chapter provides information with regard to design controls. Many factors contribute to the roadway design criteria used by designers. These factors are based upon the physical characteristics of the vehicles (vehicle types), the topography in which the road is set, operational safety and speed of traffic on the road, and even driver behavior (speed, turns, following distance, clear zones for emergencies). All of these factors are important and should be balanced when selecting the appropriate design criteria for a particular road or highway design. This chapter addresses:
functional classification; design vehicles; design speed; highway capacity and level of service; access control; frontage and access roads; fencing; right-of-way controls; value engineering; and environmental considerations.
3.1. Functional Classification
Design standards have been developed by the American Association of State Highway and Transportation Officials (AASHTO) for different functional systems of roadways. In order to qualify for federal funding, the Federal Highway Administration (FHWA) requires that each state categorize state routes by functional classification. Detailed discussions on the concept of functional classification and the characteristics of the various functional systems can be found in the AASHTO Green Book1 and FHWA Functional Classification Guidelines2,3. Additional information specific to GDOT policies related to functional classification of roadways is also available in the GDOT Plan Development Process (PDP).
Roadway functional classification serves as the foundation of an access management program. Functional classification systems establish the planned function of different types of roadways and the priority placed on access as opposed to through traffic movement. Functional classification recognizes that design considerations vary for different classes of roads in accordance with the intended use.

1 AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book).
2 FHWA. FHWA Functional Classification Guidelines. 1989 Note: The 1989 version of this publication is available online at http://www.fhwa.dot.gov/planning/fctoc.htm
3 FHWA, FHWA 2008 Updated Guidance for the Functional Classification of Highways, Memorandum from Mary B. Phillips, Associate Administrator for Policy and Governmental Affairs dated October 14, 2008.

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Streets and highways are grouped into major classes based on the type or kind of service they provide. The functional classification process is based on the fact that roads are part of a travel network and that "individual roads and streets do not serve travel independently in any major way" (Functional Classification Guidelines, 1989).
The three major functional systems are:
Freeways; Arterials; and collectors and local streets.
Freeway Classification Freeways can be distinguished from all other roadway systems in that they provide uninterrupted flow. There are no fixed interruptions on freeways. The traffic flow conditions along uninterruptedflow facilities result primarily from the interactions among vehicles in the traffic stream and between vehicles and the geometric and environmental components of the roadway.
Access to the freeway facility is controlled and limited to ramp locations, whereas access to an interrupted flow facility uses at-grade intersections. Categorization of uninterrupted and interrupted flow relates to the type of facility as opposed to the quality of the traffic flow at any given time. A freeway experiencing extreme congestion differs greatly from a non-freeway facility experiencing extreme congestion, in that the conditions creating the congestion are commonly internal to the facility, not external to the facility.
Freeway facilities may have interactions with other freeway facilities as well as other classes of roads in the vicinity. The performance of a freeway may be affected when demand exceeds capacity on these nearby road systems. For example, if the street system cannot accommodate the demand exiting the freeway, over-saturation of the street system may result in queues backing onto the freeway, which adversely affects freeway performance.
Traffic analysts and designers must also recognize that freeway systems have several interacting components, including ramps, and weaving sections. To achieve an effective overall design, the performance of each component must be evaluated separately and the interactions between components must also be considered. For example, the presence of ramp metering affects freeway demand and must be taken into consideration when analyzing a freeway facility.
Arterial Classification Arterials are a functional classification of roadway transportation facilities that are intended to provide for through trips that are generally longer than trips on collector facilities and local streets. While the need to provide access to abutting land is not the primary function, the design of arterials must also balance this important need. To further highlight the often competing demands of urban arterials, other modes of travel such as pedestrians and public transit are also present and must be accommodated.
To assure that an arterial can safely provide an acceptable level of service (LOS) for the design conditions, a number of design elements must be addressed. Since each design element is essentially determined based on separate analyses, the designer should evaluate the entire arterial system and be prepared to refine certain elements to obtain an effective and efficient overall design.

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Arterial systems are often further sub-classified into Principal or Minor arterial functional systems based on the trips served, the areas served, and the operational characteristics of the streets or highways. "Since urban and rural areas have fundamental different characteristics with regards to the density of land use, nature of travel patterns and the number of streets and highway network and the way in which these elements are related, urban and rural functional systems are classified separately as urban principal and minor arterials and rural principal and minor arterials" (FHWA. 1989). These functional systems are therefore discussed individually under the Urban Arterial Classification and Rural Arterial Classification sections below.

Urban Arterial Classification
The AASHTO Green Book defines urban areas as those places within the boundaries set by the responsible State and local officials having a population of 5,000 or more. Urban areas are further subdivided into urbanized areas (population of 50,000 and over) and small urban areas (population between 5000 and 50,000) (AASHTO). For design purposes, the designer should use the population forecast for the design year.

There are four functional systems for urban areas:

Urban Principal Arterials - almost all fully and partially controlled access facilities in urban areas are considered urban principal arterials; however, this system is not restricted to controlled access routes. FHWA further stratifies the principal arterial system as: interstate, other freeways and expressways, and other principal arterials with no control of access (Functional Classification Guidelines, 1989).

Urban Minor Arterials - includes all arterials not classified as a principal. This functional system includes facilities that:
o place greater emphasis on land access than principal arterials and offer a lower level of traffic mobility;

o interconnect with, and augment, the urban principal arterial system;

o provide service to trips of moderate length at a somewhat lower level of travel mobility than principal arterials;

o distribute travel to smaller areas than those of urban principal arterials; and

o may carry local bus routes and provide intra-community continuity, but ideally should

not penetrate identifiable neighborhoods. Note: this system should also include

urban connections to rural collector roads where such connections have not been

classified as urban principal arterials.

(AASHTO Green Book)

Collector Streets Some characteristics of collector streets are that they:
o provide access and traffic circulation within residential neighborhoods, commercial, and industrial areas;

o may penetrate residential neighborhoods, distributing trips from the arterials to destinations; and

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o collect traffic from local streets in residential neighborhoods and channel traffic to

the arterial system.

(AASHTO Green Book)

Local Streets - Some characteristics of local streets are that:
o local streets provide direct access to abutting land and access to higher systems; and

o local street systems offer the lowest level of mobility and usually contain no bus

routes. Service to through traffic movement in this system is usually deliberately

discouraged.

(AASHTO Green Book)

Rural Arterial Classification
The functional systems for urban arterials and rural arterials differ due to factors such as intensity and type of development that occurs on these systems.

Rural Principal Arterials almost all fully and partially controlled access facilities in rural areas are considered rural principal arterials; however, this system is not restricted to controlled access routes. Service characteristics of rural principal arterials include:
o traffic movements with trip length and density suitable for substantial statewide travel or interstate travel;
o traffic movements between urban areas with populations greater than 25,000;
o traffic movements at high speeds;
o divided four-lane roads; and
o desired LOS B.

Rural Minor Arterials have the following service characteristics:

o traffic movements with trip length and density suitable for integrated interstate or inter-county service;

o traffic movements between urban areas or other traffic generators with populations less than 25,000;

o traffic movements at high speeds;
o undivided lane roads;
o striped for one or two lanes in each direction with auxiliary lanes at intersections as required by traffic volumes; and

o desired LOS B.

( AASHTO Green Book)

Refer to the AASHTO Green Book, Chapter 1. Highway Functions, for additional information regarding functional classification.

Mapping of roadway functional classifications for all urban and non-urban areas in Georgia is maintained by the GDOT Office of Transportation Data. Functional Classification Maps for Georgia State roadways may be downloaded from GDOT's website at: http://www.dot.ga.gov/maps/Pages/HighwaySystem.aspx.

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3.2. Design Vehicles
In the design of any roadway facility, the designer should consider the largest design vehicle that is likely to use that facility with considerable frequency or a design vehicle with special characteristics appropriate to a particular location in selecting design vehicles.

3.2.1. Design Vehicle Types

The four general classes of design vehicles as defined by AASHTO are:
Passenger Cars - Passenger automobiles of all sizes, including cars, sport/utility vehicles, minivans, vans, and pick-up trucks;
Buses - Intercity (motor coaches), city transit, school, and articulated buses;
Trucks - Single-unit trucks, truck tractor-semi-trailer combinations, and truck tractors with semi-trailers in combination with full trailers; and
Recreational Vehicles - Motor homes (including those with boat trailers and pulling an automobile), automobiles pulling a camper trailer or a boat trailer.

Table 3.1 Minimum Design Vehicles

Roadway Type
Rural

Minimum Design Vehicle

Typical Design Speed
(mph)

Interstate / Freeway Ramp
Free-Flow Entrance / Exit Loop Primary Arterial Minor Arterial Collector Local Road

WB-67

70

WB-67 WB-67 WB-67 WB-40 or WB-62
SU SU

35 (minimum)(2) 35 (minimum)(2) 35 (minimum)(2)
65 65 55

Paved

S-BUS36

45

Gravel Urban

S-BUS36

35

Refer to the current AASHTO Green Book Chapter 2, Design Controls and Criteria, for further discussion on use of design vehicles and for detailed dimensions of design vehicles.
Table 3.1. lists minimum vehicles which should be considered when selecting an appropriate design vehicle. Design vehicle dimensions are defined in the AASHTO Green Book (2004), Exhibit 2-1. Design Vehicle Dimensions.

Interstate / Freeway Ramp Terminal Ramp
Free-Flow Entrance / Exit Loop Primary Arterial Minor Arterial Collector Residential/Local Road

WB-50

65

WB-67 WB-67 WB-40 or WB-62 WB-40 or WB-62 WB-40 or BUS-40 BUS-40 or SU

35 (minimum)(1) 35 (minimum)(1) 35 (minimum)(1)
55 45 35

SU or P

35

Turning Radii
The minimum turning path of the selected design vehicle is the primary factor in

(1) Refer to Section 3.3.3 Freeway Ramps.
Design Vehicle Type Symbols: BUS=Intercity Bus/Motor Coach, P=Passenger Car, S-BUS=School Bus, SU=Single-Unit Truck, WB=Semi Trailer

designing radii at intersections, radii of

turning roadways, median opening geometry and commercial driveways. The turning radii can

affect the cross-section width of a roadway. In other words, the larger the required turning radii to

accommodate larger design vehicles, the wider the roadway cross-section needs to be. For

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example, a semi-trailer truck would need a much larger turning radii at a median opening to properly access a business or commercial distribution center than a passenger car or van.
Design tools that can be used to determine the turning path for a given design vehicle include:
Published templates which show the wheel paths of a design vehicle, such as the AASHTO Green Book, Exhibits 2-3 through 2-23, which presents the minimum turning path for 19 typical design vehicles; and
Vehicle turn simulation software, such as AutoTURN3, which works within both MicroStation and AutoCAD.
The need to provide turning radii for larger vehicles may sometimes conflict with the need to accommodate pedestrians. The design of an intersection should not prohibit safe pedestrian movements through the intersection. Refer to the GDOT Pedestrian and Streetscape Guide4 for information specific to accommodating pedestrians. Further discussion of GDOT policies relating to intersection design can be found in this Manual in Chapter 7, At-Grade Intersections and Chapter 8, Roundabouts.
3.2.2. Local Input for Selecting a Design Vehicle
The designer should be aware of all potential types of vehicles that will use each part of the facility and larger vehicles should be accommodated, where practical. Input from local personnel should be considered by the designer when determining the proper design vehicle for each local road that intersects the project. Local personnel may include the GDOT Area Engineer, Maintenance Engineer, District Access Engineer, or local government personnel. This determination should be completed during the conceptual design phase.
Scenarios where solicitation of local government input is recommended include: areas where bicycle use is allowed on a roadway - in which case the bicycle should be
considered a design vehicle;
roadways leading to recreational areas like state parks, campgrounds, and marinas - in which case recreational vehicles, such as motor homes or pick-up trucks with boat trailers, may be the appropriate design vehicle;
some areas near timber processing facilities - in which case, "long log" trucks (trucks with logs overhanging the trailer by as much as 12-ft.) may be prevalent, as intersections in these areas may require a design that prevents overhanging logs from striking vehicles in other lanes during turning movements. This can usually be accomplished by physically separating the turning lane from adjacent through lanes; and
school bus routes.

3 AutoTURN is developed by Transoft Solutions. Additional information about this software application is available online at: http://www.transoftsolutions.com/ProductTmpl.aspx
4 GDOT/Otak. Pedestrian and Streetscape Guide. 2003 The 2003 version of this publication is available online at: http://www.dot.ga.gov/travelingingeorgia/bikepedestrian/Pages/PlanningandDesignResources.aspx

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3.3. Design Speed

3.3.1. General Considerations
"Design Speed" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for design speed options for roadway classifications in Georgia. The designer is encouraged to select a design speed that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a design speed value that does not meet the controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.

Design speed is different from other controlling criteria in that it is a design control, rather than a specific design element. In other words, the selected design speed is used to establish a range of design values for many of the geometric elements of a roadway. The selected design speed should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use and functional classification of the roadway. Design speed should be consistent with the speeds at which 85 percent of drivers are traveling (referred to as the 85th percentile) and likely to expect on the facility.

In recognition of the wide range of site-specific conditions, constraints, and contexts for roadways AASHTO defines a range of values for design speed. A design speed that is as high as practical that will provide safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and other social or political effects should be selected. Table 3.1. lists typical design speeds which should be considered when selecting an appropriate design speed.

On county roads or city streets, GDOT recommends coordination with the local jurisdictional authority to identify posted speeds on existing roadways and for the selection of the posted speed limit and the design speed for new or reconstructed roadways.

3.3.2. Intersections Approaching a Stopped Condition
To improve the angle of intersection between a local street and major road, a designer may use a lower design speed on the local street for curves approaching an intersection if it is not anticipated that the T-intersection will become a full intersection.

The design speed of the last curve prior to the intersection may be 10 mph less than the design speed of the local street.

3.3.3. Freeway Exit and Entrance Ramps
Typical freeway exit and entrance ramps may have varying design speeds which are based on the operating speed of the vehicle as it decelerates or accelerates on the ramp. A common rule to apply for ramps is that the design speed of the first curve of an exit ramp can be assumed to be 10 mph less than the design speed of the mainline. With each successive curve on the exit ramp, the design speed of the curve can be reduced based on computed vehicle deceleration. The reverse condition applies to the design speed for all entrance ramps.

The design speed for a direct system to system ramp that connects two freeway facilities should be no less than 10 mph below the design speed of the exiting facility.

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On loop ramps, adequate deceleration length should be provided prior to the loop part of the ramp. All areas of deceleration should be separated from the mainline lanes. System to system loop ramps will be evaluated on a case-by-case basis.
3.3.4. Urban Subdivision Streets
In most cases, the design speed for urban subdivision streets should be a minimum of 25 mph.
3.4. Highway Capacity
All portions of roadways that are part of major construction or reconstruction should be designed to accommodate, at a minimum, 20-year forecasted traffic volumes. The design year for the 20-year traffic volumes should be forecasted from the estimated base (or opening) year, which is the year the project is anticipated to be open for traffic use. Refer to Chapter 13, Traffic Forecasting and Analysis Concepts, of this Manual for further discussion on the traffic engineering and analysis.
If a project is not new roadway construction or reconstruction, refer to Chapter 11, Other Project Types for guidance relating to other project types.
3.5. Establishment of Access Control
3.5.1. Definitions
GDOT has adopted the following "Access Control" criteria as standard, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to design decisions. The designer is encouraged to select design elements and features that are consistent with the access control plan established for a roadway. A decision to use a design element or feature that does not meet the standard access control criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Department's Chief Engineer.
Roadways serving higher volumes of regional through traffic require greater access control to preserve their traffic function. Frequent and direct property access is more compatible with the function of local and collector roadways. The regulation of access to a roadway is referred to as "access control". It is achieved through the regulation of public access rights to and from properties abutting the roadway facilities. The Official Code of Georgia Annotated (OCGA)5 32-6-111 to 114 give GDOT this authority.
The regulation of public access rights is generally categorized as either full control of access, partial control of access, or control of access by permit (or permitted access).
Full control of access means that preference is given to through traffic by providing access connections by means of ramps with only selected public roads and by prohibiting crossings at grade and direct driveway connections.
Partial control of access means that some preference should be given to through traffic. Access connections, which may be at-grade or grade-separated, are provided with selected public roads

5 Online public access to the Official Code of Georgia Annotated (OCGA) is provided at: http://w3.lexis-nexis.com/hottopics/gacode/Default.asp?loggedIn=done

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and private driveways. In areas with partial control of access, the decision to grant access to private driveways is made at the time of project development, and thereafter, private driveway access should not be added.
Permitted access means that a permit is needed for access. A permit is required prior to performing any construction work or non-routine maintenance within the State highway right-of-way. This includes but is not limited to the following activities: grading, landscaping, drainage work, temporary access to undeveloped land for logging operations, or construction of a development. Any new driveway or revisions to any portion of existing driveways, i.e. widening and/or relocation that are within the State roadway right-of-way shall also require a permit.
3.5.2. Access Management
The following standards shall be used to establish access control:
Full control of access Full control of access shall be established on all Interstates. Full control of access shall be established on principal arterials constructed on new location with grade separated interchanges.
For projects that involve an Interstate interchange, (new construction or reconstruction), access control should be established along the intersecting route for a distance of 600-ft. in urban areas and 1,000-ft. in rural areas, where practical. At a minimum, access control shall not be less than 300-ft. This distance is measured from the radius return of the ramp termini with the intersecting route. (See Figure 3.1, Limit of Access Control Interstate/Freeway Interchange).
Where improved traffic operations and safety warrant, existing driveways may be closed and no access allowed to developed or undeveloped property. Decisions on elimination of access points should be based in part on an economic study of alternate courses of action.
Partial control of access
Partial control of access shall be established on principal and minor arterials that are constructed on a new location with intersections at-grade. Access control should not be established on portions of projects on new location which are less than one mile in length, unless the project connects to a section of roadway were access control has been or will be established or where required to preserve the functional area of an intersection as described below.
Partial control of access should be established on existing principal arterials that are being widened, when it is determined that partial access control is advisable. On this type of project, every attempt shall be made to consolidate existing access to the roadway by developing a supporting roadway network. All undeveloped property frontage should be treated in the same manner as new location construction.
Breaks in access will only be granted for the following conditions:
State or local government public road intersections

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Figure 3.1 Limit of Access Control Interstate/Freeway Interchange

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Where property that is not accessible from existing roadways or has been bisected by the new roadway alignment and no other access is provided and the appraised damages to the remaining property exceeds $50,000 in a rural area or $100,000 in an urban area. Coordination with the District right-of-way office should be performed prior to making a request for a break in access control. All breaks in access control under these conditions must be approved by the Chief Engineer.
Permitted access
On principal and minor arterials and major collector roadways that are being reconstructed, access rights should be acquired so that driveway connections are not allowed within the functional area of any intersection. The functional area of an intersection is the area where motorists are responding to the intersection, decelerating, and maneuvering into the appropriate lane to stop or complete a turn. Access connections too close to intersections can cause serious traffic conflicts that impair the function of the affected facility.
Upstream functional distance is defined as the distance traveled during perception-reaction time, plus the deceleration distance while the driver maneuvers to a stop, plus the queue storage. Downstream functional distance is defined as the stopping sight distance.
Temporary State Routes
For routes that are temporarily placed on the state route system during project development, close coordination to determine the appropriate access control should occur between the Department and the local government responsible for enforcing the access control after the oversight reverts back to the local government. "Permitted Access" should be considered when there is a strong likelihood that access breaks will be requested by potential development along the route. "Full Control of Access" or "Partial Control of Access" should be considered when the project connects to a section of roadway where similar access control has been or will be established, and to preserve the functional classification of the route or corridor. Before Right of Way acquisition begins, it is recommended that the Department receive written confirmation from the local government to enforce the established access control after the oversight reverts back to the local government.
3.6. Frontage Roads and Access Roads
AASHTO defines a frontage road as "a road that segregates local traffic from higher speed throughtraffic and intercepts driveways of residences, commercial establishments, and other individual properties along the highway" (AASHTO Green Book). Frontage roads can serve many functions depending on the type of arterial they serve and the character of the surrounding area. They are commonly used to control access to the arterial, to provide access to adjoining properties, and to maintain traffic circulation on each side of the arterial.
Most existing frontage roads were built along interstate or major arterial routes to control access to these routes and provide access to property that would otherwise be land-locked. Access roads may also be used to provide access to landlocked parcels.
Frontage roads typically run parallel to the mainline route while access roads provide access to individual properties and may not run parallel to the mainline. Access roads and frontage roads should be offset from the mainline route to allow required clear zone and future roadway widening, if anticipated.

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3.7. Fencing
The Georgia Department of Transportation has established the following guidelines for installing fence on state right-of-way and/or private property associated with the design of roadway projects. These guidelines are based on the principles published in the AASHTO An Informational Guide on Fencing Controlled Access Highways (1990).

3.7.1 Fencing on State Right-of-Way
Fencing is provided within the state right-of-way to delineate the boundary of the acquired access control, and as a physical obstacle to deter encroachment onto the roadway right-of-way from children, pedestrians, bicyclist, vehicles, machinery, and animals. Fencing may also be provided to deter access into or across specific features within the right-of-way such as drainage structures, bridges and retaining walls. The following guidelines are provided for the consistent application of fencing on state right-of-way.
Roadways with Full Control of Access are expected to provide a higher level of mobility and operate at higher speeds with protection from all forms of roadside interference. Therefore, fencing should be installed within the state right-of-way on roadways with Full Control of Access, where it is practical to do so. Fencing may not be practical or necessary in areas with steep slopes or natural barriers.
Fencing may be installed within the state right-of-way on roadways with Partial Control of Access or any portion of a state route with an acquired limit-of-access if the Department determines it necessary to deter potential or chronic encroachment.
For roadways with Full Control of Access and parallel frontage roads included within the state right-of-way, fencing should be installed between the mainline traveled-way and the frontage road. In these cases, it may not be necessary to install a duplicate fence along the right-of-way line.
Fence installed within the state right-of-way to delineate the limit-of-access should be offset a minimum of 1-ft inside the right-of-way line to ensure there is adequate space for installation and maintenance.
For non-access grade separations, fence installed along the limit-of-access will be terminated at the points where the state right-of-way intersects the normal right-of-way of the crossing grade separation.
For grade separated interchanges, fence installed along an entrance or exit ramp terminal with a cross road should terminate at the point where the state right-of-way intersects the normal right-of-way along the cross road. Fencing may be extended along the right-of-way of the cross road for the entire length of acquired access control if the Department determines it necessary to deter potential or chronic encroachment (see Figure 3.1, Limit of Access Control Interstate/Freeway Interchange.
Fence installations within the state right-of-way are not intended to control livestock from adjacent private property and should not be installed or permitted for this reason. Where fencing is required to contain livestock within adjacent private property, an independent fence on private property will be required for that purpose (see 3.7.2. Fencing on Private Property).
The installation of 6-ft height Chain Link Wire Fence should be considered on a case-bycase-basis around the perimeter of proposed permanent drainage features that will contain

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water over 24-inches deep for an extended period of time (greater than 48 hours). For example, natural ponds, detention ponds and water quality ponds within the state right-ofway. The fence should be installed with adequate space for routine maintenance and equipped with self-closing and self latching gates.
A fence or handrail should be considered on a case-by-case-basis along the top of a retaining wall with a change in elevation of 30-inches or more above the grade below. These cases should be assessed independent of fencing along a limit-of-access.

For guidance on the design and installation of fence or handrail on bridges, refer to Chapter 3.4.1.2 of the GDOT Bridge and Structures Design Policy Manual.
http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/BridgeandStructure/GDOT_Bridge_and_Structur es_Policy_Manual.pdf
For guidance on the construction of fencing, refer to GDOT Construction, Standard Specification, Section 643 Fence. http://www.dot.ga.gov/doingbusiness/theSource/specs/ss643.pdf
The Department has established the following guidelines to determine the type of fencing installation appropriate for the access control along the roadway.
Full Control of Access:
Urban Interstate or Freeway: Ga. Standard Detail 9031-N, Chain Link Wire Fence heavier gage fence typically 6-ft.
height typically used in areas with restricted cross section and limited (narrow) space between the roadway and the right-of-way, such as depressed urban freeways with retaining walls and significant changes in vertical elevation between the roadway and right-of-way may include extension arms with barbed wire strands across the top to enhance security.
Suburban Interstate or Freeway: Ga. Standard Detail 9031-N, Chain Link Wire Fence or, Ga. Construction Detail F-1, Woven Wire Fence 4-ft. height wire mesh with barbed wire
strand along the top and bottom may be used in areas with flatter more rounded sideslopes and wider (more adequate) space between the roadway and the right-of-way.
Rural Interstate or Freeway: Ga. Construction Detail F-1, Woven Wire Fence or, Ga. Construction Detail F-6, Game Fence typically 8-ft height mesh with barbed wire
strands along the top and bottom - may be used on portions of roadways to reduce crash rates related to wild game crossing.
Partial Control of Access or any portion of a roadway with an acquired limit-of-access: Ga. Standard Detail 9031-N, Chain Link Wire Fence or, Ga. Construction Detail F-1, Woven Wire Fence or, Ga. Construction Detail F-6, Game Fence

3.7.2 Fencing on Private Property
In cases where the Department is acquiring additional right-of-way or easement, and displacing fence on private property, the value of "replacement fencing" will be assessed by the right-of-way agent for settlement with the property owner.
Replacement fencing may be installed by the Department's contractor or by the property owner on private property, as determined in the settlement with the property owner and noted on the plans.

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Fence installed on private property should be offset a minimum of 1-ft outside the state right-of-way line. Typically a 5-ft wide temporary "Easement for the Construction of Fence" will be required on private property if the fence is installed by the Department's contractor.
Replacement fencing on private property may consist of chain link wire, woven wire, field fencing/barbed wire, ornamental, or specialty type fencing including gates and associated hardware. In cases where ornamental or specialty fencing is included as a contract item, a special provision with detail drawings will be required in the plans and contract proposal.
A decision to provide replacement fencing on private property will be made during right-of-way acquisition. Designers should coordinate with the Right-of-Way Acquisition Manager for direction on replacement fencing on private property prior to establishing temporary easements or adding notes to the plans.
For additional guidance involving the installation of fence on private property refer to the GDOT Right-Of-Way Manual, currently maintained by the Office of Right-Of-Way in hard-copy format.

3.8. Right-of-Way Controls
Establishing right-of-way widths that adequately accommodate construction, utilities, drainage, and proper roadway maintenance is an important part of the overall design. The border area between the roadway and the right-of-way line should be wide enough to serve several purposes, including provision of a buffer space between pedestrians and vehicular traffic (if applicable), roadway drainage, sidewalk space, lateral offset, clear zone, and an area for both underground and aboveground utilities. A wide right-of-way width allows construction of gentle slopes and also allows for utility poles to be offset further from the road, which in turn results in greater safety for motorists as well as easier and more economical maintenance of the right-of-way.

3.8.1. Rural Areas
In hilly terrain, construction limits vary considerably as the roadway passes through cut and fill sections. In these situations, the required right-of-way will likely vary, so it may be impractical to use a constant right-of-way width.

In flat terrain, it is usually both practical and desirable to establish a minimum right-of-way width that can be used throughout most of the project length. Required right-of-way widths should be set at even offsets from the centerline, typically multiples of 5-ft., unless some physical feature requires otherwise.

As a general rule, the required right-of-way line should be set a minimum of 7-ft. to 10-ft. beyond the proposed limits of construction in cut and 10-ft. to 15-ft. beyond the proposed limits of construction in fill. In areas of high fills a minimum of 20-ft. should be provided beyond the construction limits to provide room for adequate erosion control Best Management Practices (BMPs) that are necessary to minimize sediment transport. Extra right-of-way at the top of cut slopes should be provided for the construction of ditches that will intercept surface drainage and help minimize slope erosion.

If a future project will potentially connect to either end of the proposed project, the required right-ofway line is extended to the nearest property line beyond the extent of construction, if practical. This is done to avoid buying right-of-way from the property owner on two different occasions. In this case, the project limit will correspond to the limit of the required right-of-way.

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3.8.2. Urban Areas
In urban areas, right-of-way widths are governed primarily by economic considerations, physical obstructions, or environmental considerations. Along any route, development and terrain conditions may vary affecting the availability of right-of-way.
It is desirable to set right-of-way in urban areas a minimum of 1-ft beyond the shoulder break point or 2-ft. beyond the greatest required lateral offset specified in Chapter 5. Roadside Safety and Lateral Offset to Obstruction. However, property or environmental impacts may limit the amount of right-of-way that can realistically be acquired. If existing utilities are in conflict within areas of restricted right-of-way, discussions should be held at the Field Plan Reviews to determine how to adequately accommodate utility relocations.
3.8.3. Special Types of Right-of-Way
Construction Easement Construction easement is called for on the plans when an area outside the required right-of-way line is needed only during construction of the project. The most common example of this is for construction of a temporary detour road.
A permanent feature should not be placed in a construction easement. The decision to obtain permanent right-of-way or construction easement is made after considering the circumstances of each project.
The property owner is paid a fee during the time the construction easement is needed. Where applicable, the owner is also paid for damages that may be incurred during the construction process such as for removal of trees or shrubbery.
Permanent Drainage Easement Drainage easement is required when a new lateral outfall ditch is to be constructed beyond the right-of-way or when an existing lateral outfall ditch is to be improved outside of the right-of-way. Drainage easement is obtained when construction of these laterals is critical to proper drainage of the project. As with a construction easement the property owner is paid for use of the drainage easement, and for damages resulting from construction. However, with drainage easements GDOT reserves the right of permanent access to the drainage structure for maintenance purposes.
Control of Access Access rights may be purchased from property owners along major roadways having full or partial access. No roadway access crossing the limited access is allowed and the property owner is compensated for such restrictions. Where limited access is used along a roadway, it typically extends down intersecting roadways to enhance traffic flow at the intersection.
3.8.4. Accommodating Utilities
In addition to primarily serving vehicular traffic, right-of-way for streets and highways may accommodate public utility facilities in accordance with state law or municipal ordinance.
The use of right-of-way by utilities should cause the least interference with traffic using the street. If existing utilities are in conflict within areas of restricted right-of-way, discussions should be held at the Field Plan Review to determine how to adequately accommodate utility relocations. Utility

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features, such as power poles and fire hydrants, should be located as close to the right-of-way line as feasible for safety reasons.

Utilities located within the limits of construction for the roadway and drainage structures of a project may require relocation, adjustment, or encasement. The surveys should identify the utility locations, elevations, types, sizes, and owners. The plans and cross-sections will then be used to inform utility owners of how the project will impact their facilities.

Relocated utilities should normally be accommodated within the required right-of-way. This should be considered in setting required right-of-way limits.

For GDOT policies related to accommodating utilities, the designer should refer to the GDOT Utility Accommodation Policy and Standards Manual, which is available at http://www.dot.state.ga.us/doingbusiness/utilities/Pages/manual.aspx

3.9. Value Engineering
Value Engineering (VE) is defined in Code of Federal Regulations (CFR) Title 23 Part 627as follows:

"the systematic application of recognized techniques by a multi-disciplined team to identify the function of a product or service, establish a worth for that function, generate alternatives through the use of creative thinking, and provide the needed functions to accomplish the original purpose of the project, reliably, and at the lowest life-cycle cost without sacrificing safety, necessary quality, and environmental attributes of the project ().

For GDOT guidelines, policies and further information related to VE studies, the designer should refer to the current GDOT PDP, which is available in the "Other Design Related Links and Resources" section of the GDOT Repository for Online Access to Documentation and Standards (ROADS). Any applicable Design Exceptions and Design Variances shall be obtained prior to the implementation of a VE study recommendation which deviates from design standards adopted or defined by this policy.

3.10. Environmental
To the extent practical, roadways should be designed to fit into the surrounding landscape and environment. This approach helps to minimize potential impacts to the built and natural environment. Some environmental factors to consider in highway design include:
surrounding land uses and landscape elements;

historic and cultural resources;

important community features;

wetlands, streams and other natural resources;

utilities and potentially contaminated sites that are close to the roadway; and

airports and aviation facilities (located within 2 miles of the project).

GDOT encourages proactive coordination with local, and state or federal resource and regulatory agencies to identify important resources that may be of concern on a design project. Various

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techniques can be used to facilitate coordination with local jurisdictions. Several techniques are detailed in the GDOT Context Sensitive Design Online Manual, Section 2.2. Understand Community Input and Values.
Sometimes there are opportunities for a roadway project to enhance the surrounding environment. Refer to the GDOT Environmental Procedures Manual as well as the GDOT Context Sensitive Design Online Manual, Section 2.3. Achieve Sensitivity to Social and Environmental Concerns, for further guidance in this area.
While designing a roadway or major highway alignment so that it complements the surrounding terrain is an important consideration, any deviation from AASHTO or GDOT design policy standards shall require a Design Exception or Design Variance. Care should be exercised to ensure that applicable local, state, and federal environmental regulations are met in accordance with the project environmental document.

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Chapter 3 Index
Arterials Access Control, 9 Rural, 4 Urban, 3
Bicycle Facilities, 6 Buses
Design Vehicle. See Design Vehicle, Buses Classification, Functional
Arterial, 2 Freeway, 2 Rural Arterial, 4 Urban Arterial, 3 Code of Federal Regulations Title 23 Part 627 - Value Engineering, 16 Cross Section Access Roads, 11 Frontage Roads, 11 Right-of-Way Controls, 1416 Utilities, 1516 Design Context Sensitive Design (CSD), 17 Speed. See Design Speed Vehicles. See Design Vehicles Design Speed, 68 10 mph Speed Reduction, 7 Freeway Ramps, 7 Design Vehicles, 56 Buses, 5 Criteria, 4 Passenger Cars, 5 Recreational Vehicles (RVs), 5, 6 Trucks, 5 Types, 5

Easement Construction. See Right-of-Way, Easement Drainage. See Right-of-Way, Easement
Freeways Functional Classification, 2
Interchanges Access Control, 9
Intersections Access Control, 9 Turning Radii, 5
Interstates Access Control, 9
Passenger Cars Design Vehicle. See Design Vehicle, Passenger Cars
Ramps Freeways, 7
Recreational Vehicles Design Vehicle. See Design Vehicle, Recreational Vehicles
Right-of-Way Easement, Construction, 15 Easement, Drainage, 15 Rural Environment, 14 Urban Environment, 15 Utilities, 15 Width, 1416
Traffic Design Year, 8
Trucks Design Vehicle. See Design Vehicle, Trucks
Utilities, 1516 Value Engineering, 16

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Chapter 4 Contents

4. ELEMENTS OF DESIGN

1

4.1. Sight Distance

1

4.1.1. General Considerations

1

4.1.2. Stopping Sight Distance

1

4.1.3. Passing Sight Distance

2

4.1.4. Decision Sight Distance

2

4.1.5. Intersection Sight Distance

2

4.2. Horizontal Alignment

4

4.2.1. General Considerations

4

4.2.2. Types of Curves

5

4.2.3. Pavement Widening on Curves

8

4.2.4. Lane Width Transitions and Shifts

9

4.2.5. Transition in Number of Lanes

11

4.3. Vertical Alignments

14

4.3.1. General Considerations for Vertical Alignments

14

4.3.2. Maximum Vertical Grades

16

4.3.3. Minimum Vertical Grades

17

4.3.4. Vertical Curves

19

4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves

20

4.3.6. Vertical Grade Changes at Intersections

20

4.3.7. Minimum Profile Elevation Above High Water

21

4.3.8. Reporting Changes in Vertical Clearances

22

4.4. Combined Horizontal and Vertical Alignments

23

4.4.1. Aesthetic Considerations

23

4.4.2. Safety Considerations

23

4.4.3. Divided Highways

24

4.5. Superelevation

25

4.5.1. Maximum Superelevation Rates

25

4.5.2. Sharpest Curve without Superelevation

27

4.5.3. Axis of Rotation

27

4.5.4. Superelevation Transitions

28

Chapter 4 Index

33

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List of Figures

Figure 4.1. Crowned Traveled Way Revolved About Centerline

32

List of Tables

Table 4.1. Maximum Horizontal Alignment Deflection without Use of a Curve

8

Table 4.2. Pavement Widening on Curves on Two-Lane Roadways

10

Table 4.3. Miscellaneous Transition Tapers

13

Table 4.4. Turn Lane Transition Tapers

13

Table 4.5. Maximum Vertical Grades

17

Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is Considered 19

Table 4.7. Maximum Change in Grade that Does Not Require a Vertical Curve

20

Table 4.8. Vertical Profile Clearances Based on High Water

21

Table 4.9. Maximum Superelevation Rates

26

Table 4.10. Superelevation Rotation Points and Rotation Widths

29

Table 4.11. Maximum Relative Gradients

30

Table 4.12. Adjustment Factor for Number of Rotated Lanes

30

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4. ELEMENTS OF DESIGN
4.1. Sight Distance
4.1.1. General Considerations
A detailed explanation of how to apply the sight distance criteria to a roadway is described in the American Association of State Highway and Transportation Officials (AASHTO) publication, A Policy on the Geometric Design of Highways and Streets (Green Book), Chapter 3, Design Elements. In addition, Chapter 9 of the Green Book (Intersections) discusses special conditions related to sight distance at intersections.
General considerations relating to sight distance noted in the AASHTO Green Book include:
Safe and efficient operation of a vehicle is highly dependent on adequate sight distance.
Two-lane rural highways should generally provide sufficient passing sight distance at frequent intervals and for substantial distances. Conversely, passing sight distance on two-lane urban streets/arterials is normally of little value.
The proportion of a highway's length with sufficient sight distance to pass another vehicle and interval between passing opportunities should be compatible with design criteria pertaining to functional classification, as discussed in this Manual in Chapter 2, Design Policies and Standards.
Special consideration should be given to the sight distance requirements at queue backups over a hill, signals, horizontal curves, turning movements, barriers, guardrails, structures, trees, landscaping, vegetation and other special circumstances.
4.1.2. Stopping Sight Distance
"Stopping Sight Distance" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for Stopping Sight Distance for roadways in Georgia. A decision to use Stopping Sight Distance values that do not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.
Designers should note that the values for Stopping Sight Distance listed in the AASHTO Green Book are minimum values based on a 2.5 second brake reaction time. Larger stopping sight distance values may be considered by the designer, within the constraints of economic, environmental, social, and other influences. GDOT encourages designers to consider using greater values for Stopping Sight Distance when practical.
Stopping sight distance across the inside of curves plays a critical role in determining roadway horizontal curvature and applicable shoulder widths. Enough right of way should be purchased to ensure that adequate stopping sight distance is maintained. There should be no obstruction of sight distance on the inside of curves (such as median barriers, walls, cut slopes, buildings, landscaping materials, and longitudinal barriers). If removal of the obstruction is impractical to provide adequate sight distance, a design may require adjustment in the normal highway cross section or a change in the alignment.

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Because of the many variables in alignment, cross section, and in the number, type, and location of potential obstructions, the actual conditions on each curve should be checked and appropriate adjustments made to provide adequate sight distance. The AASHTO Green Book (2004), Exhibit 354 Diagram Illustrating Components for Determining Horizontal Sight Distance, provides additional information on the effects of obstructions located on the inside of horizontal curves.
4.1.3. Passing Sight Distance
Passing sight distance is the sight distance needed for passing other vehicles (applicable only on two-way, two-lane highways at locations where passing lanes are not present).
4.1.4. Decision Sight Distance
Decision Sight Distance is the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete the maneuver safely and efficiently. Examples of locations where Decision Sight Distance should be considered are: multiphase at-grade intersections, interchanges, ramp terminals on through roadways, lane drops, and areas of concentrated traffic demand where there is likely to be more visual demands and heavier weaving maneuvers.
The use of AASHTO Green Book criterion for Decision Sight Distance is encouraged by GDOT and should be considered at appropriate locations along a roadway. In cases where it is not practical to provide Decision Sight Distance, then Stopping Sight Distance shall be provided.
4.1.5. Intersection Sight Distance
Intersection Sight Distance has been identified by the Department as having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for Intersection Sight Distance. Refer to the AASHTO Green Book, Chapter 9, Intersection Sight Distance, for design criteria applicable to the traffic control conditions of an intersection. If it is not practical to provide intersection sight distance values defined by AASHTO, then a decision to select a value or retain an existing condition that does not meet the criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the GDOT Chief Engineer.
Appropriate calculations and graphical studies verifying intersection sight distance shall be conducted by the engineer and recorded in the design data book. These studies should be performed during preliminary design when both the horizontal and vertical alignments are being finalized. Graphical studies, at a minimum, should include scaled distances on plan and profile sheets and may at times necessitate plotting the sight line location on specific cross-section sheets.
Graphical studies are particularly important for the following conditions:
minor road alignment in skew;
mainline in horizontal curve;
mainline with crest vertical curve on either side of intersection;
mainline and/or minor road within a cut; and
areas where vegetation growth may obstruct the sight triangles (i.e. grass medians).

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Intersection Sight Distance is critical for urban sections with narrow shoulders and limited right-ofway where obstructions on private property may encroach into the sight triangles. Special consideration should be given to obstructions within the right of way such as: bridges, retaining walls, signs, landscaping, signal control boxes, guardrail, etc. The AASHTO Green Book (2004), Exhibit 354 Diagram Illustrating Components for Determining Horizontal Sight Distance, illustrates and provides further discussion of the affects of obstructions located on the inside of horizontal curves.
Angle of Intersection / Skew Angle Ideally, intersecting roadways should meet at or near right angles (90-degrees). This will ensure that the lines-of-sight are optimized for intersection sight distance.
"Skew Angle", also a component of Horizontal Alignment, has been identified as standard criteria, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. A decision to use a skew angle less than a 60-degree skew angle defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.
Although a minimum 60-degree intersecting angle is permissible by AASHTO standards, it does not provide the benefits of more perpendicular intersections. Therefore, GDOT has adopted a 70-degree skew angle as the minimum skew angle at intersections. A decision to use a skew angle between 60 and 70-degrees shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Department's Chief Engineer.
In general, where there is a high percentage of truck traffic, a 90-degree intersection should be provided. The closer an intersection angle is to 90-degrees, the greater the safety and operational benefits because:
exposure time for crossing movements (vehicular and pedestrian) are minimized
sharp angle turns (especially for trucks) are reduced
driver discomfort is reduced, because drivers will not have to turn their head as much to see the intersection. This is especially true for older drivers who tend to have a decline in head and neck mobility. (1)
the bodies of larger vehicles, such as ambulances, motor homes, tractor trailers, etc. tend to interfere with the drivers field of view when at skewed intersection. (2)
signing and pavement markings, channelization, and signalization layouts are simplified
When a "T" intersection becomes a four-way intersection due to extension of an existing side street or construction of a driveway opposite the side street, the new facility will usually be built at or very nearly 90-degrees to the mainline. Cross traffic operations are much safer and more efficient if the existing side street leg is at the same angle. The condition is very likely to occur on divided highways where development is concentrated at established median breaks.
The AASHTO Green Book acknowledges that sharp curves may be as great a hazard as the acuteangle crossing itself. However, rather than omitting the curves and retaining the acute-angle crossing, the effect of the curves should be mitigated. For example, warning signs for reduction of speed in advance of such curves could be provided. This is especially appropriate for "T" intersections and cross roads with low volumes of through traffic.

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(1) FHWA. Highway Design Handbook for Older Drivers and Pedestrians, 2001. The 2001 version of this publication is available online at http://www.tfhrc.gov/humanfac/01103/coverfront.htm
(2) MBTC FR 1073. Intersection Angle Geometry and the Driver's Field of View, 1997. http://ww2.mackblackwell.org/web/research/ALL_RESEARCH_PROJECTS/1000s/1073-gattis/MBTC1073.pdf
Right-of-Way Flares The preferred method to ensure adequate intersection sight distance is to acquire the area(s) within the sight triangles as right of way so the area can be properly managed and kept free of obstructions. These areas are referred to as right-of-way flares.
Right of way Flares should be obtained in order to maintain adequate intersection sight distance at intersections.
4.2. Horizontal Alignment
"Horizontal Alignment" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for elements of horizontal alignment. A decision to deviate from the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.
The location and alignment selected for a highway are influenced by factors such as physical controls, environmental considerations, economics, safety, highway classification and design policies. The horizontal alignment cannot be finalized until it is coordinated with the vertical alignment and cross section elements of the roadway.
Horizontal curves should be used for all deflections in a horizontal alignment, with the exception of alignment changes without horizontal curves as discussed in detail in Section 4.2.2. Types of Curves of this Manual. In special situations, such as roadway reconstruction or widening on existing alignment, practicality will dictate when deflection angles (PI without a curve) may be introduced in lieu of horizontal curvature. Spiral curves are generally not utilized on Georgia roadways.
Refer to the AASHTO Green Book Chapter 3, Elements of Design, when determining the radii of horizontal curves and corresponding superelevation (if applicable). Wherever possible, minimum curve radii and maximum superelevation rates should be avoided for any given speed design.
4.2.1. General Considerations
See the Green Book Chapter 3 "General Controls for Horizontal Alignment" section for general considerations when setting a horizontal alignment.
In general, the number of short curves should be kept to a minimum.
Long tangents are needed on two-lane highways such that sufficient passing sight distance is available on as great a percentage of the roadway as possible.

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Sharp curvature should be avoided near the following locations: elevated structures; at or near a crest in grade; at or near a low point in a sag or grade; at or near intersections, transit stops, or points of ingress or egress; and at or near decision points.

The concepts of stopping sight distance, intersection sight distance, decision sight distance and driver expectancy should be considered during the development of horizontal alignments. If possible, the horizontal alignments of roadways should be free of curvature in and around intersections, interchanges, bridges, railroad crossings, toll plazas, drop lanes and roadside hazards.

To facilitate pavement drainage, alignments should be laid out such that the 0% cross slope flat points associated with superelevation transitions on either end of a horizontal curve (if applicable) does not correspond to low points in the roadway vertical profile. Superelevation is discussed in this Manual in Section 4.5.

The horizontal alignment should be coordinated carefully with the vertical profile design. This subject is discussed in further detail in this Manual in Section 4.4.

The design speed of successive horizontal curves on ramps can vary as vehicles are often accelerating or decelerating. A common rule to apply to the speed design of ramps is that the design speed of the first curve of an exit ramp can be assumed to be 10 mph less than the design speed of the mainline. With each successive curve on the exit ramp, the design speed of the curve may be reduced based on computed vehicle deceleration. The process is to be reversed for entrance ramps, i.e., the design speed for curves will successively increase until the design speed of the last curve before the mainline is 10 mph less than that of the mainline.

For additional considerations and guidance in setting horizontal alignments, refer to of the AASHTO Green Book Chapter 3, Elements of Design - General Controls for Horizontal Alignment.

4.2.2. Types of Curves The following types of curves are discussed in this section:

circular curves compound curves reverse curves spiral curves broken back curves curves with small deflection angles minimum length of horizontal curve alignment changes without horizontal curves

Circular Curves
GDOT typically uses the arc definition of the circular curve. Under this definition, the curve is defined by the degree of curve (D ), which is the central angle formed when two radial lines at the
a
center of the curve intersect two points on the curve that are 100-ft. apart, measured along the arc of the curve.

D = 18,000 / ( * R) a

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Where:

D = Degree of Curve (degrees) a
R = Radius of Curve ( ft.)

L = (100 * I)/ D a Where:

L = Length of Curve ( ft.) D = Degree of Curve (degrees)
a
I = Total deflection of curve (degrees)

Compound Curves
Compound curves involve two horizontal curves of different radii sharing a common point for their point of tangent (PT) and point of curve (PC), respectively. For open highways, compound curves between connecting tangents should be used only where existing topographic controls make a single simple curve impractical.

Guidance regarding compound curves falls into two categories:

Roadways (excluding ramps), one-way or two-way - The radius of the flatter curve should not exceed the radius of the sharper curve by more than 50% (a ratio of 1.5:1).
Ramps - A ratio as great as 1.75:1 may be used on one-way interchange ramps, where compound curves are more common. Ratios greater than 2.0:1 are strongly discouraged. The compound radii ratio criteria are only applicable when the curve radii decreases from one curve to the next in the direction of travel.

Reverse Curves
Any abrupt reversal in alignment should be avoided. A reversal in alignment can be suitably designed by including a sufficient length of tangent between the two curves to provide adequate superelevation transitions. See Section 4.4. Combined Horizontal and Vertical Alignments for additional discussion of superelevation transition lengths.

The tangent distance between reverse curves should be the distance (based on the appropriate gradient or ratio) to rotate from 2/3 of the full superelevation rate of the first curve to 2/3 of the full superelevation rate of the second curve. For roadways with design speeds less than or equal to 45
mph, a minimum tangent of 100-ft. should be provided between reverse curves, even if
superelevation is not required.

With or without superelevation, extreme physical constraints may dictate the use of a reverse curve with a 0-ft. length tangent (the PT of the first curve and the PC of the second curve are at the same location). In this case, the 0% cross slope point should be placed at the shared PT/PC and use the best possible superelevation transition ratio.

Where it is impractical to provide a tangent length capable of incorporating the superelevation runoff lengths and the tangent run out lengths of both superelevated curves, the 0% cross slope point should be placed at a point derived from the best possible superelevation transition ratio between the two curves (not necessarily the center of the tangent). For an expanded discussion of superelevation refer to Section 4.4. Combined Horizontal and Vertical Alignments.

On higher-speed roadways (design speeds greater than 45 mph), curves that do not require superelevation are so flat that no tangent between the curves is necessary. However, wherever practical, a 150-ft. minimum tangent should be introduced between reverse curves. On higherspeed roadways with curves requiring superelevation, a tangent length suitable for accommodating

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the necessary superelevation transition should be provided (see Section 4.4. Combined Horizontal and Vertical Alignments). For reverse curves on a roadway with a design speed greater than 45 mph, the use of tangent lengths less than those calculated by AASHTO procedures shall require a design exception.

Spiral Curves
Spiral curves are generally not utilized on Georgia roadways, except in special cases. For overlay or widening projects, existing spiral curves may remain. For roadways to be re-constructed, existing spiral curves may be replaced with simple curves, unless existing property improvements or other controls make this impractical. Refer to the AASHTO Green Book Chapter 3, Elements of Design, for additional information on spiral curves.

Railroads typically utilize spiral curves at the beginning and end of each simple horizontal curve. A project involving a railroad crossing and possibly track relocation may require the use of spiral curves. For additional information related to the design of railroad alignments (including spiral curves), refer to the American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual for Railway Engineering.

Broken-Back Curves
Successive curves in the same direction that are separated by a short tangent are known as broken-back curves. GDOT defines this short tangent as one with a length less than:

15*V for design speeds less than or equal to 45 mph, or 30*V for design speeds greater than 45 mph. In these equations, V is the design speed in mph.

Broken-back curves are very undesirable from both an operational and an appearance standpoint. While it may not be feasible or practical in some situations to completely eliminate broken-back curves, every effort should be made to avoid this type of alignment if possible by separating, combining, or compounding curves in the same direction.

Curves with Small Deflection Angles
A short horizontal curve with a small deflection angle (less than five degrees) may appear as a kink in the roadway. As a minimum, curves should be at least 100-ft. in length for every one degree of central angle.

Minimum Length of Horizontal Curve The minimum length of horizontal curve should be in accordance with the following:

L = 15*V

Where:

L = minimum curve length (ft.) V = design speed (mph)

On high-speed controlled-access facilities that use large-radius curves, the minimum length of horizontal curve should be in accordance with the following:

L = 30*V

Where:

L = minimum curve length (ft.) V = design speed (mph)

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Alignment Changes without Horizontal Curves
There may be instances where existing constraints will make it impractical to utilize horizontal curves which maintain the minimum length criteria specified in the first seven cases cited in Section 4.2.1. Horizontal Alignment General Considerations. Right-of-way, cost, or environmental constraints could be prohibitive on widening, reconstruction, maintenance, safety, and 3R projects in both urban and rural settings.
When situations warrant, slight deflection angles may be introduced to (or maintained on) the roadways horizontal alignment. These angles will be very slight so that they do not adversely affect safety or operations. Acceptable angles of deflection will depend on the design speed of the facility. Table 4.1. lists the maximum angle of horizontal deflection for roadways in Georgia.

Table 4.1. Maximum Horizontal Alignment Deflection without Use of a Curve

Design Speed (MPH)

Maximum Angle of Horizontal Deflection
(minutes)

15

120

The use of horizontal curves is preferable to deflection angles. However, there are cases where small deflections are acceptable. For example, as shown in Table 4.1, an existing deflection angle up to 14 minutes (imperceptible to the eye) on an interstate widening project (design speed 70 mph) may be maintained.

20

90

At intersections with an all-way stop condition (with no

25

60

foreseeable signalization) and some form of constraint,

30

45

there may be a break in the roadway alignment as much

35

40

as five degrees (at the centerline crossing in the

40

35

intersection), provided intersection sight distance is

45

30

maintained in all directions.

50

25

4.2.3. Pavement Widening on Curves

55

20

60

18

On modern highways and streets that feature 12-ft. lanes and high-type alignments, the need for widening on

65

16

curves has decreased considerably in spite of high

70

14

speeds. In many cases, degrees of curvature and

75

12

pavement widths established by policies in this Design

80

10

Manual preclude the necessity of pavement widening on

roadway curves. This is especially true if the alignments

are as directional as practical, consistent with the topography, and developed properties and

community values are preserved (refer to Section 4.2.1. General Considerations). However, for

some conditions of speed, curvature, and width, it may still be necessary to widen pavements. Widening should be evaluated at the following locations:

low speed roadways with near maximum curvature ramps connecting roadways where curves sharper than those specified in this Manual are used

Specific values for pavement widening in curves are shown in Table 4.2. Pavement Widening on Curves on Two-Lane Roadways. For additional discussion and widening values, refer to the AASHTO Green Book, Chapter 3. Elements of Design Traveled Way Widening on Horizontal Curves.

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4.2.4. Lane Width Transitions and Shifts
Lane width transitions can occur at several locations including:
Lane width transitions which are to be developed for curves (see Section 4.2.3. Pavement Widening on Curves)
Connections to existing pavement such as pavement tapers which occur at the back of a turnout on an existing side road
Transitions to a wider lane such as a truck lane or a one-way, one-lane ramp Mainline lane shifts in advance of an intersection Mainline lane shifts in advance of a typical section change such as the addition of a mainline
lane Mainline lane shifts in advance of a typical section change such as a change in median width
There are two methods by which an alignment transition or "shift" may be accomplished:
The first method is to treat the transition or shift as though it were any other required alignment change. With this approach, a transition or shift would be accomplished through the use of a series of reverse curves. Quite often, the use of curve radii which do not require superelevation result in a length of transition greater than that required by providing a taper. Superelevation should be utilized if warranted by normal procedures.
The second method of accomplishing a transition or "shift" involves the use of tapers. Tapers are acceptable provided the following two conditions exist: The alignment shift is consistent with the cross slope of the roadway and does not require "shifting" over the top of an existing pavement crown
The direction of the shift is not counter to the pavement cross-slope (from a superelevation or reverse-crown consideration)

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Table 4.2. Pavement Widening on Curves on Two-Lane Roadways

Degree Curve

Radius (ft.)

30 (mph)

24-ft. Roadway

40

50

60

(mph) (mph) (mph)

70 (mph)

30 (mph)

22-ft. Roadway
40 50 60 (mph) (mph) (mph)

70 (mph)

30 (mph)

20-ft. Roadway
40 50 (mph) (mph)

60 (mph)

1.00 5,729.58 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 1.0 1.0 1.5 1.5 1.5 2.0

2.00 2,864.79 0.0 0.0 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5

3.00 1,909.86 0.0 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5 2.5

4.00 1,432.39 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5 2.5 3.0

5.00 1,145.92 0.5 0.5 1.0 1.0

1.5 1.5 2.0 2.0

2.5 2.5 2.5 3.5

6.00 954.93 0.5 1.0 1.0 1.5

1.5 2.0 2.0 2.5

2.5 3.0 3.0

7.00 818.51 0.5 1.0 1.5

1.5 2.0 2.5

2.5 3.0 3.5

8.00 716.20 1.0 1.0 1.5 9.00 636.62 1.0 1.5 2.0

2.0 2.0 2.5 2.0 2.5 3.0

3.0 3.0 3.5 3.0 3.5 4.0

10.18 562.64 1.0 1.5 12.24 488.04 1.0 2.0

2.0 2.5 2.5 3.0

3.0 3.5 3.5

15.30 374.48 2.0

3.0

4.0

19.35 296.10 2.5

3.5

4.5

22.42 255.59 3.0

4.0

5.0

26.44 216.69 3.5

4.5

5.5

Notes:

1. Values for widening (ft.) for two-lane roadways - one-way or two-way traffic

2. Disregard values less than 2.0-ft. (above heavy line and not within highlighted area) for two-lane (one-way or two-way traffic) pavements

3. For three-lane and four-lane undivided roadways multiply values by 1.5 and 2.0, respectively and round to the nearest 0.5-ft. If values are less than 2.0-ft., disregard

4. Pavement widening is intended for utilization where truck traffic is significant and the increase in pavement width is to be 2.0-ft. or greater

5. Locations for pavement widening shall be shown in the construction plans or specified by the Engineer

6. Pavement widening to occur along the inside of the normal curve. Additional width is to be shared equally by all lanes.

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Taper lengths associated with shifts on Georgia roadways should be calculated as:

Case 1 Design Speed 45 mph: L = W * s

(W * s2 ) Case 2 Design Speed < 45 mph: L
60

Where:

L = distance needed to develop widening (ft)

W = width of lane shift (ft)

s = design speed (mph)

Note: the Case 1 and Case 2 taper lengths described above are applicable to permanent conditions. For a more detailed discussion on temporary conditions associated with construction, refer to Chapter 12. Stage Construction.

4.2.5. Transition in Number of Lanes
Instances where the number of lanes on a roadway is transitioning fall into two categories lane additions and lane drops. Lane drops induce a merge situation. Adequate distance for drivers to perform the merge maneuver should thus be provided. Lane additions that do not involve a shift of the mainline lanes may be accomplished in a much shorter distance.

Lane Drops Lane drops can occur in many situations on all types of roadways, such as:

mainline lane drop due to traffic drop off mainline lane drop to meet lane balance requirements (limited access) mainline lane drop due to transition to non-widened section, etc. end of auxiliary lane end of collector-distributor (cd) system end of climbing lane ramp merges on limited access facilities

With three exceptions, lane drops (or merges) for the situations listed above should be designed based on the minimum convergence tapers provided in Section 4.2.4. Lane Width Transitions and Shifts.

Exception 1 For lane drops and merges on high-speed Limited Access facilities, where design year mainline peak hour traffic rates exceed 1,550 vehicles per lane (LOS C), the convergence ratio should be:

L = 2 * W * s Where:

L = distance needed to develop widening (ft) W = width of lane shift (ft) s = design speed (mph)

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Exception 2 Certain situations require the use of horizontal curves and possibly superelevation in association with lane reductions. An example of this would be tie-ins being constructed on projects between a proposed four-lane section (with 44-ft. median) and a two-lane existing section. In these situations, a lane should first be dropped using the taper rates specified in Section 4.2.4. Lane Width Transitions and Shifts, while still on the fourlane section (in advance of the crossover). Once the lane reduction has been attained, the tie-in to the two-lane section should be accomplished with a tie-in using AASHTO horizontal curves and superelevation rates appropriate for the design speed of the facility. If possible, the curves associated with the tie-in should be no sharper than 1 degree.

Exception 3 If a ramp merge occurs on a significant upgrade, the speed differential of a truck or bus merging into traffic should be evaluated. In general, if the mainline grades exceed 3% (upgrade in merge), the convergence ratio should be:

L = 2 * W * s Where:

L = distance needed to develop widening (ft) W = width of lane shift (ft) s = design speed (mph)

General Rules on Lane Drops lane drops on limited access facilities should occur at exits

lane drops on limited access facilities should occur on the outside lanes

upon departing an intersection, a lane (to be dropped) should be maintained for a minimum of 800-ft. from the intersection before initiating the lane drop

tapers associated with multiple, successive lane drops on the mainline should be separated by a minimum 1,000-ft. tangent section

Lane Additions
Lane additions that are not accompanied by a mainline alignment shift can be performed over a relatively short distance. A minimum 15:1 expansion taper rate should be provided. However, when spatial constraints exist, expansion tapers may be as low as 5:1 (urban) and 8.33:1 (rural).

Required lane addition taper lengths associated with median breaks and intersections can utilize taper rates less than those pertaining to through lanes. GDOT Construction Standards and Details, Construction Detail M-3 depicts turn lane taper lengths associated with Type A, B and C medians.

Table 4.3. Miscellaneous Transition Tapers summarizes taper length and taper ratio requirements as they pertain to the addition of left-turn and right-turn lanes in Georgia. The designer should attempt to meet the values found in this table. However, if constraints such as right-of-way, environmental impacts, utility conflicts and/or driveway/access issues exist, the minimum values may be utilized.
When a lane addition occurs due to the generation of a center lane or a passing lane (i.e., when a two-lane road is to be widened to a three-lane section) the transition tapers must follow the guidelines discussed in Section 4.2.4. Lane Width Transitions and Shifts.

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Table 4.3. Miscellaneous Transition Tapers

Location
Driveways Driveways Parallel Ramps on Limited Access Facilities Entrance Parallel Ramps on Limited Access Facilities Exit

Design Speed (mph)
< 45
> 45
Varies
Varies

Transition Width, W
(ft.)
12
12
12
12

Minimum Taper (ft.)
50
100
250
250

If the widening will be asymmetric or will occur only to one side, the transition width (W) is the width of the additional lane. If the widening will be symmetric, i.e., both directions of travel bifurcate symmetrically to create a center lane, then the transition width (W) can be assumed to be of the width of the additional lane. For instance, if a 14-ft. center turn lane was being generated symmetrically on a 55 mph two-lane roadway, the taper length would be:
L (14.0) *55 385.0 ft. 2
A summary of other special cases for transition tapers is included in Table 4.3. Miscellaneous Transition Tapers.
Turn Lanes in an Intersection, Median or Driveway Refer to Table 4.4. for a general guideline on minimum and desirable turn lane transition taper values.

Table 4.4. Turn Lane Transition Tapers

Design Speed (mph)

Urban or
Rural

Type A Median > 45 Rural > 45 Rural > 45 Rural
Type B Median > 45 Rural > 45 Rural > 45 Rural
Type C Median < 45 Urban*
Flush Median > 45 Rural

Median Width
(ft.)
40 44 64
32 44 64
20
14

Transition Width, W
(ft)
12 12 12
4 16 26
12
14

Minimum

Left Turn

Right Turn

Taper Ratio

Taper Length
(ft.)

Taper Ratio

Taper Length
(ft.)

8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100

15:1 60 8.33:1 100 15:1 240 8.33:1 100 15:1 390 8.33:1 100

5:1

60 8.33:1 100

8.33:1 116 8.33:1 100

Desirable

Left Turn

Right Turn

Taper Ratio

Taper Length
(ft.)

Taper Ratio

Taper Length
(ft.)

15:1 180 15:1 180 15:1 180 15:1 180 15:1 180 15:1 180

15:1 60 15:1 180 15:1 240 15:1 180 15:1 390 15:1 180

15:1 180 15:1 180

15:1 210 15:1 180

> 45 Rural Varies

14

8.33:1 116 8.33:1 100 15:1 210 15:1 180

* An urban section with a Type C Median can be used for design speeds of 45 mph

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4.3. Vertical Alignments
"Vertical Alignment", "Grade" and "Vertical Clearance" have been identified as "controlling criteria" that have substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for elements of vertical alignment, grade and vertical clearance. A decision to deviate from the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.
GDOT uses design controls for crest and sag vertical curves based on sight distance. The AASHTO Green Book Chapter 3, Elements of Design, provides additional discussion on rates of vertical curvature (K). Maximum allowable vertical grades are dependent on the classification of the facility and are discussed in the following AASHTO Green Book chapters:
Chapter 5. Local Roads and Streets Chapter 6. Collector Roads and Streets Chapter 7. Rural and Urban Arterials Chapter 8. Freeways
GDOT typically uses symmetrical parabolic vertical curves at changes in grade. Exceptions to this include spot locations such as alignment breaks near intersections and overlay transitions where vertical grade breaks can be accomplished without the use of vertical curves. The maximum grade break (%) varies based on the design speed of the facility.
4.3.1. General Considerations for Vertical Alignments
The following are general considerations for vertical alignments:
Maximizing sight distances should be a primary consideration when establishing vertical alignment.
Long, gentle vertical curves should be used wherever possible and appropriate.
"Roller coaster" or "hidden dip" profiles should be avoided by using gradual grades made possible by heavier cuts and fills or by introducing some horizontal curvature in conjunction with vertical curvature. The "roller coaster" may be justified in the interest of economy and may be acceptable in low-speed conditions, but is aesthetically undesirable.
A single long vertical curve is preferred over "broken-back" grade lines (two crest or two sag vertical curves separated by a short tangent).
Use a smooth grade line with gradual changes, consistent with the type of highway and character of terrain, rather than a line with numerous breaks and short lengths of tangent grades.
On a long ascending grade, it is preferable to place the steepest grade at the bottom and flatten the grade near the top.
Moderate grades should be maintained through intersections to facilitate turning movements. Grades should not exceed 6%, and 3% maximum is preferred.

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Sag vertical curves should be avoided in cuts as roadway flooding or ponding conditions may occur at these locations should the drainage system become clogged or overburdened.
Vertical grades should be coordinated with required acceleration and deceleration areas, wherever possible. For instance, at an interchange, it is preferable for the crossing roadway to go over the limited access facility. That way, vehicles are on an upgrade as they decelerate towards a stop condition and are on a downgrade as they are entering the limited access facility.
As much as possible, the vertical alignment should be closely coordinated with the natural topography, available right of way, utilities, roadside development, and existing drainage patterns.
Vertical alignments should be properly coordinated with environmental constraints (e.g., encroachment into wetlands).
When a vertical curve takes place partly or wholly in a horizontal curve, the vertical curvature should be coordinated with the horizontal curvature. See Section 4.4. Combined Horizontal and Vertical Alignments.
When one roadway is in a tangent section and an intersecting roadway has a continuous vertical grade through an intersection, consideration should be given to rotating the pavement cross slope on the tangent roadway to a reverse crown to better match the profile of the intersecting roadway. Standard superelevation transition rates would apply.
Additional considerations for setting vertical alignments are detailed in the AASHTO Green Book Chapter 3, Elements of Design.
Factors That Influence Roadway Grades There are several factors that influence roadway grades:
topography and earthwork control points at the beginning and end of the project vertical clearances for drainage structures intersecting railroads applicable glide slopes for roadways near airports intersecting roads and streets driveway tie-ins existing bridges to remain vertical clearances at grade separations vertical clearances for high water and flood water proposed new bridges driver expectancy at intersections

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4.3.2. Maximum Vertical Grades
The grades selected for vertical alignments should be as flat as practical, and should not exceed the values listed in Table 4.5 Maximum Vertical Grades. Maximum values vary based on types of terrain, facility classification, and design speed. The maximum design grade should be used infrequently; in most cases, grades should be less than the maximum design grade. In Table 4.5. Maximum Vertical Grades, industrial roadways are defined as local and collector streets with significant (15% or more) truck traffic. Exceptions to the maximum vertical grades listed in Table 4.5. are as follows:
For short sections less than 500-ft. and for one-way downgrades, the maximum grade may be 1% steeper than the values listed in Table 4.5.
The maximum vertical grade for local streets, collectors and arterials may be increased by as much as 2% under extreme conditions
Maximum values in Table 4.5. may be reduced when upgrades cause a speed reduction greater than or equal to 10 mph.
For streets and highways requiring long upgrades, the maximum grade should be reduced so that the speed reduction of slow-moving vehicles (i.e., trucks and buses) is not greater than 10 mph. Where reduction of grade is not practical, climbing lanes should be provided to meet these speed reduction limitations. A design exception is required where a climbing lane cannot be provided and grade cannot be reduced.
Climbing lanes, speed reductions on upgrades and the critical lengths of grade associated with speed reductions are concepts that are discussed in detail in the AASHTO Green Book Chapter 3, Elements of Design. These concepts should be considered and appropriate provisions should be incorporated into any facility in which vertical grades will cause a significant (10 mph or more) reduction in the speed of a slow-moving vehicle.
American's with Disabilities Act (ADA) Requirements That Influence Maximum Vertical Grades

Relative to roadway profiles, ADA requirements dictate that:
The running (or longitudinal) slope of sidewalks should not exceed 5%.
In urban and suburban situations where the roadway typical section includes curb and gutter, the sidewalk is normally located behind (and adjacent to or offset from) the roadway. Since topography and practicality often dictate that many curb and gutter roadways have longitudinal slopes in excess of 5%, the running slope of sidewalks often exceed 5%.

Currently, GDOT interprets the ADA requirements for running slope to be applicable only to sidewalk ramps not to longitudinal sidewalks paralleling curb and gutter roadways. However, GDOT recognizes the merit in attempting to limit longitudinal sidewalk slopes wherever possible. With regard to sidewalks, longitudinal slopes and mainline roadway profiles, GDOT offers the following approach:

o On new alignment urban roadways, roadway grades should be limited to 5%, wherever practical. Applicable overriding constraints include environmental, right-ofway, cost, topography, and context-sensitive design areas. The maximum values in Table 4.5. may be used, if necessary.

o When an existing urban roadway is to be reconstructed, the practicality of vertical reconstruction by limiting proposed grades to 5% should be evaluated. If this

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approach is found to be impractical or technically infeasible (see above), the maximum values in Table 4.5. may be used, if necessary.
In either a new location or existing reconstruction situation where roadway grades exceed 5%, the following should be considered:
o Provision of pedestrian signage and connections to an alternate pedestrian route which does not have running slopes greater than 5%. This can be a footpath parallel to the roadway (but not adjacent to the sidewalk) or a detour route.
The cross slope of cross walks at intersections should not exceed 2%. To the extent practical, profile grades and cross slopes in intersections should be minimized ideally to 2%. Where this is not technically feasible, profile grades and cross slopes in urban intersections may exceed 2%.
4.3.3. Minimum Vertical Grades Minimum vertical grades are typically used to facilitate roadway drainage. This is especially true of curbed roadway sections where drainage or gutter spread is a consideration.
Uncurbed Pavements For projects involving uncurbed pavements, longitudinal grades may be flat (0%) in areas where appropriate cross slopes are provided. In areas of superelevation transitions and/or flat cross slopes on those projects, minimum vertical grades should be consistent with those listed in Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is a Consideration. However, there are situations with uncurbed pavements where it is prudent that consideration be given to maintaining minimum vertical grades - similar to those for curbed roadway sections. These situations include:
a new location rural section
roadways with high truck percentages that experience appreciable pavement rutting
current rural roadways in urban, suburban or developing areas that have a realistic chance of being converted to a curb and gutter sometime in the foreseeable future
areas containing superelevation transitions and/or flat cross slope areas
interstate or other high speed facilities

Type of Terrain
Industrial Roadways
Level Rolling Mountainous
Local Rural Roads

Table 4.5. Maximum Vertical Grades
Maximum Grade (%) for Specified Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80
- - 44443333 - - - - - 55554444 - - - - - 66665555 - - - -

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Type of Terrain

Table 4.5. Maximum Vertical Grades
Maximum Grade (%) for Specified Design Speed (mph)
15 20 25 30 35 40 45 50 55 60 65 70 75 80

Level

9877777665 - - - -

Rolling

12 11 11 10 10 10 9 8 7 6 - - - -

Mountainous
Local Urban Streets
Level

17 16 15 14 13 12 11 10 10 - - - - 12 11 11 10 10 9 9 8 8 - - - - -

Rolling

14 13 12 11 11 10 10 9 - - - - - -

Mountainous
Rural Collectors
Level

17 16 15 14 13 12 11 - - - - - - - 777777665 - - - -

Rolling

- 10 10 9 9 8 8 7 7 6 - - - -

Mountainous
Urban Collectors
Level

- 12 11 10 10 10 10 9 9 8 - - - - 999998776 - - - -

Rolling

- 12 12 11 10 10 9 8 8 7 - - - -

Mountainous
Rural Arterials
Level

- 14 13 12 12 12 11 10 10 9 - - - - - - - - 554433333

Rolling

- - - - - 665544444

Mountainous
Urban Arterials
Level

- - - - - 877665555 - - - 8776655 - - - -

Rolling

- - - 9887766 - - - -

Mountainous

- - - 11 10 10 9 9 8 8 - - - -

Rural and Urban Freeways (Limited Access Facilities)

Level

- - - - - - - 4433333

Rolling

- - - - - - - 5544444

Mountainous

- - - - - - - 66655 - -

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Curbed Pavements

For curbed pavements, minimum longitudinal grades are controlled by the values in Table 4.6. This includes

Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is a Consideration

roadways with concrete median barriers or side barriers, V-gutter and those roadways adjacent to walls. These values will generally ensure that roadway "spread" is not

Type of Facility
Industrial Roadways with Curb and Gutter Local Urban Streets with Curb and Gutter

Minimum Grade (%)

Desirable Minimum

0.30

0.20

0.30

0.20

excessive and can be contained

Urban Collectors with Curb and Gutter

0.50

0.30

within acceptable ranges by a

Urban Arterials with Curb and Gutter

0.50

0.30

minimum (reasonable) number of

Urban Freeways or Limited Access Facilities

0.50

0.30

roadway drainage catch basins. The

minimum values in Table 4.6 should be used only under extreme conditions.

4.3.4. Vertical Curves
In almost all cases, changes in grade should be connected by a parabolic curve (the vertical offset being proportional to the square of the horizontal distance). Vertical curves are required when the algebraic difference of intersecting grades exceeds a minimum threshold (refer to Section 4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves).

Refer to the AASHTO Green Book Chapter 3, Elements of Design Vertical Curves, for considerations that must be made for vertical curves.

General Considerations
Vertical alignment has significant effect on roadway drainage. Special consideration should be given to the following:

Curbed roadways should have a minimum grade of not less than the values specified in Section 4.3.3. Minimum Vertical Grades in order to avoid excessive gutter spread. This includes roadways with concrete median barriers or side barriers, and V-gutter.

Non-curbed roadways should maintain a minimum grade consistent with the directives of Section 4.2.3. Pavement Widening on Curves and Section 4.3.3. Minimum Vertical Grades

For drainage purposes, the K value should not exceed 167 for curbed roadways (crest or sag verticals). In cases where design speeds are higher than 65 mph, this criteria does not apply.

For curbed roadways in sag vertical curves with low points, a minimum grade of 0.30% should be provided within 50-ft. of the low point. This corresponds to a K value of 167.

The minimum K values as defined by AASHTO are based on the assumption that there are significant tangent sections on either side of the vertical curve. Therefore, when using compound or unsymmetrical vertical curves, sight distances should be checked graphically to ensure that adequate sight distance is provided. Additional information can be found in the National Cooperative Highway Research Program (NCHRP) Report 504 Design Speed, Operating, Speed, and Posted Speed Practices.

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In establishing the vertical alignment, sound engineering practice should be used to strike a reasonable balance between excavation (cut) and embankment (fill). Other overriding factors must also be considered, including:
maintenance of traffic environmental impacts right-of-way impacts pedestrian (ADA) requirements safety considerations sight distance considerations (all types) drainage considerations high water considerations ability to tie the roadway profile into side roads, driveways and at grade railroad crossings. drivability and driver expectancy

4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves
GDOT typically uses vertical curves for changes in vertical grades. However, there are situations where it is either impractical or impossible to utilize a vertical curve. Such situations include:

temporary vertical tie-ins profile tie-ins such as overlay transitions avoidance and/or minimization of an environmental impact point profiles in overlay and widening sections profile reconstruction near fixed objects such as bridges and approach slabs

Table 4.7. lists the maximum vertical grade changes that do not require a vertical curve. Note that these values change per design speed. Grade breaks should only be used when necessary (vertical curves should be used, wherever practical). If two or more of these vertical grade breaks are utilized in succession (i.e., a point profile), the cumulative effect of these grade breaks in the profile shall be evaluated for stopping sight distance and it shall be verified that typical stopping sight distance is always provided. If the cumulative effect of a series of vertical grade breaks violates stopping sight distance criteria, the values in Table 4.7. may need to be reduced.

Maximum Change in Grade (%)

Table 4.7. Maximum Change in Grade that Does Not Require a Vertical Curve
Design Speed (mph) 20 25 30 35 40 45 50 55 60 65 70
1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20

4.3.6. Vertical Grade Changes at Intersections
If it is impractical to match the elevation of an intersecting road, the crossroad should be reconstructed for a suitable distance using adequate vertical geometry to make the grade adjustment. In general, a 2% maximum tangent grade break is allowed at the edges of signalized

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intersections to allow vehicles on the crossroads to pass through an intersection on a green signal safely without significantly adjusting their speed. A 4% maximum grade break is allowed in the center of an intersection corresponding to the 4% crown breakover associated with a crossing road. For the edges of unsignalized or stop condition intersections, a maximum tangent grade break of 4% may be employed.
4.3.7. Minimum Profile Elevation Above High Water
One major factor in establishing a vertical profile for either a roadway or a bridge is clearance over high water or a design flood. For roadways, this is important for two reasons:
Pavement Protection - A major factor in a roadway's durability is minimizing the amount of moisture in the base and pavement. Keeping the roadway base as dry as possible will help prevent or minimize pavement deterioration.
Safety - A roadway with a profile set above the design high water will keep water from overtopping the roadway. Overtopped roadways are a hazard to moving vehicles and can effectively shut down a facility when they are needed most, i.e., a hurricane evacuation route.
For bridges, prescribed low-chord clearances must be maintained to protect the bridge superstructure from unanticipated lateral forces associated with high-velocity flood waters.
Table 4.8. summarizes the required high water clearances for roadways and bridges in Georgia. A vertical profile that satisfies the worst-case situation for either clearance or overtopping shall be established.

Table 4.8. Vertical Profile Clearance Based on High Water

Facility
Interstate Hurricane Evacuation Routes Roads Designed as State Routes Roads Not Designed as State Routes
ADT: 0 99 ADT: 100 399 ADT: 400 1,499 ADT: 1,500 or more
Driveways Temporary Detours Permanent Bridges Temporary Bridges
Local Road with ADT < 400 All Other Roads

Designer's First Priority

Roadway Base

Bridge Low Chord Clearance

Required Clearance
1-ft
1-ft.
1-ft.

Design Flood Frequency 50-year
50-year
50-year

Required Clearance
2-ft.
2-ft.
2-ft.

Design Flood Frequency 50-year
50-year
50-year

Designer Must Check

Shoulder Break Point Clearance or Bridge Low Chord Clearance

Required Clearance

Design Flood Frequency

1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point

100-year 100-year 100-year

1-ft.

5-year

2-ft.

1-ft.

10-year

2-ft.

1-ft.

25-year

2-ft.

1-ft.

50-

2-ft.

year

1-ft.

25-year

2-ft.

1-ft.

10-year

2-ft.

1-ft.

50-year

2-ft.

5-year 10-year 25-year 50-year
25-year 10-year 50-year

1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point
Shoulder break point not overtopped Shoulder break point not overtopped
1-ft. low-chord clearance

10-year 25-year 50-year 100-year
50-year 25-year 100-year

1-ft.

2-year

2-ft.

2-year

1-ft.

10-year

2-ft.

10-year

Low-chord not overtopped Low-chord not overtopped

5-year 25-year

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Refer to the most current version of the GDOT Manual on Drainage Design for Highways (also referred to as the Drainage Manual), which may be downloaded from the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.). For roadways, designers should be familiar with the concept of culvert hydraulics and be aware that head losses associated with culverts will generally produce a headwater greater than the design flood elevation of the natural conditions. A vertical profile that provides the prescribed clearances over either the headwater of the natural conditions or the headwater created by a culvert, whichever is greater, shall be developed.
For bridges, designers should be familiar with the concept of riverine hydraulics and coordinate the bridge profile with the results of the bridge hydraulic study. As bridges will tend to generate backwater, a vertical profile that provides the prescribed clearances over the backwater created by the bridge or other nearby influencing structures shall be established. For additional information on Bridge Hydraulic guidelines, please refer to the GDOT Drainage Manual.
4.3.8. Reporting Changes in Vertical Clearances
The GDOT Office of Maintenance (Maintenance Office) has the responsibility of providing the Office of Permits and Enforcement with the height limitation of structures. The Bridge Maintenance Office and the Office of Permits & Enforcement have the responsibility of approving the proposed routing on state routes for vehicle movements which are over the legal vertical clearance.
It is extremely important for these offices to be kept informed of any change in vertical clearance as soon as possible after the change occurs. Persons (Area Engineer, Project Engineer) directly involved with vertical clearance revisions to any structure on a state route shall immediately notify:
The GDOT Maintenance Office - Such a report should be made by telephone to the Routing Engineer at (404) 656-5287 or to the Assistant State Maintenance Engineer, Bridges. The Maintenance Office will handle the reporting of the above changes to the Office of Permits & Enforcement.
The GDOT Bridge Maintenance & Inventory Office - This office should be notified of any changes in vertical clearances on the state system within 24 hours.
In cases where the actual measured minimum vertical clearance must be revised, the person directly involved with the revision (Area Engineer, Project Engineer) shall advise the District Maintenance Office of the actual measured minimum vertical clearances on his/her specific construction project(s). The revised information should then be reported to the Bridge Inventory Office, and this information will be directed to local Bridge Inspection personnel, such that the revisions to the Bridge Information System may be verified at a later date. The Bridge Inventory Office in Atlanta will initiate revisions to the system with notification to units requiring the revised information.
The actual measured minimum vertical clearance should be recorded at both edges of the pavement, the crown point (if present) and at the edges of paved shoulders (if present). In addition, measurements at any other restricting locations caused by the geometrics of the overhead structure or roadway should be recorded. Special attention should be paid to the effects of reconstruction at a restrictive location. For example, to resurface beneath a posted clearance without insuring a correction in posting misinforms the traveling public and thus creates a possible hazardous condition.

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4.4. Combined Horizontal and Vertical Alignments
Horizontal and vertical alignments are permanent design elements that warrant thorough study. Horizontal and vertical alignments should not be designed independently, but should complement each other. Poorly designed combinations can negate the benefits and aggravate the deficiencies of each. A well-designed combination, in which horizontal and vertical alignments work in concert, increases highway usefulness and safety, encourages uniform speed, and improves appearance.
4.4.1. Aesthetic Considerations
Coordination of the horizontal and vertical alignment can result in a highway that is visually pleasing. This can be achieved in several ways:
A sharp horizontal curve should not be introduced at or near the low point of a sag vertical curve, which produces a distorted appearance.
There should be a balance between curvature and grades. The use of steep grades to achieve long tangents and flat curves, or the use of excessive curvature to achieve flat grades, are considered poor design. A logical design is a compromise between the two conditions. Wherever feasible the roadway should "roll with" rather than "buck" the terrain.
If possible, every effort should be made to line up points of vertical intersection (PVI's) with horizontal points of intersections (PI's) and to maintain consistency between the horizontal and vertical curve lengths. Vertical curvature superimposed on the horizontal curvature generally results in a more visually pleasing facility. Successive changes in profile not in combination with horizontal curvature may result in a series of dips not visible to the driver. If PVI's and PI's cannot be made to coincide, the horizontal curvature should "lead" the vertical curve and the horizontal curve should be slightly longer than the vertical curve in both directions.
A balanced design which provides horizontal and vertical alignments in the middle range of values is preferable to allowing either horizontal or vertical to become extreme in order to optimize the other.
Design the alignment to enhance attractive scenic views of the natural and manmade environment, such as rivers, rock formations, parks, and outstanding buildings.
In residential areas, wherever possible, design the alignment to minimize nuisance factors to the neighborhood. Generally, a depressed facility makes a highway less visible and less noisy to adjacent residents. Minor horizontal adjustments can sometimes be made to increase the buffer zone between the highway and clusters of homes.
Refer to the GDOT Context-Sensitive Design Online Manual , for additional information.
4.4.2. Safety Considerations
The superimposed effect of horizontal and vertical alignments can influence both sight distance and driver expectancy which translate directly into safety. As safety should be the designer's primary consideration, the following guidelines are presented:
Sharp horizontal curves should not be introduced at or near the top of a pronounced vertical curve, since the driver cannot perceive the horizontal change in alignment, especially at night.

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Sharp horizontal curves should not be introduced at or near the low point of a sag vertical curve, since vehicles, particularly trucks, are traveling faster at the bottom of grades.

Both horizontal and vertical curvature should be as flat as possible at intersections where vehicles have to decelerate, stop, or accelerate.

To maintain proper pavement drainage, design vertical and horizontal curves so that the flat profile of a vertical curve will not be located near the flat cross slope of the superelevation transition. As a general rule, pavement cross slope should be at least 1.0% near vertical curve sag points and longitudinal roadway grades should be at least 0.30% at locations where the pavement cross slope is flat (0%), for instance at superelevation transitions.

On two-lane roadways, the need for safe passing sections (at frequent intervals and for an appreciable percentage of the length of the roadway) often supersedes the general desirability for combination of horizontal and vertical alignment. The Designer should strive to implement long tangent sections to secure sufficient passing sight distance.

It is generally poor practice to place the superelevation rotation point at a different point than the profile grade line.

Particular attention shall be paid to all forms of sight distance when horizontal and vertical alignments are superimposed on each other. The combination of horizontal and vertical curvature can sometimes result in effectively less sight distance than the individual affect of either horizontal or vertical curvature.

4.4.3. Divided Highways
A well designed roadway will incorporate a litany of considerations including safety, economy, and aesthetics, etc. When terrain is hilly, mountainous or undulating, the profile of the roadway should generally follow the contours of the land (barring overriding considerations). On divided highways and rural interstates, the Designer should recognize where terrain dictates, separate horizontal alignments and vertical profiles can be utilized for opposing traffic.

Independent Profiles and Increasing Median Width
On state and federal divided highways, an increase in the width of the median and the use of independent alignments to derive the design and operational advantages of one-way roadways should be considered. Where right of way is available, a superior design, without significant additional costs, can result from the use of independent alignments and profiles. Bifurcated medians are especially effective where the general fall of the terrain is significant and perpendicular to the roadway.

Increasing the width of the median and/or bifurcating the roadway should be considered in the following situations:

Where right of way is available and where the general fall of the terrain is significant and perpendicular to the roadway

In isolated areas on rural reconstruction projects where the height of vertical reconstruction is significant. This will facilitate efficiency and ease conflicts during an intermediate stage of construction. As a general rule of thumb, standard 44-ft. median width can be maintained with independent profiles until the difference in elevations in opposing PGL's is approximately 5-ft. Consideration should be given to increasing the median width (beyond 44-ft.) a minimum of 2-ft.

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for every 1-ft. of vertical profile reconstruction greater than 5-ft. Obviously, increasing the median width will result in greater right of way impacts. However, in many instances, minor right of way impacts - especially in rural areas where it is plentiful are ultimately less costly than significant vertical reconstructions that require the contractor to utilize earth stabilization techniques or sheet pile to construct.
At intersections to eliminate breakovers.
4.5. Superelevation
When a vehicle travels around a horizontal curve, it is forced radially outward by centrifugal force. When this force becomes too great for a given design speed, the roadway is "superelevated" to counter it. Five methods of counteracting centrifugal forces through curves are discussed in the AASHTO Green Book Chapter 3, Elements of Design.
4.5.1. Maximum Superelevation Rates
"Superelevation" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the Superelevation rates shown in table 4.9 as the standard for superelevation rates in Georgia. The FHWA has stated that a Design Exception is required if the State's superelevation rate cannot met. Therefore, a decision to use a Superelevation rate that does not meet the maximum Superelevation Rate shown in Table 4.9 shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer.
Horizontal alignments are composed of tangent sections connected by arcs of circular curves (GDOT does not normally use spiral curves). Vehicles traveling in a circular path counter the centrifugal force that would cause them to leave the road through a combination of two factors: lateral friction between the vehicle's tires and the road, and superelevation.

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The maximum rates of superelevation used on highways are controlled by four factors: Climatic conditions (i.e., frequency and amount
of snow and ice)
Terrain conditions (i.e., flat, rolling, or mountainous)
Type of area (i.e., rural or urban)

Table 4.9. Maximum

Superelevation Rates

Setting

Maximum Superelevation Rates
(emax)(1)

Urban (Curb and Gutter) Roads (DS < 45mph)

4%

Suburban / Developing Areas

6%

Frequency of very slow-moving vehicles whose operation might be affected by high superelevation rates

Rural (Non Curb and Gutter) Paved Roads Unpaved Roads

6% Reverse Crown

Interstates, Expressways,

Superelevation requirements for maximum

L/A Facilities

superelevation rates (0.04 to 0.12-ft./ft) for various

Rural

8%

design speeds (15 mph to 80 mph) are provided in

Urban

6%

the AASHTO Green Book Chapter 3, Elements of Design Superelevation Tables. GDOT has designated the values in Table 4.9. as the

System-to-System Ramps Rural

8%

maximum values (emax) for use on Georgia roadways.

Urban Exit-Entrance Ramps

6% 8%

Free Flowing Loop Ramps

10%

It is important for designers to realize that the minimum curve radii and maximum superelevation rates depicted in the AASHTO Green Book are extremes and should be avoided wherever possible.

Long Ramps with STOP

8%

(1) The maximum allowed values (emax) for usage on Georgia roadways, as designated by GDOT.

In general, GDOT does not require superelevation on lowspeed urban roadways or roadways with a design speed of 25 mph or less

The emax values presented in Table 4.9. requires the use of the more moderate design value ranges for curvature and superelevation. In certain situations, such as those described below, the emax values in Table 4.9. may require further reduction:

Wherever practical, consideration should be given to maximizing curve radii and minimizing superelevation rates on curves which include bridges. This is due to the increased potential for icing. Where constraints do not exist, an emax of 4% should be utilized.
Wherever possible, the maximum superelevation rates on roadways within an intersection should be limited to 4% (2% for urban areas with crosswalks). Wherever possible and when applicable in intersections, superelevation cross slopes of one roadway should be coordinated with the mainline profile grade of the intersecting roadway.

Where traffic congestion or extensive development acts to restrict top speeds on a rural roadway, a maximum rate of superelevation of 6% should be used.


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4.5.2. Sharpest Curve without Superelevation
Although superelevation is advantageous for high-speed traffic operations, various factors combine to make its use impractical in many built-up areas. Such factors include:
wide pavement areas need to meet grade of adjacent property surface drainage considerations frequency of cross streets, alleys and driveways at major intersections or other locations where there is a tendency to drive slowly because of
turning and crossing movements, warning devices, and traffic signals

The minimum curve radius is a limiting value of curvature for a given design speed and is determined from the maximum rate of superelevation and the maximum side friction factor selected for design. Very flat curves need no superelevation. In many instances, it is desirable to maintain a normal crown typical section on the roadway. In these cases, implementation of a curve with a radius flat enough as to not require superelevation should be considered.

4.5.3. Axis of Rotation
Roadway alignments are generally defined by a centerline (CL) and a profile grade line (PGL). The roadway may be rotated about various points on the typical section to achieve superelevation. Typically, the point of superelevation rotation (axis of rotation) corresponds to the PGL located on the inside edges of the travel lanes. On two-way roadways with a flush, raised or no median, the axis of rotation typically corresponds to the roadway centerline. Generally, rotation will occur about the centerline on roadways with an urban typical section. In most instances, the axis of rotation, the PGL or centerline and the pavement crown line are the same although it is not mandatory. The following represent GDOT guidelines when establishing the location of the superelevation rotation point:

For almost all situations involving two-lane, three-lane and four-lane (with raised median) typical sections, the axis of rotation is located on the centerline of the proposed pavement. One exception to this is three-lane section which is widened to one side from two-lane sections. In this case, the axis of rotation typically follows the location of the former centerline of two-lane pavement.
The actual point of rotation with a raised median is an imaginary point which is developed by projecting the left and right pavement cross slopes respectively and intersecting them with the project centerline to form a common point.

In four-lane and six-lane typical sections involving depressed medians, the axis of rotation generally follows the inside edge of the inside travel lane (Lane 1). This approach facilitates consistent median drainage but can create drainage problems near median breaks. Particular attention should be paid to pavement drainage in the areas near median breaks and should examine the pavement profile of the median break crossover.

A point of rotation at the centerline where depressed medians are in urban areas or where there is a potential for future development and the addition of future crossovers should be considered. In areas where superelevation rates would create median slopes greater than 4:1 it will be necessary to use split rotation points. When the median width is 44-ft. this typically occurs when the superelevation rate exceeds 5%.

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In a six-lane or 8-lane typical section involving a concrete median barrier, the axis of rotation will follow the lane line separating Lane 1 from Lane 2.
In typical sections which involve more than three-lanes in each direction, the profile grade line (crown point or axis of rotation) will generally begin to move from its standard location on the inside edge of the inside travel lane towards the outside in one-lane increments. This is due to the need to balance pavement drainage and to maintain practical superelevation transition and tangent runout lengths. There should never be more than a three-lane difference between the number of lanes on one side of the pavement "crown" vs. the other side.
Table 4.10. Superelevation Rotation Points and Rotation Widths, summarizes the location of the axis of rotation for various typical sections utilized by GDOT. For further information or more detail regarding typical sections, refer to Chapter 6 of this Manual or consult the typical section cells associated with the GDOT Electronic Data Guidelines.
4.5.4. Superelevation Transitions
Development of Superelevation For appearance and comfort, the length of superelevation runoff (and tangent runout) should be based on a relative gradient between the longitudinal grades of the axis of rotation and the outside edge of traveled way pavement. The maximum relative gradient is varied with design speed to provide longer runoff lengths at higher speeds and shorter lengths at lower speeds. The maximum relative gradients are depicted in Table 4.11. Maximum Relative Gradients. These values correspond to those found in the AASHTO Green Book.
Refer to the AASHTO Green Book for guidance on establishing superelevation runoff lengths, superelevation (tangent) runout lengths and locating superelevation transitions.
AASHTO guidelines shall be followed when determining and locating superelevation runoff, runout and transitions. When AASHTO values cannot be attained for superelevation parameters, a design exception is required.

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Table 4.10. Superelevation Rotation Points and Rotation Widths

Barrier Inside Barrier Outside Symmetric Widening Asymmetric Widening New Location Reconstruction

No. of Lanes

Median Width (ft.)

Median Type

Horizontal Location of Rotation Point

Rotation Width (ft.)

Urban Typical Section

2

0

3

14

3

14

5

14

4

20

6

20

4

24

6

24

N/A Flush Flush Flush Raised Raised Raised Raised

Rural Typical Section

2

0

N/A

3

14

Flush

3

14

Flush

5

14

Flush

4

20

Raised

6

20

Raised

4

24

Raised

6

24

Raised

4

32

Depressed

6

32

Depressed

4

44

Depressed

6

44

Depressed

Ramp Typical Section

1*

0

N/A

2*

0

N/A

1*

0

N/A

2*

0

N/A

Limited Access Typical Section

1*

0

N/A

2*

0

N/A

3*

0

N/A

4*

0

N/A

Hybrid Typical Section

2

44

Depressed

3

44

Depressed

4

44

Depressed

2

52

Depressed

3

52

Depressed

4

52

Depressed

2

64

Depressed

3

64

Depressed

4

64

Depressed

X
X X X X X
X
X X X X X X X X X
X X XX X XX X
XX X XX X XX X XX X
X X X X X X X X X X X X X X X X X X

X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
X X X X X X X X X X X X
X X X X X X X X X X X X
X X X X X X X X X X X X X X X X X X X X X X X X X X X

CL of pavement CL of new pavement CL of old pavement
CL CL CL CL CL
CL of pavement CL of new pavement CL of old pavement
CL of pavement CL of pavement CL of pavement Inside of TL 1 Inside of TL 1 Inside of TL 1
TL 1 Inside of TL 1
TL 1
Outside edge of TL Outside edge of TL 2 Outside edge of TL Outside edge of TL 2
Inside of TL 1 Inside of TL 1
Varies Varies
Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2 Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2 Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2

3

28

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

4

28

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

5

28

Flush w/ Barrier

X

X

X X X

Between TL 2 and TL 3

3

32

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

4

32

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

5

32

Flush w/ Barrier

X

X

X X X

Between TL 2 and TL 3

3

40

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

4

40

Flush w/ Barrier

X

X

X X X

Between TL 1 and TL 2

5

40

Flush w/ Barrier

X

X

X X X

Between TL 2 and TL 3

* One-Way

Notes: 1. Outside Typical Sections

2. Assume 12-ft. Lane Widths

3. On raised medians, PGL is located by projecting Symbols:

CL = Centerline

pavement cross slope to the centerline

TL = Travel Lane

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12 19 26 31 34 46 36 48
12 19 26 31 34 46 36 48 24 24 -
16 24 16 24
12 24 -
24 36 36 24 36 36 24 36 36
24 36 36 24 36 36 24 36 36
4-29

Table 4.11. Maximum Relative Gradients indicates that relative gradients vary per design speed.

A strict application of the maximum relative gradient criterion provides runoff lengths for four-lane undivided roadways that are double those for two-lane roadways; and those for six-lane undivided roadways would be tripled. While lengths of this order may be desirable, it is often not practical to provide such lengths in design. It is recommended that minimum superelevation runoff lengths be adjusted downward to avoid excessive lengths for multilane highways.

The recommended adjustment factors are presented in Table 4.12. Adjustment Factor for Number of Rotated Lanes. These values correspond with the values found in the AASHTO Green Book (2004).

To calculate minimum superelevation runoff length, use the equation:

L

(wN1) G

e d

* (bw )

Table 4.11. Maximum Relative Gradients

Design Speed (mph)
14 20 25 30 35 40 45 50 55 60 65 70 75 80

Maximum Relative Gradient, G (%)
0.78 0.74 0.70 0.66 0.62 0.58 0.54 0.50 0.47 0.45 0.43 0.40 0.38 0.35

Equivalent Maximum Relative Slope
1:128 1:135 1:143 1:152 1:161 1:172 1:185 1:200 1:213 1:222 1:233 1:250 1:263 1:286

where:
L = minimum length of superelevation runoff (ft.) G = maximum relative gradient (%) N = number of lanes rotated (on one side of
1
axis of rotation, not total number lanes) b = adjustment factor for number of lanes
w
rotated w = width of one traffic lane (usually 12-ft.) e = design superelevation rate (%)
d

For example, assume a five-lane roadway (12-ft. lanes)

with 0.06 (6%) superelevation and 45 mph design

speed. In the equation above, G = 0.54, N = 2.5, b =

1

w

0.7, w = 12, and e = 6.0. Inserting these numbers into

the equation gives:

Table 4.12. Adjustment Factor for Number of Rotated Lanes

Number of Lanes
Rotated (N1)

Adjustment Factor (bw)

Length Increase Relative to 1 Lane Rotated (=N1bw)

1.00

1.00

1.00

1.50

0.83

1.25

2.00

0.75

1.50

2.50

0.70

1.75

3.00

0.67

2.00

3.50

0.64

2.25

Source: AASHTO. (2004). Green Book.

L (12)(2.5)(6) * (0.7) 233.33 ft. 0.54

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Minimum Length of Superelevation Runoff There are a number of rational approaches to transitioning from a normal crown section to a superelevated section. Wherever possible, GDOT applies 2/3 of the superelevation runoff outside the curve and 1/3 of the superelevation runoff inside the curve. For the above example, the amount of superelevation applied outside the curve would be (2/3)(233.33) = 155.56-ft. and the amount of superelevation applied inside the curve would be (1/3)(233.33) = 77.78-ft.
Tangent runout is the length required to transition from a normal crown to a flat section on the outside of a horizontal curve. The tangent runout length is determined in the same manner as the superelevation runoff length. For the example above, assuming a normal crown cross slope of 2%), the tangent runout length would be:
L (12)(2.5)(2) * (0.7) 77.78 ft. length tangent runout 0.54
Calculated lengths may be rounded to the nearest foot, if desired.
If geometric constraints exist, consideration may be given to placing 50% of the superelevation runoff on the tangent and 50% of the runoff on the curve. Sometimes, conditions exist where it is not possible to develop the desirable amount of runoff (or runout) and it is impossible to locate the transition in the ideal location relative to the curve PC or PT.
Examples of this include:
Reverse curves (especially prevalent in mountainous regions) Broken back curves Approaches to intersections
These undesirable situations should be avoided, wherever feasible. However, since these instances are sometimes unavoidable (or the desirable implementation is impractical) professional judgment should be exercised when determining less-than-ideal transition rates and transition locations. Some practical guidelines for handling these situations include:
For a symmetric (equal radius) reverse curve, place the 0% cross slope point at the PT and PC common to both curves
For asymmetric reverse curves (of different radii), attempt to place the superelevation transition in a location which is proportional to the e of the two curves
max
For broken back curves, attempt to place the average e cross slope at the center of the max tangent
Pavement warping near intersection tie-ins is sometimes required (e.g. when there are superelevation transitions near intersections, ADA requirements, drainage, sight distance, and operations which should be taken into consideration)

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Figure 4.1., Crowned Traveled Way Revolved About Centerline, illustrates the development of tangent runout and superelevation runoff for a roadway with the profile control and superelevation rotation point at the center of the roadway.

Figure 4.1. Crowned Traveled Way Revolved About Centerline

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Chapter 4 Index
ADA Requirements, 17
Alignment
Aesthetic Considerations, 24 Combined Horizontal and Vertical, 2426 Divided Highways, 25 Horizontal, 414 Vertical, 1423 Broken Back Curves. See Curves Horizontal
Circular Curves. See Curves - Horizontal
Compound Curves. See Curves - Horizontal
Curves - Horizontal
Broken Back Curves, 7 Circular Curves, 6 Compound Curves, 6 Minimum Length, 8 Reverse Curves, 6 Sight Distance on, 1 Spiral Curves, 4, 7 Curves - Vertical, 20
Decision Sight Distance. See Sight Distance: Decision Sight Distance
Horizontal Alignment. See Alignment, Horizontal
Interchanges
Ramps, 6

Intersection Sight Distance. See Sight Distance: Intersection Sight Distance
Intersections
Angle, 3 T-Intersection, 3 Passing Sight Distance. See Sight Distance: Passing Sight Distance
Reverse Curves. See Curves - Reverse
Right of Way
Intersections, 4 Safety, 2425
Sight Distance
Decision Sight Distance, 2 General Considerations, 1 Intersection Sight Distance, 2 Passing Sight Distance, 2, 5 Stopping Sight Distance, 1 Spiral Curves. See Curves - Horizontal
Stopping Sight Distance. See Sight Distance: Stopping Sight Distance
Superelevation, 6, 10, 13, 16, 18, 25, 28, 2633
Vertical Alignment. See Alignment, Vertical
Vertical Curves. See Curves - Vertical
Vertical Grades, 18

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Chapter 5 Contents

5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTION

1

5.1. General Considerations

1

5.2. Rural Shoulder Lateral Offset to Obstruction

2

5.3. Urban Shoulder Lateral Offset to Obstruction

3

5.4. Lateral Offsets for Signs

4

5.4.1. Sign Placement

4

5.4.2. Sign Supports

4

5.5. Lateral Offsets for Light Standards

4

5.5.1. High Mast Roadway Lighting

4

5.5.2. Roadway Lighting

4

5.5.3. Pedestrian lighting (non-roadway)

5

5.6. Lateral Offsets for Utility Installations

5

5.6.1. General Guidance

5

5.6.2. Rural Shoulders

5

5.6.3 Urban Shoulders

5

5.7. Lateral Offsets for Signal Poles and Controller Cabinets for Signals

6

5.7.1. Rural Shoulders

6

5.7.2. Urban Shoulders

6

5.8. Lateral Offsets to Trees and Shrubs

6

5.8.1. Rural Shoulders

6

5.8.2. Urban Shoulders

6

List of Tables

Table 5.1 Minimum Lateral Offsets for Utility Installations: Rural Shoulders

5

Table 5.2 Minimum Lateral Offsets for Utility Installations: Urban Shoulders

5

Table 5.3 Minimum Lateral Offsets to Trees and Shrubs: Urban Shoulders

6

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5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTION
5.1. General Considerations
"Lateral Offset to Obstruction" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for minimum "lateral offset to obstruction" for roadway classifications in Georgia. A decision to use an offset value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer. In addition, GDOT has developed, as standard practice, the following more specific and selective criteria on "lateral offset to obstruction" for signs, light standards, utility poles, signal poles and controller cabinets, and trees and shrubs. A decision to use an offset value that does not meet the criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Chief Engineer.
It is the goal of the Georgia Department of Transportation (GDOT) to provide and maintain a high quality statewide multimodal transportation system. Addressing roadside safety is key to achieving this goal. Promoting effective relationships with stakeholders is also a GDOT goal. Often, input from stakeholders regarding roadside amenities and design requires a proactive and ongoing coordination effort with stakeholders to achieve success. While these two goals may at times seem to be in competition with one another, it is important to recognize that each goal contributes to GDOTs ability to achieve its mission of providing a safe transportation system that is sensitive to the needs of its citizens and environment.
Features and elements generally encountered in roadside design for new construction or reconstruction projects are identified in respective sections of this chapter. Therefore, this chapter addresses the area outside of the actual traveled way which is also an important component of roadway design. Under certain circumstances, the policies described in this chapter may not be applicable to permitting on existing facilities or temporary conditions and facilities.
The GDOT standard minimum lateral offsets to obstructions are listed later in this chapter. However, the reader is cautioned that the offsets alone do not present a complete solution to allow features or objects on the shoulder or roadside.
GDOT strongly discourages arbitrary reduction of design speed in order to reduce offset requirements.
Sound engineering judgment and reasonable environmental flexibility should be exercised in selecting and specifying roadside features at each location. "Roadside" is defined in the American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide as the area between the outside shoulder edge and the right-of-way limits. In curb and gutter sections, the roadside includes the urban shoulder, which is part of an urban roadway that begins at the edge of traveled way and extends to the right-of-way limit or to the breakpoint of the fore slope or back slope that ties to the natural terrain.

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The following elements should, at a minimum, be considered by the designer, even when compliance with established offsets is proposed:
current traffic volumes;
design year traffic volumes (for projects under design);
truck percentages;
current detailed crash history; posted speed limit;
design speed (if available); operating speed (85th percentile, off peak);
functional classification of the roadway; roadway setting/context (urban environment, rural, residential, commercial, historic district, etc.)
and if the proposed project fits in with the roadway setting/context;
existing operations (e.g. sight distance or vehicular operations), and the proposed projects affect on those operations;
maintenance; existing roadside elements (e.g. permitted utilities or lighting) impacted/affected by the
proposed project;
proposed roadside elements and their consistency with the needs of the corridor (e.g. safety, utility, and aesthetic needs for pedestrian, bicycle, transit, vehicular traffic; consistency needs in terms of conformity with local, regional, and state roadside amenity values); and
mitigation measures that should be considered (including the removal or relocation of fixed objects, the reduction of impact severity by implementing breakaway or traversable features, and the shielding of fixed objects with traffic barriers such as guardrail).

5.2. Rural Shoulder Lateral Offset to Obstruction
Lateral Offset to Obstruction is the horizontal distance measured from the edge of the traveled way, to the face of a roadside object or feature. The rural shoulder is the part of the roadway beyond the edge of traveled way that is graded or paved flush with the edge of traveled way to allow for emergency usage.

Lateral Offset to Obstruction for rural type shoulders, including graded or paved surfaces, is based on the concept of clear zone that is established by the AASHTO Roadside Design Guide. By definition, clear zone is the area beyond the roadway edge of traveled way which provides an environment free of fixed objects, with stable, flattened slopes which enhance the opportunity for vehicle recovery and/or reducing crash severity (AASHTO, 2006). Fixed objects include trees, large shrubs, bodies of water, and elements of the roadway facility such as road signs, structure piers, utility poles or light standards, and electrical or controller cabinets, or other non-moveable objects that can pose a safety hazard to a vehicle and its occupants if the vehicle leaves the roadway.

In determining the acceptable clear zone for a particular roadway and prevailing conditions, refer to the current AASHTO Roadside Design Guide in its entirety, and not just to the tables provided in Chapter 3 of the Guide. Principles of clear zone include safe drainage structure end treatments, ditch design, curve correction factors, and many other features that are key elements to the overall safe and aesthetically pleasing roadside design. It is not the intent of this Manual to reproduce the clear zone values that are provided in the AASHTO Roadside Design Guide.

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The designer should provide the maximum clear zone that is commensurate and practical for the prevailing conditions. The maximum clear zone values, based on the traffic volume, slope, geometry and design speeds identified in the current AASHTO Roadside Design Guide should be utilized on new construction or when providing full reconstruction of the roadway. If not practical to provide the recommended upper value due to overall highway design considerations, the minimum values shall be observed, for the respective conditions. For retro-fit types of projects, achieving the minimum clear zone values are acceptable.

Features or objects located within the accepted clear zone for a roadside should comply with the guidelines provided in the AASHTO Roadside Design Guide. If features or fixed objects cannot be removed or modified to become clear zone compliant, they shall be shielded in a cost effective manner that is consistent with current practice and standards. It is GDOTs policy that fixed objects in median areas of 64-ft or less that cannot be eliminated shall be treated with cost-effective shielding devices, such as guardrail, impact attenuators, or earth-mound redirection design.

In cases where road median widths are greater than 64-ft, but less than 84-ft, specific engineering judgment should be made by the designer. For medians wider than 84-ft, it is not necessary to protect fixed objects that are located near the center of the median and outside the required clear zone. For roadsides, it is GDOTs policy to shield objects that are within the defined clear zone. The intent of the designer should be to reduce the seriousness of the consequences of a vehicle leaving the roadway.

5.3. Urban Shoulder Lateral Offset to Obstruction
Lateral Offset to Obstruction on urban roadways is not based entirely on the clear zone concept due to various pre-existing conditions and urban roadway shoulder constraints, although clear zone considerations may apply under certain conditions, such as run-off-road (ROR) crash history, excessive volumes, geometric conditions, excessive operating speeds, new location construction, etc. Urban roadways are generally confined on the roadside and are posted at speeds of 45 mph or less. According to the AASHTO Roadside Design Guide, the presence of curb and gutter within the roadside, even barrier-faced, does not generally redirect a vehicle, especially at speeds above 25 mph. Lateral Offsets to Obstructions for urban roadways is based on the specific feature or element being considered, and generally is related to a combination of environmental, operational and safety characteristics, both for pedestrians and vehicular traffic.

According to the AASHTO Roadside Design Guide, Chapter 10, Roadside Safety in Urban or Restricted Environments, uniform lateral offsets between traffic and roadside features is desirable (2006). It is GDOTs intent to facilitate this principle as much as practical, using this design policy manual, ongoing education and collaboration with GDOT staff and participating stakeholders.

The GDOT Pedestrian and Streetscape Guide written and maintained by the GDOT Office of Planning, has direct application on urban shoulder usage. The GDOT Pedestrian and Streetscape Guide provides guidance for design professionals, developers, municipalities and others regarding the design, construction, and maintenance of pedestrian facilities.

The GDOT Office of Utilities employs the GDOT Utility Accommodation Policy and Standards Manual to guide decisions for utility facility placement on public right-of-ways. Both rural and urban conditions are addressed in this document.

The lateral offset of 1-ft, 6 in. from face of curb to face of fixed object stated in the AASHTO Green Book shall be an absolute minimum lateral offset for urban roadways. Lateral offsets
less than 1-ft, 6 in. shall require a design exception.

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5.4. Lateral Offsets for Signs
5.4.1. Sign Placement
Placement of traffic control, informational, or any other types of signs that are allowed on the road right-of-way shall be in accordance with the most current edition of the Federal Highway Administration (FHWA) Manual of Uniform Traffic Control Devices, (MUTCD), and with practices and policies of the GDOT Office of Traffic Operations.

Obstruction of sidewalks should be avoided in reconstruction projects. However, encroachments of sign placements in sidewalks, if necessary as a retrofit, shall ensure that an unobstructed, ADAcompliant sidewalk is provided.

5.4.2. Sign Supports
Sign supports, except for overhead sign supports, shall be frangible or breakaway in rural or urban shoulder environments. If the support is located outside the accepted clear zone for the roadway, frangible or breakaway design is not required.

If overhead sign supports are required within the accepted clear zone for the prevailing rural condition, the support shall be shielded with barrier or guardrail.

Overhead sign supports in urban roadways should observe the same lateral offset requirements as utility installations in urban roadways. However, if this is not practical, the minimum lateral offset from the face of curb to the face of the support is 6-ft.

5.5. Lateral Offsets for Light Standards
5.5.1. High Mast Roadway Lighting High mast lighting should be positioned outside the clear zone. If this is impractical, cost-effective shielding shall be provided in accordance with current standards for roadside barrier.

5.5.2. Roadway Lighting Roadway lighting should be placed on or along the outside shoulders as described below.

The size of the base must be considered when measuring lateral offset. Breakaway or frangible bases are generally wider than the pole.

Rural Shoulders
Light standards should be mounted outside the clear zone. Any light standards that are not located outside of the clear zone should be mounted on an AASHTO compliant breakaway mounting, or be appropriately shielded.

Urban Shoulders
In urban roadway conditions, light standards should be positioned in accordance with rural shoulder guidelines or as close to the right-of-way limit as possible.

If it is not feasible to comply with the above statement, light standards shall be placed directly outside of the sidewalk and at least 6-ft from the face of curb. Coordination of street light placement with sidewalks and other roadside features shall ensure that at least 4-ft of usable sidewalk remains, and that the lights do not conflict with other permitted features or elements on the urban shoulder.

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Normally, a breakaway mounting design should be used for urban shoulders. However, breakaway type designs should not be used on streets in densely developed, low speed, urban areas where high pedestrian volumes would be expected.

5.5.3. Pedestrian lighting (non-roadway)
All pedestrian light standards should be located at the back of the sidewalk. If sidewalk is not present, the light standards should be placed a minimum of 6-ft from the face of curb.

5.6. Lateral Offsets for Utility Installations
5.6.1. General Guidance
Utility installations are governed by the GDOT Utility Accommodation Policy and Standards Manual (UAPSM). Designers should read and understand the referenced policy, in conjunction with the policies and guidelines set forth in this Manual.

5.6.2. Rural Shoulders

Refer to Table 5.1. for GDOT minimum lateral offsets to utility installations on roadways with rural shoulders.
Table 5.1 Minimum Lateral Offsets to Utility Installations: Rural Shoulders

Posted Speeds

Slope Condition

GDOT Policy

< 60 mph

fill section with slopes 4:1 or flatter

Utility obstacles shall be located at least 30-ft from the edge of traveled way to the face of the obstacle

< 60 mph

fill section with slopes steeper than 4:1

The horizontal distance in which slopes steeper than 4:1 are encountered is not to be considered as
,,traversable and recoverable. Consult the AASHTO Roadside Design Guide and the UAPSM for full understanding.

> 60 mph

all slope conditions

Utility obstacle shall be located outside the accepted clear zone for the prevailing conditions, or 30-ft, whichever is greater.

5.6.3 Urban Shoulders Utility obstacles should be positioned as near as possible to the right-of-way or utility easement.
Utility obstacles should be placed in keeping with the nature and extent of roadside development.
Lateral offsets to utility obstacles is measured from the face of curb to the face of pole or obstacle.

Table 5.2 Minimum Lateral Offsets to

Utility Installations: Urban Shoulders

Posted Speeds

Minimum Lateral Offsets

< 35 mph

6-ft

No utility obstacle shall encroach on current sidewalk clearances required by ADA.

> 35 mph and < 45 mph

8-ft

For utility relocation on urban roadway projects, the

utility offset shall be governed by design speed, ADT,

= 45 mph

12-ft

etc.

The designer shall conform to the minimum lateral offsets listed in Table 5.2.

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5.7. Lateral Offsets for Signal Poles and Controller Cabinets for Signals
Lateral Offsets to signal poles and controller cabinets for signals are designated by the GDOT Office of Traffic Operations Traffic Signal Design Guidelines. 5.7.1. Rural Shoulders On roadways with rural shoulders, signal poles and controller cabinets for signals shall be located outside the clear zone.
5.7.2. Urban Shoulders The lateral offsets to signal poles and controller cabinets for signals shall be located a minimum of 6-ft from face of curb or behind sidewalk, whichever is greater.

5.8. Lateral Offsets to Trees and Shrubs
Guidance on lateral offsets to trees and shrubs is provided from the GDOT Office of Maintenance, which also includes approvals through the Office of Traffic Operations. Additional guidance is provided by the Office of Planning through the GDOT Pedestrian and Streetscape Guide. Utilities and intersection sight distance requirements may affect the location and diameter size of proposed trees in the lateral offsets and clear zone. Clear zone requirements can be found in the current AASHTO Roadside Design Guide or in Chapter 4 of the current GDOT Regulations for Driveway and Encroachment Control. The roadways design speed shall be used to determine lateral offset to obstruction criteria.
5.8.1. Rural Shoulders
On roadways with rural shoulders, trees and shrubs shall be located outside the clear zone.
5.8.2. Urban Shoulders
On roadways with urban shoulders with a posted design speed of greater than 45 mph, trees and shrubs shall be located outside of the clear zone. On roadways with urban shoulders with a posted design speed of 45 mph or less, refer to Table 5.3. for minimum lateral offsets for trees and shrubs.

Table 5.3 Minimum Lateral Offsets to Trees and Shrubs: Urban Shoulders

Posted / Design Speeds

Minimum Horizontal Clearance(1)

< 35 mph (Commercial Area(2))
< 35 mph
40 mph

4-ft 8-ft in median
8-ft 8-ft in median
10-ft 16-ft in median(3)

45 mph

14-ft 22-ft in median(3)

> 45 mph

Outside the clear zone

(1) From center of tree to face of curb (2) In a central Business District and/or where commercial businesses are typically directly adjacent to the right-of-way. (3)Small trees and shrubs that mature at <4" in diameter may be planted a minimum of 8 feet from the face of the curb in medians adjacent to 40 to 45 mph speeds. Tree size is diameter of the tree maturity, measured at dbh (4.5 feet) above the base of the tree. Certain situations may require an increased lateral offset for additional safety considerations. For rural shoulders, trees should be placed outside the clear zone. For Interstates, trees should have a minimum lateral offset of at least 120% of the clear zone requirement.

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Chapter 5 Index Lateral Offset, 17
General Considerations, 12 Light Poles, 45 Shoulder-Rural, 23, 4, 5, 6 Shoulder-Urban, 5, 6 Signs, 4 Traffic Signal Poles, 6 Trees and Shrubs, 6

Utilities, 56 Lighting
High Mast, 4 Highway, 45 Safety Horizontal Clearance. See Lateral Offset Roadside General Considerations, 12

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Chapter 6 Contents

6. CROSS SECTION ELEMENTS

3

6.1. Lane Width

3

6.2. Pavement Type Selection

3

6.3. Cross Slope

3

6.4. Pavement Crowns

3

6.5. Shoulders

4

6.6. Side Slopes

5

6.7. Border Area (urban shoulder)

6

6.8. Bike Lanes

7

6.9. Curbs

7

6.9.1. Curb Types

7

6.9.2. Methods of Construction

8

6.9.3. Raised Median Noses

9

6.9.4. Raised Channelizing Islands

9

6.10. Sidewalks

9

6.11. Barriers

910

6.11.1. Barrier Types

10

6.11.2. Glare Screens

11

6.11.3. End Treatments

11

6.12. Medians

1112

6.12.1. Interstate Medians

12

6.12.2. Arterial Medians

12

6.12.3. Medians at Pedestrian Crossings

13

6.13. Parking Lanes

13

6.14. Summary of Design Criteria for Cross Section Elements

1314

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i

List of Figures

Figure 6.1 Illustrates the dimensions of a 16-ft wide border area.

6

Figure 6.2. Illustration of Typical Dimensions for Urban Local Roadways

19

Figure 6.3. Illustration of Typical Dimensions for Rural Local Roadways

20

Figure 6.4 Illustration of Typical Dimensions for Collector and Arterial Roadways

21

Figure 6.5. Illustration of Typical Dimensions for Urban Freeway

22

Figure 6.6. Illustration of Typical Dimensions for Interchange Ramps

23

List of Tables

Table 6.1. Rumble Strip Placement

5

Table 6.2. Curb Types Allowed for Various Types of Roads

8

Table 6.3. Median Options for Arterials (Including GRIP Corridors)

1213

Table 6.4. Design Criteria for Local Roadways

15

Table 6.5. Design Criteria for Collector Roadways

16

Table 6.6. Design Criteria for Arterial Roadways

17

Table 6.7. Design Criteria for Freeways

18

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ii

6. CROSS SECTION ELEMENTS
6.1. Lane Width
"Lane width" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for lane width options for roadway classifications in Georgia. The designer is encouraged to select a lane width that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a lane width value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer.
6.2. Pavement Type Selection
The designer should refer to the current GDOT Pavement Design Manual for guidance relating to the pavement type selection process.
6.3. Cross Slope
"Cross slope" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for cross slope options for roadway classifications in Georgia. The designer is encouraged to select a cross slope that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a cross slope value that does not meet the controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer.
Typical practice is to provide a 2% pavement cross-slope for travel lanes. On multi- lane roadways, no more than two adjacent lanes should be constructed at the same cross slope. The cross slope may be broken at 1% intervals not to exceed 4% on any lane.
6.4. Pavement Crowns
There are four categories of pavement crowns:
One-way Tangent Crown: A one-way tangent crown slopes downward from left to right as viewed by the driver. It is used for all roadways providing one-way traffic, except as noted in the following paragraphs.
Two-way Tangent Crown: A two-way tangent crown has a high point in the middle of the roadway and slopes downward toward both edges. It is used for all roadways providing twoway traffic. For divided multi-lane highways, the pavement is sloped downward and away from the median centerline, or from the left or right edge line of the median lane on a five-lane section.
Two-way Crown Converted to One-way Use: When an existing roadway with a two-way crown is converted from two-way to one-way use, the existing crown shape can remain.

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However, if possible, leveling may be used to adjust cross-slope in order to obtain a constant cross-slope.
Cross-over Crown Break: The cross-over crown break between main lanes is limited to an algebraic difference of 4% (0.04 ft/ft). This applies at the break point of a two-way crown. The algebraic difference between the main roadway cross-slope and shoulder cross-slope should not exceed 8% (0.08 ft/ft).
6.5. Shoulders
"Shoulder width" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, the GDOT adopts the AASHTO Green Book criteria as the standard for shoulder width options for roadway classifications in Georgia. The designer is encouraged to elect a shoulder width that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a shoulder width value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer.
AASHTO defines a shoulder as, "the portion of the roadway contiguous with the traveled way that accommodates stopped vehicles, emergency use, and lateral support of the subbase, base and surface courses." GDOT has adopted 10-ft as the typical overall shoulder width for higher volume and higher speed (>45 mph) collector and arterial roadways in Georgia. This is consistent with the AASHTO desirable criteria for normal shoulder width along high-type facilities (see AASHTO Green Book, Ch. 4, Cross Section Elements).
For high speed freeways and interstates, GDOT has adopted 14-ft as the typical overall outside shoulder width with 12-ft paved adjacent to the traveled way, and 12-ft as the typical overall inside shoulder width with 10-ft wide paved adjacent to the traveled way. Interstate ramp shoulders should be 12-ft wide outside with 10-ft paved adjacent to the traveled way, and 8-ft wide inside with 4-ft paved adjacent to the traveled way.
The typical shoulder cross-slope for total shoulder width and paved shoulder width established by GDOT is 6% for outside shoulders and 4% for shoulders within the median of a multilane roadway. This can vary depending on project specifics. For instance, on some projects the paved shoulder cross-slope matches the roadway cross-slope. On four-lane divided highways, the cross-slope on the median shoulder in tangent section is controlled by the cross-over crown restrictions described in Section 6.4 of this Manual. Similarly, the outside shoulder cross-slopes (the convex side of the curve) on superelevated roadways will be controlled by the cross-over crown restrictions. As a result, the slope will depend on the superelevation rate.
On superelevated roadways, the inside shoulder will maintain its normal crown slope for superelevation rates equal to or less than the normal shoulder slope. For superelevation rates greater than the normal shoulder rate, the inside shoulder slope is the same as the superelevation rate of the roadway. For additional discussion of the superelevation, refer to Chapter 4 of this manual.

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Rumble Strips should be used as follows (see Table 6.1 for placement):
rumble strips are to be the milled-in type;
dimensions - 16 inches width, 7 inches length, inch depth, 5 inches space between;
skip pattern - 28-ft of rumble strips, 12-ft clear space.

Table 6.1. Rumble Strip Placement

Roadway Type Interstate / Freeway(1)

Rumble Strip Placement
Continuous

Multi-Lane Rural Section (design speed >50 mph)

Skip pattern

Two-Lane Rural Section (>400 ADT & >50 mph)

2-ft Paved Shoulder

No rumble strip

4-ft Paved Shoulder

Skip pattern

(1) Where bicycles are NOT allowed

Refer to GDOT Construction Detail S-8 for drawings of 4-ft. and 6.5-ft. paved shoulders, each showing the placement of the rumble strips. A paved 6.5-ft. shoulder should be provided on all multi-lane divided roadways with rural shoulders to provide for bicycle accommodation. Under special circumstances, GDOT Construction Details T-19, T-23 and T-24 provide other applications for various rumble strip/rumble patch devices.
6.6. Side Slopes
The AASHTO Roadside Design Guide specifies the maximum (steepest) side slope that should be used on a project in order to meet clear zone requirements. Where a range of slopes is given, the Designer should strive to provide as flat a slope as practical.
All front slopes (foreslopes) should be 4:1 or flatter, and no steeper than 2:1. GDOT discourages the use of 2:1 front slopes with guardrail unless economic constraints (construction costs, right-ofway impacts, or environmental impacts) outweigh the practicality of a 4:1 front slope.
GDOT prefers the use of 6:1 front slopes on ditch sections with design speeds 65 mph; however, 4:1 front slopes are allowed as long as clear zone requirements are met.
A "barn roof" is a roadway side slope that begins with a shallow slope, and is followed by a steeper traversable slope to allow the embankment to tie into the existing ground quicker than the shallower slope would. This reduces the amount of embankment and right-of-way required to construct the roadway. Figure 3.2 of the Roadside Design Guide shows an acceptable barn roof configuration. This figure shows a recoverable slope followed by a steeper non-recoverable 3:1 slope. This design provides a traversable side slope from the roadway to the bottom of the embankment.
Although a "barn roof" with a 2:1 side slope outside of the clear zone technically complies with clear zone requirements, vehicles leaving the roadway have a tendency to travel to the bottom of any slope, including recoverable slopes. For this reason, barn roof is generally not acceptable if the front slope includes a non-traversable 2:1 front slope.
In addition to the safety benefits, in urban and residential areas, slopes 4:1 or flatter can be mowed easily with a lawnmower. Efforts to save trees and other items sometimes complicate this procedure, and each residential lot should be addressed separately. Configurations should result in both a pleasing appearance and an easily maintainable configuration.
Refer to Chapter 5, Roadside Safety and Lateral Offset to Obstruction of this manual and the AASHTO Roadside Design Guide, Chapter 3 for further discussion about roadway side slopes.

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6.7. Border Area (urban shoulder)
Typically referred to as an "urban shoulder", the AASHTO Green Book (Ch.4, Pedestrian Facilities) defines "border area" as, "In suburban and urban locations, a border area generally separates the roadway from a community's homes and businesses. The main function of the border is to provide space for sidewalks...streetlights, fire hydrants, street hardware, and aesthetic vegetation and to serve as a buffer strip."
GDOT defines the limits of the border area on urban type projects to be from the outside edge-ofpavement outward, and to include the gutter, the curb, the sidewalk and any space available for buffer and/or utilities. GDOT encourages the use of a 16-ft wide border area on urban type projects, where right-of-way permits. When a roadway has multiple driveways, a 16-ft wide border area provides the buffer space needed to construct a sidewalk at a consistent 6-ft offset from the back of curb and to align with the back of a standard driveway concrete valley gutter. If a 16-ft wide border area is not practical, then a border area 10-ft wide is acceptable. In all cases, the sidewalk design must comply with ADA regulations. See Section 9.5.1 Pedestrian Facility of this manual for design criteria relating to sidewalks and pedestrian facilities in Georgia.

Figure 6.1 Illustrates the dimensions of a 16-ft wide border area.

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6.8. Bike Lanes
See Section 9.5.2 Bicycle Facility Design for design criteria relating to bicycle facilities in Georgia.

6.9. Curbs
The type and location of curbs affects driver behavior and the safety and utility of a highway. Curbs serve any or all of the following purposes:

drainage control; pavement edge delineation; right-of-way reduction; aesthetics; delineation of pedestrian walkways; reduction of maintenance operations; and assistance in orderly roadside development.

The AASHTO Green Book states that vertical curbs should not be used along freeways or other high-speed (i.e., > 45 mph) roadways, but if a curb is needed, it should be of the sloping type. Where used for pavement drainage or to intercept runoff from the roadside, V-gutter (with appropriately spaced inlets) is prefered over sloped curb.

For roadways with a design speed > 45 mph, sloped curb faces on outside shoulders should be offset to the back of paved shoulder. The width of the paved shoulder should be at least 10-ft. For multi-lane divided roadways with a design speed > 45 mph, sloped curb faces on inside shoulders should be offset at least 4-ft from the inside edge of travel lane.

Curbs may be constructed by a variety of methods. Typical shapes and dimensions for various types of curbs, including curb and gutter, are shown in GDOT Construction Standards and Details Ga. Std. 9032B.

The relationship of curb-to-guardrail is critical. If the curb is not properly located, the guardrail will not function as intended. Chapter 5 of the AASHTO Roadside Design Guide (2006) discusses the location of curb with respect to the face of the guardrail. For additional information, refer to GDOT Construction Standards and Details, Ga. Std. 4280. See also Section 6.11.1 of this manual.

6.9.1. Curb Types
Sloped Curbs or Barrier Curbs Curb shapes are generally classified as either sloped or barrier curbs. The sloped curb has a flat sloping face. The barrier curb has a characteristic steep face.

Generally, barrier curb is only used when sidewalks are provided and in the curb return of turnouts to intersecting streets. See Table 6.2 for proper use of curb.

Concrete or Asphaltic Curbs
Portland cement concrete is used for most curbs. Asphaltic curbs are limited primarily to header curbs in parking areas. Asphaltic curbs are also used to control runoff and erosion on high fills (>20-ft) with 2:1 side slopes or in guardrail sections along rural roadways. See GDOT Construction Standards and Details, Construction Detail S-4 for information regarding the placement of asphaltic curbs behind guardrail.

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Table 6.2. Curb Types Allowed for Various Types of Roads
Road Type

Curb Type(1)

Interstate Urban

State Route Design Speed
< 45 mph

State Route Design Speed
> 45 mph

Other Off Roadway Classification

Concrete Curb and Gutter

Type 1 Type 2 Type 3 Type 4 Type 7

x

x

x

x

x

x

x

x

x

x

Concrete Header Curb

Type 1

x

Type 2

x

x

x

Type 3

x

Type 4

x

Type 7 Type 8

x

x

x

x

x

x

x

Raised Median

Type 1

Type 2

x

Type 7

x

x

x

x

Raised Island

Type 1

Type 2 Type 7

x

x

x

x

V Gutter

x

x

(1) Typical shapes and dimensions for various types of curbs, including curb and gutter,

are shown in Ga. Std. 9032B. Four-inch sloped Type I curbs placed at the back of the

usable shoulder may be used on high speed facilities. For curbs on roundabouts see

Section 8.3.8 of this manual.

6.9.2. Methods of Construction

Integral Curb For concrete pavements, integral curb is preferred to curb and gutter because of economy in initial construction and maintenance. With this method, the concrete curb is poured when the concrete slab for the roadway is still in a plastic state. This creates an integral bond between the roadway and the curb. An alternate, and more popular, method of construction is to place tie bars in the concrete of the roadway slab. Later, when the pavement has hardened, the curb is poured so that the tie bars hold the curb firmly in place on the roadway. Although not truly integral with the pavement, this curb is commonly referred to as integral/tied curb. The depth of integral/tied curb should match the depth of the roadway slab.

Curb and Gutter

Concrete curb and gutter, as shown in the GDOT Construction Standards and Details, Ga. Std.

9032B, is generally used with asphaltic concrete pavement. Under this method, both the curb and

the gutter are poured together, but not at the same time as the roadway pavement. The GDOT

standard curb and gutter width is 2.5-ft for both sloped and barrier type curb and gutter. Where

curb and gutter is placed adjacent to concrete pavement on curbed sections, tie bars should be

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used to connect the curb and gutter to the adjacent pavement. This prevents separation of the curb and gutter from the edge of the pavement.
Under restrictive right-of-way conditions, a 2-ft wide curb and gutter (6-inch curb, 18-inch gutter) may be used on local streets and state routes in Georgia, as shown in the GDOT Construction Standards and Details, GA. Std. 9032C. The designer should note that reducing the gutter width by 6-inches will reduce the hydraulic gutter capacity along the roadway and thus possibly increase the amount of drainage structures required to control an acceptable gutter spread for the design storm event. In addition, a reduced gutter width will require deeper Drop Inlet structures (Ga. Std. 1019C). Therefore, the decision to use a 2-ft wide curb and gutter will require an engineering study and approval by the State Design Policy Engineer/Hydraulics Engineering Group. The engineering study must certify that the right of way savings and material savings exceed the cost of additional drainage structures required to mitigate the reduced gutter capacity.
6.9.3. Raised Median Noses
To prevent vehicles from breaking the curb in the nose of raised medians, a monolithic section of curb and median pavement should be constructed. See GDOT Construction Standards and Details, Construction Details of Median Crossovers (M-3).
6.9.4. Raised Channelizing Islands
Raised channelizing islands help control and direct the movement of traffic by reducing excess pavement areas, and channelizing turning movements at intersections. In urban locations, a sloped curb is generally used in conjunction with striping to delineate the island. In rural locations where higher speeds are likely, islands are typically delineated with a sloped curb and offset appropriately. In areas with crosswalks where raised islands will be used for pedestrian refuge, the geometry of the intersection and the right turn lanes may need to be modified to ensure that the raised islands are large enough to accommodate ramps and pedestrian refuge areas, along with support for pedestrian signals and control buttons, that are compliant with the Americans with Disabilities Act1 (ADA) guidelines.
Raised islands should be offset from the travel lane as shown in the current GDOT Regulations for Driveway and Encroachment Control. Refer to Chapter 9 of the current AASHTO Green Book for additional information. Raised islands should be offset 4-ft from travel lanes when posted speeds are < 45 mph and 10-ft from travel lanes when posted speeds are > 45 mph.
6.10. Sidewalks
See Section 9.5.1 Pedestrian Facility Design for design criteria related to sidewalks.
6.11. Barriers
Chapters 5 and 6 of the AASHTO Roadside Design Guide provide details on the application and design of various barriers, including guardrail, cable, and concrete median barriers. Recommendations on the layout and type of barrier to be used are usually obtained from the Office of Bridge and Structural Design when bridges are involved. All other applications are the responsibility of the designer.

1 Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements http://www.fhwa.dot.gov/environment/te/te_ada.htm

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6.11.1. Barrier Types
The following barrier types should be used under the various stated conditions:
Cable Barrier This is a flexible barrier capable of deflecting 12-ft or more when impacted. Barrier is typically used in the grassed medians of interstates and freeways. The designer shall account for the deflection when determining the location of the barrier.
W-Beam Guardrail A semi-flexible barrier that will deflect up to 5-ft W-beam may be used to prevent vehicles from crossing medians, traversing steep slopes or striking objects. Cannot be used 8-ft from curb face. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs.
T-Beam Guardrail Similar to W-beam guardrail, but deflects only 3-ft T-beam is used on transitions from W-Beam to a Concrete Barrier. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs.
Double Faced Guardrail Semi-flexible barrier capable of deflecting 5-ft Used in medians and other locations to prevent errant vehicles from crossing into opposing traffic.
Single Slope Concrete Barrier A rigid barrier with little or no deflection. Used for medians or side barrier directly in front of rigid objects that are near the traveled way. This includes walls and bridge bents. This is the preferred barrier for Interstates and new construction where Jersey shape barrier is not being retained.
Jersey Shaped Concrete Barrier Same uses as single slope concrete barriers. May be used on projects where portions of existing Jersey barrier can be retained to provide a consistent design and appearance. Jersey barrier cannot be retained when construction raises the pavement surface by 3-inches or higher than the bottom lip of the barrier.
Temporary Barriers The design, installation and maintenance of temporary barriers is discussed in the following documents:
AASHTO Roadside Design Guide, Chapter 9 FHWA Manual on Uniform Traffic Control Devices (MUTCD)2, part 6 DOT Specifications, Section 150 GDOT Construction Standards and Details, Details of Precast Temporary Barrier (Ga. Std.
4961).
Two methods of temporary barrier are used:
Method 1 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Report 3503 "Test Level 3" approved or meets the requirements of Ga. Std. 4961. Method 1 barrier is not suitable on bridges where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft, measured normal to the barrier.

2 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003 The 2003 version of the MUTCD is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm
3 TRB. National Cooperative Highway Research Program (NCHRP) Report 350, Procedures for the Safety Performance Evaluation of Highway Features. 1992 Available online at: http://safety.fhwa.dot.gov/roadway_dept/road_hardware/nchrp_350.htm

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Method 2 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Procedures for the Safety Performance Evaluation of Highway Features (Report 350) "Test Level 3" and does not deflect more than 1-ft under NCHRP test conditions. A Method 2 barrier shall be used on bridges and bridge approaches where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft measured normal to the barrier.
Refer to the current AASHTO Roadside Design Guide for further discussion on the properties and uses of these barriers.
6.11.2. Glare Screens
Glare screens are required on all interstate concrete median barriers. Glare screens for concrete barriers are typically constructed as concrete extensions but alternate materials may be used on a case-by-case basis.
A glare screen is required between the mainline and frontage roads with opposing traffic flows. Where concrete barriers are not used, a glare screen such as landscaping materials, fencing with inserts or walls may be used to minimize glare. With offsets greater than 40-ft, glare screens are not required, but should be evaluated to determine if needed.
6.11.3. End Treatments
All blunt approach ends of barriers should be protected in one of the following methods:
Guardrail transition with a Type 12 anchorage the Type 12 is a gating or non-gating guardrail terminal. This end treatment requires a wider shoulder than the guardrail it is attaching to, so the designer must ensure that additional shoulder width is included for the Type 12 treatment.
Energy absorption end treatment - attenuators must be installed in accordance to the manufacturer's recommendations. In general, attenuators should not be placed on a raised median. The median must be tapered so a stray vehicle impacts the barrier without being vaulted by the curb.
Flared beyond the clear zone see GDOT Construction Standards and Details for flare rates. Temporary end treatments should be used in work zones, where warranted.
Blunt ends are acceptable in urban areas where the blunt end is equal to or beyond the lateral offset specified in Chapter 5 of this Manual. For this condition, the end shall be tapered with a 6:1 slope. For additional information, refer to the current AASHTO Roadside Design Guide, Chapter 8; and all applicable GDOT Construction Standards and Details .
6.12. Medians
GDOT has adopted the following "median usage" criteria as standard, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. The designer is encouraged to select a median dimension that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a median dimension value that does not meet the standard criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the GDOT Chief Engineer.

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The following factors should be considered when determining the applicable median dimension along a roadway:
functional classification; type of development; access management plan; number of lanes; base year traffic; design year traffic; posted speed limit; design speed; and accident/crash data.

6.12.1. Interstate Medians Interstates are required to have a depressed median or positive barrier separation in areas of rightof-way restrictions, as specified in the AASHTO Green Book. Positive barrier separation is required for all median widths 52-ft or where mutually exclusive clear zone for each direction of traffic cannot be obtained. Positive barrier separation is not required for median widths > 64-ft Median barrier is optional for median widths between 52-ft and 64-ft Positive barrier separation should be considered for all existing medians where there is a history of cross median type accidents.

6.12.2. Arterial Medians
Multi-lane roadways with design speeds > 45 mph shall require the positive separation of opposing traffic using a median.

Multi-lane roadways with three or more lanes in each direction shall include positive separation of opposing traffic using a median.

A 24-ft raised median will require a sloped curb (Type 7 curb-face) inside the median, and a 2-ft additional paved shoulder offset from the edge of the inside travel-lane to the edge of the gutter (for a total of 4-ft inside shoulder width from the edge of travel-lane to the face of the curb).

Raised medians shall be constructed on multi-lane roadways at intersections that exhibit one of the following characteristics:

high turning volumes relating to 18,000 ADT (base year) and 24,000 ADT (design year); accident rate greater than the state average for its classification; and excessive queue lengths (as determined by District Traffic Engineer) in conjunction with
excessive number of driveways.

Median options for arterial roadways (including GRIP Corridors) are described in Table 6.3.

Table 6.3. Median Options for Arterials (Including GRIP Corridors)

Median Width

ADT (Base Year)

ADT (Design Year)

Design Speeds 45 mph

5-lane section (14-ft flush median) 5-lane section (14-ft flush median)(1) 20-ft or 24-ft raised median(2)

< 18,000 < 18,000 > 18,000

< 24,000 > 24,000 > 24,000

Design Speeds 55 mph

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24-ft raised median 32-ft depressed median 44-ft depressed median

n/a

n/a

n/a

n/a

n/a

n/a

Design Speeds 65 mph

44-ft depressed median

n/a

n/a

(1) The project footprint should be designed and right-of-way purchased, to incorporate a future 20-ft raised median or preferably a 24-ft raised median where practical. The need to retrofit a flush median to a raised median section should be determined by the monitoring of accidents and traffic volumes on a five-year cycle by the Safety Engineer in the GDOT Office of Traffic Operations.

(2) GDOT prefers the use of a 24-ft raised median where practical.

6.12.3. Medians at Pedestrian Crossings
Locations where a significant number of pedestrians are likely to be crossing the roadway at midblock may warrant positive separation of opposing traffic using a median for pedestrian refuge. Signals are not typically warranted at these locations. Two-phase pedestrian crossings may be required when the roadway width requires excessive pedestrian crossing time (i.e. 6-lane section with dual left turn lanes and a right turn lane, etc). In the case of a two-phase pedestrian crossing, the median shall be wide enough to provide an ADA-compliant pedestrian refuge area.
6.13. Parking Lanes
Generally, parking on arterial highways is prohibited because on-street parking decreases through capacity, impedes traffic flow, and increases accident potential. At the request of the local governing authority, consideration may be given to the inclusion of parking adjacent to the roadway in special situations if the following conditions are met: parking currently exists adjacent to the roadway; adequate off-street parking facilities are unavailable or unfeasible; the subsequent reduction in highway capacity will be insignificant; and
the local governing authority has agreed to pay for the additional costs associated with the onstreet parking, such as additional right-of-way, construction costs, etc.
When on-street parking is allowed on a roadway, parallel parking is the preferred type. Under certain circumstances, angled parking is allowed. However, angled parking presents sight distance problems due to the varying length of vehicles, such as vans and recreational vehicles. The extra length of these vehicles may also interfere with the traveled way. The type of on-street parking selected should depend on the specific function and width of the street, adjacent land uses and traffic volume.
6.14. Summary of Design Criteria for Cross Section Elements
GDOT has developed the following tables to summarize the criteria used to design typical cross section elements for roadway classifications in Georgia with Average Daily Traffic greater than 2000 vehicles per day. The criteria listed within the tables represents typical geometric dimensions used to design common rural and urban type roadways according to the selected design speed. The tables are for reference only and do not reflect every possible design option available to the designer. Drawings of commonly used typical sections are also provided to illustrate the application of the criteria listed in the tables. The designer is encouraged to select design criteria that provides

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a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment.
Table 6.4. Design Criteria for Local Roadways Table 6.5. Design Criteria for Collector Roadways Table 6.6. Design Criteria for Arterial Roadways Table 6.7. Design Criteria for Freeways

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Table 6.4. Design Criteria for Local Roadways

Cross Section Element

Rural (open ditch sections)
(ADT > 2000)(1)

Urban (curbed sections) (ADT > 2000)(1)

2-Lane

2-Lane

Design Speed Desirable Level of Service (LOS)(2)

35 mph C or D

45 mph C or D

55 mph C or D

25 mph C or D

35 mph C or D

Traveled Way Lane width (min-desirable)(3) Cross Slope (normal) Superelevation (max)

11-12-ft 2% 6%

11-12-ft 2% 6%

11-12-ft 2% 6%

10-12-ft 2% 4%

10-12-ft 2% 4%

Shoulders Overall width Paved width Cross Slope (normal)

8-ft

8-ft

10-ft

n/a

n/a

2-ft

2-ft

2-ft

n/a

n/a

6%

6%

6%

n/a

n/a

Border Area (urban shoulder) (width) Cross Slope (normal)

n/a

n/a

n/a

10-16-ft

10-16-ft

n/a

n/a

n/a

2%

2%

Sidewalk (SW) Width of Sidewalk Desirable buffer from back of curb to SW Cross Slope (max)
Width of Bike Lanes Foreslope (max/normal)(6)
Width of foreslope in cut

n/a n/a n/a 4-ft(4)
2:1/4:1 10-ft

n/a n/a n/a 4-ft(4)
2:1/4:1 12-ft

n/a n/a n/a 4-ft(4)
2:1/4:1 12-ft

5-ft 6-ft 2% 4-ft(5)
2:1/4:1 n/a

5-ft 6-ft 2% 4-ft(5)
2:1/4:1 n/a

Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8)
Clear Zone(9)

2-ft 2:1/4:1 14.5-16.75 Ch. 5
18-ft

4-ft 2:1/4:1 14.5-16.75 Ch. 5
24-ft

4-ft 2:1/4:1 14.5-16.75 Ch. 5
26-ft

n/a 2:1/4:1 14.5-16.75 Ch. 5
AASHTO

n/a 2:1/4:1 14.5-16.75 Ch. 5
AASHTO

Notes:

(1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT < 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400.
(2) LOS D is appropriate in heavily developed urban or suburban areas. (3) See AASHTO Green Book, Chapter 5, Local Roads and Streets, for conditions to construct or retain 10 and 11-ft lanes. (4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch
buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants.

(5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb.

(6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series).

(7) 14.5-ft is permissible, provided a suitable bypass exists for tall vehicles. For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual.
http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/BridgeandStructure/GDOT_Bridge_and_Structures_Policy_Manual.pdf
(8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT guidelines

on lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs.
(9) AASHTO defines Clear Zone as the unobstructed relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3.

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Table 6.5. Design Criteria for Collector Roadways

Cross Section Element

Rural (open ditch sections)
(ADT > 2000)(1)

Urban (curbed sections) (ADT > 2000)(1)

2-Lane

4-Lane

2-Lane

4-Lane

Design Speed Desirable Level of Service (LOS)

45 mph C

55 mph C

25 mph C or D(2)

35 mph C or D(2)

45 mph C or D(2)

Traveled Way Lane width (min-desirable)(3) Cross Slope (normal)

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

Superelevation (max)

6%

6%

4%

4%

4%

Shoulders (outside)

Overall width Paved width Cross Slope (normal)

8-ft

10-ft

n/a

n/a

n/a

4-ft/6.5-ft(4)

6.5-ft

n/a

n/a

n/a

6%

6%

n/a

n/a

n/a

Shoulders (median)

Overall width Paved width

n/a

6-ft

n/a

n/a

n/a

n/a

2-ft

n/a

n/a

n/a

Cross Slope (normal)

n/a

4%

n/a

4%

4%

Border Area (urban shoulder) (width) Cross Slope (normal)

n/a

n/a

10 -16-ft

10 -16-ft

10 -16-ft

n/a

n/a

2%

2%

2%

Width of Median

Depressed Raised

n/a

32 - 44-ft

n/a

n/a

24-ft

n/a

n/a 20-ft

n/a 20-ft

Flush

n/a

n/a

n/a

14-ft

14-ft

Sidewalk (SW)

Width of Sidewalk

n/a

n/a

5-ft

5-ft

5-ft

Desirable buffer from back of curb to SW Cross Slope (max)
Width of Bike Lanes Foreslope (max/normal)(6)

n/a n/a 4-ft(4)
2:1/4:1

n/a n/a 4-ft(4)
2:1/4:1

6-ft 2% 4-ft(5)
2:1/4:1

6-ft 2% 4-ft(5)
2:1/4:1

6-ft 2% 4-ft(5)
2:1/4:1

Width of foreslope in cut

12-ft

12-ft

n/a

n/a

n/a

Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8)

2-ft 2:1/4:1 16.5 -16.75 Ch. 5

4-ft 2:1/4:1 16.5 -16.75 Ch. 5

n/a 2:1/4:1 16.5-16.75 Ch. 5

n/a 2:1/4:1 16.5 -16.75 Ch. 5

n/a 2:1/4:1 16.5 -16.75 Ch. 5

Clear Zone(9)

24-ft

26-ft

AASHTO AASHTO AASHTO

Notes:

(1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT < 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400.

(2) LOS D is appropriate in heavily developed urban and suburban areas.

(3) See AASHTO Green Book, Chapter 6, Collector Roads and Streets, for conditions to construct or retain 11-ft lanes.

(4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants.

(5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb.

(6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series).

(7) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual.

(8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs.

(9) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3.

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Table 6.6. Design Criteria for Arterial Roadways

Cross Section Element

Rural (open ditch sections)
(ADT > 2000)(1)

Urban (curbed sections) (ADT > 2000)(1)

2-Lane

2-Lane

4-Lane

4-Lane

4-Lane

4-Lane

Design Speed Desirable Level of Service (LOS)

45 mph B

55 mph B

55 mph B

65 mph B

45 mph C or D(2)

55 mph C or D(2)

Traveled Way Lane width (min-desirable)(3) Cross Slope (normal)

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

11-12-ft 2%

Superelevation (max)

6%

6%

6%

6%

4%

4%

Shoulders (outside)

Overall width Paved width Cross Slope (normal)

8-ft

10-ft

10-ft

10-ft

n/a

n/a

4-ft /6.5-ft(4) 4-ft /6.5-ft(4)

6.5-ft

6.5-ft

n/a

n/a

6%

6%

6%

6%

n/a

n/a

Shoulders (median)

Overall width (cross slope)

n/a

n/a

6-ft (4%) 6-ft (4%)

n/a

n/a

Paved width (cross slope with mainline)

n/a

n/a

2-ft (2%) 2-ft (2%)

n/a

2-ft

Border Area (urban shoulder) (width)

n/a

n/a

n/a

n/a

10 -16-ft

10 -16-ft

Cross Slope (max)

n/a

n/a

n/a

n/a

2%

2%

Width of Median

Depressed

n/a

n/a

32 - 44-ft

44-ft

n/a

n/a

Raised Flush

n/a

n/a

24-ft

n/a

20-ft

24-ft

n/a

n/a

n/a

n/a

14-ft

n/a

Sidewalk (SW)

Width of Sidewalk

n/a

n/a

n/a

n/a

5-ft

5-ft

Desirable buffer from back of curb to SW

n/a

n/a

n/a

n/a

6-ft

6-ft

Cross Slope (max)
Width of Bike Lanes Foreslope (max/normal)(6)
Width of foreslope in cut

n/a 4-ft(4)
2:1/4:1 12-ft

n/a 4-ft(4)
2:1/4:1 12-ft

n/a 4-ft(4)
2:1/4:1 12-ft

n/a 4-ft(4)
2:1/6:1 18-ft

2% 4-ft(5)
2:1/4:1 n/a

2% 4-ft(5)
2:1/4:1 n/a

Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8)

2-ft 2:1/4:1 16.5-16.75 Ch. 5

4-ft 2:1/4:1 16.5-16.75 Ch. 5

4-ft 2:1/4:1 16.5-16.75 Ch. 5

4-ft 2:1/6:1 16.5-16.75 Ch. 5

n/a 2:1/4:1 16.5-16.75 Ch. 5

n/a 2:1/4:1 16.5-16.75 Ch. 5

Clear Zone(9)

24-ft

26-ft

26-ft

32-ft

AASHTO AASHTO

Notes:

(1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT< 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400.

(2) LOS D is appropriate in heavily developed urban and suburban areas.

(3) See AASHTO Green Book, Chapter 7, Rural and Urban Arterials, for conditions to construct or retain 11-ft lanes.

(4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants.

(5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb.

(6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series).

(7) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual.

(8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs.

(9) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3.

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Table 6.7. Design Criteria for Freeways

Cross Section Element

Rural (graded shoulders and
ditches) (ADT > 6000)

Urban (depressed/restricted R/W)
(ADT > 6000)

4 6 Lane

4 6 Lane

Design Speed Desirable Level of Service (LOS)

70 mph B or C(1)

55 mph C or D(2)

65 mph C or D(2)

Traveled Way Lane width Cross Slope (normal) Superelevation (maximum)

12-ft 2% 8%

12-ft 2% 6%

12-ft 2% 6%

Shoulders (outside) Overall width Paved width

14-ft 12-ft

14-ft 12-ft

14-ft 12-ft

Shoulders (median) Overall width Paved width

12-ft 10-ft(3)

12-ft 10-ft(3)

12-ft 10-ft(3)

Width of Median
Depressed Continuous Barrier (6-lanes) Continuous Barrier (8-lanes) Foreslope (max/normal)(4)
Width of foreslope in cut

52-64-ft n/a n/a
2:1/6:1 18-ft

n/a 30 40-ft 28 30-ft
2:1/6:1 n/a

n/a 30 40-ft 28 30-ft
2:1/6:1 n/a

Ditch Bottom (width) Backslope (max/normal)(4) Vertical Clearance (min-desirable)(5)(ft) Lateral Offset to Obstruction(8)
Clear Zone(7)

4-ft 2:1/4:1 16.5-17 Ch. 5
36-ft

n/a 2:1/4:1 16.5-17 Ch. 5
AASHTO

n/a 2:1/4:1 16.5-17 Ch. 5
AASHTO

Note: (1) LOS C is appropriate for developing rural and suburban areas and for auxiliary lanes. (2) LOS D is appropriate in heavily developed urban areas. (3) A 12-ft wide paved inside shoulder should be used on Freeways with six or more lanes, and truck volumes greater
than 250 vehicles/hour. (4) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier
(i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series). (5) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual. (6) For Freeways, lateral offset is measured from the edge of traveled way outward. See Chapter 5 of this Manual for
GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs. (7) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3.

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Figure 6.2. Illustration of Typical Dimensions for Urban Local Roadways

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Figure 6.3. Illustration of Typical Dimensions for Rural Local Roadways
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Figure 6.4 Illustration of Typical Dimensions for Collector and Arterial Roadways

Figure 6.5. Illustration of Typical Dimensions for Urban Freeway

Figure 6.6. Illustration of Typical Dimensions for Interchange Ramps
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Chapter 6 Index
Barriers End Treatments, 11 Glare Screens, 11 Guardrail, 10, 11 Jersey, 10 Temporary, 10 Types, 10
Cross Section Barriers. See Barriers Curbs. See Curbs Elements, 314 Medians, 1214 Parking Lanes, 14 Typical Section Geometrics, 3
Cross-over Crown Break. See Pavement, Crown
Curbs, 49 Glare Screens. See Barriers, Glare Screens

Guardrail. See Barriers, Guardrail Jersey Barrier. See Barriers, Jersey Medians
Cross Section, 1214 Interstate, 12 Pedestrian Crossings, 13 One-way Tangent Crown. See Pavement, Crown Parking Lanes. See Cross Section, Parking Lanes Pavement Crown, 3 Type Determination, 3 Pedestrian Facilities Medians. See Medians, Pedestrian Crossings Temporary Barriers. See Barriers, Temporary Two-way Tangent Crown. See Pavement, Crown

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Chapter 7 Contents

7. AT GRADE INTERSECTIONS

2

7.1. Intersection Design Elements

2

7.2. Intersection Geometrics

2

7.2.1. Angle of Intersection/Skew Angle

2

7.2.2. Right-of-Way Flares

2

7.2.3. Turn Lanes

3

7.2.4. Islands

3

7.2.5. Intersection Radii

3

7.3. Median Openings

4

7.4. Driveways

5

7.5. Signalization

5

7.5.1. New Intersections and Existing Unsignalized intersections

7

7.5.2. Signal Modification

7

7.5.3. Geometric Design Elements

8

7.6. Highway-Railroad Grade Crossings

8

7.6.1. Horizontal Alignment

9

7.6.2. Vertical Alignment

9

7.6.3. Highway-Rail Grade Traffic Control Considerations

10

7.6.4. Traffic Control Devices

11

7.6.5. Alternatives to Maintaining the Crossing

12

7.6.6. Crossing Consolidation and New Crossings

13

7.6.7. GDOT At-Grade Highway-Rail Crossing Evaluation Criteria

14

Chapter 7 Index

16

Summary of Chapter 7 Revisions

17

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7. AT GRADE INTERSECTIONS
The American Association of State Highway and Transportation Officials (AASHTO) A Policy on the Geometric Design of Highways and Streets (Green Book) defines an intersection as, "the general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area". The main objective of intersection design should be to facilitate the safe and efficient movement of motor vehicles, buses, trucks, bicycles, and pedestrians.
7.1. Intersection Design Elements
The mobility and operational characteristics of a facility will depend on proper intersection design. Intersection design should closely fit the natural paths and operating characteristics of its users. The five basic elements that should be considered in intersection design are:
Human Factors - driving habits, the ability of motorists to make decisions, driver expectations, decision and reaction time, conformance to natural paths of movement, pedestrian use and habits, bicycle use and habits.
Traffic Considerations - design and actual capacities, design-hour turning movements, size and operating characteristics of vehicle, variety of movements (diverging, merging, weaving, and crossing), vehicle speeds, transit involvement, crash experience, bicycle movements, pedestrian movements.
Physical Elements - character and use of abutting property, horizontal and vertical alignments at the intersection, sight distance, angle of the intersection, conflict area, speed-change lanes, geometric-design features, traffic control devices, lighting equipment, safety features, bicycle traffic, environmental factors, cross walks, parking, directional signing and marking.
Economic Factors - cost of improvements, effects of controlling or limiting rights-of-way on abutting residential or commercial properties where channelization restricts or prohibits vehicular movements, energy consumption.
Functional Intersection Area - boundary (much larger than the physical intersection; includes perception-reaction distance, maneuver distance, deceleration distance and queue-storage distance), access points.
7.2. Intersection Geometrics
7.2.1. Angle of Intersection/Skew Angle
Refer to Chapter 4, Elements of Design, Section 4.1.5. Intersection Sight Distance, of this manual for design policies concerning angle of intersection/skew angle.
7.2.2. Right-of-Way Flares
Refer to Chapter 4, Elements of Design, Section 4.1.5. Intersection Sight Distance, for design policies concerning right-of-way flares.

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7.2.3. Turn Lanes
The length of a turn lane consists of three components: entering taper, deceleration length, and storage length. Where practical, the total length of turn lane should be determined based on the design speed and the storage requirement for the turn lane and adjacent through-lane queue.
At a minimum, for design speeds < 45 mph, taper and deceleration lengths should be designed in accordance with the GDOT Regulations for Driveway and Encroachment Control.
At a minimum, for design speeds 45 mph, taper and deceleration lengths should be designed in accordance with Georgia Construction Detail M-3
For further design guidance relating to the design of turn lanes, refer to the AASHTO Green Book, Chapter 9, Auxiliary Lanes.
The following guidelines have been adopted by GDOT for the placement of deceleration lanes on multi-lane roadways with median widths greater than 12-ft:
Left-Turn-Lanes should be incorporated inside the median at all median opening locations. When the posted speed is 45 mph, Right-Turn-Lanes should be placed at paved public street
intersections and entrances to major traffic generators. When the posted speed is < 45 mph, Right-Turn-Lanes should be placed at paved public street
intersections and direct entrances to major traffic generators under the following conditions: a. Mainline current traffic volumes exceed 10,000 vehicles per day, and b. Traffic volumes on the side road exceed 200 vehicles per day with peak hour right turn
movements from the main road exceeding 20 vehicles per hour. In addition, every effort should be made to replace existing right turn lanes at commercial
driveways when practical. The benefits of including a turn lane may not always outweigh the impacts the turn lane will have on adjacent parcels. Sound engineering judgment should be used to determine if the benefits of replacing the right turn lane outweigh the impacts. Coordination with the Division of Engineering, Office of Traffic Operations, and District Access Management Engineer is recommended.
7.2.4. Islands AASHTO defines an island as, "the area between traffic lanes used for control of vehicle movement. Islands also provide for an area for pedestrian refuge and traffic control devices". Islands may be raised or painted. AASHTO defines a refuge island as, "A refuge island for pedestrians is one at or near a crosswalk or bicycle path that aids and protects pedestrians and/or bicyclists who cross the roadway". Refuge islands should be considered in areas where the roadway is too wide to allow a pedestrian to cross the entire intersection in one movement.
7.2.5. Intersection Radii
Turning radii treatments for intersections are important design elements that affect the operation, safety, and construction costs of the intersection. Several basic parameters should be considered in determining the appropriate corner radii and length of median opening including: intersection angle, number and width of lanes, design vehicle turning path, clearances, encroachment into oncoming or opposing lanes, parking lanes, shoulders, and pedestrian needs. The GDOT Driveway Manual provides typical radii for various applications.

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7.3. Median Openings
Median openings should be planned and designed to reflect access management objectives along a roadway. The following guidelines should be considered when designing median openings as well as when requests are received for additional median openings on completed roadway sections:

Priority should be given to establishing median openings at existing roads and streets before other locations.

The location and design of a median opening should take into consideration the taper length, deceleration length, and storage length required to adequately satisfy the traffic volumes, and whether adequate space is available between adjacent median openings to satisfy these critical dimensions. Adequate sight distance should be available at all median opening locations.

GDOT has adopted 1,000-ft. as the preferred minimum spacing between median openings in urban areas, and 1320-ft. as the preferred minimum spacing between median openings in rural areas. In urban areas, median openings may be spaced less than 1,000-ft., and greater than 660-ft. if it can be demonstrated that left turning volumes are nominal.

The maximum spacing between median openings in developed areas (including single occupied residence) should be one mile. In areas without any development or where there are no driveways due to access control, the maximum spacing between median openings should be 2 miles. In urban areas a practical maximum spacing between median openings is approximately mile. Since it is preferable to place median openings only at local roads, the opening may be shifted slightly to line up with an existing road or major traffic generator.

Median openings for new and reconstructed facilities should be constructed in accordance with GDOT Construction Standards and Details, M-3, Type A, B, or C. The Type B design is preferred and should be used where drainage can be adequately designed and speeds are greater than or equal to 55 mph. Consideration for use of Type B crossovers should also be given when engineering judgment dictates that the design is practical in median widths less than 32-ft. and when there are more than two approach through lanes.

Additional pavement for U-turns at median openings should be considered where there is a demand for access and where practical. In some cases, pavement for truck U-turns such as jug handles may be necessary to satisfy access to private property between successive median openings. Refer to the GDOT Construction Standards and Details, Construction Detail M-3, Type C Median Crossover. The designer should also refer to the National Cooperative Highway Research Program (NCHRP) report, Safety of U-Turns at Unsignalized Median Openings (Report 524), when designing intersections with U-turn capability.

For six-lane roadways, full median openings should be granted only at signalized intersections.

Median openings should not typically be installed or permitted to serve a particular development; however, when it can be demonstrated that such an installation will benefit the overall safety, traffic flow and efficiency of the roadway, then consideration will be given. Consideration for installing median openings for particular developments also involves the application of standard access control policy; therefore, if a particular development is proposing to add a median opening to a roadway, and the design does not comply with design criteria adopted by GDOT, then the approval of a Design Variance from the GDOT Chief Engineer will be required prior to incorporating the opening or feature into a project design or along an existing roadway section.

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7.4. Driveways
GDOT considers driveways, or non-roadway access points to the State Route System, as essentially low-volume intersections that merit special consideration in their design and location.
The designer should be familiar with the policies and procedures described in the current version of GDOTs Regulations for Driveway and Encroachment Control (Driveway Manual).
New driveways and modifications to existing driveways are regulated through the use of permits. Driveway permits (referred to as "access permits") are necessary in order to preserve the functional integrity of the State Highway System and to promote the safe and efficient movement of people and goods. Access permit regulations generally control right-of-way encroachment and driveway design, location, and number. Access approved for newly constructed commercial developments may, and in-fact often, stipulate parking requirements (for parking adjacent to state-owned rights of way) and setback distances to buildings and/or sign structures. When a roadway is widened, parking, setback distances, ingress/egress and parcel circulation may be impacted.
A consistent design approach should be applied to both existing driveways requiring reconstruction and proposed driveways for new developments. All reconstructed driveways should be compliant with the GDOT Driveway Manual. However, given the constraints of reconstructing an existing driveway, GDOT recognizes that it may not always be possible to reconstruct a driveway in strict accordance with the GDOT Driveway Manual. When roadways are to be widened, the replacement driveway may not require the same access/egress features, such as a right turn deceleration lane and/or acceleration lane. The need for the replacement of these features shall be evaluated on a case by case basis. In some cases replacement of access features in kind may not be justified due to excessive impacts to adjacent parcels.
The safety and efficiency of the State Highway System are affected by the amount and character of intersecting streets and driveways. While it is recognized that property owners have certain right of access, the public also has the right to travel on the road system with relative safety and freedom from interference. It is GDOTs intent to balance the often conflicting interests of property owners and the traveling public.
7.5. Signalization
The designer should be familiar with the current version of the GDOT TOPPS 6785-11, Traffic Signals. The information contained in this Section is intended to supplement the information contained in TOPPS 6785-1. The following provides some general guidelines for signalized intersection design:
All signalized intersections shall be designed in accordance with the GDOT Traffic Signal Design Guidelines.
Distance between stop bars on opposing movements should be set to minimum standards wherever possible, thus minimizing necessary clearance timings.

1 TOPPS 6785-1 is available on the GDOT Transportation Online Policies and Procedures System (TOPPS) at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/Pages/topps.aspx

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The use of pedestrian refuge islands should be considered whenever possible to minimize pedestrian clearance times.
The designer should communicate with the District Utilities Engineer to compile a list of all utilities which may be affected both underground and overhead. The location of utilities should be included on the signal plans so that they may be avoided. Special attention should be given to overhead utilities crossing the intersection to ensure that they do not conflict with the proposed signal span wire, mast arms, or signal heads, and that the design is able to meet National Electric Safety Code requirements.
Actual (existing) and projected (design) volumes, including turn movements, should be collected and determined for the intersection.
The designer should determine if the proposed signal will be part of a coordinated signal system, and if so, the development of communication plans or timing plans are needed.
The designer should closely evaluate the sequence of construction and maintenance of traffic to determine if temporary signals are needed.
Where possible signal poles / mast arms should be located to allow for use with both temporary signalization, and final signalization.
The intersection controller cabinet shall be located where it can be utilized in the temporary signals, as well as the final signal design.
Location of the PED button and PED signal, curb cut ramps, strain pole, controller cabinets, crosswalk and landing areas, should all be coordinated to ensure a fully accessible intersection. The designer should check the right of way to ensure that there is enough room to install these items.
The intersection controller cabinet shall be located to avoid creating a sight distance obstruction in all phases of construction.
Signal heads shall be designed with sufficient slack wiring to allow the heads to be relocated to different places on the span wire / mast arm for use in both the temporary and final signals.
Wherever possible, loops, pull boxes, and loop lead-ins shall be placed to be used for both the temporary signals as well as the final signals.
For signals mounted on mast arms, the designer should provide sufficient length on the arms to allow for both future signal heads, as well as field adjustments if needed.
The designer should contact the maintaining agency that is responsible for the existing intersections in the area to determine design standards which may be unique to the area.
As applicable, the construction of the signalized intersection should be carefully considered when developing maintenance of traffic plans.
Consider decision sight distance as it relates to signal head and traffic control devices, and the queue length for the signal.

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When designing a roadway or roadway improvements, particular attention should be paid to the future operations at the project intersections. Where existing signalization does not exist, the intersection should be evaluated to determine if signalization is required as part of the project. If the project includes an existing signalized intersection, the intersection should be evaluated to determine if improvements are required as part of the project.
7.5.1. New Intersections and Existing Unsignalized intersections
At existing non-signalized and new intersections which are a part of the project design, the designer should request the District Traffic Operations Engineer perform a Traffic Engineering Study (including a signal warrant analysis) to determine if signalization may be warranted. The results of the study, along with the recommendations shall be documented in a Traffic Engineering Report. The signal warrant analysis shall be performed in accordance with the current version of the FHWA Manual on Uniform Traffic Control Devices (MUTCD)2.
The Traffic Engineering Study should be performed under two separate scenarios:
At locations where the intersections exist in the field, the intersection should be evaluated under existing volumes (as determined by field counts) and future lane configuration (based on the project design). If the intersection meets warrants under these conditions, the signal design should be included in the design package, and the signal should be installed as part of the project construction.
At locations where an intersection exists in the field but does not meet warrants under existing traffic conditions, and at locations where the intersection does not exist in the field (new intersection as part of the design project) the intersection should be evaluated using design volumes (volumes developed as part of a traffic study) and future lane configuration (based on project design). Intersections that meet warrants under this scenario should be considered for inclusion in the design package. The designer should work closely with the District Traffic Operations Engineer to determine if signalization should occur as part of the project, or in a future stage.
In either case, the roadway / intersection should be designed to allow for future signalization. Necessary turn lanes should be provided, or space to develop future turn lanes should be planned. Right-of-way should be provided for future signal poles and intersection equipment.
7.5.2. Signal Modification
New signal plans should be developed for all existing signalized intersections where roadway improvements are being made. The existing signalized intersection should be evaluated to determine its existing operation. The intersection should then be analyzed with both existing volumes and design volumes using the future lane configuration to determine the appropriate intersection phasing. If future phasing changes will be needed, design allowance should be incorporated to provide room for additional signal heads, loop detectors, and mast arm lengths. Any modification to existing signals requires a revision to the existing signal permit.

2 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). The 2003 version is available online at: Available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm

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7.5.3. Geometric Design Elements
In rural areas, if there will be an auxiliary lane for acceleration after a right turn movement, it must provide adequate acceleration length to merge into traffic (as discussed in this Manual in Chapter 4, Elements of Design, Section 4.2.5. Transition in Number of Lanes). The lane must also be free of any driveways for the length of the auxiliary lane.
7.6. Highway-Railroad Grade Crossings
When a Highway- Railroad grade crossing is included on a project, designers should coordinate with the GDOT Railroad Crossing Manager, Railroad Crossing Improvement Unit3, in conjunction with concept development for a transportation improvement project.
The designer should be familiar with most current versions of the following resources:
AASHTO A Policy on the Geometric Design of Highways and Streets (Green Book), Chapter 9. Intersections
American Railway Engineering and Maintenance of Way Association (AREMA) specifications (visit www.arema.org for additional information)
Railway company regulations
GDOT Standard Drawing and Specifications
FHWA Manual on Uniform Traffic Control Devices (MUTCD)
A highway-railroad crossing involves either a separation of grades or a crossing at-grade. GDOT strongly encourages consideration of grade separated highway-railroad crossings. However, topographical and/or right-of-way limitations may make at-grade crossings the more feasible option.
When an at-grade, highway-railroad crossing is included in the design of a roadway construction/reconstruction project, train-activated warning devices (i.e. gates, lights, and bells) shall be included in the design. Train-activated warning devices provide drivers with a positive indication of the presence or the approach of a train at the crossing.
The geometric design of a highway-railroad grade crossing involves the elements of alignment, profile, sight distance, and cross section. The roadway should cross the railroad at- or nearly at- a right angle. The roadway gradient should be flat at- and adjacent to- the railroad crossing to permit vehicles to stop, when necessary, and then proceed across the tracks without difficulty. The vehicle operator can observe an approaching train and bring the vehicle to a stop prior to encroaching into the crossing area. Also the roadway width at all crossings should be the same as the roadway width approaching the crossing.

7 The Railroad Crossing Improvement Office (see http://www.dot.state.ga.us/dot/operations/traffic-safetydesign/subunit/rrcross.shtml) is a unit of the GDOT Office of Traffic Safety and Design (home page: http://www.dot.state.ga.us/dot/operations/traffic-safety-design/index.shtml).

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7.6.1. Horizontal Alignment As per the AASHTO Green Book (2004), to the extent practical:
The highway should be designed to intersect the railroad tracks at a right angle.
There should be no intersections or driveways, and in areas where a highway intersection is close to a railroad crossing, sufficient distance between the tracks and the highway intersections should be provided to enable highway traffic in all directions to move expeditiously. Where adequate storage distance between the main track and a highway intersection is not available, interconnection of the highway traffic signals with the trainactivated warning devices and appropriate signage and pavement markings is strongly recommended.
Placement of crossings on highway or railroad curves should be avoided because a roadway curvature can inhibit a drivers view of the crossing ahead, a railroad curvature may inhibit a drivers view down the tracks from both a stopped position at the crossing and on the approach to the crossing, and crossings located on both highway and railroad curves present maintenance problems and poor rideability for highway traffic due to conflicting superelevations.
7.6.2. Vertical Alignment
As per the AASHTO Green Book (2004), to the extent practical:
Highway and railroad intersections should be level:
The crossing surface should be at the same plane as the top of the rails for a distance of 2ft. outside the rails. This is done to prevent low clearance vehicles from becoming caught on the railroad tracks.
The surface of the highway should not be more than three inches higher or lower than the top of the nearest rail at a point 30-ft. from the rail, unless track superelevation makes a different level appropriate.
If a roadway approach section is not level, or if the rails are superelevated, adequate rail clearances should be determined through a site-specific analysis.
Vertical curves should be of sufficient length to ensure an adequate view of the crossing.
Vertical curves should be used to traverse from the highway grade to a level plane at the elevation of the rails.

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7.6.3. Highway-Rail Grade Traffic Control Considerations
Highway-rail grade crossing traffic control considerations are discussed in detail in the FHWA publication, Guidance on Traffic Control Devices at Highway-Rail Grade Crossings4. The following discussion summarizes the key points of this FHWA publication.
At a highway-rail grade crossing, the train always has the right of way. The process for determining the types of highway traffic control device(s) that are needed at a highway-rail grade crossing, or if a highway-rail crossing should exist, involves two-steps:
Required Information - identifying what information the vehicle driver needs to be able to cross safely
System operating characteristics - determining if the resulting driver response to a traffic control device is "compatible" with the intended system operating characteristics of the highway and the railroad facility.
Required Information The first step involves three essential elements required for ,,safe passage through an at-grade crossing, which are incidentally the same elements a driver needs for crossing a highway-highway intersection:
Advance notice / stopping sight distance this element involves the drivers ability to see a train and/or the traffic control device at the crossing ahead to bring the vehicle to a stop at least 15-ft. short of the near rail.
Traffic control device comprehension this element is a function of the types of traffic control devices at the highway-rail crossing. According to FHWA, "there are typically three types of control devices, each requiring a distinct compliance response per the Uniform Vehicle Code, various Model Traffic Ordinances, and state regulations" (2002). These three types of control devices are: crossbuck, operating flashing lights that have the same function as a STOP sign, and flashing lights with lowered gates that have the same function as a red vehicular traffic signal.
Driver decision to proceed through the grade crossing - this element concerns the drivers decision to safely proceed through the grade crossing. It involves sight distance available both on the approach and at the crossing itself.
System Operating Characteristics The second step involves a traffic control device selection process considering respective highway and rail system operational requirements. Within these contexts, FHWA notes the following operation and safety variables that should be considered (2002):
highway - AADT (Annual Average Daily Traffic), legal and/or operating speed

8 FHWA. Guidance on Traffic Control Devices at Highway-Rail Grade Crossings. 2002 The 2002 version of this publication is available online at: http://safety.fhwa.dot.gov/media/twgreport.htm

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railroad - train frequency, speed and type (passenger, freight, other) highway - functional classification and/or design level of service railroad - FRA class of track and/or high speed rail corridors proximity to other intersections proximity to schools, industrial plants, and commercial areas proximity to rail yards, terminals, passing tracks, and switching operations available clearing and corner sight distance prior accident history and predicted accident history proximity and availability of alternate routes and/or crossing other geometric conditions
"Special consideration should also be given to situations where highway-rail crossings are sufficiently close to other highway intersections that traffic waiting to clear the adjacent highway intersection can queue on or across the tracks, and when there are two or more sets of tracks sufficiently close to each other that traffic stopped on one set could result in a queue of traffic across the other" (FHWA, 2002).
Highway Operational Requirements
FHWA describes the following with respect to highway operational requirements of highway-rail grade crossings (2002):
Passive highway-rail grade crossings with a restricted sight distance require an engineering study to determine the safe approach speed based upon available stopping and/or corner sight distance.
As a minimum, an advisory speed posting may be appropriate, or a reduced regulatory speed limit might be warranted.
Active devices improve highway capacity and level of service near a crossing, particularly where corner sight distances are restricted; however, the effects of such a stop delay will increase as traffic volumes increase which will result in vehicle delay increases.
The type of control installed at highway-rail crossings should be evaluated in the context of the highway system classification and level of service.
Railroad Operational Requirements
"Function, Geometric Design, and Traffic Control - Functional classification is important to both the highway agency and railroad operator. Where the highway intersects a railroad, the crossing, whether grade separated or at-grade, should be designed consistently with the functional classification of the highway or street. These design considerations can also extend to traffic control" (FHWA, 2002).
7.6.4. Traffic Control Devices
The purpose of traffic control at highway-rail grade crossings is to permit safe and efficient operation of both vehicle and train traffic over such crossings. Highway vehicles approaching a highway-rail grade crossing should be prepared to yield and stop, if necessary, if a train is at or approaching the crossing.

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Refer to the current FHWA Guidance on Traffic Control Devices at Highway-Rail Grade Crossings and the current FHWA MUTCD for additional information relating to the following types of highwayrail grade crossing traffic control devices:
Passive Devices - all highway-rail crossings having signs and pavement markings (if appropriate to the roadway surface) as traffic control devices that are not activated by trains. Passive highway-rail crossing devices include: highway-rail grade crossing (crossbuck) signs, STOP signs, and YIELD signs.
Active Devices - all highway-rail grade crossings equipped with warning and/or traffic control devices that gives warning of the approach or presence of a train. Active devices are generally categorized as standard active devices (i.e. flashing-light signals, cantilever flashing-light signals, and automatic gates) and supplemental active devices (i.e. active warning signs with flashers, or active turn restriction signs.
Median Separation - the numbers of crossing gate violations can be reduced by restricting driver access to the opposing lanes. The use of median separation devices have resulted in a significant reduction in the number of vehicle violations at crossing gates. Other positive-barrier devices that can be used to prohibit crossing gate violations include: barrier walls, wide raised medians, non-mountable curb islands, mountable raised curb systems, four-quadrant traffic gate systems, and vehicle arresting barrier system - barrier gates.
Train Detection Systems - Joint study and evaluation is needed between the highway agency and the railroad to make a proper selection of the appropriate train detection system. Refer to the current FHWA Guidance on Traffic Control Devices at Highway-Rail Grade Crossings for additional information relating to issues specific to train detection systems, such as warning time, system credibility, various types of detection systems, as well as railroad train detection time and approach length calculations.
7.6.5. Alternatives to Maintaining the Crossing
Refer to the current FHWA publication, Guidance on Traffic Control Devices at Highway-Rail Grade Crossings, for additional information on the following alternatives to maintaining a highway-rail grade crossing:
Crossing Closure "The crossing closure decision should be based on economics; comparing the cost of retaining the crossing (maintenance, crashes, and cost to improve the crossing to an acceptable level if it would remain, etc.) against the cost (if any) of providing alternate access and any adverse travel costs incurred by users having to cross at some other location. Because this can be a local political and emotional issue, the economics of the situation cannot be ignored" (FHWA, 2002). FHWA recommends two documents that provide guidance with regard to political, emotional, and economic ramifications of closing an at-grade highway-railroad crossing: a joint FRA/FHWA publication entitled Highway-Railroad Grade Crossings: A Guide to Crossing Consolidation and Closure (1994), and a March 1995 AASHTO publication, Highway-Rail Crossing Elimination and Consolidation.
Grade Separation FHWA notes that the decision to grade separate a highway-rail crossing should be based on long term, fully allocated life cycle costs, including both highway and railroad user costs, rather than on initial construction costs (2002). A 1999 Texas Transportation Institute report entitled Grade Separations-When Do We Separate? provides a stepwise procedure for evaluating the grade separation decision and also describes a rough screening method based on train and roadway vehicular volumes. Evaluation of the feasibility of highway-rail grade separation should consider many factors, including but not limited to:

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o eliminating train/vehicle collisions (including the resultant property damage and medical costs, and liability)
o savings in highway-rail grade crossing surface and crossing signal installation and maintenance costs
o driver delay cost savings o costs associated with providing increased highway storage capacity (to
accommodate traffic backed up by a train) o fuel and pollution mitigation cost savings (from idling queued vehicles) o effects of any "spillover" congestion on the rest of the roadway system o the benefits of improved emergency access o the potential for closing one or more additional adjacent crossings o possible train derailment costs
7.6.6. Crossing Consolidation and New Crossings
Crossing Consolidation Guidelines for crossing consolidation can be found in publications such as:
FRA/FHWA. Highway-Railroad Grade Crossings, a Guide to Crossing Consolidation and Closure. Federal Railroad Administration/Federal Highway Administration. 1994.
FRA/FHWA. Highway-Rail Crossing Elimination and Consolidation, A Public Safety Initiative. National Conference of State Railway Officials. March 1995.
Furthermore, GDOT, road authorities, or local governments may choose to develop their own criteria for closures based on local conditions. The FRA and FHWA strongly encourage the use of specific criteria or an approach to consolidating railroad crossings, so as to avoid arbitrarily selecting a crossing for closure.
New Crossings Similar to crossing closure/consolidation, consideration of opening a new public highway-rail crossing should likewise consider public necessity, convenience, safety, and economics. Generally, new grade crossings, particularly on mainline tracks, should not be permitted unless no other viable alternatives exist and, even in those instances, consideration should be given to closing one or more existing crossings to offset the additional risks associated with creating an additional crossing. If a new grade crossing is to provide access to any land development, the selection of traffic control devices to be installed at the proposed crossing should be based on the projected needs of the fully completed development. Communities, developers, and highway transportation planners need to be mindful that once a highway-rail grade crossing is established, drivers can develop a low tolerance for the crossing being blocked by a train for an extended period of time. If a new access is proposed to cross a railroad where railroad operation requires temporarily holding trains, only grade separation should be considered.
(FRA/FHWA, 2002)

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7.6.7. GDOT At-Grade Highway-Rail Crossing Evaluation Criteria

Peabody-Dimmick Formula
The Peabody-Dimmick empirical method should be used to evaluate and establish an unadjusted "hazard index" for at-grade highway-railroad crossings. The Peabody-Dimmick Formula (often referred to as the Bureau of Public Roads Formula) is used to determine the expected number of train-vehicle crashes in five years. The formula is:

A5 1.28*((V 0.170 *T ) 0.151 / P0.171 ) K

Where:

A = Expected number of train-vehicle crashes in five years (Unadjusted Hazard 5
Index Rating, as it is not adjusted for school buses) V = Annual Average Daily Traffic (AADT) T = Average Daily Train Traffic P = At-grade Crossing Protection Coefficient K = Balancing factor used to offset variations in empirical data

Note: The hazard index only provides an initial approximation of the relative hazard rating of each crossing. While the Peabody-Dimmick formula takes into account the number of daily trains, the vehicular AADT, and a factor for the existing warning devices (protection coefficient); the designer must consider other factors that must be considered before reaching an Adjusted Hazard Index rating for a crossing. These factors include:

visibility and sight distances speed (both train and vehicle) number of past train-vehicle crashes at the location number of tracks highway approach grades highway alignment number of highway approach lanes type of terrain nearby intersections condition of existing equipment

Based on site-specific information not included in the formula, GDOTs current practice is that the Unadjusted Hazard Index rating produced by the Peabody-Dimmick Formula shall not account for more than 50% of the Adjusted Hazard Index rating.

Adjusted Hazard Index Rating
The Adjusted Hazard Index (AHI) Rating is the summation of the Unadjusted Hazard Index rating, the Adjustment Factor for School Buses, and the Adjustment for Train-Vehicle Crash history.

AHI = A5 + S + A

Where:

A = Unadjusted Hazard Index Rating 5

S = Adjustment factor for School Buses

A = Adjustment for train-vehicle crash history

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Adjustment Factor for School Buses
An adjustment factor should be added to the hazard index when a highway route intersects a railroad ,,at-grade. The adjustment factor, S, takes into account the number of school buses traversing the highway-rail crossing during a 24-hour period.

S (4 *TPD 8* Buses) 8 10

Where:

S = Adjustment Factor for School Buses TPD = Number of Trains per day Buses = Number of Buses per day

Note: The adjustment factor for school buses shall only be applied to the Unadjusted Hazard Index rating for highway-rail grade crossings that utilize passive warning devices. If a highway-rail grade crossing utilizes train-activated warning devices, then S = 0.

Adjustment Factor for Train-Vehicle Crash History
An adjustment factor should be added to the hazard index based on crash history at a highway-rail crossing. The adjustment factor, A, takes into account the number of fatalities, injuries, or property damage only cases when train-vehicle crashes occur.

A = 2 * F + 1 * I + 0.5 * PD

Where :

A = Adjustment Factor for Accidents F = A train-vehicle crash resulting in a fatality I = A train-vehicle crash resulting in an injury PD = A train-vehicle crash resulting in property damage only

Note: If a train-vehicle crash results in a fatality, the Adjustment Factor for the train-vehicle crash is 2. (It should be assumed that subject vehicles occupants were injured and the vehicle involved in the incident was damaged).

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Chapter 7 Index
At-Grade Crossings
Highway-Railroad, 1320 Horizontal Alignment, 14 Vertical Alignment, 14 Driveways, 5
Intersections
Geometrics, 23 Highway-Railroad Grade Crossings. See
At-Grade Crossings New Intersections, 7

Signalization, 58 Intersections (At-Grade), 120
Sight Distance
Stopping Sight Distance, 15 Traffic
Signal Modification, 7 Traffic Engineering Study, 7

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Chapter 8 Contents

8. ROUNDABOUTS

1

8.1. Introduction

1

8.2. Roundabout Validation Process

2

8.2.1. Planning Level Assessments

2

8.2.2. Roundabout Feasibility Studies

5

8.2.3. Review of Feasibility Studies

7

8.2.4. Lighting

7

8.2.5. Public Involvement

8

8.3. Design Guidelines

9

8.3.1. Review of Construction Plans

9

8.3.2. Design Vehicle

10

8.3.3. Alignment of Approaches

10

8.3.4. Splitter Islands

10

8.3.5. Pedestrian Design Considerations

10

8.3.6. Bicycle Design Considerations

11

8.3.7. Treatments for High Speed Approaches

11

8.3.8. Drainage

11

8.3.9. Curbing

12

8.3.10. Pavement

12

8.3.11. Staging of Improvements

12

8.3.12. Traffic Control Devices

12

8.3.13. Landscaping

12

8.3.14. Construction

13

8.4. References

13

8.4.1. Primary References

13

8.4.2. Additional References

14

8.5. Definition of Terms

15

8.5.1. Roundabout Physical Features

15

8.5.2. Roundabout Design Elements

17

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List of Tables

Table 8.1. Planning-level Estimates of Lane Requirements.

5

List of Figures

Figure 8.1. Roundabout Validation Process

3

Figure 8.2. Key Roundabout Physical Features

15

Figure 8.3. Key Roundabout Design Elements

17

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8. ROUNDABOUTS
8.1. Introduction
A modern roundabout is a type of circular intersection characterized by channelized approaches, a generally circular shape, yield control at entry, and geometric features that create a low-speed environment. They have been demonstrated to provide a number of safety, operational, and other benefits when compared to other types of intersections. Specifically, they have fewer conflict points, lower speeds, provide for easier decision making and have been found to reduce crashes (especially those including fatalities and injuries), traffic delays, fuel consumption, and air pollution.
Roundabouts can be categorized into three basic types: mini-roundabouts, single-lane roundabouts, and multilane roundabouts. A detailed introduction to each is provided in Chapter 1 of the National Cooperative Highway Research Program (NCHRP) Report 672, Roundabouts: An Informational Guide. This chapter of the GDOT Design Policy Manual specifically addresses singlelane and multilane roundabouts; for the design of mini-roundabout refer to NCHRP 672.
In 2008 FHWA released Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures, which identifies roundabouts as one of nine safety countermeasures recognized and supported by FHWA. This document states the following:
Roundabouts are the preferred safety alternative for a wide range of intersections. Although they may not be appropriate in all circumstances, they should be considered as an alternative for all proposed new intersections on federally-funded highway projects, particularly those with major road volumes less than 90 percent of the total entering volume. Roundabouts should also be considered for all existing intersections that have been identified as needing major safety or operational improvements. This would include freeway interchange ramp terminals and rural intersections.
GDOT also considers roundabouts as the preferred safety and operational alternative for a wide range of intersections on public roads. Specifically, a roundabout shall be considered as an alternative in the following situations:
for any intersection being designed on new location or to be reconstructed;
for all existing intersections that have been identified as needing major safety or operational improvements; and
for all intersections where a request for a traffic signal has been made.
A traffic engineering study (TE study) is prepared for all intersections where a signal permit is requested, as required by the GDOT Plan Development Process (PDP). This study includes a planning level assessment as to whether or not a roundabout is expected to perform acceptably. If a roundabout is expected to perform acceptably, a roundabout feasibility study (feasibility study) should be prepared.
Each proposal for a roundabout should be developed and evaluated based on the guidelines contained within NCHRP 672, and the guidelines presented in the following sections of this chapter. Additional guidance documents are listed in Section 8.4.1.

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8.2. Roundabout Validation Process
When considering a roundabout, a variety of alternatives should be evaluated to determine whether or not a roundabout is the most appropriate alternative. These alternatives should include all conventional intersection forms appropriate for the intersection being considered and will often include two-way stop control, all-way stop control, and/or signal control. Chapter 3 of NCHRP 672 provides guidance for comparing the performance of a roundabout to these three forms of intersection control. A signalized intersection is only considered if signal warrants are met, as determined by a TE study.

Figure 8.1 presents a validation process which should be used to validate the decision to use a roundabout for a given intersection. This validation process includes: (1) an initial planning level assessment performed as part of a TE study; (2) a roundabout feasibility study; (3) obtaining agreement from local government to participate in lighting costs; and (4) a program of public outreach. The final result of this validation process is a decision to proceed with either a roundabout or conventional (i.e., or nonroundabout) intersection design, or to suspend project development.

For stand-alone intersection projects, the roundabout validation process should be completed prior to submission of the concept report for review and approval. Where the intersection is part of a larger project this process should be completed prior to requesting the preliminary field plan review.

8.2.1. Planning Level Assessments
The roundabout validation process begins with a planning level evaluation to assess the general suitability of constructing a roundabout at the intersection. This evaluation is performed as part of a TE study, but may be included in the feasibility study. Exhibit 3-1 of NCHRP 672 provides an excellent overview of key planning principles.

Listed below are conditions where roundabouts are commonly found to be advantageous over other forms of intersection control. An overview of the primary advantages and disadvantages of roundabouts is presented in Exhibit 2-5 of NCHRP 672.
Safety Intersections with historically high crash rates. Roads with a historical problem of excessive speeds. Intersections with more than four legs or with difficult skew angles.

Operation
Intersections with a high percentage of turning movements and intersections that must accommodate U-turns.
Intersections with high traffic volumes at peak hours but relatively low traffic volumes during non-peak hours.
Intersections where widening one or more approach may be difficult or cost-prohibitive. While roundabouts may have a larger footprint on the corners of the intersection, the overall space requirement for a roundabout is often less than for a conventional intersection. This is due to the shorter queues generated by a roundabout, thereby requiring less queue storage space on approach legs.
Ramp terminal intersections within freeway service interchanges. Roundabouts often make more efficient use of an existing bridge by reducing the queues at each ramp terminal intersection.

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Intersections where traffic growth is expected to be high and future traffic patterns are uncertain. A single-lane roundabout can be constructed with allowance for future expansion to a multilane roundabout, and be expanded if and when significant increases in traffic volumes occur.
Locations where the speed environment or the number of through lanes of the road changes, for instance, at the fringe of an urban environment.
Intersections where signalization cannot provide an adequate level of service.
Traffic Control Existing two-way stop-controlled intersections with high side-street delays, particularly those
that do not meet signal warrants. Intersections or corridors where traffic calming is a desired outcome of the project.
Aesthetics Intersections at a gateway or entry point to a campus, neighborhood, commercial development,
or urban area. These may be locations with a need to provide a transition between land-use environments such as between residential and commercial areas. Intersections where community enhancement may be desirable.
The presence of any of the following conditions will normally be unfavorable for a roundabout. These conditions do not preclude a roundabout from further consideration, but should be carefully considered when choosing and designing a roundabout.
Intersections in close proximity to a signalized intersection where queues may spill back into the roundabout (e.g., coordinated arterial signal systems).
Locations with steep grades and unfavorable topography that may limit visibility of the roundabout.
Intersections in close proximity to an at-grade railroad crossing. Intersections where an unacceptable delay to the major road could be created. Roundabouts
introduce some geometric delay to all through and left turning traffic entering the intersection, including the major street.
Heavy pedestrian or bicycle movements in conflict with high traffic volumes that consequently may require pedestrian signals.
Table 8.1 can be used to estimate the number of circulatory lanes required for a single- or two-lane roundabout. One and two-lane roundabouts should operate acceptably below these thresholds and are based on Exhibit 3-12 of NCHRP 672. In addition, the opening and design year volumes for traffic entering the roundabout from the major road should normally be less than 90% of the total volume entering the roundabout.
Where turning movement data is available, an estimate of the required number of entry lanes at each leg can be obtained using Exhibit 3-14 of NCHRP 672. Sample calculations are provided in Exhibits 3-15 and 4-3.

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Table 8.1. Planning-level Estimates of Lane Requirements.

No. of Circulatory Lanes

ADT1 (design year)

% Traffic on Major Road2 (opening & design year)

Single-lane

< 25,000

< 90

Two-lane

< 45,000

< 90

1Based on traffic entering the circulatory roadway, for a four-leg roundabout. A reasonable approximation for a three leg roundabout is 75% of the values shown. 2The volume of traffic entering the roundabout from the major road divided by the total traffic volume entering the roundabout, as a percentage.

If traffic volumes are above the thresholds shown in Table 2.1, or if site conditions are unfavorable to a roundabout, an acceptable conventional intersection type may be selected without further evaluation. Nevertheless, a roundabout may still operate better than a conventional intersection and may be carried forward for more detailed consideration as part of a feasibility study.
8.2.2. Roundabout Feasibility Studies
A feasibility study should be prepared for all roundabouts. The objective of the feasibility study is to document the decision-making process which demonstrates that a roundabout is (or is not) the most appropriate intersection control form for a specific intersection. The feasibility study also includes a geometric layout of the selected roundabout alternate which can be carried forward to preliminary design. For a stand-alone intersection project, the project concept report may be formatted to incorporate the feasibility study.
A well-prepared feasibility study is important for identifying and supporting the selection of a roundabout. Nevertheless, the scope of a feasibility study will vary depending on project conditions and the type and complexity of the proposed roundabout. For example, an intersection of two state routes having a history of injury crashes may not require a detailed cost comparison, considering the significant reduction in injuries that can be expected with a roundabout. On the other hand, the use of a roundabout within a highly urbanized corridor having closely spaced, coordinated signals may require a very detailed feasibility study that goes beyond the scope of what is outlined below.
A typical feasibility study can be organized as follows:
Section 1, Project Background & Site Conditions: include a summary of the project need, a description of the corridor, and a sketch of existing conditions in the vicinity of the intersection. The sketch should show land-use, access, existing right-of-way, and any physical constraints that may affect the location and design of a roundabout.
Section 2, Safety Assessment: include a tabulated analysis of crash data for the three most recent years (at minimum) for which data is available and a comparison to statewide averages. If the purpose of considering a roundabout is to improve the safety at an existing intersection, it is recommended that a crash diagram be prepared. The crash diagram should show the types of crashes and the direction each car was travelling.
A roundabout is particularly favorable for addressing crashes involving crossing and turning traffic. Further information regarding safety and roundabouts is presented in Chapter 5 of NCHRP 672.
Section 3, Alternate Sketches: include sketches of all design alternates being considered. These can be effectively presented on an aerial photo base map of the intersection and vicinity.

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Section 4, Operational Analyses: include operational analyses using peak hour traffic volumes for each design alternate and for opening and design years. The results of each analysis should be presented by lane group in terms of volume-to-capacity ratio, average control delay, level of service, and 95th percentile queue. Based on the results of these analyses the performance of each alternate should be evaluated, and intersection types providing adequate performance identified. Further guidance on evaluating the operational performance of roundabouts can be found in Chapter 4 of NCHRP 672.
Analyses should be performed using more than one analysis methodology, to identify a range of expected performance. For example, analyses can be performed using the GDOT Roundabout Analysis Tool to implement the NCHRP Report 572 method and a second method, either the "SIDRA Standard" method using the software package SIDRA Intersection or the empirical method using the software package ARCADY.
SIDRA Intersection does not provide a precise implementation of the NCHRP 572 method and should not be used for that purpose. Simulation software packages should be considered where modeling of a network of closely spaced intersection is necessary.
Section 5, Cost Comparison: where multiple alternates are expected to provide adequate operational performance, a cost comparison should be prepared. This analysis may be either qualitative or quantitative, but should consider significant benefits relating to safety, operational, and environmental factors and significant costs relating to construction, required right-of-way, operations, and maintenance. Further guidance on estimating benefits and costs can be found in Section 3.7 of NCHRP 672. A detailed benefit-to-cost analysis can be helpful for communicating the benefits of a roundabout to local governments and the public.
Section 6, Alternate Selection: include a brief summary of the findings of the above studies (usually in a bulleted form) followed by a recommendation of the most favorable alternate. All assumptions and constraints important to this decision should be included.
Section 7, Conceptual Roundabout Design: include a concept level geometric layout of the roundabout and approaches. This layout should include the size and location of the roundabout and the alignment and arrangement of approaches. Major geometric components should be shown including splitter islands, circulatory roadway, truck aprons, center island, and bypass lanes (if required).
Geometric and performance checks should include, at minimum - fastest path, design vehicle swept paths, and stopping sight distance for approaches. Other performance checks can be completed during preliminary design (See Section 6.7 of NCHRP 672).
A list of the criteria used to develop the selected layout and key dimensions should be provided. It is noted that the selection of the most favorable roundabout configuration and layout may require the development and comparison of multiple roundabout layouts.
If a single-lane roundabout is found to be adequate for ten years after the opening year, consideration should be given to constructing a single-lane roundabout. This single-lane roundabout should be designed to be easily retrofitted to a multilane roundabout when traffic volumes grow to warrant the increased capacity. To allow for this future expansion, the ultimate configuration of the multilane roundabout should be defined and the footprint of the constructed roundabout designed to match the footprint of the future multilane roundabout (See Section 6.12 of NCHRP 672).
Section 8, Recommendations: briefly state the reasons for selecting the recommended alternate. Any specific requirements or constraints to be considered during preliminary design should be listed and the expected approach for staging briefly described.

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8.2.3. Review of Feasibility Studies
Feasibility studies prepared by GDOT engineers must be reviewed in accordance with the Department's QC/QA Manual, and studies prepared by consultants in accordance with their own approved QC/QA procedures. Informal reviews by the Office of Design Policy and Support or the Office of Traffic Operations can be requested at any time during the plan development process, by sending an e-mail to roundabouts@dot.ga.gov or by contacting a GDOT roundabout SME directly.

Peer review of feasibility studies will be performed for all roundabout projects, unless approval to omit this review is received from the State Design Policy Engineer. Peer reviews are performed by a consultant peer reviewer having extensive experience with the planning, analysis, and design of single-lane and multilane roundabouts. Consultant peer reviewers must be pre-approved by the Office of Design Policy and Support.

The objective of the peer review is to verify that a roundabout is the most favorable design alternate and to establish a layout which addresses project needs without unnecessary impacts and costs. Refinement of the layout early in the plan development process has the advantage of allowing for necessary changes to be made without major revisions to construction plans.

It is recommended that the feasibility study be peer reviewed prior to the concept team meeting for stand-alone intersection projects where a complex roundabout is proposed. Complex roundabouts include: all multilane roundabouts; and single lane roundabouts having more than four legs, with approach skews less than 60 degrees, and/or closely spaced where the operations of one may have and impact on the operations of another. For other roundabouts, it is recommended that peer reviews should be performed prior to the preparation of preliminary construction plans.

Any peer review recommended changes which are not implemented should be coordinated with the Office of Design Policy and Support. If the design engineer proposes not to implement a peer review recommendation, a written response will be submitted along with the peer review report to the Office of Design Policy and Support. If implementation of a peer review recommendation can be (and is to be) delayed until after concept development, written responses along with the peer review report are to be attached to the concept report.

8.2.4. Lighting
The lighting of a roundabout has been identified by the Department as having substantial importance to the operational performance and safety of this type of intersection such that special attention should be given to the design and lighting for a roundabout. Therefore, GDOT adopts the recommended illumination levels in Table 1 of the Illuminating Engineering Society DG-19-08, Design Guide for Roundabout Lighting (IES DG-19-08) as a standard for the design of lighting systems for roundabouts. If it is not practical to provide the illumination levels defined by this table, then the decision to select a value or retain an existing condition that does not meet this criteria shall require a comprehensive study by the engineer and the prior approval of a Design Variance from the GDOT Chief Engineer.

Both NCHRP 672 and IES DG-19-08 emphasize the safety importance of roundabout lighting for all users of roundabouts. Section 8.1 of NCHRP 672 begins with the following statement:

For a roundabout to operate satisfactorily, a driver must be able to enter the roundabout, move through the circulating traffic, and separate from the circulating stream in a safe and efficient manner. Pedestrians must also be able to safely use the crosswalks. To accomplish this, a driver must be able to perceive the general layout and operation of the intersection in time to make the appropriate maneuvers. Adequate lighting should therefore be provided at all roundabouts.

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Section 8.2 of NCHRP 672 explains the two main purposes of lighting roundabouts, as follows:
It provides visibility from a distance for users approaching the roundabout; and
It provides visibility of the key conflict areas to improve users' perception of the layout and visibility of other users within the roundabout.

Pedestrians are the most vulnerable users at a roundabout. Thus, an important function of lighting at a roundabout is to ensure that any pedestrian in the crosswalk is visible to vehicles approaching and entering the roundabout. Roadway lighting also provides increased safety to cyclists at the approach to the roundabout where they begin to mix with traffic, and throughout the circulatory roadway where they are integrated into the traffic stream.
The guidelines presented in the IES DG-19-08 should be used to develop lighting plans. Lighting plans are normally prepared during the final phase of plan development. NCHRP 672 reproduces Table 1 of IES DG-19-08 as Exhibit 8-1.

In order for the design of a roundabout to move forward to detailed design a written commitment must be received from a local government agreeing to share the costs of lighting by funding the energy, operation and maintenance of the lighting system.

8.2.5. Public Involvement
A public involvement process should include outreach to local government officials and the local community and should be initiated as soon as practical during concept development. At minimum, a public information open house (PIOH) should be held for all multilane roundabouts and for singlelane roundabouts where there are no other well-functioning roundabouts in the locality or nearby along the corridor. This includes minor projects for which a PIOH may not otherwise be required.

In localities where there is little familiarity with roundabouts, it is recommended that a meeting be held with local government officials prior to a PIOH. A roundabout subject matter expert or an individual with considerable knowledge of roundabouts should be present at this meeting.

Below are suggested "best practices" for preparing to hold a PIOH or informational meeting. Prepare several large-sized copies of a color display that shows the proposed location and
configuration of the roundabout. The display should include aerial photography and property lines. The following may also be included:
- proposed pavement markings with lane arrows;
- proposed landscaping in the central and splitter islands; and
- truck turning paths (on a separate display).

In urban areas special attention should be given to minimizing right-of-way impacts. Where possible, use construction easements to reduce project costs and impacts to adjacent properties.

Be prepared with a comparison of cost, safety, and operational performance of the roundabout and other alternate intersection forms evaluated as part of a roundabout feasibility study. Specifically, the following information should be available for use during the meeting:

- construction cost estimates;

- crash history and an assessment roundabout safety benefits; and

- operational and signal warrant analyses.

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Bring visual aids (e.g. videos, simulations, and brochures) to help familiarize the public with how to drive through a roundabout. Some visual aids are available on GDOT's roundabout website (http://www.dot.state.ga.us/travelingingeorgia/roundabouts/pages/default.aspx) and on FHWA's roundabout website (http://safety.fhwa.dot.gov/intersection/roundabouts/). Additional information regarding public involvement/public education is presented in Section 3.8 of NCHRP 672).

8.3. Design Guidelines
This section presents design guidelines which should be used along with NCHRP 672 for the design of roundabouts. Exhibit 6-1 of NCHRP 672 provides an excellent overview of the general design process.
A roundabout should be designed with appropriate geometric features to ensure optimal safety and operational performance for users entering, circulating, and exiting the intersection. The following key principles are taken from Section 6.2 of NCHRP 672:
provide slow entry speeds and consistent speeds through the roundabout by using deflection;
provide the appropriate number of lanes and lane assignment to achieve adequate capacity, lane volume balance, and lane continuity;
provide smooth channelization that is intuitive to drivers and results in vehicles naturally using the intended lanes;
provide adequate accommodation for the design vehicles;
design to meet the needs of pedestrians and cyclists; and
provide appropriate sight distance and visibility for driver recognition of the intersection and conflicting users.
For multilane roundabouts, below are additional considerations (See Section 6.5 of NCHRP 672): lane arrangements to allow drivers to select the appropriate lane on entry and navigate through the roundabout without changing lanes;
alignment of vehicles at the entrance line, into the correct lane within the circulatory roadway;
accommodation of side-by-side vehicles through the roundabout (e.g., a truck or bus traveling adjacent to a passenger car);
alignment of the legs to prevent exitingcirculating conflicts; and
accommodation for all travel modes.
Satisfying these key principles involves balancing the sometimes competing needs for safety and operational performance. Accordingly, engineers preparing roundabout designs should be familiar with NCHRP 672 and apply a high level of Quality Control/Quality Assurance (QC/QA) practices throughout the design process.
8.3.1. Review of Construction Plans
As with feasibility studies, GDOT prepared construction plans must be reviewed in accordance with the Department's QC/QA Manual, and construction plans prepared by consultants in accordance with their own approved QC/QA procedures.

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Prior to the Final Field Plan Review (FFPR), a peer review of the construction plans should be performed. Peer review will normally include all roundabout-related construction plan information. This should include: (1) the horizontal layout; (2) vertical design elements (e.g., typical sections, profiles and grading); (3) drainage; (4) signing and marking plans; (5) landscaping plans; (6) lighting plans; and (7) staging plans.
The objective of the peer review is to verify that all design information necessary for construction and operation of the roundabout is provided. Careful consideration is given to design details which can significantly affect performance of the roundabout are current with "best practices" for design and construction.
Peer review comments will be added to the FFPR report by Engineering Services and red-lined construction plans provided to the project manager.
8.3.2. Design Vehicle
The design vehicle should be an AASHTO WB-67 for all roundabouts on state routes and interchange ramp terminals. The roundabout geometry should accommodate the swept path of the design vehicle tires and body and should be evaluated using a CAD-based vehicle turning path program for each of the turning movements. Buses (BUS-40) in urban areas and single-unit trucks (SU) in rural areas should be accommodated within the circulatory roadway without tracking over the truck apron. For further information on the selection of a design vehicle refer to Section 3.2 of this design policy manual. See also Sections 3.5.4.1, 6.2.4. 6.4.7, and 6.5.7 of NCHRP 672.
If needed, roundabouts can be designed with a gated roadway through the central island to accommodate oversized vehicles.
8.3.3. Alignment of Approaches
The centerline of the roundabout approaches are often aligned through the center of the roundabout, or be offset to the left of the roundabout center point to enhance deflection of the entry path. Approach alignments offset to the right of the roundabout center point should be avoided unless other geometric features can be applied to produce acceptable fastest path speeds. See Section 6.3.2 of NCHRP 672 for a more in-depth discussion on the alignment of approaches.
8.3.4. Splitter Islands
Splitter islands should be incorporated into all roundabouts and should include cut-throughs to accommodate pedestrian traffic.
The total length of the raised island should be 100 ft, at minimum. This minimum may be reduced to 50 ft on urban roadways with design speeds less than 45 mph. For high speed approaches splitter islands should be lengthened as described in Section 6.8.5.3 of NCHRP 672. See Sections 6.4.1 and 6.5.5 of NCHRP 672 for more information on the design of splitter islands.
8.3.5. Pedestrian Design Considerations
Pedestrians should be considered and accommodated at all roundabout intersections. Pedestrian accommodations should include cut-throughs on splitter islands, two-stage perpendicular crossings, curb ramps and accessibility features such as detectable warning surfaces. Pedestrian activated signals should be considered for multi-lane roundabouts with high pedestrian traffic volumes.

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Sidewalks should be set back from the edge of the circulatory roadway with a landscape buffer. Landscape buffers should have a minimum width of 2 ft, with 6 ft being desirable. Stamped and colored concrete should be considered for landscape buffer to assist sight-impaired pedestrians.

At singlelane approaches and departures, the pedestrian crossing should be located one car length (approximately 20 ft) away from the inscribed circle. At multilane approaches and departures, the pedestrian crossing should be located one or two car lengths away from the inscribed circle.

Further information for the design of pedestrian accommodations for roundabouts is provided in Section 6.8.1 of NCHRP 672.

8.3.6. Bicycle Design Considerations
Where bicycle lanes are used on approach roadways, they should be terminated in advance of roundabouts using tapers to merge cyclists into traffic for circulation with other vehicles. For bike routes where cyclists remain within the traffic lane, it can be assumed that cyclists will continue through the roundabout in the travel lane.

At multi-lane roundabouts consider providing bicycle ramps to allow bicyclists to exit the roadway onto the sidewalk and travel as pedestrians. Ramps should not normally be used at urban, onelane roundabouts except where the complexity of the roundabout would make circulating like other vehicles more challenging for bicyclists.

Further information for the design of bicycle accommodations for roundabouts is provided in Section 6.8.2 of NCHRP 672.

8.3.7. Treatments for High Speed Approaches
The primary safety concern in rural locations where approach speeds are high is to make drivers aware of the roundabout with sufficient advance distance to comfortably decelerate to the appropriate speed for entering the roundabout. Where possible, the geometric alignment of approach roadways should be constructed to maximize the visibility of the central island and the shape of the roundabout.

Speed reduction treatments should be used for approach roadways where the design speed of the approach is greater than 45 mph. These treatments may include geometric and/or nongeometric techniques. Examples of geometric treatments include the use of horizontal curvature on approaches and the extension of splitter islands upstream of the entry yield line - for a distance equal to the length required to decelerate from the approach roadway design speed to the entry speed of the roundabout. Examples of nongeometric treatments include the addition of successive sets of rumble strips placed in advance of the roundabout, speed reduction markings placed transversely across travel lanes, advance warning signs supplemented by warning beacons, and landscaping of splitter islands to increase their prominence.

Further information on treatments for high speed approaches is provided in Section 6.8.5 and 7.4.4 of NCHRP 672.

8.3.8. Drainage

Drainage structures should normally be placed on the outer curb line of the roundabout and upstream of crosswalks, but should not be placed in the entry and exit radii of the approaches. Drainage structures located on the outer curb line of the circulatory roadway should be designed to withstand vehicle loading (e.g., Type E, Standard Drop Inlet with Hood shown on GDOT Standard

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Drawing 1019A). Maximum gutter spreads should match the requirements for the approach roadways as outlined in the GDOT manual on the Drainage Design for Highways.
Refer to Section 6.8.7 of NCHRP 672 for a discussion of vertical alignment considerations which includes drainage.
8.3.9. Curbing
Concrete curb and gutter with a Type 2 curb face should be used along the outside edge of all roundabouts which includes the entry radius, the circulatory roadway, and the exit radius. For rural roadways it is desirable to extend outside curbing along approaches to the length of the required deceleration distance to the roundabout.
A Type 2 curb face should also be used for splitter islands. A Type 9 or Type 9a concrete header curb should be used between the truck apron and the circulatory roadway, as specified on GDOT Construction Detail 9032B.
Further information on the principles of using curbs on roundabouts Sections 6.8.7.4 and 6.8.8.1 of NCHRP 672.
8.3.10. Pavement
Asphalt or dark colored concrete is the recommended material for the circulatory roadway to differentiate it from the concrete truck apron. A proposed pavement design should be prepared for each roundabout and be submitted for review and approval in accordance with the GDOT PDP.
Further information on the design of pavements for roundabouts is provided in Section 6.8.8 of NCHRP 672.
8.3.11. Staging of Improvements
When projected traffic volumes indicate that a multilane roundabout is required for the design year, the duration of time that a single-lane roundabout can be expected to operate acceptably should be estimated. Consideration should be given to first constructing a single-lane where a single-lane roundabout is expected to be sufficient for ten years or more from the date the roundabout would be open for traffic.
To allow for this future expansion, the right-of-way and geometric needs of both the single-lane and multilane roundabout should be defined. For further information refer to Section 6.12 of NCHRP 672.
8.3.12. Traffic Control Devices
Traffic control devices for roundabouts shall be in accordance with the 2009 Manual on Uniform Traffic Control Devices. Chapter 7 of NCHRP 672 provides a helpful presentation of the application of traffic control devices to roundabouts.
8.3.13. Landscaping
Landscaping plans should be included as a part of the design, especially in the center island to provide visual awareness of the roundabout location. Specifically, landscaping in the central island should adequately block the through sight lines of an approaching driver so that the driver sees the central island. Landscaping within the central island should discourage pedestrian traffic to and through the central island.

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Any landscaping that is provided along the perimeter of the central island should consist of low-lying shrubs, grass or groundcover so that stopping and intersection sight distance requirements are maintained for vehicles. Shrubs and columnar growing species may be appropriate within the inner portion of the central island. Consideration should be given to the size and shape of mature plants.
Further information on the principles of landscaping for roundabouts is provided in Chapter 9 of NCHRP 672.
8.3.14. Construction
Construction time and cost can be reduced by constructing a roundabout while maintaining traffic on an off-site detour, or otherwise outside the footprint of the roundabout (e.g. a roundabout on new location). If this cannot be accomplished and traffic must pass through the work zone, the below is one possible sequence for construction.
1. Install signing and lighting (signing should initially be covered).
2. Maintain traffic on existing roadways. Construct the portion of the roundabout located outside the existing intersection footprint. This should include drainage structures and a portion of the circulatory roadway but not the shoulder outside the circulatory roadway. Construct temporary pavement outside the circulatory roadway for maintaining traffic in the next stage.
3. Remove covered signage and shift traffic from the existing roadways to the temporary circulatory roadway. The intersection should function as a roundabout, the temporary circulatory roadway should be wide enough to accommodate the design vehicle.
4. Construct splitter islands and central island with truck apron. Finish construction of the circulatory roadway and finish any pavement markings.
5. Shift traffic from the temporary circulatory roadway to the final circulatory roadway.
6. Remove temporary pavement and construct shoulders. Complete drainage structures and relocate signing to appropriate locations within the islands.
Staging narratives for construction plans will vary considerably from one project to another, and must be specific to the design and constraints of each project. The above is a only brief explanation meant to illustrate a possible sequence of construction. Further information on the stage construction including other staging sequences are presented in Section 10.3 of NCHRP 672.
8.4. References
8.4.1. Primary References
For the planning and design of roundabouts refer to the most current edition of the following publications.
2010 Highway Capacity Manual, Transportation Research Board, National Academies of Science, Washington DC, work in progress.
Design Guide for Roundabout Lighting, DG-19-08, Roundabout Lighting Committee, Illuminating Engineering Society of North America, New York, NY, June 2009.
Highway Capacity Manual, Special Report 209, Transportation Research Board, National Academies of Science, Washington DC, 2000.

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Manual on Uniform Traffic Control Devices, Federal Highway Administration, US Department of Transportation, 2009.
Roundabouts: An Informational Guide, 2nd Edition, National Cooperative Highway Research Program Report 03-78A, Transportation Research Board, National Academies of Science, Washington, DC, 2010.
8.4.2. Additional References
Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities, National Cooperative Highway Research Program Report 03-78A, Transportation Research Board, National Academies of Science, Washington, DC, 2011.
Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures 5. Roundabouts, Federal Highway Administration, US Department of Transportation, July, 1, 2009.
Highway Design Handbook for Older Drivers and Pedestrians, Publication No. FHWA-RD-01103, Federal Highway Administration, US Department of Transportation, May 2001.
Mini-Roundabout Technical Summary, Report FHWA-SA-10-007, Federal Highway Administration, US Department of Transportation, Feb. 2010.
Pedestrian Access to Modern Roundabouts: Design and Operational Issues for Pedestrians Who are Blind, US Access Board.
Roundabouts in the United States, NCHRP Report 572, National Cooperative Highway Research Program, Transportation Research Board, National Academies of Science, Washington DC, 2007.
Roundabout Technical Summary, Report FHWA-SA-10-006, Federal Highway Administration, US Department of Transportation, Feb. 2010.
Signalized Intersections: An Informational Guide, Publication No. FHWA-HRT-04-091, Federal Highway Administration, US Department of Transportation, August 2004.

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8.5. Definition of Terms
Figures 8.2 and 8.3 illustrate key roundabout physical features and design elements. These figures were modified from the report, Technical Memorandum: Planning-Level Guidelines for Modern Roundabouts prepared by the Center for Transportation Research and Education at Iowa State University [2008]. Definitions for key terms are provide below each figure and most are taken or adapted from either the above report or NCHRP 672.
8.5.1. Roundabout Physical Features

Figure 8.2. Key Roundabout Physical Features
Apron (or Truck Apron) the mountable portion of the central island adjacent to the circulatory roadway. Used in some roundabouts to accommodate the wheel tracking of large vehicles.
Bike Ramp Allows for bicyclists to exit the traveling lane to the sidewalk and use the crosswalk as a pedestrian would. It is recommended that only experienced bicyclists be encouraged to use the roadway and that novice riders exit the roadway, dismount their bikes and use the sidewalk and crosswalks. [See Section 6.8.2.2 of NCHRP 672 for further reference.]
Central Island (or Center Island) the raised area in the center of a roundabout around which traffic circulates. The central island does not necessarily need to be circular in shape. In the case of mini-roundabouts the central island is traversable.

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Circulatory Roadway the curved path used by vehicles to travel in a counterclockwise fashion around the central island.
Entrance Line (or Yield Line) a pavement marking used to mark the point of entry from an approach into the circulatory roadway and generally marked along the inscribed circle. Entering vehicles must yield to any circulating traffic coming from the left before crossing this line into the circulatory roadway.
Landscaping Buffer (or Landscaping Strip) Landscape strips separate vehicular and pedestrian traffic and assist with guiding pedestrians to the designated crossing locations. This feature is particularly important as a wayfinding cue for individuals who are visually impaired. Landscape strips can also significantly improve the aesthetics of the intersection.
Lighting Provides illumination for all potential conflict areas, including the beginning of the splitter island, all crosswalks, and entries and exits to the circulatory roadway. Also, provides illumination to make the roundabout visible from a distance, for users approaching the roundabout.
Mini-roundabout small roundabouts used in low-speed urban environments. The central island is fully mountable, and the splitter islands are either painted or mountable. [See Exhibit 1-10 of NCHRP for a layout showing the features of a typical mini-roundabout.]
Modern Roundabout a term used to distinguish newer circular intersections, conforming to the characteristics of roundabouts, from older-style rotaries or traffic circles. [See Section 1.2 of NCHRP 672 for a detailed explanation of the characteristics of a modern roundabout and comparison to older types of circular intersections.]
Multilane roundabout a roundabout that has at least one entry with two or more lanes, and a circulatory roadway that can accommodate more than one vehicle travelling side-by-side. [See Exhibit 1-16 for examples of multilane roundabouts.]
Outside Curbing Non-mountable curb defining the outside edge of the pavement on each approach, around the circulatory roadway, and continuing outside the adjacent exit. Curbs improve delineation and discourage corner cutting, which helps to maintain lower speeds. Ideally begins at the deceleration point on each approach. [See Section 6.8.5.2 of NCHRP 672 for further reference.]
Right-Turn Bypass Lane a lane provided adjacent to, but separated from, the circulatory roadway, that allows right-turning or through movements to bypass the roundabout. Also known as a right-turn slip lane. [See Section 6.8.6 of NCHRP 672 for further reference.]
Sidewalk used in urban areas to accommodate pedestrians.
Splitter Island the raised or painted area on an approach, used to separate entering from exiting traffic, deflect and slow entering traffic, and provide storage space for pedestrians crossing the intersection approach in two stages.

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8.5.2. Roundabout Design Elements

Figure 8.3. Key Roundabout Design Elements

Approach Width the width of the roadway used by approaching traffic upstream of any changes in width associated with the roundabout. The approach width is typically no more than half the total roadway width.

Circulatory Roadway Width the width between the outer edge of the circulatory roadway and the central island, not including the width of any apron.

Conflict Point a location where the paths of two vehicles, or a vehicle and a bicycle or pedestrian, merge, diverge, cross, or queue behind each other. [See Exhibits 5-1 and 5-2 of NCHRP 672 for illustration of vehicle conflict points at 3- and 4-leg roundabouts and conventional intersection.]

Deflection the change in trajectory of a vehicle imposed by geometric features of the roadway. Entry deflection helps control vehicle speeds and discourages wrong-way movements on the circulatory roadway. [See Exhibit 6-10 of NCHRP 672 for a comparison on entry alignments with and without deflection.]

Entry Flare the widening of an approach to multiple lanes to provide additional capacity at the yield line and storage. [See Exhibit 1-8(e) of NCHRP 672 for an example of an entry flare for a multilane roundabout and Section 6.5.2 of the same report for further reference.]

Entry Speed the speed a vehicle is traveling as it crosses the yield line.

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Entry Width the width of the entry where it meets the inscribed diameter, measured perpendicularly from the right edge of the entry to the intersection point of the left edge line and the inscribed circle.
Fastest Path The fastest path allowed by the approach and roundabout geometry determines the negotiation speed for that particular movement into, through, and exiting the roundabout. It is the smoothest, flattest path possible for a single vehicle, in the absence of other traffic and ignoring all lane markings. [See Section 6.7.1 of NCHRP 672 for a detailed presentation. Exhibit 6-46 for of NCHRP 672 illustrates the five critical path radii that must be checked for each approach.]
Geometric Delay the delay caused by the alignment of the lane or the path taken by the vehicle on a roadway or through an intersection. [See Section 4.5.8 of NCHRP 672 for further reference.]
Inscribed Circle Diameter the basic parameter used to define the size of a roundabout, measured between the outer edges of the circulatory roadway. It is the diameter of the largest circle that can be inscribed within the outline of the intersection.
Locking stoppage of traffic on the circulatory roadway caused by queuing backing into the roundabout from one of the exits, resulting in traffic being unable to enter or circulate.
Natural Path The path an approaching vehicle will take through a multi-lane roundabout, assuming traffic in all lanes. The speed and orientation of the vehicle at the yield line determines the natural path. [See Section 6.7.2 of NCHRP 672 for further reference.]
Path Alignment a roundabout should naturally align entering lanes into their appropriate lane within the circulatory roadway and then to the appropriate lanes on the exit. [See Sections 3.5.4.2 and 6.2.3 of NCHRP 672 for further reference.]
Roundabout Capacity the maximum number of entering vehicles that can be reasonably expected to be served by a roundabout during a specified time period.
Vehicle Path Overlap - Path overlap occurs on multi-lane roundabouts when the natural path through the roundabout of one vehicle overlaps that of another vehicle. Occurs most commonly on the approach when a vehicle in the right lane cuts off a vehicle in the left lane as the vehicle enters the circulating lane. [See Exhibits 6-28 and 6-33 of NCHRP 672 for illustrations of entry and exit vehicle path overlap, and Section 6.2.3 of the same report for a discussion of appropriate path alignment.]
View Angle - View angle is measured as the angle between a vehicle's alignment at the entrance line and the sight line required according to intersection sight-distance guidelines. The intersection angle between consecutive entries must not be overly acute in order to allow drivers to comfortably turn their heads to the left to view oncoming traffic from the immediate upstream entry. [See Section 6.7.4 of NCHRP 672 for further guidance.]

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Chapter 9 Contents

9. BICYCLE & PEDESTRIAN ACCOMMODATIONS

2

9.1. Overview

2

9.1.1. Americans with Disabilities Act

2

9.1.2. Definition of Accommodations

2

9.1.3. Incremental Approach

2

9.2. Typical Users & Needs

2

9.2.1. Pedestrians

2

9.2.2. Bicyclists

3

9.2.3. Non-Motorized Needs and Volumes

3

9.3. Bicycle Route Networks

4

9.4. Warrants for Accommodation

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9.4.1. Pedestrian Warrants

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9.4.2. Bicycle Warrants

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9.4.3. Exclusions

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9.5. Facility Design

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9.5.1. Pedestrian Facility Design

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9.5.2. Bicycle Facility Design

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9.5. Work Zone Accessibility

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List of Figures

Figure 9.1. Examples of designated Bicycle Routes:

4

Figure 9.2. Georgia Statewide Bicycle Route Network

5

Figure 9.3. Illustrations of Pedestrian Facility Design

10

Figure 9.4. Illustration of Bike Lane Design along Rural and Urban Roadways

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9. BICYCLE & PEDESTRIAN ACCOMMODATIONS
9.1. Overview
Bicycle and pedestrian accommodations are incorporated into transportation projects as a means to improve the safety and mobility of non-motorized users. The result should be a system that allows choice among both motorized and non-motorized modes of transportation.

This Bicycle and Pedestrian Accommodations policy is based on principles from the Georgia DOT Pedestrian and Streetscape Guide (2003), the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities (2004), the AASHTO Guide for the Development of Bicycle Facilities, and the Public Right of Way Accessibility Guidelines (PROWAG) developed under the umbrella of the United States Access Board and the Americans with Disabilities Act of 1990 (ADA). The latest PROWAG can be downloaded at: http://www.access-board.gov/prowac/draft.htm.

9.1.1. Americans with Disabilities Act
The ADA was enacted by the U.S. Congress and signed into law on July 26, 1990, and later amended with changes effective January 1, 2009. The ADA is a wide-ranging civil rights law that prohibits, under certain circumstances, discrimination based on disability. ADA design guidelines for accessible buildings and facilities are published in the ADA Accessibility Guidelines (ADAAG). ADA design guidelines for accessible public rights-of-way are published in the PROWAG.

9.1.2. Definition of Accommodations
An accommodation is here defined as any facility, design feature, operational change, or maintenance activity that improves pedestrian and bicycle travel. The type of accommodation may vary by location and the needs of typical users, but the safety and accessibility of all modes should be considered in every situation. Accommodations may include the provision of: bike lanes, shared-lane markings, or paved shoulders; sidewalks or shared-use paths; intersection and midblock treatments such as marked crosswalks, signs, lighting, and accessible features; and/or other treatments as necessary.

9.1.3. Incremental Approach
Bicycle and pedestrian accommodations are included as components of larger transportation projects. This strategy is a long-term incremental approach to developing a statewide network. All necessary segments being consistently designed and implemented will provide for the safe and efficient movement of bicyclists, pedestrians, and motorists throughout the state.

9.2. Typical Users & Needs
Pedestrians and bicyclists are often grouped together when referring to non-motorized users. Both users generally travel at the far right or outside of the roadway, are generally slower than adjacent motor vehicles, and are more influenced by their immediate surroundings. Since both non-motorized modes travel under their own power and are more exposed to the elements, both often prefer direct routes or shortcuts to minimize their effort and time. However, there are significant differences between both pedestrians and bicyclists and within each of the two groups.

9.2.1. Pedestrians
All transportation trips begin or end with walking. Many pedestrians choose to walk for convenience, personal health, or out of necessity. They often prefer greater separation from the roadway, require additional time to cross roadways, and are the most vulnerable of all roadway users. Pedestrians will

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often seek to minimize travel distance, choosing direct routes and shortcuts even when facilities are not provided. Walking trips are often combined with public transit for traveling longer distances, making consideration of accessibility to transit stations and stops a critical factor. Pedestrians also include children, senior citizens, or people with physical disabilities; these groups may require additional design considerations.
9.2.2. Bicyclists
Bicyclists utilize pubic roadways for most trips and are therefore subject to vehicular laws. Therefore, the bicycle facility should be designed to encourage cycling behavior that is as predictable as possible when interacting with vehicular traffic. Bicycling trips serve both utility and recreation purposes, often in the same trip. Utilitarian and commuter cyclists will generally choose whichever roadway provides for the most direct, safe and comfortable travel to their destinations. Younger, less experienced or recreational riders will typically choose routes for comfort or scenery and may feel more comfortable on separated facilities. Bicycle facilities should be context sensitive and should be selected based on the characteristics of the road corridor, the expected needs of typical users, the accessibility of the facility to area destinations, and other considerations.
There are two general types of bicycle facilities; on-road facilities including bike lanes or shared lanes; and off-road facilities such as shared-use paths, cycle tracks, or greenway trails. On-road facilities allow cyclists to circulate with traffic, allow easier access to destinations, and help cyclists behave more predictably. Off-road facilities may allow greater separation from high-speed traffic but need careful consideration at driveways, intersections, and constrained areas. These two facility types are not interchangeable and careful examination of their application should be conducted on a case-by-case basis.
9.2.3. Non-Motorized Needs and Volumes
Planning studies for bicycle and pedestrian travel normally consider the number of users, their typical needs, and significant barriers to travel. This includes measuring current and projecting future travel, evaluating existing conditions, and identifying constraints and opportunities. Typical planning tools may include non-motorized traffic counts, Bicycle or Pedestrian Level of Service formulas, Latent Demand Scores, user surveys, and public input; these tools all help establish user levels, destinations, and facility needs above the most basic routine project accommodations.
The degree of non-motorized users and their needs should be determined during the project planning or concept development phase. Defining the degree of non-motorized use and their needs will often require local input and for most projects can be accomplished during the initial concept meeting, reconnaissance of the project area, and meetings with local officials and stakeholders. PIOH meetings are also a useful venue for obtaining this information.
The findings and decisions of investigations relating to non-motorized users should be documented in the concept report as part of the "Need and Purpose" statement. This information may be qualitative in nature but must be sufficient for use by the design phase leader to evaluate the bicycle and pedestrian warrants presented in Section 9.4 of this chapter. The evaluation of warrants should be included as a separate section in the concept report. If the project is expected to adversely impact existing bicycle or pedestrian accommodations, this should also be noted.

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9.3. Bicycle Route Networks
Roads and bikeways form a network of bicycle routes that facilitate travel for bicyclists by connecting metropolitan areas or regional destinations of important scenic, historic, cultural, and recreational value. An important role of planning is to help ensure that bicycle routes provide for reasonably direct travel. An important role of design is to help reduce other impediments (which discourage bicycle travel) by incorporating bicycle provisions into construction projects. Consequently, rural cycling routes and longdistance routes routinely consider the populations of the areas they connect rather than the populations along the actual route.
The Georgia DOT maintains a network of cross-state bicycle routes to facilitate long-distance bicycle travel in Georgia (see Figure 9.1., Georgia Statewide Bicycle Route Network). Regional planning commissions and local governments in Georgia have developed bicycle route networks which connect destinations within regions or facilitate local trips. These routes consist primarily of on-road facilities (such as paved shoulders, bicycle lanes, or shared lanes) and way finding or cautionary signs. Local, regional, and state bike routes are on file in the State Bicycle and Pedestrian Coordinator's office in the Office of Planning.
Routes identified as part of the Georgia Statewide Bicycle Route Network shall, at a minimum, comply with the basic bicycle accommodations outlined below:
all long-distance bicycle routes will meet the criteria for an approved numbered bicycle route system established by the American Association of State Highway and Transportation Officials (AASHTO), Manual on Uniform Traffic Control Devices (MUTCD), and GDOT guidelines; Georgia state bicycle routes will be coordinated with neighboring states to ensure consistency for regional or national networks and allow for inter-state bicycle travel; and
long-distance bicycle routes should include the installation of bicycle route number signs and way finding or cautionary signs where necessary.
While bicycle routes provide information to traveling cyclists, cyclists are allowed to ride on any road legally open to bicycles regardless of the presence or absence of specific bicycle accommodations or designations.
Figure 9.1. Examples of designated Bicycle Routes:

Scenic Byway, North Georgia

Bike Lane, Sugarloaf Parkway, Gwinnett County

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Figure 9.2. Georgia Statewide Bicycle Route Network

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9.4. Warrants for Accommodation
The Georgia Department of Transportation has established the following standards and guidelines to ensure that bicycle and pedestrian accommodations are provided on all appropriate infrastructure projects where pedestrians and bicyclists are permitted to travel. Warrants for bicycle and pedestrian accommodations will be evaluated as part of project concept development, and documented in the concept report.

If it is not practical to comply with the criteria below denoted as "standards", then agency approval and documentation will be required by formal Design Variance before the accommodation can be modified or excluded from the project. To obtain a Design Variance, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP). Examples of cases where bicycle and pedestrian accommodations may be excluded from projects are provided in Section 9.4.3, Exclusions.
9.4.1. Pedestrian Warrants
Standards Pedestrian accommodations shall be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are either located in an urban area (typically where curb and gutter is provided) or are located in areas with any of the following conditions:
on corridors with pedestrian travel generators and destinations (i.e. residences, commercial locations, schools, public parks, etc), or areas where such generators and destinations can be expected within the projected lifespan of the project; where there is evidence of pedestrian traffic (e.g. worn path along roadside); on corridors served by fixed-route transit in urban and suburban areas; where there is an occurrence of "walking along the roadway" type crashes; and where a need is identified by a local government through a planning study and public involvement process.
Guidelines Pedestrian accommodations should be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are located in areas with any of the following conditions:
within close proximity (i.e. 1 mile) to any school, college or university; and any location where engineering judgment or planning analysis determines a need.
As part of Preventative Maintenance (PM) projects and Resurfacing, Restoration, or Rehabilitation (3R) projects, improvements and/or repairs to curb ramps should be assessed on a case-by-case basis. The Office of Maintenance will determine the eligibility for improvements and/or repairs to curb ramps at the formal field plan review.
9.4.2. Bicycle Warrants
Standards Bicycle accommodations shall be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are located in areas with any of the following conditions:
where there is an existing bicycle facility in place (including bike lanes, paths, shoulders, wide curb lane, and/or signage); if the project is on a state, regional, or local bike route; and where there is a demonstrated need, with bicycle travel generators and destinations (i.e. urban areas, residential neighborhoods, commercial centers, schools, colleges, public parks, etc), or areas where such generators and destinations can be expected within the projected lifespan of the project.

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Guidelines Bicycle accommodations should be considered on projects that are located in areas with any of the following conditions:
within close proximity (i.e. 2 miles) to any school, college or university; where a project will provide connectivity between two or more existing bikeways; where a local bike route is identified by a local government through a planning study; along bicycle routes that connect metropolitan areas and regional destinations; on resurfacing projects in urban areas, the Department may consider restriping the roadway and narrowing travel lanes to provide additional shoulder width or wide curb lane. Restriping will be considered where space is available and where there is no significant history of sideswipe crashes. The Office of Maintenance will coordinate with the Office of Planning and Office of Traffic Operations to define an appropriate crash threshold for determining eligibility for restriping on a project-by-project basis; on projects where a bridge deck is being replaced or rehabilitated with Federal financial participation, and where bicycles are permitted to operate at each end of the bridge, the bridge deck may be replaced or rehabilitated to provide safe bicycle accommodations; and any location where engineering judgment or planning analysis determines a need.
9.4.3. Exclusions
Bicycle and pedestrian accommodations are excluded from routes that have been designated as "Full Access Control" such as freeways and interstate highways."
A sidewalk may be excluded on side road tie-ins where there is no existing sidewalk and the additional widening of shoulders for sidewalk would result in excessive impacts as determined by the design team on a case-by-case basis. Sidewalks are not required in rural areas where curb and gutter is placed at the back of the useable shoulder for the purpose of reducing construction limits.
Either of the following conditions may be considered justification for a Design Variance to exclude bicycle and pedestrian facilities:
1. projects where the cost of providing bicycle and pedestrian facilities would be excessively disproportionate to the need or probable use. Excessively disproportionate is defined as exceeding twenty percent (20%) of the total cost of the project; and
2. bridge projects where the existing width will provide adequate shoulders (at least 4-ft. of smooth pavement) for non-motorized use.

9.5. Facility Design
9.5.1. Pedestrian Facility Design
The Georgia DOT has compiled the following design criteria as recommended dimensions when designing sidewalk and pedestrian facilities in Georgia. The criterion was developed with reference to the PROWAG developed under the umbrella of the United States Access Board and the ADA. In some cases, GDOT provides more specific and selective criteria relating to the design of sidewalks. If it is not practical to comply with the following GDOT criteria, then the designer shall, at a minimum, comply with the criteria published in the PROWAG.
If an engineer determines that the nature of an existing facility makes it technically infeasible to comply fully with the accessibility standards published in the PROWAG, then the design or alteration shall provide accessibility to the "maximum extent feasible". The approval of a Design Variance from the

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GDOT Chief Engineer will be required before a design or alteration can be retained or incorporated into a project that does not comply with the criteria published in the PROWAG. For design options involving pedestrian facilities in urban areas, GDOT recommends the report "Accessible Public Rights-of-Way Planning and Design for Alterations", published by the Public Rightsof-Way Access Advisory Committee (PROWAAC). The report is located on-line at: http://www.accessboard.gov/prowac/alterations/guide.htm.
Location of Sidewalk Sidewalks are typically provided along urban shoulders, wherever curb and gutter is utilized along the outside edges of pavement of the mainline. See Chapter 6.7 Border Area (urban shoulder) of this Manual for a more complete definition of an urban shoulder.
Width of Sidewalk GDOT recommends the minimum width of sidewalk be 5-ft of clear unobstructed space. A 5-ft sidewalk width should allow adequate space for two wheelchairs to pass without conflict. Higher pedestrian usage may warrant the use of wider sidewalks.
The PROWAG (R301.3) specifies that "walkways in pedestrian access routes that are less than 5-ft in clear width shall provide passing spaces at intervals of 200-ft maximum. Pedestrian access routes at passing spaces shall be 5-ft wide for a distance of 5-ft" When right-of-way is limited at intersections, the designer should be careful not to violate this requirement by placing a strain pole or pedestrian signal head in a way that would reduce this 5-ft x 5-ft area.
Buffer Space The buffer space is defined as the area between the back of curb and edge of sidewalk. The buffer space provides important safety and comfort benefits for walkers as well as allows room to place utilities or street furniture without obstructing the pedestrian travel way.
GDOT recommends a 6-ft wide buffer space between the back of curb and the sidewalk. If a roadway has multiple driveways, a 6-ft buffer space will provide the offset required to connect the sidewalk perpendicular to the back of a standard concrete valley gutter driveway.
The minimum buffer space between the back of curb and sidewalk should be at least 2-ft wide, to provide a degree of separation between pedestrian and vehicle, and to allow for utilities. A minimum 2ft wide grass or paver strip is preferred because it provides a color contrast which assists visually impaired pedestrians to better distinguish between the sidewalk and roadway. A minimum 2-ft wide buffer also provides some protection from overhanging objects from vehicles, and also creates a psychological barrier, enhancing pedestrian comfort.
Where right-of-way constraints will not permit a 2-ft buffer width, sidewalk may be constructed adjacent to the back of curb. For example, this may occur in Central Business Districts or where buildings are adjacent to the right-of-way.
Cross-Slope The maximum allowable sidewalk cross-slope shall not exceed 2.0% (PROWAG R301.4.1).
Longitudinal Slope The longitudinal slope (grade) of a sidewalk shall not exceed the general grade established for the adjacent street or roadway (PROWAG R301.4.2). In cases where sidewalk alignment deviates from the adjacent roadway, the longitudinal slope of the sidewalk shall not exceed 8.3% (PROWAG 303.2.1.1).

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Curb Ramps The ADA requires accessible curb ramps be included on pedestrian facilities.
Ramp profile shall have a running slope between 5 percent minimum and 8.3 percent maximum (PROWAG R406.2). The ramp should be placed in line with pedestrian flow and crosswalks, and the edges of a diagonal curb ramp must be parallel to the direction of pedestrian flow. The bottom of diagonal curb ramps shall have 48 in. minimum clear space between the curb line and the vehicle traveled way line.
Refer to GDOT Construction Standards and Details, Construction Details A-1, A-2, A-3, and A-4 for additional information regarding the typical location and design of sidewalks and curb ramps.
Sidewalk Surface The surface of the pedestrian access route shall be firm, stable and slip resistant. Surface discontinuities shall not exceed " maximum vertical or horizontal (PROWAG R301.5.2).
In situations where existing sidewalk will be retained, vertical discontinuities between in. and in maximum shall be beveled at 1:2 minimum. The bevel shall be applied across the entire level change. In situations where existing sidewalk will be retained, the project must repair/replace areas of sidewalk that has heaved (vertical) more than in., or if there are more than in. gaps (horizontal) in the sidewalk.
Detectable Items for the Impaired Detectable warnings are devices that alert a visually impaired person that they are entering or exiting a potentially hazardous area. All wheelchair ramps shall incorporate a detectable warning surface (see GDOT Detail A4). The minimum width of the detectable warning surface is the width of the curb ramp exclusive of flared sides (R304.1.4). Detectable audible warning systems should be used where a need has been determined.
Crosswalks Crosswalk design, placement, and the selection of additional safety treatments (where necessary) should meet GDOT's most recent guidance located in Section 12.2.3 of the GDOT Signing and Marking Design Guidelines and in GDOT Construction Details.
Bridges A typical sidewalk width across a bridge in an urban area is 6-ft without a buffer space between the back of curb and sidewalk. Therefore, the width of the sidewalk should transition from the roadway cross section to the bridge cross section before the approach slab. This should also include eliminating the buffer space in advance of the bridge.
When sidewalk is tapered to match the bridge shoulder, this is typically done in an area 50-ft to 100-ft in advance of the bridge. Where guardrail is used on the bridge approaches, the sidewalk transition should follow the guardrail offset transition.

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Figure 9.3. Illustrations of Pedestrian Facility Design

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9.5.2. Bicycle Facility Design
GDOT adopts the design guidance published in the AASHTO Guide for the Development of Bicycle Facilities. Design consistency with local or regional bicycle plans should be considered wherever possible. There are three types of bicycle facilities commonly designed by GDOT.
1. On-Street Bicycle Facility preferred by GDOT where practical, an on-street bicycle facility has a designated one-way "bike lane" with painted stripe and symbols directly adjacent to the travel lane for preferential or exclusive use by bicyclists.
On-street bicycle facilities are generally preferred for commuter cyclists because they allow bicyclists to travel with the flow of traffic and have a minimal amount of conflict points with pedestrians and driveways.
Consistent with AASHTO, GDOT has adopted 4-ft as the typical "bike lane" width for both rural and urban type roadways. GDOT recommends the dimensions indicated below.
On rural roadways, the 4-ft bike lane is incorporated into the overall width of paved shoulder to include a 16-in rumble strip offset 12-in from the traveled way. The shoulders are designed with a gap pattern rumble strip to allow bicyclists to smoothly enter and exit the bike lane. Refer to Ga. Construction Detail S-8 for additional information regarding the design of bike lanes and rumble strips on paved shoulders.
On urban roadways with curb & gutter, the 4-ft bike lane is developed between the traveled way and gutter. The bike lane does not include the gutter width.
The designer should note, if the space to the right of the traveled way stripe is less than 4-ft wide, the route cannot be signed or marked as a "bike lane" facility and will be referred to as a shoulder (refer to design of signed shared roadway facility).
2. Signed Shared Roadway Facility where it is not practical to design a designated minimum 4-ft "bike lane", a signed shared roadway facility may be considered. A signed shared roadway facility requires that vehicles and bicycles share the travel lanes of the roadway. Signed shared roadways are identified by signing as a preferred bike route. A signed shared roadway facility should provide a wide outside lane or paved shoulder to accommodate bicycle travel. The additional shoulder width is especially desirable if vehicle speeds exceed 50 mph and the percentage of large vehicles is high. The measurement of usable shoulder width should not include the width of a gutter pan.
3. Shared-Use Paths a paved or unpaved facility physically separated from motorized vehicular traffic by an open space or barrier; either within the highway right-of-way or within an independent right-of-way. Shared-use paths (also referred to as multi-use paths) are used by bicyclists, pedestrians, skaters, joggers, or other non-motorized users. Shared-use paths are considered offroad transportation routes for bicyclists and others and serve as a necessary extension or supplement to on-road bicycle facilities. Shared-use paths should not be considered a substitute for on-street improvements.
Bicycle safe drop-inlet grates are required for all roadways that meet the warrants for bicycle accommodations defined in this policy.

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Figure 9.4. Illustration of Bike Lane Design along Rural and Urban Roadways

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9.5. Work Zone Accessibility
For pedestrian accessibility requirements during construction see GDOT Special Provision, Section 150.02 K. Pedestrian Considerations. The current GDOT SP 150 Traffic Control is located on the Department's website at the following address. http://www.dot.ga.gov/doingbusiness/theSource/special_provisions/shelf/sp150.pdf

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Chapter 11 Contents

11. OTHER PROJECT TYPES

1

11.1. Preventative Maintenance (PM), Resurfacing, Restoration, or Rehabilitation (3R), and Reconstruction

Guidelines for Federal Aid Projects

1

11.1.1. Procedures and Guidelines

2

11.1.2. Controlling Criteria for Non-Interstate Systems (GDOT 3R Standards)

5

11.1.3. Other Design Considerations for 3R Projects (GDOT 3R Standards)

8

11.2. Special Design Considerations for Other Project Types

10

11.2.1. Bridge Fencing Projects

10

11.2.2. Bridge Jacking Projects

11

11.2.3. Intelligent Transportation System (ITS) Projects

11

11.2.4. Signing & Marking Projects

11

11.2.5. Traffic Signal Projects

12

11.2.6. Noise Abatement Projects

12

11.3. Design Elements for Other Project Types

12

11.3.1. Survey Requirements

12

11.3.2. Construction Plans

14

11.3.3. Pavement Design

14

11.3.4. Environmental

14

11.3.5. Earthwork

14

11.3.6. Drainage

15

11.3.7. Guardrail and/or Barrier

15

11.3.8. Erosion Control Plans

15

11.3.9. Traffic Signal Plans

15

11.3.10. Signing & Markings

15

11.3.11. Utilities

15

11.3.12. Traffic Control Plans

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Chapter 11 Index

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List of Figures Figure 11.1. PDP Process for PM, 3R, and Reconstruction Projects
List of Tables Table 11.1. Geometric and Safety Guidelines for 3R, PM, and Reconstruction Projects Table 11.2 Usable Shoulder Width for Two Lane Roadways Table 11.3 Minimum Bridge Widths for Non-interstate Highways Rural Sections (2-Lanes) Table 11.4. Minimum Bridge Widths for Non-interstate Highways Multilane Rural Sections Table 11.5. Minimum Bridge Widths for Local Roads and Streets (Rural Sections) (1) Table 11.6. Horizontal Clearance Table 11.7. Horizontal Alignment for Existing Features not meeting 3R Guidelines

3
4 5 5 6 6 6 7

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11. OTHER PROJECT TYPES
The Georgia Department of Transportation (GDOT) Road Design Policy Manual is primarily written to provide guidance for the preparation of construction documents for projects involving the new construction or major reconstruction of state roadways. Guidelines, design policies, and practices discussed in this chapter address the following other types of projects:

preventative maintenance (PM); roadway resurfacing, restoration, or rehabilitation (3R); and reconstruction projects
bridge fencing and bridge jacking projects intelligent transportation system (ITS) projects signing and pavement marking projects traffic signal projects guardrail and/or barrier projects
The policies in this manual apply to permanent construction of Georgia roads and highways, and different controls and criteria may be applicable to temporary facilities.

11.1. Preventative Maintenance (PM), Resurfacing, Restoration, or Rehabilitation (3R), and Reconstruction Guidelines for Federal Aid Projects
The purpose of this Section is to provide design guidelines and procedures that cover GDOT's Pavement Maintenance and Resurfacing, Restoration, or Rehabilitation Program. This program includes preventative maintenance (PM); resurfacing, restoration, or rehabilitation (3R); and reconstruction projects per the agreement between the GDOT and the Federal Highway Administration (FHWA).

PM projects are defined as the planned strategy of cost effective treatments to an existing roadway system and its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system without increasing structural capacity.

The following are examples of PM projects:

shoulder repair, including mitigation of edge drop offs, upgrading guardrail, and/or barrier components

the addition of paved or stabilization of unpaved shoulders

installation of milled rumble strips

activities related to asphalt pavement surface preservation (e.g. crack sealing, joint sealing, slurry seal, isolated deep patching etc.)

asphalt resurfacing that includes replacement of the surface lift of dense-grade asphalt, or an open-graded friction course (if present) not to exceed three inches.

activities related to treatments for Portland Cement Concrete (PCC) pavements (e.g. joint sealing, grinding, dowel retrofit and partial depth repair)

PCC slab replacement that does not exceed more than 50% of slabs.

restoration or extension of drainage systems

installation or replacement of signs and or pavement markings.

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removal of vegetation in clear zone addition and/or replacement of landscaping execution of encroachment permits activities relating to bridge preservation (e.g. crack sealing, joint repair, scour
countermeasures and painting.) removal or shielding of roadside obstacles
Guidelines and procedures for PM projects shall be governed by the terms of GDOT's FHWAapproved preventive maintenance agreement.
3R projects are generally defined as any pavement treatment that is neither PM nor reconstruction. The following are examples of 3R projects:
resurfacing, restoration or rehabilitation activities related to structural asphalt pavement , including isolated base repair
mill and inlay deeper than the first dense course, but not including the base course activities related to PCC pavement treatments (e.g. continuous slab replacement project that
exceed more than 50 percent of the slabs being replaced in any given lane or area) widening of lanes and shoulders that does not increase the number of lanes selected alterations to vertical and horizontal alignments intersection improvements passing lane projects bridge and culvert rehabilitation or widening that does not increase the number of lanes
Reconstruction projects are generally more complex in project scope and carry a higher cost than PM or 3R projects. The following are examples of reconstruction projects:
activities related to asphalt pavement reconstruction (e.g. the removal of the entire pavement structure through the base course except for isolated base repair associated with PM or 3R projects)
activities related to PCC pavement reconstruction (e.g. slab removal and replacement that is continuous throughout the project or when a significant amount of base is being replaced)

11.1.1. Procedures and Guidelines
Refer to Figure 11.1. and the following text to determine appropriate preconstruction process that should be followed for each of the different categories (PM, 3R or reconstruction projects). PM projects do not need to follow the Plan Development Process (PDP)1. However, PM projects on Interstate highways require both a concept meeting and a brief concept report. 3R projects shall follow a Streamlined PDP, which is summarized in Figure 11.1. Some exceptions are listed below.
3R projects prepared by the GDOT Office of Maintenance and/or Office of Preconstruction shall follow the PDP with the following exceptions/changes:

1 GDOT. Plan Development Process (PDP). Available on the GDOT R.O.A.D.S. website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/Other%20Resources/index.shtml

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Chapter 4. Project Planning and Programming
o Generally, most of this chapter will not apply to 3R projects that are using only lumpsum maintenance funds. However, in all cases, TPro2 shall be updated, as prescribed by Chapter 10 of the PDP.

Figure 11.1. PDP Process for PM, 3R, and Reconstruction Projects
Chapter 5. Concept Stage o 3R projects will not require an initial concept meeting
o To ensure early coordination from other GDOT offices, a concept meeting, report, and solicitation of comments on the report is required. However, some of the PDP's specific requirements for a concept meeting and report may not apply if there are no right-of-way, utility, or environmental impacts
o For 3R projects being developed by the GDOT Office of Maintenance, the Assistant Preconstruction Director will be responsible for distributing the concept report for comments, consolidating comments, recommending approval of the concept report, and forwarding the concept report to the Chief Engineer for approval.
Chapter 6. Preliminary Design (If applicable) o A Project Design Data Book is not required

2 Refer to the GDOT PDP for additional information about TPro, the GDOT Preconstruction Project Management System.

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o The preliminary and final field plan reviews may be combined if recommended by Engineering Services
Chapter 7. Final Design o If no right-of-way is required, neither the Location and Design Report nor the advertising of location approval is required.
Chapter 8. Design Guideline Variances o As intended by the PDP, future projects in the Statewide Transportation Improvement Plan, (STIP) and Regional Transportation Plan (RTP) will be considered in the review and approval of design exception requests.
Reconstruction Projects shall follow the Plan Development Process The geometric and safety guidelines for PM, 3R, and reconstruction projects are summarized in Table 11.1.

Table 11.1. Geometric and Safety Guidelines for 3R, PM, and Reconstruction Projects

Classification

Type of Work

National Highway System (NHS)

Reconstruction

and 3R

Interstate

PM

Freeway NonInterstate

Reconstruction and 3R
PM

Reconstruction

Design Standards

Upgrade Guardrail if not meeting:

Update Cross Slope and SE

AASHTO Green Book / Interstate Stds. n/a
AASHTO Green Book
n/a
AASHTO Green Book

NCHRP 350 NCHRP 350 NCHRP 350 NCHRP 350 NCHRP 350

Yes
If crash history warrants
Yes
If crash history warrants
Yes

Design Exception Approval
FHWA n/a
GDOT n/a
GDOT

Non-Freeway

3R

GDOT 3R Standards (1) NCHRP 230

Yes

GDOT

Non-NHS

PM Reconstruction

n/a

NCHRP 230 (2) Not required

n/a

AASHTO Green Book NCHRP 350

Yes

GDOT

Non-NHS All Roads

3R PM State Route

GDOT 3R Standards (1) n/a

NCHRP 230 NCHRP 230

Yes Not required

PM LARP Work

n/a

Not Required Not required

Notes: (1) Per AASHTO Green Book, as amended by this Manual, Section 11.1.2. and Section 11.1.3. (2) Upgrade existing guardrail and end terminals, if not meeting referenced standards Source: Transportation Research Board (TRB), National Cooperative Highway Research Program.

GDOT n/a n/a

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11.1.2. Controlling Criteria for Non-Interstate Systems (GDOT 3R Standards)
Guidelines for non-interstate 3R projects will follow the current edition of the American Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) for all projects except the controlling criteria listed below will apply.

Design Speed
The design speed shall be equal to or greater than the posted speed. If the existing roadway does not meet the design speed criteria and cannot be reasonably corrected, a design exception must be requested and approved.

For projects on roadways with no posted speed limit, an appropriate design speed should be selected by the designer. For information on selection of design speed, refer to Chapter 3. Design Controls, Section 3.2. Design Speed of this Manual.

Lane Width

Lane widths shall be 12-ft., except where it has been determined that a lesser width is appropriate for a given situation. For lane widths less than 12-ft., a design exception/variance must be requested.

Usable Shoulder Width
The usable shoulder widths for two-lane roadways is determined by classification and Average Daily Traffic (ADT). Refer to Table 11.2.

Table 11.2 Usable Shoulder Width for Two Lane Roadways

Roadway

ADT

Classification < 400

ADT 400 1,500

ADT 1,5002,000

ADT > 2,000 or
DHV > 200

Local Road

2-ft.

5-ft.

6-ft.

8-ft.

Multi-Lane Roadways
All multi-lane roadways should have at least an 8-ft. usable shoulder.

Collector Arterial

2-ft.

5-ft.

6-ft.

8-ft.

4-ft.

6-ft.

6-ft.

8-ft.

Bridge Widths
Geometric design standards shall be in accordance with the AASHTO Green Book. Summaries of minimum bridge widths for 2-lane and multilane bridges on non-interstate highways having state route numbers are provided in Table 11.3. and Table 11.4., respectively.

Table 11.3 Minimum Bridge Widths for Non-interstate Highways Rural Sections (2-Lanes)

Design Speed
< 50 mph > 50 mph All Speeds All Speeds All Speeds

Design Year ADT
0-399 0-399 400-1,999 (DHV < 200) 2,000 4,000 (DHV = 200-400) > 4,000 (DHV > 400)

Bridge Width Clear Distance
30-ft. 32-ft. 38-ft. 40-ft. 40-ft.

Design Live Loading
HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18)

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Table 11.4. Minimum Bridge Widths for Non-interstate Highways Multilane Rural Sections

Divided/Undivided
Undivided (4 or more lanes)
Divided

Bridge Width Clear Distance Pavement Width + 20-ft.
Pavement Width + 14-ft.

Minimum Shoulder Width
10-ft. right and left 4-ft. inside
10-ft. outside

Minimum bridge widths for local roads and streets not having state route numbers are described below and in Table 11.5.:

Table 11.5. Minimum Bridge Widths for Local Roads and Streets (Rural Sections) (1)

Design Speed All Speeds

Design Year ADT
0-399(2)

Bridge Width Clear Distance
28-ft.

Design Live Loading
HS-20 (MS-18)

All Speeds

400 999

30-ft.

HS-20 (MS-18)

All Speeds < 50 mph > 50 mph All Speeds

1,000 1,999 (DHV = 100 199)
2,000 4,000 (DHV = 200 400)
2,000 4000 (DHV = 200 400)
> 4,000 (DHV > 400)

32-ft. 38-ft. 40-ft. 40-ft.

HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18)

Notes:
(1)Two lanes without curb. For low volume roads with an approach roadway width of one lane, a minimum bridge width equal to the approach roadway width may be selected with concurrence of the Chief Engineer.

(2)For low volume roads with an approach pavement width of 20-ft., a bridge width of 24-ft. is permissible.

In urban sections (with curb), the minimum clear width for all new or reconstructed bridges shall be the curb-to-curb width of the approaches, with the exception of 2-lane, 2-way bridges, where the minimum clear width shall be 28-ft.
Sidewalks shall be provided on bridges where curb and gutter is provided on the approach roadway.
The replacement of existing concrete post and open railing systems constructed prior to 1964 shall be evaluated on a case by case basis.

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Table 11.6. Horizontal Clearance

Structural Capacity The structural capacity for existing / retained bridges shall be: HS-15 (MS-13.5). The structural capacity for new bridges shall be: HS-20 (MS-18). Refer to the current GDOT Bridge and Structures Policy Manual3 for further guidance related to structural capacity.
Horizontal Clearance The minimum horizontal clearances by posted speed are listed in Table 11.6. Note: The clearances listed are based on 1996 AASHTO Roadside Design Guide using a 50% lateral to extend probability.
For curbed areas, horizontal clearance width shall be 18-inches from face of curb.

Posted Speed

Horizontal Clearance

35 mph

4-ft.

40 mph

4-ft.

45 mph

5-ft.

50 mph

6-ft.

55 mph

7-ft.

60 mph

8-ft.

65 mph

9-ft.

Source: AASHTO. Roadside Design Guide, 1996

Vertical Clearance
A minimum of 14.5-ft. shall be maintained as vertical clearance at all existing structures. Resurfacing shall be performed so as not to violate this requirement.

Horizontal Alignment
In cases where AASHTO guidelines are not met, refer to the conditions and corresponding policies listed in Table 11.7.

Table 11.7. Horizontal Alignment for Existing Features not meeting 3R Guidelines

Condition

Accident History

Policy

< 10 mph below AASHTO guidelines

Low, compared with statewide average

Retain. The designer shall address and justify existing features to be retained which do not meet 3R guidelines.

< 10 mph below AASHTO guidelines

Directly related accident history compared with statewide average

Correct to AASHTO guidelines or to the highest design speed practicable and request a design exception.

> 10 mph below AASHTO guidelines

Not applicable

Correct to AASHTO guidelines if practicable. If not, correct to highest design practicable and request a design exception

Vertical Alignment
The same policies described in Table 11.7. for horizontal alignment shall apply to vertical alignment.
Cross Slope Pavement cross slope shall be a minimum of 1.5% and desirable 2.0%. Cross slope should be increased to 2.5% in areas where an increase is practicable and justified. For wide pavements, cross slope can be increased with each additional lane width.

3 GDOT. Bridge and Structures Policy Manual. The current manual is available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/DesignPolicies/

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Grades In areas where accident history indicates a grade-related problem the designer shall correct to AASHTO guidelines; otherwise a request for a design exception will be necessary. In areas with no grade-related problems, existing grades may be retained.
Superelevation Rural Collectors and Arterials: The maximum superelevation for rural collectors and arterials shall be 10%. Urban Collectors and Arterials: The maximum superelevation for urban collectors and arterials shall be 4% to 6%
11.1.3. Other Design Considerations for 3R Projects (GDOT 3R Standards)
Design Speed on Roadways with no Posted Speed Limit If a roadway is paved and does not have a posted speed limit, the designer should select a design speed commensurate with the functional classification and existing geometric features of the roadway, provided such features are not defective. The selected design speed should be consistent with the speeds that drivers are traveling and are likely to expect on the facility. For county roads or city streets, the designer should coordinate with the local jurisdictional authority on the selection of the posted speed limit and the recommended design speed. Efforts should be made to have the local jurisdictional authority post a speed limit on the road equal to or less than the selected design speed.
The designer should select a design speed as high as practical to attain a desired degree of safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and other social or political effects.
On unpaved country roads or city streets, the selected design speed shall be 35 mph or greater. A design exception will be required where this is not practical or appropriate.
Shoulder Treatment and Procedures for Passing Lane, Turning Lane, or Lane Addition Projects GDOT's policies on the required widths of existing shoulders are as follows:
On the widened side:
Existing shoulders shall be widened to meet AASHTO Guidelines. Clear zone requirement for the specific design situation should be followed. Refer to
Chapter 5, Roadside Safety and Horizontal Clearance and the AASHTO Roadside Design Guide for further guidance on clear zone requirements. On the non-widened side:
Where sufficient right of way exists, shoulder widths should meet AASHTO guidelines. Where sufficient right of way does not exist and the accident data does not indicate that the
existing shoulder contributes directly to the accident history, the existing shoulder may be retained. Where sufficient right of way does not exist and the accident data indicates that the existing shoulder contributes directly to the accident history, AASHTO width shoulders shall be provided unless a design exception is requested and approved.

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Guardrail and/or Barrier Guardrail and/or barrier at bridge ends within the project limits shall be upgraded to current AASHTO guidelines. The designer shall evaluate the need for guardrail and/or barrier at other locations with existing warrants and consideration should be given for correction consistent with existing warrants. The designer should also take into account accident history when considering the need for additional guardrail and/or barrier.
Existing guardrail and/or barrier shall be evaluated under current warrants and if warranted, upgraded to current AASHTO guidelines. If an existing guardrail and/or barrier is not warranted, it shall be removed.
Where it is determined that a guardrail and/or barrier is to be replaced or installed, the additional shoulder width defined as T in GDOT Construction Standards4 shall be obtained. In some cases, obtaining the T distance may require placing guardrail and/or barrier over a portion of the existing shoulder, which would thus reduce the usable shoulder width. If this occurs, the controlling criteria described in Section 11.1.2. of this Manual shall apply, and a design exception will be required if the minimum usable shoulder width cannot be maintained.
Drainage Structures All minor drainage structures shall be extended to avoid encroachment on the minimum shoulder widths as described in Section 11.1.2. of this Manual or the prevailing existing shoulder width, if it is greater.
Major drainage structures shall be evaluated on a case by case basis. Major drainage structures must be extended, where necessary, to achieve the minimum (3R) shoulder widths. Where such structures encroach on existing shoulders, but are beyond the minimum widths, the designer should consider extensions or the installation of guardrail and/or barrier.
Delineation (Advance Warning Signs) Delineation can be especially effective where minimum or less than desirable geometric features are involved. Since 3R projects often involve such features, GDOT allows liberal application of delineation techniques. Bridges narrower than the approach roadway and sharp curves should be delineated using reflective delineators, chevron alignment signs, or other appropriate devices.
Signs and Pavement Markings The designer shall include standard signing and pavement markings in accordance with the current Manual of Uniform Traffic Control Devices (MUTCD)5.
Railroad grade crossings shall be treated in accordance with current criteria. Where active protective devices are needed, they may be installed as a separate project under the Rail-Highway Crossing Improvement Program.

4 GDOT Construction Standards are available online in English and Metric units at: http://tomcat2.dot.state.ga.us/stds_dtls/index.jsp
5 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). The 2003 version of this publication is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm

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Design Exceptions Where existing features that do not meet these guidelines are proposed to be retained or constructed, the designer shall submit requests for design exceptions to Engineering Services for approval. The request for design exceptions must identify the sub-standard features, give the justification for retention, and describe any proposed mitigation.
The designer shall examine accident data with the objective of identifying causative factors that could be corrected as a part of the project. If physical correction is not feasible or cost effective, mitigation measures must be considered and resolution documented in the request for design exception. The process for submitting design exception requests is outlined in the GDOT PDP.
Americans with Disabilities Act (ADA) All areas shall be in compliance with Americans with Disabilities Act (ADA) requirements6 on all projects within the project limits. There are no exceptions to ADA requirements.
11.2. Special Design Considerations for Other Project Types
GDOT determines the need for projects other than the traditional roadway project. The following section discusses design guidelines that are intended to provide for a uniform design approach for these types of stand alone projects. These guidelines are not intended to replace the Plan Development Process or to be a comprehensive or detailed manual for the design of these facilities, but guidelines for designers in preparing plans for these other project types. In many cases the intent of the project is clear and the designer should strive to achieve the purpose and design intent of the project within the context of earlier chapters of this Manual. Each topic contains the GDOT resource office with the most experience with a type of non-traditional, stand alone project to contact for additional information.
Guidelines for the following types of projects are included in this section:
bridge fencing projects; bridge jacking projects; ITS projects; signing and marking projects; and noise abatement projects.
11.2.1. Bridge Fencing Projects
The resource office for bridge fencing projects is the GDOT Office of Bridge Design.
The primary purpose of a bridge fencing project is to create a raised barrier that will deter persons from dropping or throwing objects from the bridge onto vehicles or pedestrians below the bridge. The raised barrier on bridge fencing projects is typically a fence that is added to an existing bridge. The project limits should be defined as the extent required to accommodate the bridge fencing. Standard fence details should be utilized whenever possible.

6 Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements http://www.fhwa.dot.gov/environment/te/te_ada.htm

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11.2.2. Bridge Jacking Projects
The resource office for bridge jacking projects is the GDOT Office of Bridge Design.
The primary purpose of a bridge jacking project is to raise an existing bridge to correct a deficient vertical clearance or in anticipation of a change in the existing feature underneath the bridge that would cause a deficient vertical clearance.
Roadway approaches to the existing bridge should be designed to account for the elevation difference from raising the bridge. The project limits should be defined as the extent required to accommodate the bridge jacking.
Upgrading major roadway items within the project limits to current standards is not required. In addition, bridge widths and shoulders that do not meet current standards are not required to be upgraded with the bridge jacking project.
Minor design elements within the project limits of the bridge jacking project should be upgraded to current standards. Minor roadway elements include such items as: guardrail, signing and marking, etc.
Major design deficiencies within the project limits and minor design deficiencies outside the project limits should be noted and reported to the GDOT Office of Planning, which may then consider adding a future project to the current GDOT construction work plan. Bridge deficiencies noted in the field should be reported to the GDOT Office of Maintenance immediately.
11.2.3. Intelligent Transportation System (ITS) Projects
The resource offices for ITS Projects are the GDOT Office of Traffic Operations (concept) and the GDOT Office of Traffic Safety and Design (design).
The primary purpose of an ITS project is for congestion mitigation or traffic management. ITS projects include the design of systems of real-time traffic conditions sensors, surveillance devices, traffic control devices, and motorist information devices. These systems may be designed for installation along an existing roadway corridor as a stand alone project, or for inclusion into a project for other improvements to a roadway corridor.
The installation of ITS devices shall not interfere with or affect the visibility of the existing signing or sight distance. Where conflicts are unavoidable, the ITS plans will include replacement signing meeting the standards and guidelines in the MUTCD and meeting GDOT standard installation details.
11.2.4. Signing & Marking Projects
The resource office for signing and marking projects is the GDOT Office of Traffic Safety and Design.
The primary purpose of a signing and marking project is to provide stand alone signing and marking improvements. For interstate facilities, FHWA requires all interstate safety features be upgraded to current standards within the project limits. For non-interstate projects, generally other items that do not meet current standards will not be addressed on these projects.

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11.2.5. Traffic Signal Projects
The resource office for Traffic Signal Projects is the GDOT Office of Traffic Safety and Design.
The primary purpose of a Traffic Signal Project is to provide a traffic signal design for at-grade intersections. The majority of projects will be for the replacement and upgrade of obsolete equipment at intersections with existing signals, but this type of project may also be for the design of a new traffic signal.
Geometric improvements such as turn lanes are often included in traffic signal projects, but only to the extent to provide the efficient operation of the signal.
Substandard radius returns on the side streets and storage/taper lengths shall be improved wherever feasible.
Raised concrete islands should be considered during design to facilitate pedestrian movements as necessary.
For skewed angle intersections, turning-radius templates for an appropriate design vehicle shall be used to determine the appropriate opening. The width of the side street shall also be considered in determining the length of the median opening.
11.2.6. Noise Abatement Projects
The resource office for noise abatement projects is the GDOT Office of Environmental Services (OES). Refer to Policy and Procedure 4415-11, Highway Noise Abatement Policy for Federal Aid Projects for further guidance relating to noise abatement.
11.3. Design Elements for Other Project Types
11.3.1. Survey Requirements
Typically field surveys shall be considerably more limited with these other projects. Prior to commencing field surveys, the design team shall hold a pre-survey meeting and/or an onsite inspection to determine surveying requirements. Maximum use shall be made of "as-built" construction plans in order to minimize the requirements for collection of field data. As-built drawings, however, shall be verified before relying on them for accurate representation of existing conditions.
Limits of surveys should be determined on a case by case basis prior to the start of surveys. The limits of surveys will depend upon the type of project.
Bridge Fencing Projects For bridge fencing projects, survey sketches of each site are typically adequate as a database. The designer or design team member can perform the bridge sketches, noting the number of lanes, width of sidewalk, length and type of guardrail, etc.
Each bridge should be treated as a stand-alone location, with no relationship to other bridges in the project corridor, except where bridges are close enough together to affect the design. Projectlength horizontal or vertical survey controls are not necessary.

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Bridge Jacking Projects
Designers should communicate with the District office and verify there is not another project planned for each bridge jacking location to determine if the bridge jacking should be included in that project and not as a separate project.

Bridge Jacking Project limits will depend upon the amount of bridge raising and the impact to each roadway approach anticipated and the topography of the side slopes. Field surveys should generally include, but not be limited to:

existing bridge features geometry digital terrain model (DTM) existing right-of-way (in the absence of right of way plans or visible markers, the designer
may assume that the fence is the right-of-way line.) drainage structures within the project limits (curb & gutter, catch basins, manholes, median
drop inlets, cross culverts, side drain pipes etc.) existing guardrail driveway locations utility poles and strain poles signage other significant topographic features

ITS Projects
When an ITS project is included in other roadway improvement activities, the field survey detail will be determined by the requirements of the roadway work. However, it will be necessary for the designer to obtain detailed field information at the location of the support structures required for dynamic message signs (DMS), camera support poles and other field devices such as junction boxes. Detailed topographic diagram information that includes the location of existing signs, guardrail and drainage structures is essential. Project-length horizontal or vertical survey controls are generally not necessary. Limits of surveys will be determined by the scope of the project or by the project design where the ITS devices are a supplement to other work proposed.

Signing and Pavement Marking projects and Traffic Signal projects
Project-length horizontal or vertical survey controls are not necessary, except in areas where sign/signal sight distance is an issue.

Necessary control should be determined at a pre-survey site visit. The limits of surveys will depend upon the length of project and the topography of the roadway. Field surveys should generally include but not be limited to:

existing geometry of the roadway existing right-of-way (in the absence of right of way plans or visible markers, the designer
may assume that the fence is the right-of-way line.) drainage structures within the project limits (curb & gutter, catch basins, manholes, median
drop inlets, cross culverts, side drain pipes etc.) existing guardrail driveway locations

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utility poles and strain poles signage bridges other significant topographic features The design database shall include a schematic diagram of each roadway's geometry and significant features instead of the highly detailed mapping normally required for roadway project design. Cross sections are not required for either signing and marking projects or traffic signal projects. However, if additional safety features are to be upgraded with the project, the project manager and designer should determine whether cross sections are warranted to accomplish the design. If required, ground slopes outside existing roadways shall be provided at 50-ft. to 100-ft. intervals, as deemed appropriate by terrain conditions. Cross sections shall only be provided at areas requiring significant excavation or embankment, and may be substituted with "original plan" or "as-built" templates as long as accurate earthwork estimates can be determined.
The designer shall use the ground survey data or template information to estimate earthwork quantities and to determine construction limits. In most cases, cross sections will not be required for medians, unless conditions warrant (e.g., split profile, drainage structures that may require adjustment or unusual circumstances).
Noise Abatement Projects For noise abatement projects, necessary control should be determined at a pre-survey site visit. The limits of surveys and cross sections will depend upon the length of project, the topography of the roadway and ground slopes between the right of way and limits of roadway.
11.3.2. Construction Plans
Unless noted otherwise, all of these other projects will be developed through the streamlined PDP or similar process. The respective resource office, in consultation with Engineering Services and the project manager, will determine the appropriate process.
11.3.3. Pavement Design
Where required, it is anticipated that most pavement designs will consist of milling, overlay and leveling. Pavement designs will be provided and/or approved by the GDOT Office of Materials and Research upon completion of the existing pavement analysis and soil survey.
11.3.4. Environmental
It is expected that most sites will involve a NEPA Categorical Exclusion (CE). The GDOT Office of Environment and Location shall be notified as soon as possible of any anticipated impacts to existing waterways, including streams and wetlands.
11.3.5. Earthwork
If earthwork is required, normal standards shall apply; however, because earthwork is generally minimal, the earthwork shall be let as "Grading Complete - Lump Sum." The designer should calculate earthwork volumes, but no quantities shall be shown in the plans. Removal of vegetation within the clear zone shall be included within the project limits.

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11.3.6. Drainage
If drainage is required, normal standards shall apply. Existing drainage structures in conflict with the proposed improvements should be extended or relocated in order to maintain adequate drainage. Existing drainage patterns shall not be altered significantly without justification.
11.3.7. Guardrail and/or Barrier
At locations with existing guardrail to be retained, the designer shall determine if the guardrail meets current GDOT standards discussed in earlier chapters of this Manual. All guardrail and/or guardrail anchorages within the project limits that do not meet current GDOT standards will be replaced.
In locations where the guardrail extends outside the project limits, the designer shall determine if the new guardrail should tie into the existing guardrail or whether the entire run of existing guardrail should be replaced and the project limits extended.
11.3.8. Erosion Control Plans
Where required, erosion control items shall be shown clearly on the construction plan sheets. Typically these other projects do not require separate Comprehensive Monitoring and Erosion Control Plans unless any one site within the project involves land disturbance of more than one acre.
11.3.9. Traffic Signal Plans
The designer shall notify the GDOT Office of Traffic Operations of any anticipated impacts to existing traffic signals.
11.3.10. Signing & Markings
All signs located within the project limits shall be removed and replaced unless otherwise directed. The plans should note that all signs and pavement markings shall be in accordance with MUTCD and GDOT standards. In event that MUTCD requirements or guidelines conflict with GDOT policy, GDOT policy shall take precedence.
For bicycle lanes and bicycle shoulders, signs and pavement marking shall be replaced in kind.
11.3.11. Utilities
The designer shall coordinate with the GDOT Office of Utilities and the District Office Utilities Engineer regarding the location of utilities. Base plan sheets shall be submitted at the earliest possible time in order to facilitate obtaining existing utilities information from utilities owners. It is anticipated that no significant public utilities relocations or adjustments will be required.
11.3.12. Traffic Control Plans
In most cases, traffic control plans are not required. Standard details for traffic control should be utilized.

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Chapter 11 Index
Americans with Disabilities Act (ADA), 10 Bridges
Fencing Projects. See Other Project Types, Bridge Fencing
Jacking Projects. See Other Project Types, Bridge Jacking
Design Database, 1214 Guardrail Projects. See Other Project Types,
Guardrail and/or Barrier Intelligent Transportation System (ITS)
Design Considerations, 11 Design Database, 13 ITS. See Intelligent Transportation System (ITS) Noise Abatement Projects Design Database, 14 Other Project Types Bridge Fencing, 10 Bridge Fencing, Design Elements, 12 Bridge Jacking, 11 Bridge Jacking, Design Elements, 13 Construction Plans, 14

Drainage, 15 Earthwork, 14 Environmental, 14 Erosion Control Plans, 15 Guardrail and/or Barrier, 15 Pavement Design, 14 Signing & Markings, 15 Traffic Control Plans, 15 Traffic Signal Plans, 15 Utilities, 15 Resurfacing, Restoration, or Rehabilitation Design Guidelines (3R) Controlling Criteria, 58 Signing & Marking Projects Design Considerations, 11 Signing & Pavement Marking Projects Design Database, 13 Signing and Marking, 11 Traffic Signal Projects Design Considerations, 12

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Chapter 13 Contents

13. TRAFFIC FORECASTING AND ANALYSIS CONCEPTS

1

13.1. Traffic Forecasting Process

1

13.1.1. Data Collection

1

13.1.2. Functional Roadway Classification

12

13.2. Freeway Traffic Analysis and Design

12

13.2.1. ITS Technology

13

13.2.2. Capacity Analysis and Level of Service

13

13.2.3. Ramps and Ramp Junctions

15

13.2.4. Traffic Management Strategies

16

13.3. Arterial Traffic Analysis and Design

18

13.3.1. Capacity Analysis and Level of Service (LOS)

19

13.3.2. Traffic Analysis Procedures

19

13.3.3. Intersection Traffic Control and Design

20

13.4. Trip Generation and Assignment for Traffic Impact Studies

24

13.4.1. Trip Generation Data

24

13.4.2. Traffic Assignment

26

Chapter 13 Index

28

Summary of Chapter 13 Revisions

29

List of Figures

Figure 13.1. Directional Counts at Three-Leg Intersections

3

Figure 13.2. Example for Determining Growth Rates Using Urban Area Transportation Models

8

List of Tables Table 13.1. Urbanized Areas with Associated Counties Table 13.2. Common ITE Land Use Codes

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13. TRAFFIC FORECASTING AND ANALYSIS CONCEPTS
13.1. Traffic Forecasting Process
This chapter explains the traffic forecasting process including how traffic analysis relates to roadway design.
During the course of the design process, the design engineer shall request traffic data for roadway capacity analysis to ensure that the functional requirements of the roadway are met. In addition, the traffic volumes are used to determine the pavement structure of the road. For Georgia DOT projects designed in-house, traffic volumes are supplied by the GDOT Office of Environment and Location (OEL). For consultant designed projects, the traffic volumes may be provided by GDOT, if available, or by the consultant as part of the scope of services in the consultants design contract.
13.1.1. Data Collection
Site Visit The traffic engineer should conduct a site visit to gather current traffic information that is not readily available from other sources. The site visit should be conducted when preparing the scope of the project or when development of the project concept begins. The Manual on Uniform Traffic Control Devices (MUTCD)1 should be followed when collecting new data. The presence and needs of children, elderly persons, disabled, transportation disadvantaged, pedestrians, and bicyclists should be included in a typical site visit. Data to be collected during the site visit generally includes the following information:
number of lanes, lane usage, and presence and type of medians curves and grades (if significant enough to affect capacity or traffic operations) lane, median, and shoulder widths traffic control devices traffic signal phasing traffic signs (particularly regulatory signs and posted speed limits) regulatory pavement markings pavement conditions sidewalks, bicycle lanes, and multi-use paths marked and unmarked crosswalk locations presence and type of on-street parking and parking regulations street lighting driveways for major vehicle generators or truck generators (collect the same information as
would be collected for side streets) transit stop locations and amenities, transit schedules, and types of transit vehicles in
service

1 FHWA. Manual on Uniform Traffic Control Device (MUTCD). The 2003 version of this publication is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm

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adjacent land use, density, and occupancy roadway functional classification route governmental jurisdiction travel times
Other data that may be needed includes sight distances, vertical and lateral clearances, any safety hazards, utility information (such as utility poles, storm drain, and valve cover locations), and road right-of-way locations.
The (Georgia) State Roadway Functional Classification Map2 and Roadway Characteristics (RC), RCInfo file3 contain speed limits, lane widths, shoulder widths, and information on many other roadway characteristics. These resources should be reviewed prior to a site visit. The designer should contact GDOT immediately if a site visit yields information that differs from that of existing GDOT data sources.
Existing Traffic Data The traffic engineer should collect existing traffic data for the analysis. Before collecting existing traffic data, the traffic engineer should send a memorandum and map that summarizes the project and site visit to the GDOT Office of Traffic Operations to confirm the locations and types of counts to be collected and to request current information.
Typical traffic data requests include 24-hour volume counts (summarized by hourly or 15-minute intervals) and peak-hour (or peak period) turning movement counts. The highest traffic volumes are usually during the weekday morning (7:00 a.m. 9:00 a.m.) and evening (4:00 p.m. 6:00 p.m.) peak travel periods. However, in some areas, such as near major shopping centers or recreational areas, the highest traffic volumes may be in the evenings or on weekends. The peak hours may also change over time, especially in developing areas. The time and duration of peak periods should be verified by careful review of 24-hour volume counts.
The traffic engineer should contact local government or jurisdictions to determine if there are hazardous or high-accident locations within the study area. Law enforcement agencies collect this data in many communities. Traffic engineering agencies may also collect collision data.
Existing traffic data should generally be no more than one year old if available Existing traffic data needed for the analysis frequently include the following information:
peak period turning movement counts (including cars, single-unit trucks and buses, and multi-unit or combination trucks)
one-day directional volumes, speed; and, in some locations, vehicle classification machine counts (7-day counts in recreational areas)
historic daily volume counts for the most recent fifteen years that are available (contact the GDOT Office of Transportation Data)

2 GDOT. Functional Classification Map. 2006 Available through the GDOT Office of Transportation Data website at: http://www.dot.state.ga.us/dot/planprog/transportation_data/function_class_maps/index.shtml
3 RCInfo files are generated through the GDOT Network. Access to the network can be obtained through the GDOT Division of Information Technology.

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accident history for the most current three years at locations identified by the local jurisdiction (contact the GDOT Office of Traffic Operations)
Bicycle and pedestrian counts should not be requested as part of the traffic study unless the project is located where there are high concentrations of pedestrians and bicyclists, such as at a university campus, event center or a central business district. Daily machine traffic counts should be adjusted by seasonal and axle factors to estimate existing AADT volumes. The GDOT Office of Transportation Data can furnish factors from previous years, but data from nearby count locations should be used to determine the seasonal factors. Nearby tube counts can be used to determine vehicle classification and thus the axle factor. Any adjustments to raw traffic counts should be discussed and mutually agreed upon between the traffic engineer and the person responsible for review and approval.
Establish Existing Traffic Patterns
Directional roadway volumes and turning movements for a.m. peak hour and p.m. peak hour at the study intersections need to be established. The traffic engineer can accomplish this by collecting new counts where data is needed. Since counting all traffic data locations may not always be practical, GDOT has established the a procedure for estimating the existing turning movement counts from directional counts at three-leg intersections, as illustrated in Figure 13.1.

A, B, and C are the approach volumes on each leg.
X = (A + B + C) / 2
Where: X - C = A to B and B to A X - B = A to C and C to A X - A = B to C and C to B
Source: TRB. Highway Capacity Manual. 2003
Figure 13.1. Directional Counts at Three-Leg Intersections

For four-leg intersections, the traffic engineer should first make assumptions about the traffic on the minor leg, then follow the three-leg procedure for the other three legs. Furthermore, GDOT assumes that at the intersection of two major routes, 55% to 70% of the trips on each approach are going straight.

Daily Volumes and Their Uses
Traffic volume data is commonly reported as a daily value. Daily volumes are typically used for highway planning, as is general observations of volume trends and the design of pavement structures. The following four daily volumes are typical or widely used:

Average Annual Daily Traffic (AADT) is defined as the average 24-hour traffic volume at a given location over a full, 365-day year. This means the total of vehicles passing the site in a year divided by 365. The GDOT Office of Transportation Data maintains Georgias State

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Traffic and Report Statistics (STARS) web site (http://www.dot.state.ga.us/dot/planprog/transportation_data/TrafficCD/index.shtml), which provides AADT counts collected from permanent and portable traffic collection devices throughout the state during the years 1999-2005 for every segment of Georgia's State Highway System.
Average Daily Traffic (ADT) is defined as the average 24-hour traffic volume at a given location for some period of time less than a year. While AADT is a full year, an ADT may be measured for six months, a season, a month, and a week or as little as two days. Therefore, an ADT is valid only for the period for which it was measured.
Average Annual Weekday Traffic (AAWT) is defined as the average 24-hour traffic volume occurring on weekdays over a full year. This volume is of considerable interest when weekend traffic is light, so that averaging 24-hour volumes over 365 days would mask the impact of weekday traffic. AAWT is computed by dividing the total weekday traffic for the year by 260.
Average Weekday Traffic (AWT) is defined as the average 24-hour traffic volume occurring on weekdays for some period of time less than one year.
The unit by which all of these volumes are measured is vehicles per day (vpd). Daily volumes are typically not differentiated by direction or lane, but are the totals for the entire facility at a given location.
Base Year and Design Year Traffic For all GDOT projects, the design engineer should request traffic volumes for the base year and design year. The base or opening year is the year the project is anticipated to be open for traffic use. The designer should not confuse this year with the construction programmed date or the project let (bid award) date. For example, if a project is scheduled for a let date sometime in 2006 and it is estimated that the project will take two years to construct, then the volumes for the base year 2008 should be requested.
The design year is the anticipated future life of the project. For all GDOT projects, the future traffic volumes will be 20 years from the base year. For example, the design engineer would request 2028 design year traffic volumes for the base year 2008. For some projects the design year may be shorter than 20 years (i.e., two years or five years) such as for minor safety and intersection improvement projects or interim projects that may be programmed to address a short-term operational problem at a location along the roadway. The design engineer is advised to confirm the base and design years early in the concept development stage of the project.
The base year ADT for an existing roadway should be calculated from real traffic counts and adjusted to reflect appropriate axle factors and seasonal factors. For accuracy, the axle factors should be obtained from a vehicle classification count conducted at the same time as the traffic counts. Many count machines can collect both types of data simultaneously. Truck percentages and seasonal adjustment factors can also be found in the GDOT RC database available from the Office of Transportation Data. Base year and design year ADTs should be determined for each link of the roadway between major intersections and for each side street.
Design year traffic volumes can be developed by use of either an Urban Area Transportation Model or historical traffic growth trends. The historical growth calculations are also useful for checking the reasonableness of projections from the urban traffic model.

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Urban Area Transportation Models
Georgia presently includes fifteen different Metropolitan Planning Organizations (MPOs) with a population of more than 50,000 people. The fifteen areas range from an area of one county to several counties. GDOT develops a long-range traffic forecasting model for each MPO, except for Atlanta and Chattanooga. GDOT updates each model every five years. The fifteen Georgia MPOs are presented in Table 13.1.
The forecasting model is a transportation tool for determining long range traffic volumes on the functionally classified road network (collector roads and above). There are eight recommended model networks that may be developed for each of the different MPOs. These models may not include all of the counties within the urbanized area, since MPOs are required to only include 75% of the urbanized areas. The counties that are in the long range transportation models are determined by the MPOs. The MPOs are responsible for collecting the social and economic data for the base year model and future year model. The social and economic data includes population, employment, school enrollment, growth trends, and other demographic information. The MPOs are also responsible for disseminating information from the models to the public. The eight recommended models developed by GDOT are described below. Networks 2 through 7 build upon and address deficiencies of lower numbered networks.

Table 13.1. Urbanized Areas with Associated Counties

Urbanized Area Albany Athens
Atlanta
Augusta Brunswick Chattanooga Columbus Dalton

County Dougherty Lee
Clarke Oconee Madison
Barrow Bartow Cherokee Clayton Cobb Coweta DeKalb Douglas Fayette Forsyth Fulton Gwinnett Henry Newton Paulding Rockdale Spalding Walton
Columbia Richmond Aiken
Edgefield Glynn
Catoosa Walker Hamilton
Muscogee Lee Russell
Whitfield

State Georgia Georgia
Georgia Georgia Georgia
Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia
Georgia Georgia South Carolina
South Carolina Georgia
Georgia Georgia Tennessee
Georgia Alabama Alabama
Georgia

Base Year (Network 1) - This network

Gainesville

should include all functionally-classified roads in the study area open to traffic in the

Hinesville

base year (for example, 2003 base year).

Macon

Functional classification is based on GDOTs

RCInfo file. Functionally-classified roads

Rome

include all roadways not coded as urban

Savannah

local = 19 or rural local = 9. Local roadways

may appear in the base year network but are Valdosta

not required to be there. Once this network is

calibrated, it should replicate the travel

Warner Robins

patterns that existed in the base year. The

base year may not be the same as the projects base year.

Hall Liberty Long Bibb Jones
Floyd Chatham Lanier
Lowndes Berrien
Houston Peach

Georgia Georgia Georgia Georgia Georgia
Georgia Georgia Georgia
Georgia Georgia
Georgia Georgia

Do-Nothing System Projects (Network 2) - This network is intended to show what would happen in the plan year 2030 model if no new projects were built.

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Network 2 basically reflects "now" roadways with resulting capacity deficiencies from future traffic conditions. Network 2 consists of the base year network plus any projects under construction, opened to traffic since the base year, or projects for which funds have been authorized but construction has not yet begun. Network 2 examples include: projects under construction in the base year; projects opened to traffic since the base year; projects authorized for construction at the time of preparing this network.
Existing + Committed (E+C) System Projects (Network 3) - This network is intended to show what would happen in the future if only existing and presently committed projects were built. Network 3 basically reflects "committed" short range improvements. Committed projects are defined as those projects in the current State Transportation Implementation Plan/Transportation Improvement Program (STIP/TIP) having either right-of-way (ROW) or Construction dollars shown. Projects with only preliminary engineering (PE) monies in the STIP/TIP are not considered "committed" when building such a model system. No long range plan projects would appear in this Network. A Network 3 example is projects with ROW or construction in the FY05-07 STIP/TIP.
Remainder of TIP, PE, and TIER 2 Projects and Construction Work Program (CWP4) Projects (Network 4) - Network 4 basically reflects previously programmed mid-range improvements. Network 4 includes programmed projects from TIER 25, the second phase of the TIP document (last three years). Programmed projects in TIER 2 should coincide with the last three years of the CWP. Projects with PE monies would be included in this network. MPOs sometimes place "desired" projects in the TIER 2 section of the TIP document without an identified dedicated funding source. If a project has not been programmed (does not have a GDOT Project Locator number) or does not have locally dedicated funds allocated, it should not be included in this network. A Network 4 example is projects with any phase programmed for FY08-10 in the FY05-2010 TIP/TIER2/CWP.
Remainder of Programmed LRTP Projects (Network 5) - Network 5 basically reflects programmed long range projects from the current LRTP. This network includes current Long Range Transportation Plan (LRTP) projects that are programmed by GDOT as long range. Current LRTP projects not yet programmed are not to be included in Network 5. If local jurisdictions have a method of documenting programmed local projects already included in the current LRTP, those projects could be included in this network. A Network 5 example is projects with PE, ROW or construction programmed by GDOT for LR = beyond the CWPs last year of 2010.
NOTE: If time for completing the traffic forecasting is limited, Networks 5 and 6 may be combined.
Remainder of LRTP Projects (Network 6) - This network includes projects in the current LRTP that have not been captured in any of the previous networks. A Network 6 example is projects listed in the current LRTP that have not advanced from their status as LRTP "recommendations".

4 The CWP is a GDOT document listing state and federally funded projects approved by the Transportation Board for preliminary engineering, ROW acquisition, and/or construction scheduled in the current and next five fiscal years (total six years), e.g., FY05-10 CWP.
5 TIER 2 refers to the last three years of projects typically included in the MPOs TIP document, but not considered part of the official TIP recognized by FHWA, e.g., FY05-07 TIP; FY08-10 TIER 2.

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New Projects Recommended Plan for Public Comment (Network 7) - This network includes any new project that does not appear in the current LRTP, including LR projects programmed by GDOT but not included in the current LRTP. This network provides the opportunity to test various improvement scenarios and could actually consist of several networks, possibly deleting projects included in previous networks. This series of analyses could produce two networks for public comment: (1) an aspirations plan, and (2) the financially constrained recommended plan. The latter plan is required to receive public review and comment.
Recommended Financially Constrained Plan6 Post Public Comment (Network 8) This network may or may not be needed. Upon reviewing and responding to public comments received on the draft LRTP, the MPOs staff or committees may request Network revisions or additional scenarios. If significant changes are made, for example new projects not previously presented to the public, additional public comment may be needed. If the public had the opportunity to comment on the projects proposed for revision, additional public comment may not be needed. These decisions are for the MPO staff or are handled through the committee process. Whatever action is decided must be consistent with the MPOs adopted public involvement process (PIP). The final network must be consistent with the financially constrained LRTP adopted by the Policy Committee.
Traffic Projections from the Urban Area Transportation Model
For a roadway improvement project on an existing roadway, the traffic engineer should use the E+C model to determine the routes estimated traffic volumes. For a roadway improvement project on a new roadway, or a roadway not included in the E+C model, the volumes from the first model where it is included should be used. To determine design year traffic for a project using an urban area transportation model, the volumes can be prorated or extrapolated based on the growth in traffic between the base model year and the year of the E+C Model. However, if there is a discrepancy between the existing model and existing counts, it is better to determine that difference and add this to the existing traffic.
A more general approach for using the model would be to obtain an average percent growth of all the roads in the project area from the travel demand model between the base year and the future year and apply this percent growth to the proposed roadway improvement.
In most cases, volumes from the model should not be used as design traffic. The model traffic can be used to determine the absolute growth (i.e. future volume minus base year volume) for each modeled roadway, then that absolute growth can be added to the traffic count for the roadway segment. This method removes any error that was present in the base year model. An example of this is shown in Figure 13.2. Socio-economic data is also available within the model, including a population, number of households, employment, and school enrollment for each Traffic Analysis Zone (TAZ).
6 Financial Constraint: The LRTP must demonstrate that anticipated revenues meet or exceed anticipated costs for the LRTPs recommendations. This requires that the cost of all projects be summed together and that this total cost be compared to anticipated monies available. It must be shown that there are enough monies available to pay for the projects. If the lead transportation agency calculates that monies available are less than the sum of project costs, then projects must be removed. All plan projects including roads, bridges, bike/pedestrian, transit, passenger rail, and maintenance should be accounted for in the project cost estimates and the revenues available analysis to show a financially constrained plan.

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Figure 13.2. Example for Determining Growth Rates Using Urban Area Transportation Models

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Establish Traffic Growth Rate Trends
The traditional traffic forecasting method relies greatly on historical trends. Historical counts for the past fifteen years should be used if available. The counts should be smoothed to eliminate any bad counts and to show the general trend. Using the least squares method (Excel program), calculate base year and design year volumes based on the last fifteen, ten, and five years, giving the most weight to the ten year trend. This calculation is performed for each coverage count location along the project and for the cross streets. The base year volume is divided by the existing year volume to get the base year factor, and the design year volume is divided by the base year volume to get the design year growth factor.

Historical trend analysis is only part of the traffic forecasting process. Other factors to consider are population growth data, land use plans, planned development, and anything else that might affect future traffic. This information should be available from city/county officials, planners, and other roadway designers. Trips from major real estate development or other major traffic generator should be added based on techniques described in the latest edition of the ITE Trip Generation Handbook.

Using all available information, the traffic forecaster must use his/her judgment to decide the future growth rates for the project. When an existing route is paralleled by a much more attractive new route or improved facility, the total traffic on the two roads will be greater than that on the old road before the new one was opened. The additional traffic above that which can be accounted for by diversion and normal growth is defined as "generated traffic." This generated traffic is made up of the following classes of trips:

1. Trips which would not have been made at all, or made less frequently, if the improvement was not available.

2. Trips which would have been made to other destinations or from other origins. For example, shopping or business trips might be changed because of a shift in relative ease of travel.

3. Trips diverted from other forms of transportation. This mostly applies to new interstate routes.

4. Trips resulting from new developments along the road that are developed simultaneously with the construction of the new road.

Generated traffic is greatest for new interstate routes and other freeways. A little generated traffic can be expected for widening projects. Judgment is used to decide how much to modify the normal growth factor. Generally the normal growth factor should be multiplied by a range of 1.00 (no adjustment) to about 1.60 (for new interstates) to account for generated traffic.

Traffic Projections for New Roadway Corridors
Traffic projections for a new roadway or bypass route can be determined based upon traffic counts, an origin-destination study, or from the local MPO transportation model. The percentage of traffic that will be relocated to the new route can be determined in several ways.

For a minor bypass route, existing traffic counts obtained on nearby roadways will generally show a trend that can be used to determine how much of the traffic would continue along the bypass and how much traffic would be distributed to the local network of the community being bypassed. A more accurate determination of the percentage of traffic that would use a bypass route within a non-

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urbanized area is to conduct an origin-destination study. Refer to the current Institute of Transportation Engineers (ITE) Manual on Uniform Transportation Engineering Studies for procedures for conducting an origin-destination study. The questions to be asked during the origindestination study interview should be included in the Traffic Data Memorandum and submitted to the Office of Environment and Location (OEL) for approval. Another method for an origindestination study is to conduct a license plate study, either manually or electronically.
Within an urbanized area, the transportation model should be used to determine the amount of traffic on a new bypass route. Typically, new roadways are already included in the transportation model. Their design traffic volumes can be read directly from the loaded model network. If this is not the case, the new route should be added to the future year model to determine the design year traffic.
Preliminary Traffic Projections
Using traffic growth rates developed in accordance with the preceding methodology, calculate future traffic for several sections along the project and compare this with traffic projections from the urban area transportation model where available. The two projections should be within 10 percent of each other. It is important to consider whether or not the future roadway can handle the expected traffic volumes. If not, adjustments may need to be made because of limited road capacity.
Adjustments to Design Year ADT Volumes
For some roadway design projects, the traffic engineer may be required to adjust the volumes projected by OEL. These adjustments will be required in anticipation of major land developments or significant changes in nearby street/ highway networks that will affect future traffic volumes expected on the roadway under design. Adjustments in traffic volumes for major land developments should follow any procedures established by OEL and the impacts should be approved by OEL before the adjusted volumes are used in design by the design engineer. The design engineer should document any assumptions made and the procedures used in the adjustment of the traffic volumes.
Detailed Traffic Forecast
Using the established growth rates, base year and future year turning movements are calculated for each intersection along the project limits. The existing year turning movements should be used as a pattern. The traffic engineer must decide if the same pattern will hold in the future as exists now. The traffic engineer should also examine each intersection for reasonableness of the growth rate, and make adjustments as needed. For example, a built-out subdivision will have little, if any, growth, while other roads in the same general vicinity might grow at a higher rate. The traffic forecaster must use his/her judgment. Turns might need adjustment based on future land use and/or development. In most cases, the volumes in each direction should be the same. If there is a difference, the traffic engineer should provide a reasonable explanation.
Design Hourly Volumes
While daily volumes are very useful in planning, hourly volumes are also needed for the design process. Volumes may vary significantly during the course of a 24-hour day with periods of maximum volume occurring during the morning or afternoon rush hours. The single hour of the day that has the highest hourly volume is called the "peak hour". Capacity and other traffic analyses typically focus on the peak hour of traffic volumes, because it represents the most critical period for operations and has the highest capacity requirement. This peak-hour volume will vary from day to day or from season to season.

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The relationship between the hourly volume and the maximum rate of flow within an hour is defined as the peak-hour factor (PHF). For design and traffic analysis, peak volumes are usually measured for a period of time less than an hour, usually a 15-minute period. The design engineer should use the 15-minute period for all road capacity analysis.
The design hour volume (DHV) is the traffic volume used to determine the number of traffic lanes on the roadway. The following formula expresses the relationship between the design hour volume and the average daily traffic volume:
DHV = AADT x K
where: DHV = design hour volume of traffic (total, 2-way)
AADT = average 24-hour weekday, 2-way volume of traffic
K = ratio of design hour volume to AADT
At major intersections and at driveways leading to major activity centers, the design hour turning volumes are important in determining the intersection capacity, resulting number of lanes, and the storage length for exclusive turning lanes required for each approach. For intersections being reconstructed and that are in fully developed areas, existing turning movement percentages will be collected in the field and assumed to be the same for the future design year. For new intersections or for those significantly impacted by new land developments or major changes in nearby street/highway networks, existing and projected traffic data along with engineering judgment will be used to reassign vehicle trips on nearby street networks to derive the turning movements at project intersections.
Future traffic volumes shall be used to ensure that the road has enough traffic carrying capacity. The traffic volume during a period of time shorter than a day shall be used for design purposes, reflecting peak hour periods. For roads with unusual or highly seasonal fluctuation in traffic volumes, the 30th highest hour of the design year should be used. This can be computed using seasonal adjustment factors discussed in the previous section. Locations where this technique may be necessary include beach or mountain resorts, and roadways serving major sporting arenas or performance halls.
The directional design hour volume is the traffic volume for the rush hour period in the peak direction of flow. Use directional distribution factors based on existing traffic counts. If this information is not available the traffic engineer should assume that 60% of the traffic is going in one direction. For a more detailed analysis of intersection and road capacity, procedures should be used as described in the latest version of the TRB Highway Capacity Manual.
Using short-term counts along the project, peak hour and directional factors can be calculated and compared to any automatic traffic recorder (ATR) locations along the route. If there are no ATR locations along the route, ATR locations along nearby routes with the same functional class can be used. Appropriate K and D factors must be discussed and approved with appropriate GDOT staff. The K and D factors are applied to the ADT derived above to calculate the a.m. and p.m. design hour volumes. Since the DHV is the 30th highest hour, the p.m. movement is usually the return movement from the a.m. movement. In some cases, separate a.m. and p.m. volumes may need to be calculated. Also, sometimes the base year peak hour volumes (PHV) are needed. They are calculated the same way using the base year ADT.

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Determine Truck Factors Appropriate data sources must be used to determine 24-hour and peak hour truck percentages. As described previously in this chapter, the traffic engineer must seriously consider the new traffic counts taken specifically for this purpose. The 24-hour percentage should be given as Single Unit (SU) trucks, Classes 4 through 7 and Multi-Unit or Combination (MU) trucks, Classes 8 through 15. Single Unit trucks include buses.
Finalize Traffic Forecast The traffic projections and design factors are finalized and submitted as MicroStation design files to GDOT, Head of Traffic Analysis Section for approval. The submittal should meet section standards as to size of drawings and lettering.
13.1.2. Functional Roadway Classification
Refer to Chapter 3. Design Controls, Section 3.1. Functional Classifications for Freeways, Arterials, Collectors and Local Roads, for a detailed discussion relating to functional roadway classification.
13.2. Freeway Traffic Analysis and Design
Traffic Analysis and Design The purpose of this section is to provide some traffic analysis guidance for design engineers on some of the factors and design elements to consider in operational and road capacity analysis. This information is intended as a supplement to GDOT adopted standards and procedures outlined in the Transportation Research Board (TRB) Highway Capacity Manual.
The TRB Highway Capacity Manual provides comprehensive guidelines related to freeway traffic analysis and design. Some considerations that must be made during the traffic analysis and design process include, but are not limited to:
A freeway experiencing extreme traffic congestion differs greatly from a non-freeway facility experiencing extreme congestion since the travel conditions creating the congestion are internal to the facility, not external to the facility.
Freeway facilities may have interactions with other freeway facilities in the area as well as other classes of nearby roads, and the performance of the freeway may be affected when travel demand exceeds road capacity on these nearby road systems. For example, if the street system can not accommodate the demand exiting the freeway, the over-saturation of the street system may result in queues backing onto the freeway, which adversely affects freeway travel.
The traffic analysis and design process must also recognize that the freeway system has several interacting components, including ramps and weaving sections. The performance of each component must be evaluated separately and their interactions considered to achieve an effective overall design. For example, the presence of ramp metering affects freeway demand and must be taken into consideration in analyzing a freeway facility.
High occupancy vehicle (HOV) lanes require special analysis. If an HOV facility has two or more lanes in each direction all or part of the day and if access to the HOV facility is limited from adjacent freeway lanes (i.e. 1 mile or greater access point spacing), these procedures may be used. Otherwise, HOV lane(s) will have lower lane capacities.

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13.2.1. ITS Technology
Intelligent transportation systems (ITS) strategies aim to increase the safety and performance of roadway facilities. For freeway and other uninterrupted-flow highways, ITS may achieve some decrease in headways, which would increase the capacity of these facilities. In addition, even with no decrease in headways, level of service might improve if vehicle guidance systems offered drivers a greater level of comfort than they currently experience in conditions with close spacing between vehicles. "Many of the ITS improvements, such as incident response and driver information systems, occur at the system level. Although ITS features will benefit the overall roadway system, they will not have an impact on the methods to calculate capacity and level of service for individual roadways" (TRB, 2000 p. 2-6).

13.2.2. Capacity Analysis and Level of Service
TRB defines capacity as the maximum hourly rate at which persons or vehicles reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a given period under prevailing roadway, traffic, and control conditions; adding that "Capacity analysis is a set of procedures for estimating the traffic-carrying ability of facilities over a range of defined operational conditions (2000, p. 2-1)".

Service flow rates are similar because they define the flow rates that be accommodated while still maintaining a given level of service.

There are numerous factors that affect capacity and LOS:

base conditions prevailing roadway conditions (including geometric and other elements) prevailing traffic conditions, which also account for vehicle type (e.g. heavy vehicles) and
distribution of vehicles For design LOS for GDOT roadways, refer to Chapter 6, Tables 6.1 through 6.4 of this Manual.

Traffic Flow Characteristics
Traffic flow on a freeway can be highly varied depending on the conditions constraining flow at upstream and downstream bottleneck locations. Bottlenecks can be created by ramp merge and weaving segments, lane drops, maintenance and construction activities, accidents, and objects in the roadway. An incident does not have to block a travel lane to create a bottleneck. For example, disabled vehicles in the median or on the shoulder can influence traffic flow within the freeway lanes.

Freeway research has resulted in a better understanding of the characteristics of freeway flow relative to the influence of upstream and downstream bottlenecks. Freeway traffic flow can be categorized into three flow types: (1) under-saturated, (2) queue discharge, and (3) oversaturated. Each flow type is defined within general speed-flow-density ranges, and each represents different conditions on the freeway.

Under-saturated flow represents traffic flow that is unaffected by upstream or downstream conditions. This regime is generally defined within a speed range of 55 to 75 mph at low to moderate flow rates and a range of 40 to 60 mph at high flow rates.

Queue discharge flow represents traffic flow that has just passed through a bottleneck and is accelerating back to the free-flow speed of the freeway. Queue discharge flow is characterized by relatively stable flow as long as the effects of another bottleneck downstream are not present. This

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flow type is generally defined within a narrow range of 2,000 to 2,300 passenger cars, per hour, per lane (pcphpl), with speeds typically ranging from 35 mph up to the free-flow speed of the freeway segment. Lower speeds are typically observed immediately downstream of the bottleneck. Depending on horizontal and vertical alignments, queue discharge flow usually accelerates back to the free-flow speed of the facility within 0.5 to 1 mile downstream from the bottleneck. Studies suggest that the queue discharge flow rate from the bottleneck is lower than the maximum flows observed before breakdown. A typical value for this drop in flow rate is approximately 5 percent.

Oversaturated flow represents traffic flow that is influenced by the effects of a downstream bottleneck. Traffic flow in the congested regime can vary over a broad range of flows and speeds depending on the severity of the bottleneck. Queues may extend several thousand feet upstream of the bottleneck. Freeway queues differ from queues at intersections in that they are not static or ,,standing. On freeways, vehicles move slowly through a queue, with periods of stopping and movement.

Speed-Flow and Density-Flow Relationships
The free-flow speed of passenger cars (mph) on freeways is relatively insensitive to flow rate of passenger cars per hour per lane (pcphpl) in the low to moderate range (0 pcphpl to 1,200 pcphpl). Studies have shown that passenger cars operating at a free-flow speed of 70 mph maintain the operating speed for flows up to 1,300 pcphpl For lower free-flow speed, the region over which speed is insensitive to flow extends to higher flow rates. In general terms, the lower the flow rate, the higher free-flow speed of the vehicle. Similarly, the higher the flow rate, the higher the density, which is measured in passenger car per mile per lane (pc/mi/ln).

Refer to the current TRB Highway Capacity Manual Chapter 13, Freeway Concepts, for a detailed discussion and exhibits specific to Speed-Flow and Density-Flow Relationships and factors that affect free-flow speed.

Passenger-Car Equivalents
The concept of vehicle equivalents is based on freeway conditions in which the presence of heavy vehicles, including trucks, buses, and recreational vehicles, creates less than base operating conditions. These diminished operating conditions include longer and more frequent gaps of excessive length both in front of and behind heavy vehicles, the speed of vehicles in adjacent lanes, and the physical space taken up by a large vehicle (typically two to three times greater than a passenger car). To allow for these lesser travel conditions and ensure the method for freeway capacity is based on a consistent measure of flow, each heavy vehicle is converted to a passengercar equivalent. The conversion results in a single value for flow rate in terms of passenger cars per hour per lane (pcphpl). The conversion factor depends on the proportion of heavy vehicles in the traffic stream and the length as well as the severity of the roadway grade.

Driver Population
Studies have shown that non-commuter driver populations display different, less aggressive characteristics than regular commuters. For recreational traffic, capacities have been observed to be as much as 10 to 15 percent lower than for commuter traffic traveling on the same segment

Level of Service (LOS)
Although speed is a major concern of drivers as related to service quality, freedom to maneuver within the traffic stream and proximity to other vehicles are equally noticeable concerns. These qualities are related to the density of the traffic stream. Unlike speed, density increases as flow increases up to capacity, resulting in a measure of effectiveness that is sensitive to a broad range of flows.

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The following brief descriptions summarize the different levels of service:

LOS A - Free flow, with low volumes and high speeds (about 90% of free-flow speed). Control delay at signalized intersection is minimal.

LOS B - Reasonably free flow, speeds (70% of free-flow speed) beginning to be restricted by traffic conditions. Control delay at signalized intersection is not significant.

LOS C - Stable flow zone, most drivers restricted in freedom to select their own speed (50% free-flow speed).

LOS D - Approaching unstable flow, drivers have little freedom to maneuver (40% free-flow speed).

LOS E - Unstable flow, may be short stoppages. High volumes, lower speeds (33% free-flow speed).

LOS F - Forced or breakdown flow. Intersection congestion is likely at critical signalized locations with high delays and high volumes and extensive queues.
Operating characteristics are represented by a specified LOS ranging from LOS A describing freeflow operations to LOS F describing breakdowns in vehicular flow. Breakdowns occur when the ratio of existing demand to actual capacity or of forecast demand to estimated capacity exceeds 1.00. Vehicular flow breakdowns occur for a number of reasons:

Traffic incidents can cause a temporary reduction in the capacity of a short freeway segment, so that the number of vehicles arriving at the point is greater than the number of vehicles that can move through it.

Points of recurring congestion, such as merge or weaving segments and lane drops, experience very high demand in which the number of vehicles arriving is greater than the number of vehicles discharged.

In forecasting situations, the projected peak-hour (or other) flow rate can exceed the estimated capacity of the location.

Freeway Weaving
Weaving is defined as the crossing of two or more traffic streams traveling in the same direction along a significant length of highway without the aid of traffic control devices (with the exception of guide signs). Weaving segments are formed when a merge area is closely followed by a diverge area, or when an entrance ramp is closely followed by an exit ramp and the two are joined by an auxiliary lane. Weaving segments may exist on any type of facility: freeways, multilane highways, two-lane highways, interchange areas, urban streets, or collector-distributor roadways.

Refer to the current version of the TRB Highway Capacity Manual,Chapter 24, for guidance related to freeway weaving.

13.2.3. Ramps and Ramp Junctions
A ramp is a length of roadway providing an exclusive connection between two highway facilities. On freeways, all entering and exiting maneuvers take place on ramps that are designed to facilitate smooth merging of on-ramp vehicles into the freeway traffic stream and smooth diverging of offramp vehicles from the freeway traffic stream onto the ramp.

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Refer to the current version of the TRB Highway Capacity Manual for guidance related to ramps and ramp junctions.

Capacity of Merge and Diverge Areas
There is no evidence that merging or diverging maneuvers restrict the total capacity of the upstream or downstream basic freeway segments. Their influence is primarily to add or subtract demand at the ramp-freeway junction. Thus, the capacity of a downstream basic freeway segment is not influenced by turbulence in a merge area. The capacity will be the same as if the segment were a basic freeway segment. As on-ramp vehicles enter the freeway at a merge area, the total number of ramp and approaching freeway vehicles that can be accommodated is the capacity of the downstream basic freeway segment.

Similarly, the capacity of an upstream basic freeway segment is not influenced by the turbulence in a diverge area. The total capacity that may be handled by the diverge junction is limited either by the capacity of the approaching (upstream) basic freeway segment or by the capacity of the downstream basic freeway segment and the ramp itself. Most breakdowns at diverge areas occur because the capacity of the exiting ramp is insufficient to handle the ramp demand flow. This results in queuing that backs up into the freeway mainline.

Another capacity value that affects ramp-freeway junction operation is an effective maximum number of freeway vehicles that can enter the ramp junction influence area without causing local congestion and local queuing. For on-ramps, the total entering flow in lanes 1 and 2 of the freeway plus the on-ramp flow can not exceed 4,600 pc/h. For off-ramps, the total entering flow in Lanes 1 and 2 can not exceed 4,400 pc/h. Demands exceeding these values will cause local congestion and queuing. However, as long as demand does not exceed the capacity of the upstream or downstream freeway sections or the off-ramp, breakdown will normally not occur. Thus, this condition is not labeled as LOS F, but rather at an appropriate LOS based on density in the section.

If local congestion occurs because too many vehicles try to enter the merge or diverge influence area, the capacity of the merge or diverge area is unaffected. In such cases, more vehicles move to outer lanes (if available), and the lane distribution is approximated.

Levels of service in merge and diverge influence areas are defined in terms of density for all cases of stable operation, LOS A through E. LOS F exists when the demand exceeds the capacity of upstream or downstream freeway sections or the capacity of an off-ramp.

Required Input Data and Estimated Values
Exhibit 13-17, listed on page 13-24 of the TRB Highway Capacity Manual, provides default values for input parameters in the absence of local data (Number of Ramp Lanes, Length of Acceleration/Deceleration Lane, Ramp free-flow speed, Length of Analysis Period, PHF, Percentage of Heavy Vehicles, and Driver Population). Exhibits 13-18 and 13-19, listed on page 1325, provide direction in the determination of acceleration and deceleration lane lengths. Service volumes for ramps are difficult to describe because of the number of variables that affect operations. Exhibit 13-20, listed on page 13-26 of the TRB Highway Capacity Manual, provides approximate values (for illustrative purposes only) associated with LOS for single on- and offramps.

13.2.4. Traffic Management Strategies
Freeway traffic management is the implementation of strategies to improve freeway performance, especially when the number of vehicles desiring to use a portion of the freeway at a particular time exceeds its capacity. There are two approaches to improving system operation. Supply

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management strategies work on improving the efficiency and effectiveness of the existing freeway or adding additional freeway capacity. Demand management strategies work on controlling, reducing, eliminating, or changing the time of travel of vehicle trips on the freeway while providing a wider variety of mobility options to those who wish to travel. However, in actual application, some strategies may address both sides of the supply/demand equation. The important point is that there are two basic ways to improve system performance.
Supply management strategies are intended to increase capacity. Capacity may be increased by building new pavement or by managing existing pavement. Supply management has been the traditional form of freeway system management for many years. Increasingly, the focus is turning to demand management as a tool to address freeway problems. Demand management programs include alternatives to reduce freeway vehicle demand by increasing the number of persons in a vehicle, diverting traffic to alternate routes, influencing the time of travel, or reducing the need to travel. Demand management programs must rely on incentives or disincentives to make these shifts in behavior attractive.
Freeway traffic demand management strategies include the use of priority for high-occupancy vehicles, congestion pricing, and traveler information systems. Some alternative strategies such as ramp metering may restrict demand and possibly increase the existing capacity. In some cases, spot capacity improvements such as the addition of auxiliary lanes or minor geometric improvements may be implemented to better utilize overall freeway system capacity.
Freeway Traffic Management Process
Freeway traffic management is the application of strategies that are intended to reduce the traffic using the facility or increase the capacity of the facility. Person demand can be shifted in time or space, vehicle demand can be reduced by a shift in mode, or total demand can be reduced by a variety of factors. Factors affecting total demand include changes in land use and elimination of trips due to telecommuting, reduced workweek, or a decision to forgo travel. By shifts of demand in time (i.e. leaving earlier), shifts of demand in space (i.e. taking an alternative route), shifts in mode, or changes in total demand, traffic on a freeway segment can be reduced. Likewise, if freeway capacity has been reduced (i.e. as the result of a vehicle crash that has closed a lane or adverse weather conditions), improved traffic management can return the freeway to normal capacity sooner, reducing the total delay to travelers.
The basic approach used to evaluate traffic management is to compare alternative strategies. The base case would be operation of the facility without any freeway traffic management. The alternative case would be operation of the facility with the freeway traffic management strategy or strategies being evaluated. The alternative case could have different demands and capacities based on the conditions being evaluated. The evaluations could also be made for existing or future traffic demands. Combinations of strategies are also possible, but some combinations may be difficult to evaluate because of limited quantifiable data.
Freeway traffic management strategies are implemented to make the most effective and efficient use of the freeway system. Activities that reduce capacity include incidents (including vehicle crashes, disabled or stalled vehicles, spilled cargo, emergency or unscheduled maintenance, traffic diversions, or adverse weather), construction activities, scheduled maintenance activities, and major emergencies. Activities that increase demand include special events. Freeway traffic management strategies that mitigate capacity reductions include incident management; traffic control plans for construction, maintenance activities, special events, and emergencies; and minor design improvements (i.e. auxiliary lanes, emergency pullouts, and accident investigation sites). Freeway traffic management strategies to reduce demand include plans for incidents, special

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events, construction, and maintenance activities; entry control/ramp metering; on-freeway HOV lanes; HOV bypass lanes on ramps; traveler information systems; and road pricing.

Capacity Management Strategies - Incident management is the most significant freeway strategy generally used by operating agencies. Incidents can cause significant delays even on facilities that do not routinely experience congestion. It is generally believed that more than 50 percent of freeway congestion is the result of vehicle crashes. Strategies to mitigate the effects of vehicle crashes include early detection and quick response with the appropriate resources. During a vehicle crash, effective deployment of management resources can result in a significant reduction in the effects of the incident. Proper application of traffic control devices, including signage and channelization, is part of effective incident management. Quick removal of crashed vehicles and debris is another part. Incident management may also include the use of accident investigation sites on conventional streets near freeways for follow-up activities.

Demand Management Strategies - The number of vehicles entering the freeway system is the primary determinant of freeway system performance. Entry control is the most straightforward way to limit freeway demand. Entry control can take the form of temporary or permanent ramp closure. Ramp metering, which can limit demand on the basis of a variety of factors that can be either preprogrammed or implemented in response to a measured freeway conditions, is a more dynamic form of entry control. Freeway demand can be delayed (changed in time), diverted (changed in space to an alternative route), changed in mode (such as HOV), or eliminated (the trip avoided). The difficult issue in assessing ramp metering strategies is estimating how demand will shift as a result of metering.

HOV alternatives such as mainline HOV lanes or ramp meter by pass lanes are intended to reduce the vehicle demand on the facility without changing the total number of person trips. Assessing these types of alternatives also requires the ability to estimate the number of persons who make a change of mode to HOV. In addition, it is necessary to know the origin and destination of the HOV travelers to determine what portions of the HOV facility they can use, since many HOV facilities have some form of restricted access.

Special events result in traffic demands that are based on the particular event. These occasional activities are amenable to the same types of freeway traffic management used for more routine activities such as daily commuting. In the case of special events, more planning and promotion are required than are typically needed for more routine activities.

Road pricing is a complex and evolving freeway traffic management alternative. Initially, road pricing involved a user fee to provide a means to finance highways. More recently, toll roads have been built as alternatives to congestion. Now, congestion-pricing schemes are being implemented to manage demand on various facilities or in some cases to sell excess capacity on HOV facilities. The congestion-pricing approach to demand management is to price the facility such that demand at critical points in time and space along the freeway is kept below capacity by encouraging some users during peak traffic periods to consider alternatives. Nontraditional road pricing schemes are still in their infancy, so little information is currently available on their effects compared with more traditional toll roads, which view tolls only as a means to recover facility costs.

13.3. Arterial Traffic Analysis and Design
Arterials are a functional classification of street transportation facilities that are intended to provide for through trips that are generally longer than trips on collector facilities and local streets. While the need to provide access to abutting land is not the primary function, the design of arterials must also balance this important need. To further highlight the often competing demands of urban arterials, it

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should be recognized that other modes of travel such as pedestrians and public transit are also present and must be accommodated.
To assure that arterials can safely provide acceptable levels of service for the design conditions, a number of design elements must be addressed. Since each design element is essentially determined based on separate analyses, the designer should then evaluate the entire arterial system and be prepared to refine certain elements to obtain an effective and efficient overall design.
13.3.1. Capacity Analysis and Level of Service (LOS)
Capacity analysis is the key method to establish the number of travel lanes that will be needed to accommodate the design conditions. The design principles of this document are intended to be consistent with the methodology as outlined in the latest edition of the TRB Highway Capacity Manual (HCM).
Capacity analysis software is essential to allow the designer to evaluate design alternatives in a timely manner. Several capacity analysis programs are acceptable, including The Highway Capacity Software (HCS), Synchro, and CORSIM. Other analysis packages should be discussed with the GDOT project manager prior to submitting as project documentation.
When conducting capacity analysis, the analyst will use reasonable timing parameters. When the arterial has a number of signalized intersections that are spaced less 1,500-ft., then system operation is likely. In such cases, the capacity analysis will use the cycle length requirements from the critical intersection for all intersections.
The traffic analysis will also consider pedestrian requirements. When significant pedestrian crossing volumes are expected, the capacity analysis will include minimum pedestrian intervals.
The arterial LOS in the current HCM is based on the average travel speed for the segment, section or entire arterial under consideration. This is the basic measure of effectiveness (MOE). The design engineer should refer to the current HCM for detail discussion and description of LOS.
The analysis method in the current HCM uses the AASHTO distinction between principal and minor arterials, but uses a second classification step to determine the design category for the arterial. The design criteria depend on factors such as: posted speed limit, signal density, driveway/access- point density, and other design features.
The third step in the capacity analysis process is to determine the appropriate urban arterial class on the basis of a combination of functional category and design category. Refer to the HCM Chapter 10, for a detailed description of functional and design categories.
13.3.2. Traffic Analysis Procedures
The traffic analysis and design generally includes the following elements: the typical section, access management, and intersection design. The following sections will address each of these areas.
Determination of Typical Section
To begin the conceptual design of an arterial, the number of travel lanes that are needed on the mid-block segments can be estimated based on ideal capacities. The ideal capacity of a two lane roadway is 1,700 vehicles per hour (vph) in each direction. The ideal capacity of a multi-lane roadway is 2,000 vph per lane. Capacity analysis should be used to check that acceptable levels of

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service can be achieved with the selected typical section and the design traffic data. The following general guidelines are provided to assist in the process of establishing typical sections:
Two-lane roadways are generally acceptable only if the DHV are less than 800 vph in either direction.
Undivided multi-lane roadways are typically limited to areas where the posted speed limit is no greater than 40 mph and the DHV does not exceed 3,000 vph in either direction.
Continuous two-way left turn lanes may be considered for roadways with typical sections having a number of closely spaced intersections with low-volume streets when the main roadway has no more than four lanes.
Access Management
Access management involves many techniques, ranging from zoning and subdivision regulations to highway design aspects and driveway access controls. For additional information related to Access Management, see Section 3.5. of this Manual.
For additional information relating to driveway and access controls, including permit procedures, access criteria, and geometric design criteria, refer to the most current version of the GDOT Regulations for Driveway and Encroachment Control7.
13.3.3. Intersection Traffic Control and Design
After the typical section is determined and the location of median breaks are determined (if the facility is divided), the traffic analysis should then focus on the intersections. It will be necessary to determine the type of traffic or right of way control and the need for turning lanes. Since the type of traffic control affects the intersection design, it is first necessary to determine if traffic signal control will be needed. An example of this influence on intersection design is that designers will typically limit the number of lanes on stop controlled approaches to avoid vehicles stopping abreast of each other and blocking sight distance from the other vehicle. When multiple lanes are needed on stop controlled approaches, the design will include islands and/or increased turning radii to separate through and turning vehicles.
The need for traffic signal control is obvious at many intersections that are currently signalized. However, at other intersections traffic signal warrant analysis may be needed to establish the need for traffic signal control. At some intersections, where traffic signals are not currently needed, future traffic increases may warrant signal control. For such intersections, a warrant analysis should be conducted for both the construction year volumes as well as for the design year volumes. Warrant analyses should be conducted using the guidelines of the most current edition of the MUTCD.
Signal warrants are typically conducted using hourly volumes throughout the normal day (not just peak hour volumes). Since the design volumes are limited to peak hour and daily volumes, it will be necessary to derive estimates of the volumes that occur during the remaining hours of the day.
An important signal warrant is Warrant 1, Eight-Hour Vehicular Volume. Therefore, the traffic analysis should estimate the eighth-highest volume of the day. The eighth-highest volume can be compared to the requirement of Warrant 1 to estimate if this important warrant will be satisfied with the projected volumes.

7 GDOT. (2006). Regulations for Driveway and Encroachment Control. Available online at:http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/DesignPolicies/index.shtml

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The eighth-highest volume can be estimated as representing 5.6 % of the daily volume. If the eighth-highest volume exceeds the minimum volumes for Warrant 1 using the construction year volumes, then signal control should be considered for installation during the construction project.
If Warrant 1 is only met using the design year conditions, then signalization may not be included with construction, but the design may reflect the need for future signal control. For example, turn lanes may be constructed and striped out until signals are installed.
Traffic Signal Permitting Process
There are three distinct roadway systems in Georgia. These are the county roads, the city streets and the state routes. The Georgia Department of Transportation has authority over the state route system. Georgia Law empowers GDOT with the authority to set standards for all public roads in Georgia. Because traffic signals are used at many intersections where state routes cross city streets or county roads, and because traffic signals are most often installed to meet a Local community need, a permit process to allow local governments to erect, operate and maintain traffic signals on state routes has been established. This formal process has been ongoing since the early 1950's. The authority to create uniform regulations and to place or cause to place traffic control devices on state routes is described in section 32-6-50 of the Official Code of Georgia.
Requests for traffic signals come to GDOT from a wide variety of sources. State, city and county elected officials responding to their constituents will often request GDOT to evaluate an intersection for a traffic signal. Requests may also be received directly into GDOT from concerned citizens. All inquiries are considered a request for assistance and should be investigated to determine if a signal or some less restrictive improvement should be implemented.
Requests for signals are evaluated using the warranting values found in the MUTCD. These warrants will be the minimum criteria for further study. Intersection evaluations indicating a signal will not meet any warrant may be denied by a letter of response from the District Traffic Operations Office. Intersections that will meet one or more of the MUTCD warrants will be studied further for justification.
All traffic signal devices erected on the state route system must have a permit application from the local government to GDOT and a Traffic Signal Authorization issued by GDOT prior to their installation. These permit documents serve as the agreement between GDOT and the local government for the signal. Even in communities where signals are maintained by GDOT, a formal document of agreement is needed. The permit application is used to allow the local government to formally request the use of a traffic signal. This application indicates the approval of the local government for the use of the signal. It also commits local government to provide electrical power and telephone service for the intersection.
The Traffic Signal Authorization is the permit indicating the formal approval of GDOT for the use of the traffic signal at the intersection. Design drawings are a part of the authorization form showing the intersection details, the signal head arrangement, the signal phasing and the detector placement. Regardless of the method of funding and installation, a signal authorization is needed. The original of this authorization is kept in the Office of Traffic Operations with copies sent to the District Office and from the District Office to the local government for their records.
Once a request is received, the District Traffic Engineer, using the methods described in the Manual on Uniform Traffic Control Devices, should initiate an engineering study. The study should first consider less restrictive measures such as improved signing, marking, sight distance, operational improvements, etc. If less restrictive measures can not be effectively implemented, a traffic signal

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should be considered if the conditions at the intersection satisfy one or more of the warrants in the MUTCD.

The completed Traffic Engineering Study shall have a signature page that includes the conclusions of the study and the recommendations of the District Traffic Engineer. Approval blocks should be included for the District Engineer (optional), State Traffic Engineer, and Division Director of Operations.

Once completed, the Traffic Engineering Study will be sent to the Office of the Traffic Operations for review and approval. If the signal is found to be justified by the Traffic Engineering Study, a Traffic Signal Authorization will be recommended for approval by the State Traffic Engineer. A permit approval form will be prepared by the Office of Traffic Operations, and the entire package will be sent to the Division Director of Operations for recommendation and to the Chief Engineer of GDOT for final approval. A copy of the approved permit and the design will be returned to the District Traffic Operations Office for transmittal to the local government for their records.

Signal permit revisions will be required for all changes made to the signal operation or design. Any addition of vehicle or pedestrian phases, modifications in phase sequences, modifications to signal head arrangements or other similar operational changes will require a permit revision. A request from the District outlining the changes needed and justifying the changes will be submitted in writing. A permit revision authorization will be issued with the appropriate design drawings similar to those required for a new signal.

It is appropriate for new signals to be included in roadway projects if a need has been identified. Even in these circumstances the permit application, the signal authorization and Traffic Engineering Study are necessary for new signals to be installed in roadway projects. Existing signals requiring upgrading to meet the needs of the reconstructed roadway may be included in the construction project. A permit revision should be requested as outlined above.

The Traffic Engineering Study prepared for the intersection proposed for signalization must adequately document two things. First, there is a need for this degree of control, and second, the analysis demonstrates that the signal operation will be beneficial to the state highway system. When these conditions are met, the State Traffic Engineer will recommend approval of the permit to the Division Director of Operations and Chief Engineer. The District Traffic Engineer should be the primary initiator for new signals on construction projects. This is to be accomplished as early in the project life as is possible, preferably at the design concept stage, and certainly should be accomplished by the preliminary field inspection (PFPR) since the use of signals will usually affect the roadway design.

Due to the detrimental effect of traffic signals on the flow of arterial traffic a traffic signal may not always be to the benefit of the state highway system. Therefore, it is likely that signals which are justified by design year traffic volumes will be denied or deferred if initial traffic volumes do not warrant their inclusion in the project. The Traffic Engineering Study is even more important in this case as it will document conditions at a point in time and will assist in the decision making process to determine the right time to approve signalization.

Pedestrian Accommodations at Signalized Intersections
Crosswalks and pedestrian signal heads, including ADA considerations, shall be installed on all approaches of new traffic signal installations or revised traffic signal permits unless an approach prohibits pedestrian traffic. Exceptions may be granted if the pedestrian pathway is unsafe for pedestrians or the Traffic Engineering Study documents the absence of pedestrian activity. The District traffic engineer, project manager, consultant, local government, or permit applicant must

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document the conditions and justification for eliminating pedestrian accommodations for each approach being requested. The documentation will be included in the permit file if accepted.
In the case of one or more pathways being determined unsafe to cross at a signalized intersection, appropriate MUTCD signing prohibiting pedestrian traffic must be erected. Use of MUTCD signing may also be appropriate when it is necessary to restrict access to one pedestrian pathway.
Prior to the Traffic Engineering Study recommending that pedestrian accommodations be eliminated based on the absence of pedestrian activity, the entity preparing the report should consider the existing development near the intersection, expected development within the next five year period, and input from local government. If any of these indicators project potential pedestrian activity the report should recommend pedestrian accommodations be included.
Turn Lanes at Stop Controlled Intersections At stop controlled intersections, the number of lanes on the stop controlled approaches will normally be minimized. However, it may be desirable to provide a separate, channelized lane for the right turning traffic.
It is desirable to provide separate lanes for vehicles that are preparing to turn off of the arterial roadway, when such turning volumes are significant. Guidelines for determining when such volumes are significant can be found in National Cooperative Highway Research Program (NCHRP) Evaluating Intersection Improvements: An Engineering Study Guide8, commonly referred to as NCHRP Report 457.
Turn Lanes at Signal Controlled Intersections The need for turn lanes at signal controlled intersections can also be evaluated using the guidelines found in NCHRP 457. However, capacity analysis will also be the basis for establishing the need for turn lanes and determining when multiple turn lanes are needed.
Although capacity analysis is used to identify potential needs for installing multiple turn lane bays, judgment must be used. For example, when providing dual left turn lanes, turn phases are generally operated in an "exclusive-only" manner. If dual turn lanes provide only marginal improvement over single turn lanes operated with protected/permitted phasing, it should be recognized that single turn lanes actually operate better during the off-peak times.
After the need for turn lanes is established, it is then necessary to define the length of tapers and full storage. Capacity analysis will result in estimated lengths of queues. In general, full width storage will be provided that is sufficient to store the estimated queue lengths of turning vehicles.
The traffic engineer will use judgment to evaluate the interaction of queues resulting from the different movements at the approach to an intersection. For example, left turn bays are sometimes "starved" due to the presence of long vehicle queues in the through lanes that block access to the left turn bay. When the estimated queue lengths of turning vehicles is less than but comparable to the queues for through vehicle, then the turn lane for the turn movement should be extended based on the queues in the through lanes. However, engineering judgment should be employed when making such decisions. As an example, if the through queues are estimated to be 800-ft. and the volume of left turn traffic is only 10 vph, then the left turn lane should not be extended to 800-ft. for such a small volume.

8 NCHRP. CHRP Report 457, "Evaluating Intersection Improvements: An Engineering Study Guide." 2001

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Drop Lanes When multiple turn lane bays are found to be needed on the arterial, it may be necessary to widen the intersecting roadway to accommodate an additional receiving lane. This widening should be extended to the next downstream intersection. However, as a minimum, the widening should be a sufficient distance downstream from the intersection in order to make the multiple turn lanes operate effectively and provide an adequate merging area. The additional lane may need to be expanded to the next downstream intersection.
The traffic analysis will consider the distance that should exist on the receiving lanes prior to a lane drop. The length of this distance will affect the lane utilization and appropriate lane utilization factors will be included in the capacity analysis. The traffic analysis will provide a recommended length of widening based on the capacity analysis and the expected lane utilization.
Highly Congested Urban Areas In many highly developed urban areas, it may be infeasible to meet the desirable level of service criteria. The following are examples:
Capacity analysis indicates a high number of lanes (more than 6 lanes) needed to accommodate the design volumes
Capacity analysis indicates grade separation would be required at major intersections The required improvements would require the acquisition and demolition of significant
existing structures When the traffic analysis indicates that it will be infeasible to meet the LOS standard, these conditions will be documented in the traffic analysis. The traffic engineer will then prepare an incremental analysis. An incremental analysis will typically address each five-year period within the twenty-year design period.
The traffic engineer must then request incremental traffic projections or assume linear increase throughout the design period. The incremental analysis will enable the traffic engineer to identify feasible improvements and report the expected operating conditions with these improvements at each incremental time period.
13.4. Trip Generation and Assignment for Traffic Impact Studies
Trip Generation is the process used to estimate the amount of traffic associated with a specific land use or development. A manual estimate of trip generation from the development will be required for all analyses. Trip Assignment involves placing trips generated by the new development onto specific roadways and adding them to specific turning movements at each area intersection.
13.4.1. Trip Generation Data

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Table 13.2. Common ITE Land Use Codes

ITE Land Use Code

Land Use Name

210

Single Family Detached Housing

220

Apartment

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For the purposes of this Design Policy Manual, a trip is

310

Hotel

a single vehicular movement with either the origin or destination within the study site and one origin or destination external to the land use. Trip generation is estimated through the use of "trip rates" or equations

520

Elementary School

565

Day Care Center

710

General Office Building

that are dependent on some measure of intensity of

770

Business Park

development of a particular land use. Gross leasable area (GLA) is the most common measure, but there are other measures such as number of employees, number of parking spaces, or number of pump islands (as at a

814

Specialty Retail Center

820

Shopping Center

832

High Turnover (Sit-Down) Restaurant

gasoline station) that are included as well.

834

Fast Food Restaurant with Drive-

Through Window

The current ITE Trip Generation Handbook contains the most comprehensive collection of trip generation data available. The rates and equations provided in this

853

Convenience Market with Gasoline

Pumps

912

Drive-In Bank

handbook are based on nationwide data. Some rates or Source: ITE. (2003).Trip Generation Handbook, 7th Ed.

equations, especially newer land use categories, are

supported with a limited number of studies. However, this manual is accepted as the industry

standard. Therefore, the rates and equations from the most current edition of the ITE Trip

Generation Handbook shall be applied. Deviation from rates, equations, or applications described in

most current edition of the Trip Generation Handbook must be discussed and approved by

appropriate GDOT staff prior to use in any study.

Trip generation data includes:

Land Uses - Each land use type within Trip Generation is identified with a unique numeric land use code. Similar land use types have code numbers that are close together. Some of the more common ITE land uses are listed in the Table 3.2.
Primary Trips, Passer-By Trips, and Diverted Trips The total trip generation volumes are typically computed as described previously and the generated trips are divided into these three components:
Primary trips are made for the specific purpose of visiting the development. Primary trips are new trips on the roadway network.

Passer-by trips are trips made as intermediate stops on the way from an origin to a primary destination. Passer-by trips are attracted from traffic already on adjacent roadways to the site.

Diverted trips are similar to passer-by trips except that they are attracted to a development from a nearby street or roadway that is not directly adjacent to the development. Like passer-by trips, diverted trips are not new to the roadway system overall. However, unlike passer-by trips, diverted trips use new routes to get to and from the development compared to their original route and thus have more impacts to the nearby roadway network than passer-by trips.

Study Network - The study network consists of the roadways in the vicinity of the

development that traffic must use to enter and leave the study area. The study network

includes the site access intersections onto adjacent off-site roadways and the sections of

these off-site roadways that are located within the study area. The study network is further

identified as a series of key intersections, which are the critical points and potential

bottlenecks in urban and suburban roadway networks. Roadways within the study area can

be further subdivided as described below.

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Site Access Points - These include key entrance roadways and driveways that serve the development and their intersections with the adjacent street and roadway network. These entrances/access points are usually newly constructed as part of the development.
Existing Roadway Network - At a minimum, these are the streets and roadways that immediately adjoin the development. For larger developments, the network of streets and roadways to be included in the study can extend a considerable distance away from the immediate vicinity of the site. The key intersections along the roadways within the study area are the source of most delay and are what should be evaluated. The number and location of intersections that are to be included in the traffic impact study will be determined in consultation with GDOT prior to preparation of the study.
Roadway Improvements Proposed as Part of Development - These include public streets and roadways that are proposed to be relocated, widened, or newly constructed as part of the proposed site development. The traffic assignment will take into account changes in traffic patterns caused by any proposed changes or additions to the roadway network.
Committed Offsite Roadway Improvements - These include proposed roadway and intersection improvement projects that will be constructed by others within the time period of the study. The "others" are usually GDOT or local governments, but they could also include projects that will be constructed by other developers within the study area. Changes/improvements to roadways and intersections caused by these projects will be included in the traffic impact study. If it is uncertain whether or not a particular project will be completed, then alternative scenarios must be evaluated.
Land Uses Not Identified in the ITE Trip Generation Manual
The vast majority of real estate developments can be identified or approximated with land uses identified within Trip Generation. However, the commercial and residential real estate markets are constantly evolving, and new land use types, especially commercial and retail, are created all the time. Since Trip Generation is updated on a periodic basic, new land use categories are already in widespread use before being incorporated into Trip Generation.
New types of "big-box" retail establishments are constantly being created that do not neatly fit in any single land use category included in Trip Generation. There are even new land use types that combine aspects of offices and warehouses and even retail. Large entertainment land uses such as casinos or theme parks may generate large numbers of trips, but are so specific as to not be covered by the more general land use categories included in Trip Generation.
For land uses that are not found within Trip Generation, trip generation volumes can be estimated using other available information. However trip generation is estimated, each assumption must be clearly stated with backup information provided to the satisfaction of the reviewer. Permissible methods are listed below.
Utilizing available marketing studies prepared by the client/developer
Patronage estimates for rail/bus stations by transit agency
Available parking spaces and assumptions on parking turnover per peak hour
Using an existing ITE land use that most closely resembles the new land use, and modifying or adjusting generated trips, with all assumptions/calculations clearly stated

13.4.2. Traffic Assignment

Traffic assignment is the process of placing site-generated trips onto the roadway network within the study area. Traffic assignment is done either manually or with modeling software. Traffic

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assignment for small to medium sized developments is more commonly handled with manual methods, while modeling software is often used for larger developments that have a regional impact. The site-generated trips (usually vehicles per peak hour) are added to the "background" traffic, which usually consists of the existing peak hour turning movement volumes at each intersection plus additional turning movements which account for compounded annual growth and sometimes traffic attributed to other nearby developments. The combined site-generated and background traffic form the total assigned traffic (intersection turning movements) that is used to measure level of service and determine necessary roadway improvements to accommodate the new development.
Traffic Assignment for Phased Developments
Many large developments are constructed in several phases over a period of years. The traffic impact study can reflect this reality by analyzing one or more intermediate phases, plus the full build-out scenario. Each new phase will assign additional traffic onto the assumed roadway network for that year. Background traffic for each new phase must include traffic assigned from previously opened phases of development.
Traffic Assignment of Three Major Trip Types
The three major trip types are primary trips, passer-by trips, and diverted trips. Each trip type will be separated when assigning site-generated traffic throughout the study network. This makes it easier for the reviewer to follow the assignment process and identify errors.
Primary trips are made for the specific purpose of visiting the development and they are new trips on the roadway network. Traffic will be assigned for primary trips throughout the study network according to the trip distribution percentages to and from the study area.
Passer-by trips are trips made as intermediate stops on the way from an origin to a primary destination. Passer-by trips are attracted from traffic already on adjacent roadways to the site. These trips are separately assigned to the study network only at site-access intersections and on internal circulation roadways within the site development itself. Turning movement volumes will be added at these intersections for entering and exiting traffic, while the through movements will be reduced by an equal amount.
Diverted trips are similar to passer-by trips except they are attracted to a development from a nearby street or roadway that is not directly adjacent to the site development. Like passer-by trips, diverted trips are not new to the roadway system overall, but their route will include off-site roadways and intersections on the study network. Like passer-by trips, these volumes will be deducted from the through traffic on the original roadway that they were traveling on, and the diverted volumes will be added to the revised route to and from the new developments. For more information on passer-by and diverted trips, please refer to the ITE Trip Generation Handbook, a companion to the ITE Trip Generation. The Handbook also includes helpful insight in preparing traffic impact studies, including studies for multi-use developments.

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Chapter 13 Index
Capacity Analysis. See Traffic, Analysis Capacity
Level of Service (LOS). See Traffic, Analysis-Level of Service (LOS)
Traffic Analysis - Arterials, 1824 Analysis - Capacity, 1314 Analysis - Freeway, 1218 Analysis Level of Service (LOS), 1415 Forecasting, 112 Management Strategies, 1618

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Chapter 14 Contents

14. LIGHTING

1

14.1. General Considerations

1

14.1.1. Roadway Lighting Warrants

1

14.1.2. Roadway Lighting Agreements

2

14.1.3. GDOT Assistance in Funding

3

14.1.4. No GDOT Assistance In Funding

4

14.1.5. Roadway Lighting Plan Preparation

5

14.2. Types of Lighting Projects

7

14.3. Illumination Requirements

7

14.3.1. Roadway

7

14.3.2. Vehicular Tunnels

7

14.3.3. Rest Areas and Welcome Centers

8

14.3.4. Park & Ride Lots and Pedestrian Tunnels

8

14.4. Lighting Calculations

8

14.5. Design Considerations

8

14.5.1. Standard Location Guidance

8

14.5.2. Luminaires

8

14.5.3. Electrical Materials

9

14.5.4. Roadway Lighting

9

14.5.5. Interchange Lighting

9

14.5.6. Truck Weigh Stations

12

14.5.7. Vehicular Tunnels

12

14.5.8. Rest Areas and Welcome Centers

12

14.5.9. Park & Ride Lots and Pedestrian Tunnels

12

14.5.10. Pedestrian and Security Lighting

12

14.6. Power Service

12

14.6.1. Grounding System

13

14.6.2. Photo Controls

15

Chapter 14 Index

16

Summary of Chapter 14 Revisions

17

List if Figures

Figure 14.1. Example of a Lighting Gore Detail

11

Figure 14.2. Example of Service Point Single Line Diagram

14

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14. LIGHTING
This chapter provides information on the various procedures and policies required for lighting future new construction and reconstruction projects and permitted lighting features on the state highway system in Georgia. It is not intended that existing lighting systems be modified as a result of the criteria outlined in this policy.

GDOT has adopted the current edition of the American Association of State Highway and Transportation Officials (AASHTO) policy Roadway Lighting Design Guide for the state of Georgia. The remainder of this policy document will address items not included in the AASHTO guide or provide clarification or emphasis on included items.

There are many reference publications that are available to the lighting designer, including but not limited to: AASHTO, Federal Highway Administration (FHWA), and the Illuminating Engineering Society of North America (IESNA) provide the most engineering information and knowledge in their handbooks and guides with regard to lighting design.

Standard definitions of terms for lighting can be found in the AASHTO design guide. Refer to the References section of this manual for details on how to obtain these and other lighting reference publications.

14.1. General Considerations
The Georgia Department of Transportation (GDOT) is generally responsible for providing lighting on state highways for the following purposes:

roadway (corridor, and intersection/roundabouts)

interchange

tunnel (roadway, and pedestrian/multi use)

underpass

pedestrian (sidewalks, multi use paths, and streetscape)

parking facilities (welcome centers, rest areas, truck weigh stations, and park and ride lots)

aesthetics (enhancement projects, bridges, etc.)

sign structures illumination of sign structures will be handled by the GDOT Office of Traffic Safety and Design and is not addressed in this document.

14.1.1. Roadway Lighting Warrants
It is best that lighting requirements be coordinated at the concept stage. All lighting requirements for existing or proposed systems shall be coordinated with the Roadway Lighting Group of the GDOT Office of Road and Airport Design.

Lighting should be considered for all Interstate projects (roadway and/or interchange), especially in urban areas, and be included in any interstate and or interchange upgrade project, assuming the local government will agree to the energy and maintenance costs for the newly installed system.

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If while reconstructing existing roadways and/or adding lanes the proposed construction work does not conflict with existing roadway lighting structures, the new lane configuration still requires that the photometrics be evaluated based on current AASHTO and IESNA requirements. The majority will require a new lighting system to be provided. In addition, the lifespan of the major lighting system components (towers, poles, luminaires etc.) is typically 20 to 25 years. Retaining components longer can greatly increase the maintenance requirements of the lighting system.
If an existing roadway lighting system is present and requires relocation, upgrade or replacement, then the required work for the lighting system will be included in the GDOT roadway project. The responsible Local Government shall continue to pay for Energy, Maintenance and Operations of the system. GDOT shall retain the ownership of the system.
If no existing roadway lighting system is present AND the site does not meet the AASHTO warranting conditions for roadway lighting, THEN a written request for lighting must come from the Local Government for the inclusion of roadway lighting to be included in a programmed GDOT project to be considered.
GDOT will include lighting with roadway projects or assist in the funding of lighting projects if requested by the local government and the local government will agree to the long term energy, maintenance and operations costs.
14.1.2. Roadway Lighting Agreements
A lighting agreement and/or permit shall be required for all lighting facilities placed on GDOT's right of way.
The Roadway Lighting Group prepares all lighting agreements for lighting included in all Let and Force Account projects. They also keep GDOT's archives for lighting agreements dating back to the late 1960's. Any inquiries to the existence of or the need for a new lighting agreement should be forwarded to the Roadway Lighting Group.
The Office of Utilities will review all lighting permits as well as keeping the GDOT archives for all lighting permits. Any inquiries to the existence of a lighting permit should be forwarded to the Office of Utilities. For projects that have no GDOT funding, refer to Section 14.1.4. of this Manual.
Lighting Agreements are not required for lighting GDOT owned and operated facilities such as welcome centers, rest areas and truck weigh stations.
The Project Manager should coordinate through the Roadway Lighting Group for a local government lighting agreement or for any lighting requirements associated with their projects.
Lighting agreements typically involve one local government, but multiple local governments may be involved (i.e. County and City). The physical location of the lighting system does not necessarily have to be within the jurisdictional area of the responsible local government. A local government may request to be responsible for a lighting system that is outside of their respective jurisdiction.
Lighting Agreements are site specific, NOT construction project specific. Lighting Agreements cover a 50 year time period. This allows the Department to retouch the site multiple times without acquiring a new lighting agreement until such time that the agreement expires. Example: If the original agreement covered roadway lighting for a specific Interchange and GDOT reconstructs that Interchange and the proposed new lighting system matches the verbal description of the original agreement then no new agreement is required. But if the new project extends the coverage by

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adding additional roadway lighting along the roadway (down mainline or crossroad) and no longer matches the verbal description in the existing agreement, then a new agreement would be required.
14.1.3. GDOT Assistance in Funding When GDOT and a Local Government enter into an Agreement to provide a roadway lighting system the project can be funded and constructed in accordance with one of the five basic scenarios of lighting projects. The four scenarios that include GDOT funding at various levels of participation are as follows:
Scenario 1 Lighting system included in a GDOT let roadway or maintenance project
Request for lighting assistance is received from the corresponding Local Government(s)
and GDOT has an existing programmed project to which the work can be added
and Local Government(s) sign a lighting agreement to pay for the energy, maintenance and operations of the lighting system
Then the work is added to the GDOT project at no cost to the Local Government for design, materials and installation
GDOT shall retain ownership of the lighting system
This is the preferred scenario of GDOT
Scenario 2 Lighting system included in a stand-alone force account lighting project
Request for lighting assistance is received from the corresponding Local Government(s)
and GDOT does NOT have an existing programmed project to which the work can be added
and the site is on the National Highway System
and a Cost Justification Report is provided showing it is more cost effective to install the lighting system via local government forces versus a Let project
and the Local Government(s) sign a lighting agreement agreeing to be responsible for the design, installation, energy, maintenance and operations of the lighting system.
Then a Stand-alone Force Account project can be set up with the Department being responsible for the funding of materials only
GDOT shall retain ownership of the lighting system
This is the second most commonly used scenario
Scenario 3 Lighting system included in stand-alone local government-let lighting project
Request for lighting assistance is received from the corresponding Local Government(s)
and GDOT does NOT have an existing programmed project to which the work can be added

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and the site is on the National Highway System

and the Local Government(s) sign a lighting agreement agreeing to be responsible for the design, installation, energy, maintenance and operations of the lighting system

Then a Stand-alone Local Government Let project can be set up with the Department being responsible for the funding of materials only

GDOT shall retain ownership of the lighting system

Scenario 4 Lighting system included in stand-alone GDOT-let lighting project

Request for lighting assistance is received from the corresponding Local Government(s).

and GDOT does NOT have an existing programmed project to which the work can be added.

and the Local Government(s) sign a lighting agreement agreeing to be responsible for the energy, maintenance, and operations of the lighting system.

and approval is received from GDOT Management.

Then a Stand-alone Let GDOT project can be set up at no cost to the Locals for design, materials and installation

GDOT shall retain ownership of the lighting system

This scenario is used on a very limited basis and is for extreme circumstances approved on a case by case basis only

14.1.4. No GDOT Assistance In Funding
In the event that GDOT will not be assisting in the funding, then a Utility Lighting Permit may be issued by GDOT with the Local Government or applicant being responsible for 100% of all associated costs while still meeting all state requirements for lighting design. The Department shall review and approve the plans. The Local Government or applicant retains ownership of the system under the following scenario. The scenario that includes no GDOT funding is as follows:

Scenario - Utility Permit to Local Government or applicant for Lighting Roadway

All lighting permits that are requesting to place lighting facilities on GDOT right of way are to be applied through appropriate District Utilities Office. The District Office will review and determine exactly what type of Lighting Permit has been received. There will be four different guidelines or types as follows:

Residential Lighting Consisting of 1 or 2 luminaires only for purpose of lighting private property utilizing existing pole facilities. Applicant is paying for entire cost. District Utilities Office will review electrical hookups and District Traffic Operations Office will review the height of lights and position. Once reviewed and accepted by both the District Utilities and the District Traffic Operations offices, the District Engineer will approve the utility permit via the District Utilities Office. A copy shall be sent to the State Utilities Office.

Business Lighting Consisting of 2 or more luminaires on existing pole facilities for the purpose of lighting private property with the Local Government or Applicant paying for entire

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cost. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations will review the height of lights and position. Once reviewed and accepted by both the District Utilities and the District Traffic Operations offices, the District Engineer will approve the utility permit via the District Utilities Office with a Special Provision that the Local Government or Applicant will design and construct the lighting in accordance with this Manual.

If the request consists of 2 or more luminaires, on new pole facilities, for the purpose of lighting private property with the Local Government or Applicant paying for entire cost then the District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations will review the height of lights and position. The State Utilities Office will develop a Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) before the utility permit can be approved. Once reviewed and accepted by both the District Utilities and District Traffic Operations offices and signatures have been received by the State Utilities Office, the District Engineer will approve the utility permit via the District Utilities Office with the Memorandum of Agreement attached. A complete copy of the approved utility permit (including the Memorandum of Agreement) shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design.

Governmental Lighting (Minor) - Consisting of a request to light a section of a state route that is not located on the National Highway System and the Local Government or Applicant is paying for the entire cost of the lighting system with no more than 4 luminaires. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations Office will review the height of lights and position. State Utilities Office will develop the Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) before the utility permit can be approved. Once reviewed and accepted by both the District Utilities and District Traffic Operations offices and signatures have been received by the State Utilities Office, the District Engineer will approve the utility permit via the District Utilities Office with the Memorandum of Agreement attached. A complete copy (including the Memorandum of Agreement) of the approved utility permit shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design.

Governmental Lighting (Major) - Consisting of a request to light sections of a state route that is not located on the National Highway System and the Local Government or Applicant is paying for the entire cost of the lighting system with 5 or more luminaires. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations Office will review the height of lights and position. State Utilities Office will develop the Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) and forward the complete permit package to the Roadway Lighting Section of the Office of Road and Airport Design for the review of the lighting plan. Once reviewed and accepted by all three Offices and signatures have been received in the State Utilities Office; the District Engineer will approve the utility permit via the District Utilities Office, with the Memorandum of Agreement attached. A complete original copy of the approved utility permit shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design.

14.1.5. Roadway Lighting Plan Preparation
The Office of Road & Airport Design's Roadway Lighting Group shall coordinate the preparation of lighting plans for all Let and Force Account projects for but is not limited to the following:

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road design
urban design
consultant design
all district offices
Office of Maintenance
other State agencies (i.e. Jekyll Island Authority)
Local Governments (County and City)
Lighting plans shall not be developed until after an executed lighting agreement is in place.
All roadway lighting must be included GDOT's environmental evaluation processes. Most standalone lighting projects are handled with a Categorical Exclusion (CE) Environmental Document. This applies to Let or Force Account projects.
For roadway projects that lighting is added to after the Environmental Document has been prepared, coordination with GDOT's Office of Environment/Location (OEL) is needed to ensure there are no historical or environmental conflicts. NEPA clearance can take up to 6 months to acquire dependent on the sensitivity of the site. Some examples of environmental and historical conflicts that can affect roadway lighting are:
Endangered species: Sea turtles in coastal regions.
Archeological conflicts: Indian mounds and other archeologically significant sites.
Historic resources: Light trespass into historic districts or individual properties. Height restrictions adjacent to historic or individual properties.
Environmental conflicts: Wetland impacts requiring directional bore in place of traditional trenching to run conduits. Possible restrictions as to the limits of vegetative clearing.
The preparation of lighting plans that are to be included in a parent set of roadway or maintenance plans should not be started until AFTER the PFPR comments have been implemented into the roadway plans. The horizontal and vertical alignments, bridges plans, drainage, proposed utility plans etc. need to be set before the lighting plans can be developed.
When requesting lighting plans for inclusion in parent project, a request must be sent to the Roadway Lighting Group with the following information:
Confirmation of an executed Local Government Lighting Project Agreement (LGLPA) for the site (handled by request to the Roadway Lighting Group)
Parent Project Number and PI Number
Current Management Let Date
Brief description of site and work to be covered by the lighting plans

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Proposed delivery date for Final Lighting Plans

The Roadway Lighting Group will prepare a scope and man hour estimate to include with each request for a Task Order Contract for lighting plans. After the Roadway Lighting Group has requested the Task Order and approval for the Task Order has been received; Program Delivery issues the Task Order through the Lighting Master Task Order Contract or through one of the general Master Task Order Contracts.

Once the design consultant has been selected the following information will be required from the Project Manager:

CD with the DGN files for the plan view covering the area to be lighted (minimum 1,000-ft. before the exit ramp gores and 1,000-ft. beyond the entrance gores along the interstate if interchange lighting).

Full-size hardcopy set: cover, typical sections, plan, profile, drainage cross-sections/profiles, bridge plan and elevation (for all bridges located within the proposed lighting boundaries) and proposed utility plans.

14.2. Types of Lighting Projects
Prior to the design of a lighting system, the designer must determine the project type and the particular location where lighting may be warranted. The following types of lighting projects are included and their design requirements discussed further in this chapter:

roadway lighting interchange lighting truck weigh stations tunnels and underpass park and ride lots rest areas and welcome centers

pedestrian and security lighting

14.3. Illumination Requirements
If lighting is included in the project then the design shall be based upon AASHTO and IESNA guidelines, the designer should then determine the uniformity ratios and Light Loss Factors (LLF) for each specific lighting project. For roadways, tunnels, rest areas, welcome centers and park &ride lots, the guidance is as follows:

14.3.1. Roadway
The roadway maintained average illuminance, uniformity ratio and veiling luminance ratio shall be in accordance with the AASHTO Roadway Lighting Design Guide and the IESNA RP-8. A LLF of 0.7 shall be used to compute the maintained illuminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations.

14.3.2. Vehicular Tunnels

The maintained average luminance values in the tunnel threshold and interior zones shall be in

accordance with the AASHTO Roadway Lighting Design Guide and the IESNA RP-22. A LLF of 0.5

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shall be used to compute the maintained luminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations.
14.3.3. Rest Areas and Welcome Centers
The maintained average illuminance values for the parking and pedestrian areas shall be in accordance with the AASHTO Roadway Lighting Design Guide and the IESNA G-1. A LLF of 0.7 shall be used to compute the maintained illuminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations.
14.3.4. Park & Ride Lots and Pedestrian Tunnels
The illuminance values for pedestrian tunnels shall be in accordance with IESNA G-1. A LLF of 0.7 shall be used to compute the maintained illuminance values.
14.4. Lighting Calculations
As part of the steps for determining the appropriate lighting system for a particular project, the lighting designer must calculate the required illumination. Various factors are considered when making this determination, such as roadway width, lighting setback and mounting height, and the type of lighting system to be used. The designer determines the lighting calculations for a particular project by using a computer program, such as AGi32 by Lighting Analysts, Inc. The calculation shall show illuminance values on the roadway with point to point intervals of 6 ft. longitudinally and transversely. Also, when a section of roadway is being analyzed, the entire section of roadway that is being illuminated shall be analyzed completely as a self-contained area.
The lighting calculations shall show the tabulated values for average, minimum and maximum footcandles, uniformity and veiling luminance ratios. The lighting designer shall submit files of the complete roadway or area under consideration with point by point illuminance values in Adobe Acrobat (.pdf) format. It may be necessary for the lighting designer to consider other lighting options and to substantiate that the lighting design is optimum and cost effective. The lighting designer shall be prepared to explain the lighting system choice and present all documentation to GDOT to substantiate the lighting recommendation.
14.5. Design Considerations
This section provides guidance to the lighting designer with regard to roadways, interchanges, truck weigh stations, tunnels and underpasses, rest areas, welcome centers, park & ride lots, and pedestrian and security lighting. These design considerations, along with the lighting designer's experience and engineering knowledge of lighting design, should prove valuable in determining the most appropriate lighting system for each project.
14.5.1. Standard Location Guidance
See Chapter 5, Roadside Safety and Horizontal Clearance, of this manual for locating light standards and high mast towers. In addition, light standards and high mast towers shall also be located to provide proper clearances from utility lines, airport glide paths, railroads, etc. The lighting designer shall ensure that the design is coordinated with other utility features.
14.5.2. Luminaires
All luminaires shall be high pressure sodium and be in accordance with GDOT's Qualified Products List (QPL) and standard specifications. High mast luminaires with Type V symmetrical distribution is preferred. Other distributions may be used to accomplish proper roadway illumination or to avoid

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spillage on adjacent properties. Cut-off optics shall be used for both high mast and conventional luminaires if required by project specific issues.

14.5.3. Electrical Materials
All electrical materials, such as conduit, cables, wires and junction boxes, shall be new U.L. listed and meet the requirements of the National Electrical Code, and the American National Standards Institute. Electrical conduits, wires, circuit breakers, fuses, ground rods and ground conductors shall meet GDOT's Standard Specifications and shall be in accordance with GDOT's Qualified Products List (QPL).

14.5.4. Roadway Lighting
Continuous roadway lighting generally uses conventional lighting systems consisting of high pressure sodium offset type luminaires. The use of mast arms with cobra head luminaires is discouraged and shall require approval on a case by case basis. The nominal mounting height shall be 30-ft. to 50-ft. The luminaries shall be 150W, 250W, or 400W depending on the roadway geometry and mounting heights. Lighting standards may be placed on one or both the sides of the highway either opposite each other or staggered. The lighting standard setback measured from the face of a non-mountable curb or edge of pavement to the centerline of the lighting standard shall be 5-ft. 6-in. minimum.

Lighting standards located inside the clear zone shall be provided with AASHTO compliant breakaway transformer bases or breakaway couplings and breakaway wiring connectors unless shielded by a barrier. The lighting standards may also be located on the median barrier wall with specific approval from GDOT. GDOT will ensure that the maintenance on these luminaires will not pose an unacceptable level of safety or an unacceptable level of service if lane closures are required for lighting maintenance. Offset type luminaries with very short mast arms may be used for median barrier wall mounted lighting standards.

Where it is more cost effective to do so, high mast lighting may be used for roadway lighting.

14.5.5. Interchange Lighting
High mast lighting shall be used for interchange lighting unless the location has constraints on the pole height such as near airport boundaries. Conventional lighting may be used in the areas determined to have height constraints.

At interchanges, the high mast poles shall have 100-ft. nominal mounting height. The high mast luminaries should be 1,000 Watt. Lower wattage luminaires may be utilized if satisfactory justification is first provided to GDOT. The lighting designer shall provide an optimum and cost effective lighting design for GDOT's approval.

High mast lighting shall be provided to cover a minimum of 1,000-ft. from the farthest gore point on exit/entrance ramp. High mast lighting shall be provided to cover the distance to the point where the travel lane and taper is 12-ft. but shall not be less than 1,000-ft. from the gore point. (see Figure 14.1. Example of a Lighting Gore Detail). High mast luminaries with type V symmetrical distribution are preferred. Other types of light distributions may be used to accomplish proper roadway illumination or to avoid spillage on adjacent properties up to and including the use of offset luminaires.

Shields shall be used to control light spillage on residences or other areas where the spilled light may be considered objectionable. The lighting designer needs to consider this type of impact to surrounding areas and land uses when developing the proper lighting system.

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For high mast pole foundations, design analysis shall be performed. Soil borings shall be done at each proposed location of the high mast pole and the results used in the foundation design. The high mast pole foundation design shall be approved by the GDOT Office of Bridge Design prior to installation. High mast light poles located on a 2:1 or greater slope shall be provided with maintenance platforms.
All underpasses within the illuminated limits of the interchange shall maintain the same illuminance levels as the adjacent roadway. This may require the installation of underpass luminaires.

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Figure 14.1. Example of a Lighting Gore Detail

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14.5.6. Truck Weigh Stations
The truck weigh station shall be provided with a High Mast lighting system similar to the system described for interchange lighting. The entrance and exit ramps to the truck weigh station shall be provided with conventional lighting. See Section 14.5.5. of this Manual for the requirements of the limits of lighting coverage for the ramps.
14.5.7. Vehicular Tunnels
The reflective characteristics of pavement, wall and ceiling materials shall be taken into account for computing roadway luminance values. The lighting designer shall also take into account daylight penetration into the tunnel.
The luminaires shall preferably be mounted on the ceiling of the tunnel or shall be wall mounted. Specific approval shall be obtained from GDOT for ceiling mounting the luminaries. GDOT will ensure that the maintenance on these luminaires will not pose an unacceptable level of safety or an unacceptable level of service if lane closures are required for lighting maintenance.
14.5.8. Rest Areas and Welcome Centers
The lighting for rest areas, welcome centers, and Park & Ride lots shall meet the requirements of IESNA RP-20 and G-1. Conventional lighting with high pressure sodium luminaires shall be used for all parking areas. High Mast Lighting shall be considered if the rest area or welcome center has large parking areas away from the buildings.
Post top high pressure sodium luminaires shall be used in the picnic areas of rest areas and welcome centers. Conventional lighting with high pressure sodium luminaires shall be used for entrance and exit ramps into these special areas off the main highway. See Section 14.5.5. of this Manual for the requirements of the limits of lighting coverage for the ramps.
14.5.9. Park & Ride Lots and Pedestrian Tunnels
Park & ride and pedestrian tunnels shall meet the requirements of IESNA G-1. All non tunnel mounted luminaires shall be full cut off or cut off HPS. All pedestrian tunnel luminaires shall be HPS and vandal proof. Cut-off optics shall be used if required by project specific issues.
14.5.10. Pedestrian and Security Lighting
The pedestrian and security lighting shall meet the requirements of IESNA G-1. Conventional lighting shall be used. The lighting designer should consider the use of vandal-resistant luminaires and other electrical equipment for particular types of security lighting.
14.6. Power Service
The lighting designer shall contact the power company and determine the availability of power service for lighting. A request shall be made to obtain the power service at locations desired by the lighting designer. The lighting designer shall provide the power company with information for estimated load at each service point location. A lighting site visit to meet with a power company representative may be necessary to coordinate power service for a roadway lighting project.
The lighting designer shall coordinate with the power company and the local government or jurisdiction responsible for paying the utility bills to determine if the power services will be metered.

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If the local government enters into a contract with the power company to provide power at a fixed monthly charge, light metering will not be required.
The standard power services available from the power company are as follows:
Single phase 3 wire: 120/240V and 240/480V, the latter is preferred.
Three phase 4 wire: 480/277V. This power service is preferred when available for lighting projects with large loads.
The electrical power distribution design shall meet the National Electrical Code and local codes. The power company may want to provide lighting contactors and photocells to control the lighting when the power service is not metered. In this case, the lighting designer shall include lighting contactors and photocell in the design to control the unmetered lighting system.
All the electrical equipment, such as main circuit breakers, lighting contactors and load centers, shall be in NEMA-4X stainless steel enclosures that can be padlocked and shall be U.L. listed. A surge suppressor shall be provided at each power service. The surge suppressor shall be in NEMA-4X enclosure, UL1449 and UL1283 listed suitable for connection to the power service. The surge suppressor shall have a minimum surge current rating of 130,000A per phase and shall be provided with status indicating lights.
The electrical equipment and distribution system shall be designed to take into account any possible future expansion. The electrical equipment short circuit ratings shall exceed the available fault current. The lighting designer shall obtain the available fault current values from the power company.
The lighting designer shall size all the cables to limit the voltage drop to approximately 3.5%; and in no case more than a 5% drop in power service voltage. The voltage drop calculations shall be submitted to GDOT for approval.
The lighting designer shall include a diagram of each service point. See Figure 14.2. Example of a Service Point Single Line Diagram, for an example of format and content.
14.6.1. Grounding System
The ground rods shall be copper clad steel, minimum -in diameter, 10-ft. long. The buried ground conductors shall be stranded copper. All the underground connections in the grounding system shall be made using exothermic weld (cadweld) process.
A ground rod shall be provided at each conventional light pole and connected in the pole base using a ground conductor. A ground grid consisting of four ground rods at the corners of the high mast lighting foundation shall be provided. The rods shall be connected to each other using #2 AWG stranded copper conductor to form a square ground grid. A #2 AWG bare stranded copper conductor shall be cadwelded to the grid and brought into the tower base to connect to the pole.
A ground grid consisting of three ground rods located at the apexes of a 10-ft. equilateral triangle and connected to each other using #2 AWG stranded copper conductors shall be provided at each power service. An adequately sized stranded copper conductor shall be connected to the ground grid and routed to main service disconnecting means. Appropriately sized insulated ground conductor(s) shall be provided in the conduits with the branch circuits

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Figure 14.2. Example of Service Point Single Line Diagram

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14.6.2. Photo Controls
All nighttime only lighting systems shall have a photocell control that operates independently of the power service provider controls.

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Chapter 14 Index
Illumination. See Lighting: Illumination Interchanges
Lighting, 911 Lighting Design, 9 Lighting Calculations, 8 Funding No GDOT Assistance, 4 Funding GDOT Assistance, 3 Illumination Requirements, 7 Power Service, 1112 Project Types, 7 Roadway Lighting Agreements, 2 Roadway Lighting Plan Preparation, 5 Park & Ride Lots Illumination Requirements, 7 Lighting Design, 11 Pedestrian Lighting Design, 11

Lighting Design, 11 Rest Areas
Illumination Requirements, 7 Lighting Design, 11 Roadway Illumination Requirements, 7 Lighting Design, 8 Security Lighting Design, 11 Truck Weigh Stations Lighting Design, 11 Tunnels Illumination Requirements, 7 Lighting Design, 11 Welcome Centers Illumination Requirements, 7 Lighting Design, 11

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Glossaries

EN-EX Entrance followed by exit (as in ramp terminals)

Acronyms

ETI Engineering Traffic Investigation (Report)

3R Roadway Resurfacing, Restoration, or Rehabilitation (Project)
A/C Access Control
AADT Average Annual Daily Traffic
AAWT Average Annual Weekday Traffic
AASHTO American Association of State Highway and Transportation Officials (http://www.transportation.org)
ADA Americans with Disabilities Act
ADDS Automated Data/Design Standards
ADT Average Daily Traffic
AHI Adjusted Hazard Index
AREMA American Railway Engineering and Maintenance of Way Association (http://www.arema.org)
ATR Automated Traffic Recorder
AWG American Wire Gauge

EX-EN Exit followed by entrance (as in ramp terminals)
EX-EX Exit followed by exit (as in ramp terminals)
FAA Federal Aviation Administration (http://www.faa.gov/)
FDR Freeway Distributor Road
FFPR (GDOT) Final Field Plan Review
FHWA Federal Highway Administration (http://www.fhwa.dot.gov/)
FRA Federal Railroad Administration (http://www.fra.dot.gov/)
GDOT Georgia Department of Transportation (http://www.dot.state.ga.us)
GLA Gross Leasable Area
GRIP Governor's Road Improvement Program (http://www.dot.state.ga.us/DOT/planprog/planning/programs/grip/)

AWT Average Weekday Traffic C-D Collector-Distributor CDR Collector Distributor Road

GRTA Georgia Regional Transportation Authority (http://www.grta.org/)
HCM Highway Capacity Manual (see References for additional information)

CFR Code of Federal Regulations CL Centerline CORSIM Corridor Simulation Software CWP (GDOT) Construction Work Program dBA Decibels, A-Scale DHV Design Hour Volume DMS Dynamic Message System DTM Digital Terrain Model EN-EN Entrance followed by entrance (as in
ramp terminals)

HCS Highway Capacity Software (http://mctrans.ce.ufl.edu/hcs/)
HOV High Occupancy Vehicle
IES Illuminating Engineering Society
IESNA Illuminating Engineering Society of North America (http://www.iesna.org)
ISTEA Intermodal Surface Transportation Equity Act (http://www.bts.gov/laws_and_regulations/)
ITE Institute of Transportation Engineers (http://www.ite.org/)

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L/A Limited Access
LARP Local Assistance Road Program
LOS Level of Service
LR Long Range
LRFD (AASHTO) Load and Resistance Factor Design
LRTP Long Range Transportation Plan
MPO Metropolitan Planning Organization
MUTCD Manual on Uniform Traffic Control Devices (FHWA) see References for additional information.
NCHRP National Cooperative Highway Research Program (http://www4.nationalacademies.org/trb/crp. nsf)
NHS National Highway System
OCGA Official Code of Georgia (http://www.lexisnexis.com/hottopics/gacode/default.asp)
OEL (GDOT) Office of Environment and Location (http://www.dot.state.ga.us/preconstruction/ oel/index.shtml)
PDP (GDOT) Plan Development Process
PE Preliminary Engineering
PHF Peak Hour Factor
PGL Profile Grade Line
PI Point of Intersection (intersection of tangents to a curve)
PC Point of Curvature (where a curve begins)
PCC Portland Cement Concrete
PFPR Preliminary Field Plan Review
PHV Peak Hour Volume
PM Preventive Maintenance
PT Point of Tangent (where a curve ends)

PVI Point of Vertical Intersection
QPL (GDOT) Qualified Projects List
RCInfo Roadway Characteristics Information
RDG (AASHTO) Roadside Design Guide (https://bookstore.transportation.org/item_d etails.aspx?ID=148)
ROR Run-off-Road (as in crash)
ROW Right-of-Way
RTV Right Turn Volume
RV Recreational Vehicle
SIDRA Signalized and Unsignalized Intersection Design and Research Aid
SPUI Single Point Urban Interchange
SRTA State Road and Tollway Authority
STARS (Georgia) State Traffic and Report Statistics (http://www.dot.state.ga.us/dot/planprog/transportation_data/TrafficCD/index.sh tml)
STIP Statewide Transportation Improvement Plan, also referred to as SWTP
SWTP Statewide Transportation Plan (http://www.dot.state.ga.us/dot/planprog/planning/swtp/index.shtml)
TAZ Traffic Analysis Zone
TIP Transportation Improvement Program
TL Travel Lane
TOPPS Transportation Online Policy and Procedure System (http://www.dot.state.ga.us/topps/index.sht ml)
TRB Transportation Research Board
TWLT Two-Way Left Turn
UAPSM (GDOT) Utility Accommodation Policy and Standards Manual. See References for additional information.

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USGS United States Geological Survey (http://www.usgs.gov/)
VE Value Engineering Vpd Vehicles per day
WB Wheel Base (of a design vehicle)

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Definition of Terms
3R Project A non-interstate resurfacing, restoration, or rehabilitation project. For additional information, see Chapter 11. Other Project Types
85th Percentile The speed at or below which 85 percent of the motor vehicles travel (FHWA MUTCD, 2003).
AASHTO Green Book American Association of State Highway and Transportation Officials (AASHTO) publication named A Policy on Geometric Design of Highways and Streets. See References for additional information.
Access Entrance to or exit from land adjacent to a public road. (GDOT Driveway Manual, 2004)
Access Control see Control of Access
Access Management Providing (or managing) access to land development while simultaneously preserving the flow of traffic on the surrounding road system in terms of safety, capacity, and speed.
ADA (Americans with Disabilities Act) A federal law that was enacted in 1990 for the purpose of ensuring that all Americans have the same basic rights of access to services and facilities. The ADA prohibits discrimination on the basis of disability. To effect this prohibition, the statute required certain designated federal agencies to develop implementing regulations.
Adjusted Hazard Index Rating the summation of the Unadjusted Hazard Index rating, the Adjustment Factor for School Buses, and the Adjustment for Train-Vehicle Crash history. (AHI = A5 + S + A)
Aesthetics Consideration and/or evaluation of the sensory quality of resources (e.g. sight & sound).

Approach Width: The half of the roadway that is approaching the roundabout. It is also referred to as approach half-width.
Approved Bike or Bicycle Route See bicycle route, approved
Arterial Functional classification for a street or highway that provides the highest level of service at the greatest speed for the longest uninterrupted distance, with some degree of access control.
Arterial, Rural see Rural Arterial
Arterial, Urban see Urban Arterial
Asymmetrical Having a different configuration on either side of a centerline
At Grade A crossing of two highways or a highway and a railroad at the same level.
Attenuator A device used on roads and highways that acts as a buffer and absorbs the energy of a collision with an automobile.
AutoTURN An advanced CAD-based software tool developed by TRANSoft Solutions used for analyzing and evaluating vehicle maneuvers for projects such as intersections, roundabouts, bus terminals, loading bays or any on or off-street projects that may involve access, clearance, and maneuverability checks. Additional information about AutoTURN ver 5.1 is available online at: http://www.transoftsolutions.com/transoft/pr oducts/at/product_overview.asp (TRANSoft, 2006).
Auxiliary Lane See Lanes Auxiliary.
Average Annual Daily Traffic (AADT) - The average 24-hour traffic volume at a given location over a full 365 day year. This means the total of vehicles passing the site in a year divided by 365.
Average Daily Traffic (ADT) The total volume during a given time period (in whole

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days), greater than one day and less than a year, divided by the number of days in that time period (GDOT Driveway Manual, 2004).
Average Annual Weekday Traffic (AAWT) The average 24-hour traffic volume occurring on weekdays over a full year.
Average Weekday Traffic (AWT) - The average 24-hour traffic volume occurring on weekdays for some period of time less than one year.
Axle Factor An adjustment factor that may be applied to traffic counts taken with portable traffic counters that account for two axle impacts as one vehicle. The Axle Factor provides for vehicles with more than two axles, such as trucks with three or more axles.
Backwater "The increase in water surface elevation relative to the elevation occurring under natural channel and floodplain conditions induced upstream from a bridge or other structure that obstructs or constricts a channel (GDOT Manual on Drainage Design, 2005)."
Base Conditions An assumed set of geometric and traffic conditions used as a starting point for computations of capacity and level of service (LOS).
Base Year The year the project is completed and anticipated to be open for traffic use.
Bicycle/Bike Route, Approved - any roadway where there is an existing bikeway or any location where a bicycle facility is identified for such roadway in a state, regional, or local transportation plan.
Bifurcate An asymmetrical median that typically exceeds a normal median width where both directions of the roadway have independent alignments. The median area may be very wide and may contain natural vegetation and topography. Recommended for use on rural interstates and freeways.

Big Box Retailer A large retail establishment (50,000+ sqft.) that is characteristic of a large windowless rectangular single-story building and large parking areas with few community or pedestrian amenities.
Broken Back Curves See Curves: Broken Back
Capacity the maximum hourly rate at which persons or vehicles reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a given period under prevailing roadway, traffic, and control conditions.
Centerline (1) For a two-lane road, the centerline is the middle of the traveled way; and for a divided road, the centerline may be the center of the median. For a divided road with independent roadways, each roadway has its own centerline. (2) The defined and surveyed line shown on the plans from which road construction is controlled.
Center Turn Lane See Lanes: Center Turn Lane.
Central Business District the commercial core of a city that can be typified by a concentration of commercial and retail land uses and the greatest concentration and number of pedestrians and traffic.
Central Island See Island, Central Island
Channelizing Island See Islands, Channelizing Island
Chevron Alignment Sign Sign that is typically used on a roadway indicate alignment, a curve, or intersection. Chevron Alignment Signs are characterized by single or multiple reflectorized arrows.
Circulatory Roadway: The roadway around the central island on which circulating vehicles travel in a counterclockwise direction. The width of the circulatory

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roadway depends mainly on the number of entry lanes and the radius of vehicle paths.
Clear Zone The area beyond the roadway edge of travel which provides an environment free of fixed objects, with stable, flattened slopes which enhance the opportunity for reducing crash severity. For further clarification on the definition of Clear Zone, refer to the current edition of the AASHTO Roadside Design Guide.
Cloverleaf Interchange See Interchanges, Cloverleaf Interchange.
Collector Functional classification for a street or highway that provides a less highly developed level of service than an arterial, at a lower speed for shorter distances by collecting traffic from local roads and connecting them with arterials.
Collector, Rural See Rural Collector.
Collector, Urban - See Urban Collector.
Collector-Distributor (CD) Road A parallel, controlled-access roadway that separates through traffic from local traffic that is entering and exiting the freeway or interstate system. CD roads are typically used to reduce conflicts associated with weaving.
Consensus a general agreement among the members of a given group or community.
Construction Standards A standard drawing published by GDOT and approved by FHWA.
Control of Access Regulating access (ingress and egress) from properties abutting highway facilities.
Full control of access Where preference is given to through traffic by providing access connections by means of ramps with only selected public roads and by prohibiting crossings at grade and direct driveway connections.

Partial control of access Where preference is given to through traffic to a degree. Access connections, which may be at-grade or grade-separated, are provided with selected public roads and private driveways.
CORSIM A comprehensive microscopic traffic simulation, applicable to surface streets, freeways, and integrated networks with a complete selection of control devices (i.e., stop/yield sign, traffic signals, and ramp metering). It simulates traffic and traffic control systems using commonly accepted vehicle and driver behavior models. (FHWA). Additional information about CORSIM can be found online at: http://ops.fhwa.dot.gov/trafficanalysistools/c orsim.htm
Cross Section The transverse profile of a road showing horizontal and vertical dimensions.
Cross Slope The rate of elevation change across a lane or a shoulder.
Crown
Normal Crown Roadway cross section which typically occurs when the roadway is a tangent section. No superelevation is present. Roadway cross slopes (typically 2%) in Georgia drain the roadway from either side of the pavement crown. The high point of the road is generally at the centerline or median, and the road slopes down from there.
Reverse Crown Roadway cross slope that occurs when the normal crown slope (typically 2%) is continuous across a roadway section. This typically occurs as a normal part of a superelevation transition.
Culvert Any structure under the roadway with a clear opening of 20 feet or less measured along the center of the roadway. Culverts are typically built to carry stormwater.

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Curb Cut Ramp A ramp that provides access between the sidewalk and the street for people who use wheelchairs which leads smoothly down from a sidewalk to a street, rather than abruptly ending with a curb and dropping roughly 4 to 6 inches (www.Wikepedia.org).
Curves
Broken Back Curves Successive curves in the same direction separated by a short tangent.
Circular Curve A curve that has an arc of a constant radius. Note: most horizontal curves on Georgia roadways are circular curves.
Compound Curve A curve that involves two horizontal curves of different radii sharing a common point for their PT and PC, respectively.
Reverse Curve A curve consisting of two arcs of the same or different radii curving in opposite directions and having a common tangent or transition curve at their point of junction. The tangent section between the two arcs has 0 length.
Spiral Curve see Transition Curve
Transition Curve A curve of variable radius intended to effect a smooth transition from tangent to curve alignment, also known as a Spiral Curve.
Vertical Curve A curve on the longitudinal profile of a road providing a change of gradient. Vertical curves are parabolic in shape.
dBA The noise levels in decibels measured with a frequency weighting network, corresponding to the "A-Scale" on a standard sound level meter.
Decision Sight Distance See Sight Distances: Decision Site Distance.

Department, The The Georgia Department of Transportation.
Departure Width - The half of the roadway that is departing the roundabout. It is also referred to as departure half-width.
Design Exception A design condition that does not meet AASHTO guidelines and requires specific approval from FHWA to be built.
Design Speed A selected speed used to determine the various geometric design features of a roadway. The maximum safe speed that can be maintained over a specified section of the road when conditions are so favorable that the design features of the road govern.
Design Variance A design condition that meets AASHTO guidelines, but does not meet GDOT policy. A design variance requires specific approval from the GDOT Chief Engineer to be built.
Design Vehicle A selected motor vehicle, the weight, dimensions, and operating characteristics of which are used as a control in road design. As defined by FHWA: the longest vehicle permitted by statute of the road authority (state or other) on that roadway (MUTCD, 2003).
Design Volume A volume determined for use in design, representing the traffic expected to use the road.
Design Year The anticipated future life of the project. For all GDOT projects, the design year is 20 years from the base year.
Diamond Interchange See Interchanges, Diamond Interchange.
Directional Interchange See Interchanges, Directional Interchange.
Diverging Dividing a single stream of traffic into separate streams.

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Divided Highway A highway, street or road with opposing directions of travel separated by a median.
Driver Expectancy What the typical driver would expect to encounter on a roadway.
Easement Area where GDOT purchases the rights to perform work on a section of property, but does not acquire title to the property.
Embankment An earthwork structure that raises the roadway higher than surrounding terrain.

Free Flow Traffic flow in which the speed of any driver is not impeded.
Free-Flow Speed The mean speed at which traffic travels when it is at free flow.
Freeway A controlled access highway system that provides non-interrupted flow of traffic.
Freeway Capacity - The maximum sustained 15-minute flow rate, expressed in passenger cars per hour per lane, that can be accommodated by a uniform freeway segment under prevailing traffic and roadway conditions in one direction of flow.

Enhancements Aesthetic additions to a project, such as trees or streetscaping.
Entry Radius: The minimum radius of curvature measured along the right curb at entry of a roundabout. Smaller radii may decrease capacity, while larger radii may cause inadequate entry deflection.
Entry Width: The perpendicular distance from the right curb line of the entry to the intersection of the left edge line and the inscribed circle of a roundabout.
Exit Radius: The minimum radius of curvature measured along the right curb at the exit of a roundabout.
Exit Width: The perpendicular distance from the right curb line of the exit to the intersection of the left edge line and the inscribed circle. Exits should be easily negotiable in order to keep traffic flowing through the roundabout and accelerate out of it. Exit radii should then be larger than entering radii.
Flat Spot Location in a superelevation transition where the pavement cross slope is 0%
Footcandle The illumination of a surface with an area of one sqft. on which is uniformly distributed a flux of one lumen. A footcandle is equivalent to one lumen per square foot.

Frontage Road "A road that segregates local traffic from higher speed through-traffic and intercepts driveways of residences, commercial establishments, and other individual properties along the highway (AASHTO Green Book, 2004, p. 339)."
Functional Classification The grouping of all streets and highways according to the character of traffic service that they are intended to provide. There are three highway functional classifications: arterial, collector, and local roads.
Geometric Design The arrangement of the visible elements of a road, such as alignment, grades, sight distances, widths, slopes, etc.
GDOT Policy A guideline adopted by the Georgia Department of Transportation that must be followed.
Glare Screen a partition, either continuous or a series of objects of such width and spacing, that is positioned on a median to block the glare from oncoming vehicle headlights.
Gore The paved area of a roadway between two merging or diverging travel lanes. Travel within the gore area is prohibited.
Grade (1) The profile of the center of the roadway, or its rate of ascent or descent.

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(2) To shape or reshape an earth road by means of cutting or filling. (3) Elevation.
Grade Separation A crossing of two highways or a highway and a railroad at different levels.
Green Book See AASHTO Green Book.
Gutter Width Distance between the edge of traveled way and the face of curb.
High Occupancy Vehicle Vehicles with two or more living, not pre-infant, persons.
High Water The elevation of the highest known specific flooding event at a specific location.
Highway A general term denoting a public way for purposes of vehicular travel, including the entire area within the right-ofway (NJDOT, 2006).
Highway Section The part of the highway included between top of slopes in cut and the toe of slopes in fill (NJDOT, 2006).
Horizontal Alignment Horizontal geometrics of the roadway.
Horizontal Clearance The lateral distance measured either from the traveled way or the face of curb, to the face of a roadside object or feature. The rural shoulder is the part of the roadway beyond the edge of travel that is graded or paved flush with the edge of travel to allow for emergency usage (AASHTO Roadside Design Guide, 2006).
Horizontal Curve A curve by means of which a road can change direction to the right or left.
Human Factors Driving habits, ability of drivers to make decisions, driver expectance, decision and reaction time, conformance to natural paths of movement, pedestrian use and habits, bicycle traffic use and habits.

Inscribed Circle: The circle formed just inside of the outer curb line of a circulatory roadway.
Interchange Area where grade separated roadways are connected, and at least one roadway is free flowing.
Cloverleaf Interchange An interchange that uses loop ramps to accommodate left-turns at an intersection and outer ramps to provide for the right turns.
Diamond Interchange An interchange that connects a free flowing major road with a minor road. Diamond interchanges typically consist of four one-way diagonal ramps, one in each quadrant and two at-grade intersections on the minor road. The minor road has two stop signs, two signals, or one stop sign and one signal.
Directional Interchange A free flowing interchange that allows vehicles to travel from one freeway to another freeway at relatively fast and safe speed.
Semi-directional Interchanges An interchange that provides indirect connection between freeways yet more direct connection than loops.
Service Interchange An interchange that connects a freeway to a lesser facility (such as a rest area or weigh station), as opposed to another freeway or minor road.
Three Leg Interchange Also known as T or Y interchanges, this type of interchange is where a major highway begins or ends.
System Interchange An interchange that connects a freeway to freeway.
Single Point Urban Interchange (SPUI) An interchange that features a

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GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

single traffic signal at the center of the interchange which controls all left turns. Opposing left-turn movements are completed simultaneously under the protection of this signal.
Intersection The general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area (AASHTO Green Book, 2004).
Intersection Sight Distance See Sight Distances: Intersection Sight Distance.
Islands: Devices used to separate or direct traffic in order to facilitate the safe and orderly movement of vehicles. An island may be a raised area that provides a physical barrier to channel traffic movements or a painted area. Specific types of islands include:
Central Island The roundabout island around which traffic circulates. The central island may either be raised (nontraversable) or flush (traversable). Its size is determined by the width of the circulatory roadway and the diameter of the inscribed circle. The width of any truck apron provided is included in the central island width.
Channnelizing Island - "At an intersection, the area defined by curbs, pavement markings, or unpaved areas formed by pavement edges for the purpose of directing traffic into defined paths, providing refuge areas for pedestrians or providing locations for traffic control devices (AASHTO Green Book, 2004)."
Splitter Island: An island placed within the approach leg of a roundabout to separate entering and exiting traffic, provide a refuge for crossing pedestrians and bicyclists, and prevent wrong way movements. It is usually designed with raised curbing to deflect, and thereby reduce the speed of, entering traffic, and to provide a safer refuge.

L10 A sound level that is exceeded 10 percent of the time for the period under consideration. This value is an indicator of both the magnitude and frequency of occurrence of the loudest noise events.
Lane Balance The condition where the number of lanes leaving a diverge is one more than the number of lanes approaching the diverge.
Lanes
Acceleration Lane - A speed-change lane, including tapered areas, for the purpose of enabling a vehicle entering the roadway to increase its speed to a rate at which it can more safely merge with through traffic. Also called an "accel lane" (GDOT Driveway Manual, 2004).
Auxiliary Lane The portion of the roadway adjoining the traveled way to help facilitate traffic movements: by providing for parking, speed change, turning, storage for turning, weaving, truck climbing, or for other purposes.
Center Turn Lane A lane within the median to accommodate left-turning vehicles.
Deceleration Lane A speed-change lane, including tapered areas, for the purpose of enabling a vehicle that is making an exit turn from a roadway to slow to a safe turning speed after it has left the mainstream of faster-moving traffic. Also called a "decel lane"; it denotes a right turn lane or a left turn lane into a development (GDOT Driveway Manual, 2004).
Left Turn Lane A speed-change lane within the median to accommodate left turning vehicles.
Inside Lane - On a multi-lane highway the extreme left hand traffic lane, in the direction of traffic flow, of those lanes available for traffic moving in one direction.

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Parking Lane An auxiliary lane primarily for the parking of vehicles.
Passing Lane
(1) A section of two-lane, two-directional road where sufficient clear sight distance exists to allow a safe passing maneuver to be performed.
(2) An additional (third) lane that has been added to a two-lane roadway specifically for passing.
Turn Lane A traffic lane within the normal surfaced width of a roadway, or an auxiliary lane adjacent to or within a median, reserved for vehicles turning left or right at an intersection.
Traffic Lane The portion of the traveled way for the movement of a single line of vehicles in one direction.
Letting The date GDOT opens sealed bids from prospective contractors.
Level of Service A qualitative rating of a road's effectiveness relative to the service it renders to its users (from A-best to F-worst). LOS is measured in terms of a number of factors, such as operating speed, travel time, traffic interruptions, freedom to maneuver and pass, driving safety, comfort, and convenience.
Lighting
High Mast Roadway Lighting Illumination of a large area by means of a group of luminaires designed to be mounted in fixed orientation at the top of a high mast, generally 80 feet or higher (AASHTO Roadway Lighting Design Guide, 2005).
Pedestrian Lighting Illumination of public sidewalks for pedestrian traffic generally not within rights-of-way for vehicular traffic roadways. Included are skywalks (pedestrian overpasses), sub-walks (pedestrian tunnels), walkways giving

access to park or block interiors and crossings near centers of long blocks (AASHTO Roadway Lighting Design Guide, 2005).
Roadway Lighting - Illumination of roadways by means of fixed luminaires in order to reduce driver conflict with other vehicles and pedestrians.
Limited Access Facility A street or highway to which owner or occupants abutting land have little or no right of access.
Local Road Functional classification that consists of all roads not defined as arterials or collectors; primarily provides access to land with little or no through movement.
Longitudinal Barrier A barrier that is intended to safely redirect an errant vehicle away from a roadside or median hazard (CODOT, 2006)
Loop Detector A traffic monitoring tool that is used to detect the presence of vehicles at an intersection to activate a traffic signal.
Median The portion of a divided roadway separating the traveled ways for traffic in opposite directions (NJDOT, 2006).
Median Crossover An opening constructed in the median strip of a divided highway designed to allow traffic movements to cross from one side of the highway to the other. In some cases, the Access Management Engineer may require the design to be such that some movements be physically prohibited (GDOT Driveway Manual, 2004).
Median Width The overall width of a median measured from edge of travel lane to edge of travel lane.
Merging The converging of separate streams of traffic to a single stream.

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Mitigation sequentially avoiding impacts, minimizing impacts, and compensating for any unavoidable impacts (WSDOT, 2005).
Mitigation Plan document(s) that contain all information and specifications necessary to fully implement and construct a compensatory mitigation project (WSDOT, 2005).
Nominal Safety A design alternative's adherence to design criteria and standards.
Normal Crown See Crown: Normal Crown
Operating Speed Actual speed at which traffic flows.
Pace Speed The highest speed within a range of speeds (typically within 10 mph) that represents more vehicles than in any other like range of speed (FHWA MUTCD, 2003)
Parametrics A modeling platform with application areas that include urban, highway, public transport, congested, free flow, ITS and HOV. Additional information about Parametrics is available online at: http://www.parametrics.com
Parking Lane See Lanes: Parking Lane
Passenger Car A passenger automobile with similar size and operating characteristics of a car, sport/utility vehicle, minivan, or pickup truck.
Passing Lane See Lanes: Passing Lane.
Passing Sight Distance See Sight Distances: Passing Sight Distance.
Pavement Markings Devices or paint placed on the roadway to mark pavement for vehicular and pedestrian traffic control.
Pedestrian Georgia State law defines a Pedestrian as: "Any person who is afoot" (GLC 40-1-1). By state definition, roller skaters, in-line skaters, skateboarders, and

wheelchair users are also considered pedestrians.
Pedestrian Refuge Also referred to as a refuge island/area or pedestrian island, is a section of pavement or sidewalk where pedestrians can stop before finishing crossing a road (www.wikipedia.org).
Permit A legal document issued by the Department authorizing an applicant to do specific work on state rights-of-way (GDOT Driveway Manual, 2004).
Posted Speed The speed limit posted on a section of roadway.
Preventative Maintenance (PM) Projects the planned strategy of cost effective treatments to an existing roadway system and its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system without increasing structural capacity.
Profile A longitudinal section of a roadway, drainage course, etc.
Profile Grade Line The point for control of the vertical alignment. Also, normally the point of rotation for superelevated sections (NJDOT, 2006).
Project "A portion of a highway that a State proposes to construct, reconstruct, or improve as described in the Preliminary Design Report or applicable Environmental Document (FHWA VE Website, 2005)."
Queue When one or more vehicles is traveling less than 7 mph. (SimTraffic, 2006) A vehicle is considered queued when it is either stopped at a traffic light or stop sign or behind another queued vehicle.
Ramp Metering Use of a traffic control device for the intent of regulating the flow of traffic entering a freeway. The device, which is typically a traffic signal or a two-phase (red

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GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

and green, no yellow) light, prevents multiple vehicles entering a freeway ramp.
Reaction Time "The time from the onset of a stimulus to the beginning of a driver's (or pedestrian's) response to the stimulus, by a simple movement of a limb or other body part. (FHWA, 2001 http://www.tfhrc.gov/safety/pubs/97135/glos sary.htm#r)."
Retaining Wall A structure that prevents dirt from sliding or eroding.
Reverse Crown See Crown: Reverse Crown
Reverse Curve See Curves: Reverse Curve
Right-of-way (ROW or R/W) - All land under the jurisdiction of, and whose use is controlled by the Department (GDOT Driveway Manual, 2004).
Right-of-Way Flares Areas needed for sight distance triangles at an intersection that should be kept free of obstructions in order to provide adequate sight distance.
Roadside The area adjoining the outer edge of the roadway (NJDOT, 2006).
Roadway The portion of a highway, including shoulders, for vehicle use (NJDOT, 2006).
Roadway Characteristics The geometric characteristics of the freeway segment under study, including the number and width of lanes, right-shoulder lateral clearance, interchange spacing, vertical alignment, and lane configurations.
Running Speed For all traffic, or a component thereof, the summation of distances traveled divided by the summation of running time.
Rural Area "Those areas outside the boundaries of urban areas (AASHTO Green Book, 2004)."

Rural Arterial Functional classification for a street or highway that integrates interstate and inter-county service, provides for movements between urban areas, and provides for relatively high travel speeds with minimum interference to through movement (AASHTO Green Book, 2004).
Rural Collector - A street or highway that "generally serves travel of primarily intracounty rather than statewide importance and constitute those routes on which (regardless of traffic volume) predominant travel distances are shorter than on arterial routes. Consequently, more moderate speeds may be typical, on the average (AASHTO Green Book, 2004)."
Rural Section Any roadway without curb and gutter.
Rural Shoulder The part of the roadway beyond the edge of travel that is graded or paved flush with the edge of travel to allow for emergency usage.
Semi-Directional Interchange See Interchanges, Semi-Directional Interchange
Service Interchange See Interchanges, Service Interchange.
Shoulder The portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles, for emergency use, and for lateral support of base and surface courses (NJDOT, 2006).
Shoulder Rumble Strip "A longitudinal design feature installed on a paved roadway shoulder near the travel lane. It is made of a series of indented or raised elements intended to alert inattentive drivers through vibration and sound that their vehicles have left the travel lane. On divided highways, they are typically installed on the median side of the roadway as well as on the outside (right) shoulder (FHWA, 2001, Roadway Shoulder Rumble Strips Technical Advisory Website

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GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

http://www.fhwa.dot.gov/legsregs/directives/ techadvs/t504035.htm)."
Sidewalk The portion of a street between the curb lines, or the lateral lines of a railway, and the adjacent property lines, intended for use by pedestrians (Georgia Code and Rules 40-1-1).
Sight Distances The length of roadway ahead visible to a driver.
Decision Sight Distance Sight distance that allows a driver to determine and complete the most efficient maneuver in response to an unexpected condition
Intersection Sight Distance Sight distance needed for decisions at complex locations such as intersections. Values are substantially greater than Stopping Sight Distance.
Passing Sight Distance Sight distance needed for passing other vehicles (applicable only on two-way, two-lane highways at locations where passing lanes are not present).
Stopping Sight Distance - Sight distance needed for a driver to see an unexpected condition and stop the vehicle. At a minimum, Stopping Sight Distance is required at all locations on all roadways.
Sight Distance Triangle Specified areas along intersection approach legs and across their included corners that should remain clear of obstructions. (AASHTO Green Book, 2004)
Slope The face of an embankment or cut section; any ground the surface of which makes an angle with the plane of the horizon.
Speed Design See Design Speed
Speed Zone a section of highway with a speed limit that is established by law but which might be different from a legislatively

specified statutory speed limit (FHWA MUTCD, 2003).
Spiral See Curves: Transition Curve
Standard Criteria having recognized and usually permanent values which are established formally as a model or requirement.
Stopping Sight Distance See Sight Distances: Stopping Sight Distance.
Superelevation The elevating of the outside edge of a curve to partially offset the centrifugal force generated when a vehicle rounds the curve.
Superelevation Runoff "The length of roadway needed to accomplish a change in outside lane cross slope from zero (flat) to full superelevation, or vice versa (AASHTO Green Book, 2004, p. 175). "
Superelevation (Tangent) Runout The longitudinal distance required to transition between normal crown and 0% cross slope (or vice versa).
Superelevation Transition "The superelevation runoff and tangent run out sections (AASHTO Green Book, 2004, p. 175)."
Sustained Grade A continuous road grade of appreciable length and consistent, or nearly consistent, gradient.
Synchro software application used for traffic analysis, specifically to optimize traffic signal timing and perform capacity analyses. The software supports the Universal Traffic Data Format (UTDF) for exchanging data with signal controller systems and other software packages.
System Interchange See Interchanges, System Interchange
T Interchange - See Interchanges, Three-Leg Interchange

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GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

Traffic Characteristics any characteristic of the traffic stream that may affect capacity, free-flow speed, or operations, including the percentage composition of the traffic stream by vehicle type and the familiarity of drivers with the freeway.
Traffic Control Device A sign, signal, marking or other device placed on or adjacent to a street or highway by authority of a public body or official having jurisdiction to regulate, warn, or guide traffic.
Traffic Lane See Lanes: Traffic Lane.
Transfer Road A road that connects core roadways and C-D roads
Transition A section of variable pavement width required when changing from one width of traveled way to a greater or lesser width.
Transition Curve See Curves: Transition Curve
Traveled Way The portion of the roadway provided for the movement of vehicles, exclusive of shoulders, auxiliary lanes and bicycle lanes (NJDOT, 2006).
Truck Apron The mountable portion of a roundabout central island that is drivable specifically provided to accommodate the path of the rear left wheels of larger vehicles.
Turn Lane See Lanes: Turn Lane.
Turning Path The path of a designated point on a vehicle making a specified turn.
Urban Area "Places within boundaries set by the responsible State and local officials having a population of 5,000 or more (AASHTO Green Book, 2004)."
Urban Arterial Functional classification for a street or highway that serves urbanized areas and provides the highest level of service at the greatest speed for the longest

uninterrupted distance, with some degree of access control.
Urban Collector A street or highway that provides both land access service and traffic circulation within residential neighborhoods, commercial or industrial areas. It differs from the arterial system in that facilities on a collector system may penetrate residential neighborhoods, distributing trips from the arterials through the area to the ultimate destination. Conversely, the collector street also collects traffic from local streets in residential neighborhoods and channels it into the arterial system (AASHTO Green Book, 2004).
Urban Roadway A roadway that is classified functionally as an Urban Arterial, Urban Collector, or Urban Local Street that operates at speeds generally less than or equal to 45 mph and features curb and gutter.
Urban Shoulder The part of an urban roadway beginning at the edge of travel and extending to the breakpoint of the fore slope or back slope that ties to the natural terrain.
Value Engineering "The systematic application of recognized techniques by a multi-disciplined team to identify the function of a product or service, establish a worth for that function, generate alternatives through the use of creative thinking, and provide the needed functions to accomplish the original purpose of the project, reliably, and at the lowest life-cycle cost without sacrificing safety, necessary quality, and environmental attributes of the project. (CFR Title 23 Part 627). "
Variance See Design Variance.
Vertical Alignment (Profile Grade) The trace of a vertical plane intersecting the top surface of the proposed wearing surface, usually along the longitudinal centerline of the roadbed, being either elevation or

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GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

gradient of such trace according to the context.
Vertical Curve See Curves: Vertical Curve.
Weaving The crossing of two or more traffic streams traveling in the same general direction along a significant length of highway without the aid of traffic control devices (with the exception of guide signs). Weaving segments are formed when a merge area is closely followed by a diverge area, or when an on-ramp is closely followed by an off-ramp and the two are joined by an auxiliary lane. (TRB Highway Capacity Manual, 2000)
Work Zone The work area and the section of highway used for traffic control devices related to the work area (NJDOT, 2006).
Yield Line: A broken line marked across the entry roadway where it meets the outer edge of the circulatory roadway and where entering vehicles wait, if necessary, for an acceptable gap to enter the circulating flow.
Y Interchange - See Interchanges, Three-Leg Interchange.

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References

Referenced Publications

This section includes reference information, descriptions of publications, and where available, links to referenced publications. Publications are listed alphabetically by source.
Page

American Association of State Highway and Transportation Officials (AASHTO)

1

AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). 2004

1

AASHTO. A Policy on Design Standards---Interstate System, 5th Edition. 2005

1

AASHTO. Guide for the Development of Bicycle Facilities, 3rd Edition. 1999

1

AASHTO. Guide for High-Occupancy Vehicle (HOV) Facilities, 3rd Edition. 2004

1

AASHTO. Guide for Park-and-Ride Facilities, 2nd Edition. 2004

1

AASHTO. Guide Specifications for Horizontally Curved Steel Girder Highway Bridges. 2003

2

AASHTO. Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400), 1st Edition. 2001

2

AASHTO. Highway-Rail Crossing Elimination and Consolidation. 1995

2

AASHTO. Roadside Design Guide, 3rd Edition. 2006.

2

AASHTO. Roadway Lighting Design Guide. 2005

2

AASHTO. Standard Specifications for Highway Bridges, 17th Edition. 2002

2

American Railway Engineering and Maintenance of Way Association (AREMA)

3

AREMA. Manual for Railway Engineering. 2006

3

Federal Highway Administration (FHWA)

3

FHWA. Americans with Disabilities Act (ADA) and Transportation Enhancements (TE). 2006

3

FHWA. Flexibility in Highway Design. 2004

3

FRA/FHWA. Guidance On Traffic Control Devices At Highway-Rail Grade Crossings. 2002

3

FRA/FHWA. Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure. 1994

3

FHWA. Highway Traffic Noise in the United States - Problem and Response. 2006

3

FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003

3

FHWA. Roundabouts: An Informational Guide FHWA-RD-00-67. 2000

3

FHWA. Value Engineering and The Federal Highway Administration (Website). 2005

3

FHWA. Roadway Lighting Handbook. 1978

3

Georgia Department of Transportation

3

GDOT. Bridge and Structures Policy Manual. 2006 GDOT. DRAFT Manual on Drainage Design for Highways. 2005 GDOT. Construction Standards and Details. 2006 GDOT. GDOT Context Sensitive Design Online Manual, Version 1.0. 2006 GDOT. Environmental Procedures Manual. 2006 GDOT. DRAFT Pavement Design Manual. 2005 GDOT. Pedestrian and Streetscape Guide. 2003 GDOT. Plan Development Process (PDP). 2006 GDOT. Plan Presentation Guide. 2002 GDOT. Regulations for Driveway and Encroachment Control. 2006 GDOT. GDOT Standard Specification Book. 2001 GDOT. Traffic Analysis and Design Manual. 2006 GDOT. Traffic Signal Design Guidelines. 2003 GDOT. Utility Accommodation Policy and Standards Manual. 1988

3 3 3 3 4 4 4 4 4 4 4 Error! Bookmark not defined.4 4 4

GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

References

i

Georgia Soil and Water Conservation Commission (GSWCC)

4

Georgia Soil and Water Conservation Commission. Manual for Erosion and Sediment Control in Georgia, 5th Edition. 2000

4

Illuminating Engineering Society of North America (IESNA)

5

IESNA. Guideline for Security Lighting for People, Property and Public Spaces (G-1-03). 2005

5

IESNA. Lighting Handbook, 9th Edition. 2000

5

IESNA. Lighting For Parking Facilities (RP-20-98). 1998

5

IESNA. Recommended Lighting for Walkways. 1994

5

IESNA. Recommended Lighting for Walkways and Class 1 Bikeways (DG-5-94). 1994

5

IESNA. Roadway Lighting ANSI Approved (RP-8-05). 2005

5

IESNA. Roadway Sign Lighting (RP-19 -01). 2001

5

IESNA/AHNSI. Tunnel Lighting (RP-22-05). 2005

5

Institute of Transportation Engineers (ITE)

5

ITE. Manual of Uniform Transportation Engineering Studies. 2000

5

ITE. Trip Generation Handbook, 7th Edition. 2003

6

National Cooperative Highway Research Program (NCHRP)

6

NCHRP. Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504]. 2003

6

NCHRP. Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457]. 2001

6

NCHRP. Impacts of Access Management Techniques [NCHRP Project 3-52]. 1998

6

NCHRP. Modern Roundabout Practices [Synthesis 264]. 1996

Error! Bookmark not defined.6

NCHRP. Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report 350]. 1992

6

National Fire Protection Association (NFPA)

6

NFPA. National Electrical Code [NFPA-70]. 2005

6

Texas Transportation Institute (TTI)

6

TTI. Grade Separations - When Do We Separate? Highway-Rail Crossing Conference. 1999

6

Transportation Research Board (TRB)

7

TRB. Highway Capacity Manual. 2000

7

GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

References

ii

American Association of State Highway and Transportation Officials (AASHTO)
AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). 2004
This publication may be ordered online at: https://bookstore.transportatio n.org/item_details.aspx?ID=1 10
Notes: ISBN Number: 156051-263-6 "This fifth edition of AASHTO's `Green Book' contains the latest design practices in universal use as the standard for highway geometric design and has been updated to reflect the latest research on superelevation and side friction factors as presented in NCHRP Report 439" (AASHTO, 2006).
AASHTO. A Policy on Design Standards--Interstate System, 5th Edition. 2005
This publication may be ordered online at: https://bookstore.transpor tation.org/item_details.as px?ID=100
Notes: ISBN Number: 156051-291-1 "Complements A Policy on Geometric Design of Highways and Streets and Standard Specifications for Highway Bridges. Topics include traffic design, right-of-way, geometric controls and criteria, cross section elements, interchanges, and bridges and other structures" (AASHTO, 2006).
AASHTO. Guide for the Development of Bicycle Facilities, 3rd Edition. 1999
This publication in hard copy or CD format may be ordered online at: https://bookstore.transportatio n.org/ item _details.aspx?ID=104

development of new facilities to enhance and encourage safe bicycle travel. Planning considerations, design and construction guidelines, and operation and maintenance recommendations are included" (AASHTO, 2006).
AASHTO. Guide for HighOccupancy Vehicle (HOV) Facilities, 3rd Edition. 2004
This publication may be ordered online at: https://bookstore.transportatio n.org/item_details.aspx?ID=1 14
Notes: ISBN Number: 156051-295-4 "This guide suggests methods and designs for dedicated facilities to encourage greater use of existing transportation systems, such as increased use of public transit (primarily buses), carpools, vanpools, or other ridesharing modes to help attain the above goals. Guidance is given for planning and design of preferential treatment for high-occupancy vehicles" (AASHTO, 2006).
AASHTO. Guide for Parkand-Ride Facilities, 2nd Edition. 2004
This publication may be ordered online at: https://bookstore.transporta tion.org/item_details.aspx?I D=121
Notes: ISBN Number: 156051-294-6 "Information presented in this guide is intended to provide a general knowledge of the park-and-ride planning and design process. Applicable local ordinances, design requirements, and building codes must be consulted for their affect on the planning and design process. Local data resources, development patterns, and transit networks may present unique opportunities for parkand-ride implementation, and should be explored.

Notes: "Supersedes the 1981 Guide for Development of New Bicycle Facilities. Provides information on the

GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

References

1

Chapter content includes: Defining the Park-and-Ride System, Park-and-Ride Planning Process, Operations and Maintenance of Park-and-Ride Facilities, Design Considerations for Park-and-Ride Facilities, and Architecture, Landscape, and Art: Integral Parts of the Park-and-Ride Facility" (AASHTO, 2006).
AASHTO. Guide Specifications for Horizontally Curved Steel Girder Highway Bridges. 2003
Notes: [GHC-4] "Now with step-by-step design examples, this title supercedessupersedes the 1993 edition of Guide Specifications for Horizontally Curved Highway Bridges (formerly GHC-3). It reflects the extensive research on curved-girder bridges that has been conducted since 1980 and many important changes in related provisions of the straight-girder specifications" (Techstreet.com, 2006).
This publication may be ordered online at: http://www.techstreet.com/cgibin/detail?product_id=1083781
AASHTO. Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400), 1st Edition. 2001
This publication may be ordered online at: https://bookstore.transportati on.org/item_details.aspx?ID= 157
Notes: "[This publication] addresses the unique design issues highway designers and engineers face when determining appropriate costeffective geometric design policies for very low-volume local roads. This approach covers both new and existing construction projects. Because geometric design guidance for very low-volume local roads differs from the policies applied to high-volume roads, these guidelines may be used in lieu of A Policy on Geometric Design of Highways and Streets, also known as the Green Book" (AASHTO, 2006).
AASHTO. Highway-Rail Crossing Elimination and Consolidation. 1995
Explains the purpose and benefits of crossing consolidation from a national and local perspective, and from a highway and railroad perspective.
Additional information regarding this publication is available online at: http://safety.transportation.org/prgpub.aspx?pid=1855

AASHTO. Roadside Design Guide, 3rd Edition. 2006.
This publication may be ordered online at: https://bookstore.transportati on.org/item_details.aspx?ID= 148
Notes: ISBN Number: 156051-132-X "A synthesis of current information and operating practices related to roadside safety presented both in metric and U.S. customary units. The searchable CD-ROM of the text is included" (AASHTO, 2006). Includes March 2006 errata and also includes a revised Appendix A to accompany RSAP. This revised Appendix A is available for download at: http://downloads.transportation.org/RSDG-3Appendix%20A%20(revised).pdf
AASHTO. Roadway Lighting Design Guide. 2005
Notes: [GL-6] This guide replaces the 1984 publication entitled An Informational Guide for Roadway Lighting. It has been revised and brought up to date to reflect current practices in roadway lighting. The guide provides a general overview of lighting systems from the point of view of the transportation departments and recommends minimum levels of quality. The guide incorporates the illuminance and luminance design methods, but does not include the small target visibility (STV) method.
AASHTO. Standard Specifications for Highway Bridges, 17th Edition. 2002
Notes: "Replaces the 16th edition and its interims (19972003). The structural design standards used by state bridge engineers, engineering colleges and universities, and practicing engineers worldwide. Now features separate tables of contents for figures and tables. Updates provided on bridge web site for download and printing. For the first time, includes easy-to-use CD-ROM (HB-17-CDM)" (www.AASHTO.org).
Additional information regarding this publication is available online at: https://bookstore.transportation.org/item_details.aspx?I D=51

GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007

References

2

American Railway Engineering and Maintenance of Way Association (AREMA)

FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003
Available online at: http://mutcd.fhwa.dot.gov/kno2003r1.htm

AREMA. Manual for Railway Engineering. 2006
Notes: A new manual is published each year. The full manual or individual chapters may be ordered online through AREMA at http://www.arema.org
Federal Highway Administration (FHWA)
FHWA. Americans with Disabilities Act (ADA) and Transportation Enhancements (TE). 2006
Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements: http://www.fhwa.dot.gov/environment/te/te_ada.htm
FHWA. Flexibility in Highway Design. 2004
Available online at: http://www.fhwa.dot.gov/envir onment/flex/
FRA/FHWA. Guidance on Traffic Control Devices at Highway-Rail Grade Crossings. 2002
Available online at: http://safety.fhwa.dot.gov/media/twgreport.htm
FRA/FHWA. Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure. 1994
Information regarding this publication is available online at: http://www.fra.dot.gov/downloads/Safety/gxlistofpubs20 06.pdf
FHWA. Highway Traffic Noise in the United States Problem and Response. 2006
Available online at: http://www.fhwa.dot.gov/environment/probresp.htm

FHWA. Roundabouts: An Informational Guide FHWARD-00-67. 2000
Available online at: http://www.tfhrc.gov/safety/00068.htm
FHWA. Value Engineering and The Federal Highway Administration (Website). 2005
Available online at:
http://www.fhwa.dot.gov/ve/index.cfm
FHWA. Roadway Lighting Handbook. 1978
Notes: Implementation Package 78-15. Reprinted April 1984. Washington, D.C.
Georgia Department of Transportation
GDOT. Bridge and Structures Policy Manual. 2006
Available online at: http://www.dot.state.ga.us/dot /preconstruction/r-o-a-ds/DesignPolicies/ documents/pdf/GDOT%20Bri dge%20and%20Structures% 20Policy%20Manual.pdf
GDOT. DRAFT Manual on Drainage Design for Highways. 2005
Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies /documents/pdf/GA8-ALL.pdf
GDOT. Construction Standards and Details. 2006
Construction Standards and Details are available online at: http://tomcat2.dot.state.ga.us/stds_dtls/index.jsp
GDOT. GDOT Context Sensitive Design Online Manual, Version 1.0. 2006
Available online at: http://www.dot.state.ga.us/csd

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GDOT. Environmental Procedures Manual. 2006
Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/documents/pdf/GDOT%20Environme ntal%20Procedures%20Manual.pdf
GDOT. Pavement Design Manual. 2007
Provides guidance for developing the history and necessary information that may be needed in designing both a rigid and flexible pavement structure.
Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/documents/pdf/Pavement%20Design %20Manual.pdf
GDOT. Pedestrian and Streetscape Guide. 2003
Provides direction to design professionals, developers, municipalities and others regarding the design, construction, and maintenance of pedestrian facilities. The Guide will also aid in continuing to address the goals put forth in GDOT's 1995 Bicycle and Pedestrian Plan.
Available online at: http://www.dot.state.ga.us/dot/planprog/planning/projects/bicycle/ped_streetscape_guide/i ndex.shtml
GDOT. Plan Development Process (PDP). 2006
Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/Other%20Resources/index.shtml
GDOT. Plan Presentation Guide. 2002
Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/PPC/index.shtml
GDOT. Regulations for Driveway and Encroachment Control. 2006
GDOT regulations, which are developed as guidelines for the maximum protection of the public through orderly control of traffic entering and leaving a part of the State highway system, updated October 2006.

Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/index.shtml
GDOT. GDOT Standard Specification Book. 2001
This publication may be ordered through the GDOT Office of Contract Administration at: http://tomcat2.dot.state.ga.us/ContractsAdministration/
The order form for this and other specification publications may be downloaded from: http://tomcat2.dot.state.ga.us/ContractsAdministration/u ploads/availpub.PDF
GDOT. Traffic Signal Design Guidelines. 2003
Published by the GDOT Office of Traffic Safety and Design. Available online at: http://www.dot.state.ga.us/dot/operations/traffic-safetydesign/Documents/PDF/1.%20Traffic%20Signal%20De sign%20Guidelines.pdf
GDOT. Utility Accommodation Policy and Standards Manual. 1988
Contains the current policy of the Georgia DOT Office of Utilities regarding utility accommodation on the public highway right-of-way.
The three-part document and addenda are available online at: http://www.dot.state.ga.us/dot/operations/utilities/88ma nual.shtml
Georgia Soil and Water Conservation Commission (GSWCC)
Georgia Soil and Water Conservation Commission. Manual for Erosion and Sediment Control in Georgia, 5th Edition. 2000
Entire document (note: this is a 47.9 megabyte file, and will take several minutes to load on a high-speed Internet connection): http://s150378756.onlinehome.us/docs/green_book_5e d.pdf or Document index:

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http://gaswcc.georgia.gov/00/topic_index_channel/0,20 92,28110777_29155149,00.html#M
Illuminating Engineering Society of North America (IESNA)
IESNA. Guideline for Security Lighting for People, Property and Public Spaces (G-1-03). 2005
Guideline for design and implementation of security lighting, which covers basic security principles, illuminance requirements for various types of properties, protocol for evaluating current lighting levels for different security applications, and security survey and crime search methodology. Also includes exterior and interior security lighting practices for the reasonable protection of persons and property.
Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=1098026
IESNA.. Lighting Handbook, 9th Edition. 2000
Referred to by industry professionals as the "Bible of Lighting." This comprehensive reference includes explanations of concepts, techniques, applications, procedures and systems, as well as detailed definitions, tasks, charts and diagrams. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=229514
IESNA. Lighting For Parking Facilities (RP-20-98). 1998
A guideline for designing fixed lighting for parking facilities. Its recommendations only apply to the design of new lighting systems for parking facilities. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14417
IESNA. Recommended Lighting for Walkways. 1994
A guideline for designing fixed lighting for parking facilities. Its recommendations only apply to the design of new lighting systems for parking facilities. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14320

IESNA. Recommended Lighting for Walkways and Class 1 Bikeways (DG-5-94). 1994
Consolidates references made in previous IESNA publications with certain new information for designing lighting systems for walkways and Class I bikeways.
Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14320
IESNA. Roadway Lighting ANSI Approved (RP-8-05). 2005
Provides the design basis for lighting roadways, adjacent bikeways, and pedestrian ways. This publication deals entirely with lighting and does not give advice on construction. It is not intended to be applied to existing lighting systems until such systems are redesigned. This publication revises and replaces the previous edition which was published in 1983 and reaffirmed in 1993.
Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=739518
IESNA. Roadway Sign Lighting (RP-19 -01). 2001
A guideline that discusses elements of roadway sign lighting, both internally and externally lighted signs, as well as maintenance factors, sign surface reflectance and color change considerations.
Publication may be ordered online through IESNA at: http://www.techstreet.com/cgibin/detail?product_id=926898
IESNA/AHNSI. Tunnel Lighting (RP-22-05). 2005
A guideline to assist engineers and designers in determining lighting needs, recommending solutions, and evaluating resulting visibility at tunnel approaches and interiors.
Publication may be ordered online through IESNA at: http://www.techstreet.com/cgibin/detail?product_id=1260805
Institute of Transportation Engineers (ITE)
ITE. Manual of Uniform Transportation Engineering Studies. 2000
Additional information and order forms for this publication are available online at: http://www.ite.org/tripgen/trippubs.asp

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Notes: "Shows in detail how to conduct several transportation engineering studies in the field. Discusses experimental design, survey design, statistical analyses, data presentation techniques, and report writing concepts. Provides guidelines for both oral and written presentation of study results. Includes useful forms for various transportation studies. Proceeded by the Manual of Traffic Engineering Studies" (www.ite.org, n.d.).
ITE. Trip Generation Handbook, 7th Edition. 2003
Additional information and order forms for this publication are available online at: http://www.ite.org/tripgen/trippubs.asp
Notes: "The 7th Edition of Trip Generation includes numerous updates to the statistics and plots published in the 6th Edition. A significant amount of new data has been collected and several new land uses have been added" (www.ite.org, n.d.).
National Cooperative Highway Research Program (NCHRP)
NCHRP. Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504]. 2003
Available online at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_50 4.pdf
NCHRP. Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457]. 2001
An enhanced online version of the report is available at http://onlinepubs.trb.org/onlinepubs/ nchrp/esg/esg.pdf
NCHRP. Impacts of Access Management Techniques [NCHRP Project 3-52]. 1998
This report may be ordered online through TRB's website at: http://www.trb.org/trbnet/projectdisplay.asp?projectid=7 97
NCHRP. Modern Roundabout Practices [Synthesis 264]. 1996
"This synthesis presents information on current practices with respect to the planning, design, and operation of modern roundabouts in the United States. It will be of interest to state and local highway design

engineers, traffic engineers, maintenance engineers, as well as officials concerned with roadway safety. It will also be useful to design and traffic engineering consultants who may be assisting communities with the implementation of roundabouts" (www.TRB.org, n.d.).
Available online at: http://trb.org/publications/nchrp/nchrp_syn_264.pdf
NCHRP. Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report 350]. 1992
This document is no longer in print, but may be accessed through the following link: http://safety.fhwa.dot.gov/roadway_dept/road_hardwar e/nchrp_350.htm.
National Fire Protection Association (NFPA)
NFPA. National Electrical Code [NFPA-70]. 2005
This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for: (1) Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings (2) Yards, lots, parking lots, carnivals, and industrial substations FPN to (2).
Publication may be ordered online at: http://www.nfpa.org/aboutthecodes/AboutTheCodes.as p?DocNum=70 or through the IENSA website at: http://www.techstreet.com/cgibin/detail?product_id=1160845
Texas Transportation Institute (TTI)
TTI. Grade Separations - When Do We Separate? Highway-Rail Crossing Conference. 1999
Available online through the Texas Transportation Institute at: http://tti.tamu.edu/publications/catalog/

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Transportation Research Board (TRB)
TRB. Highway Capacity Manual. 2000
This publication may be ordered online at: http://trb.org/news/blurb_detai l.asp?id=1166
Notes: "TRB Special Report 209: Highway Capacity Manual, 3rd Edition is a collection of state-of-the-art techniques for estimating capacity and determining level of service for many transportation facilities and modes. The 3rd Edition of this manual was updated in 2000 as Highway Capacity Manual 2000" (TRB, 2006).

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