The National Academies

NCHRP 07-29 [Pending]

Development of the 8th Edition of AASHTO's A Policy on the Geometric Design of Highways and Streets (Green Book)

  Project Data
Funds: $1,000,000
Contract Time: 24 months
Staff Responsibility: B. Ray Derr

The objective of this research is to develop a draft 8th Edition Green Book (GB8) suitable for balloting through AASHTO processes.


Proposals have been received and are under review by the project oversight panel.
The research plan shall include delivery of:
  • White paper concisely stating the purpose of the GB8 and how it is intended to be used by designers, other transportation professionals, and agency policy makers. Of particular interest is balancing practitioners’ need for clear guidance when approaching a project while encouraging flexibility and good judgment in addressing the project’s unique challenges. 
  • A map of AASHTO documents related to the Green Book that describes their relationships, identifies overlapping or shared topics, and recommends approaches to establishing and maintaining consistency and coherence for the interfaces and joint topics. Relationships to other national “standards” (e.g., Manual on Uniform Traffic Control Devices, Highway Capacity Manual, Highway Safety Manual, Design Guides developed by the National Association of City Transportation Officials (NACTO) and the Institute of Transportation Engineers (ITE)) and U.S. Department of Transportation policies and regulations should also be described.
  • An Authors’ Guide for the GB8 to promote consistency across the writing team. The Authors’ Guide should include, at a minimum, (1) a consistent approach to document layout; (2) glossary of terms and phrases to be used and avoided in the GB8; (3) principles and specifications for graphics, pictures, and drawings to more effectively convey information to readers; and (4) document template for carrying content from draft to publication. The Authors’ Guide should draw upon experiences with the NACTO, ITE, and other publications that have adopted new presentation approaches for technical material.
  • Review of research and other efforts that could be expected to provide content suitable for inclusion in the GB8. This review should include the likelihood that the material will be available in time to be incorporated into the development and review process.
  • An annotated outline for the GB8 that shows how GB7 content will be incorporated into the new context-based structure. Parts I and II should present a cohesive approach that addresses the goals and principles outlined in the Background. In addition, those parts should address: (1) identification of challenges posed by the project (e.g., state of good repair, safety, mobility, resilience, equity, public health); (2) selection of appropriate performance measures given the facility’s context and role within the network; (3) approaches to trading off among these performance measures and other considerations across modes (including their use in design-build projects); and (4) documentation of design decisions. The outline should consider how new technologies (e.g., automated vehicle technologies, Mobility as a Service, micromobility) should be addressed in the GB8 and subsequent editions, recognizing how other documents can complement the GB8.
  • A communication and outreach plan for critical AASHTO and other groups that includes the objectives of interacting with each group. These groups will include the AASHTO Technical Committee on Geometric Design, Committee on Design, Council on Highways and Streets, Council on Active Transportation, committees responsible for AASHTO documents with critical relationships to the Green Book, the FHWA, ITE, NACTO, and AAMPO. AASHTO staff may be able to help in coordinating amongst AASHTO groups.
  • Review plan that concentrates on the project oversight panel and the AASHTO Technical Committee on Geometric Design. The AASHTO Technical Committee on Geometric Design is currently assigning members to each chapter who will represent the Technical Committee during the development and review of those chapters. Submittal of review material should be staggered to avoid overloading reviewers.
  • Document management plan for the development, review, and revision of GB8 content.
  • Interim reports and panel meetings to provide suitable opportunities for panel oversight of the project. This schedule should allow the panel to stay current with developments and provide meaningful oversight but not be excessive.
  • The draft GB8, suitable for AASHTO balloting. References in each chapter should be checked to make sure that they are up to date.
  • A final report that documents the entire research effort with an executive summary that outlines the research results. The report should document the basis of all Green Book design criteria, identify those based solely on past practices and professional judgment, and include draft research needs statements to confirm or update those criteria and their effects on the performance of the facility. The report should also recommend approaches for establishing and maintaining coherence among AASHTO documents related to the Green Book and potential ramifications of the GB8 content on common approaches to performance measurement and analysis, including data implications, for all travel modes. 
  • Presentation materials for a variety of audiences, including relevant AASHTO committees and councils and agency design policy makers.
  • An implementation plan that identifies future opportunities for dissemination and moving research into practice (see Special Note E). This plan should describe how a typical state department of transportation could incorporate the GB8 into their design policies and standards, including design exception processes. This plan will also describe training activities that would advance the understanding and application of the GB8 throughout the profession.
The research plan may include additional deliverables as well as additional panel meetings via teleconferences. The schedule will include 3 months for panel review and for contractor revision of the final research product(s). 

The project will be coordinated with NCHRP Project 15-72, “Identification of AASHTO Context Classifications,” NCHRP Project 15-76, “Designing for Target Speed,” and NCHRP Project 15-77, “Aligning Geometric Design with Roadway Context.” In addition to the sources mentioned in the Background, the project should be informed by NCHRP Legal Research Digest 74: Liability of State Departments of Transportation for Design Errors and NCHRP Legal Research Digest 83: Guidelines for Drafting Liability Neutral Transportation Engineering Documents and Communication Strategies. 

AASHTO’s A Policy on Geometric Design for Rural Highways (the Blue Book, first published in 1954) and A Policy on Arterial Highways in Urban Areas (the Red Book, first published in 1957) were early nationally recognized standards for geometric design. In 1984, the Blue Book and Red Book were combined to create the first edition of AASHTO’s A Policy on the Geometric Design of Highways and Streets (commonly known as the Green Book). The 1984 Green Book was organized around roadway Functional Classification (Local, Collector or Arterial) and broad Context Classification (Urban or Rural) with design criteria based primarily on motor vehicles. Subsequent Green Book editions retained this basic framework for geometric design guidance. While the basic 10 chapter framework in the Green Book has served practitioners well for new construction or new location projects, it lacks the guidance needed for today’s challenging projects where transportation professionals must balance safety, mobility, and other concerns for all modes of travel.
Public works projects are more sensitive to funding than ever before and cost magnitude and cost effectiveness often play large roles in scoping projects. In some locations, especially constrained ones, designing to recommended Green Book criteria is neither feasible nor necessary and a flexible approach can produce a better performing design that is sensitive to the context, environment, and the needs of all of the users of the facility. Design decisions made must consider the effects on safety, mobility, reliability, resilience, accessibility, equity, public health, the environment, land use, and other factors and the rationale for these decisions be clear to the public. 
Over the past 15 years, the AASHTO Technical Committee on Geometric Design (TCGD) has been exploring how the Green Book could have greater value to the designers of today. Notable efforts include:
  • NCHRP Report 785: Performance-Based Analysis of Geometric Design of Highways and Streets
  • NCHRP Report 839: A Performance-Based Highway Geometric Design Process
  • NCHRP Report 855: An Expanded Functional Classification System for Highways and Streets
  • NCHRP Report 876: Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects
  • NCHRP Report 880: Design Guide for Low-Speed Multimodal Roadways
  • Direction on Flexibility in Design Standards [AASHTO Standing Committee on Highways Resolution, May 25, 2016]
  • A Policy on Geometric Design of Highways and Streets, 7th Edition [AASHTO, 2018]
  • Guidelines for Geometric Design of Low-Volume Roads [AASHTO, 2019]
  • Planning for a Comprehensive Update and Restructuring of AASHTO’s A Policy on Geometric Design of Highways and Streets [NCHRP Project 20-07/Task 423]
Based on these efforts and ongoing discussion, the AASHTO TCGD has established the following goals for the 8th Edition of the Green Book (GB8):
  • Fully address the issues raised in the AASHTO Standing Committee on Highways (SCOH) resolution of 2016 Direction on Flexibility in Design Standards,”
  • More fully develop the consideration of all transportation modes and the importance of project context to decisions,
  • Change in emphasis from green field construction to projects on existing alignment, and
  • Incorporate performance-based design using modern analysis tools to find effective solutions to actual problems.
The TCGD also developed the following principles for the GB8.
  • Addresses the issues cited in the SCOH resolution of 2016, namely the increase in non-motorized traffic and severe crashes nationwide.
  • Presents an approach and thought process of designing in and for a multi-modal transportation system.
  • Recognizes that public works profoundly affect the health, safety, and welfare of citizens and accepts the charge to improve the public’s quality of life as an overarching objective.
  • Fully integrates the thought process of performance-based design into all aspects of project development and design decision-making.
  • Takes to heart the inherent fiscal limitations of the industry and advocates for a financially sustainable design process at both the program and project levels.
  • Utilizes context as the primary organizing basis of road and street design—and thereby of this design guidance.
  • Champions a flexible design approach as the only way to harmonize user needs and functional performance with environmental, contextual, and community considerations.
  • Appreciates the merit of predictability and uniformity across the roadway system—and, with that, the need to balance flexibility with consistency.
  • Acknowledges the changed nature of our industry, specifically the movement from new construction to the reconstruction and preservation of the existing system.
  • Makes progress toward realizing a primary recommendation of NCHRP Report 839, that dimensional design criteria have known and proven research, empirical, or experiential bases.
  • Maintains the prominence of the fundamentals of facility design, especially the traditions of engineering care and craftsmanship.
Lastly, the TCGD developed the draft GB8 chapter outline presented below. NCHRP Project 15-77, “Aligning Geometric Design with Roadway Context,” is currently developing draft chapters for Part IV. 
Draft GB8 Chapter Outline
AASHTO Technical Committee on Geometric Design
September 2019
Part I - Introduction
Performance-Based Design Concepts
Design Decision Making
Part II - Performance-Based Evaluations
Performance Metrics
Design Model  
Applying a Performance Based Process Framework
Part III - Geometric Elements and Configurations
Design Information and Sources
Elements of Design
Cross-Section Elements
Intersection Fundamentals
Freeways and Controlled Access Fundamentals
Interchange Fundamentals
Part IV - Facility Design in Context
Context and Facility Type Considerations
Rural and Natural Areas
Rural Towns
Suburban Roadways
Urban Roadways
Urban Core Roadways
Industrial, Warehouse or Port Roads


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