The National Academies

NCHRP 07-29 [Active]

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
Staff Responsibility: Dr. Zuxuan Deng
Research Agency: Texas A&M Transportation Institute
Principal Investigator: Ingrid Potts
Effective Date: 5/10/2021
Completion Date: 10/31/2024
Comments: Research in progress.


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


Research in progress.


Task 1. Hold a kickoff meeting between the research team, NCHRP, and the NCHRP 7-29 project panel to review and discuss the project objectives, tasks, and schedule. The call will also provide a forum for the research team to ask the panel questions and to seek guidance at the beginning of the project

Task 2. Review materials from past and ongoing projects that could provide content or considerations for the GB8. These resources will provide important background to the white paper prepared in Task 3 and to activities throughout the project. 

Task 3. Develop a white paper on the purpose of the GB8 and how it is intended to be used by planners, designers, other transportation professionals, and agency policy makers. Unlike previous editions of the Green Book, which focused on the dimensional criteria for geometric design, the GB8 will focus on a flexible geometric design process that fits within an agency’s project development process and incorporates, to the maximum extent possible within the current state of knowledge, explicit consideration of quantitative performance measures.  

Task 4. Draft the GB8 Author’s Guide that promotes consistency among authors by providing a clear, concise, and prescriptive description of the intent, formatting, organization, and the “look and feel” of individual GB8 elements.

Task 5. Develop an Annotated Outline for the GB8. The annotated outline will be consistent with the objectives presented in the Task 3 white paper. Specifically, the annotated outline should address how GB8 should be applied to:

·         Identification of challenges posed by the project (e.g., state of good repair, safety, mobility, resilience, equity, and public health), as defined in the project purpose and need statement.

·         Selection of appropriate performance measures given the facility’s context and role within the transportation network.

·         Approaches to trading off among these performance measures and other considerations (including their use in design-build projects).

·         Documentation of design decisions. 

Task 6. Develop Work Plans for Phase II, namely:

·         A document management plan for development, review, and revision of GB8 content.

·         A review plan that provides for organized review of the GB8 content by the project panel and the AASHTO TCGD.

·         A communication and outreach plan for interacting with and seeking input from other AASHTO committees and outside groups concerning GB8 content and the relationship of GB8 to the publications and policies of those groups.

Task 7. Prepare and submit the Interim Report presenting the results of Tasks 2 through 6. Meet with the NCHRP and the NCHRP 07-29 panel to review the report.

Task 8. Develop and submit the First Draft of the GB8 by drafting individual parts and chapters. These portions of the GB8 will be submitted on a staggered schedule and reviewed as separate pieces.

Task 9. Develop and submit the Second Draft of GB8. The second draft will be comprehensive and reviewed as such.

Task 10. Prepare and submit the other final deliverables, namely:

  • Final report that documents the entire research effort and includes an executive summary outlining the research results. The report will document the basis of all Green Book design criteria and identify those criteria that are based solely on past practices and professional judgment. Draft research needs statements, to confirm or update those criteria and their effects on the performance of the facility, will be included. The report will 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 implementation, for all travel modes.
  • Implementation Plan
  • Presentation Materials

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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