The AASHTO Greenbook is the foundation for Highway Design-it's objectives have been to assure highway safety by providing uniform and cost-effective roadway features for motorists.

Management Structure

Establishing Design Criteria - The AASHTO Policy on Geometric Design

The foundation for highway design in the United States is the technical background and recommendation design values published in the AASHTO Policy on Geometric Design for Highways and Streets (referred to as the "Green Book"). The five pilot states, and indeed, with very few exceptions, most state DOTs refer to the AASHTO Green Book for technical guidance in their work.
The design concepts and values found in the AASHTO Green Book are based on established practice and research. AASHTO's objectives have been to assure highway safety by providing uniform and cost-effective roadway features for motorists. The AASHTO Green Book has been developed and refined over the years through the cooperative efforts of the 50 states, the Federal Highway Administration (FHWA), and numerous research entities, including the Transportation Research Board (TRB). AASHTO policies are continually refined and revised based on results of research conducted at the state and national level. Beginning with "A Policy on Highway Classification" published in 1938, AASHTO has published numerous policies covering all aspects of highway design over the 60+ years since the original policy, with the most recently issued updated policy in 2001. Research continues in anticipation of further updates to Policy as needs change and knowledge increases.

AASHTO has developed the Policy to be flexible, recognizing the importance of its applicability across a wide range of conditions. AASHTO's Bridging document to FHWA's Flexibility in Highway Design discusses at length the flexibility in the Policy and the intent of its use.

A related design policy is the AASHTO Roadside Design Guide (RDG). This document addresses design of slopes, clear zones and recovery areas, traffic barriers (guardrail, bridge rail, median barrier), roadside hardware, curbs, and median treatments.