U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
AASHTO’s A Policy on Geometric Design of Highways and Streets (the Green Book) is the principal source for design values and ranges for highway and roadway design criteria and other geometric elements. For projects on the Interstate system, AASHTO’s A Policy on Design Standards, Interstate System should be consulted for design values and ranges. These two publications, through the federal rule-making process, establish the minimum design criteria to be used on the NHS, including the Interstate system.
Other publications that offer complementary guidance to these two resources include the following:
Many States also publish their own design manuals. Sometimes these manuals specify design criteria that are more stringent than criteria cited in the Green Book. FHWA only requires that the minimum values cited in the Green Book are met. If the chosen design value should not meet minimum State criteria, that State may choose to formally analyze, approve, and document a design exception, independent of FHWA.