American Association of State Highway and Transportation Officials

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AASHTO, the American Association of State Highway and Transportation Officials, is a standards setting body which publishes specifications, test protocols and guidelines which are used in highway design and construction throughout the United States. Despite its name, the association represents not only highways but air, rail, water, and public transportation as well.

The voting membership of AASHTO consists of the Department of Transportation of each State in the United States, as well as that of Puerto Rico and the District of Columbia. The United States Department of Transportation, some U.S. cities, counties and toll-road operators, most Canadian provinces as well as the Hong Kong Highways Department and the Turkish Ministry of Public Works and Settlement have non-voting associate memberships.

The American Association of State Highway Officials (AASHO) was founded on December 12, 1914. Its name was changed to American Association of State Highway and Transportation Officials on November 13, 1973. The name change reflects a broadened scope to cover all modes of transportation, although most of its activities are still specific to highways.

AASHTO is not a government body, but does possess quasi-governmental powers in the sense that the organizations that supply its members customarily obey most AASHTO decisions. It is an example of a general tendency in the American style of government to outsource many governmental functions to nongovernmental organizations, whose decisions are then routinely ratified by appropriate government agencies.

Some noteworthy AASHTO publications are:

A Policy on Geometric Design of Streets and Highways, often called "The Green Book" because of the color of its cover. This book covers the functional design of roads and highways including such things as the layout of intersections, horizontal curves and vertical curves.
Standard Specifications for Transportation Materials and Methods of Sampling and Testing.

In addition to its publications AASHTO performs or cooperates in research projects. One such project is the AASHO Road Test, which is a primary source of data used when considering transport policies and the structural design of roads. Much of AASHTO's current research is performed by the National Cooperative Highway Research Program (NCHRP) which is administered by the Transportation Research Board (TRB) of the National Research Council.

The AASHTO Materials Reference Laboratory (AMRL) accredits laboratories. AMRL accreditation is often required to submit test results to State DOTs. For example, a contract for the construction of a highway bridge may require a minimum compressive strength for the concrete used. The contract will specify AASHTO Test Designation T22 "Compressive Strength of Cylindrical Concrete Specimens" as the means of determining compressive strength. The laboratory performing T22 will be required to be accredited by AMRL in that test.

AASHTO coordinates the numbering of Interstate Highways, U.S. Highways and U.S. Bicycle Routes.