American Association of State Highway and Transportation Officials

The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that 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.

Although AASHTO sets transportation standards and policy for the United States as a whole, AASHTO is not an agency of the federal government; rather it is an organization of the states themselves. Policies of AASHTO are not federal laws or policies, but rather are ways to coordinate state laws and policies in the field of transportation.

Purpose
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.

While AASHTO is not a government body, it does possess quasi-governmental powers in the sense that the organizations that supply its members customarily obey most AASHTO decisions.

Membership
The voting membership of AASHTO consists of the Department of Transportation of each state in the United States, as well as those 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, the Turkish Ministry of Public Works and Settlement, and the Nigerian Association of Public Highway and Transportation Officials have non-voting associate memberships.

Publications
Some noteworthy AASHTO publications are:
 * A Policy on Geometric Design of Highways and Streets, 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.
 * AASHTO LRFD Bridge Design Specifications. This manual is the base bridge design manual that all DOTs use across the US.
 * Manual for Assessing Safety Hardware (MASH), crash testing criteria for safety hardware devices for use on highways; it updates and replaces NCHRP Report 350.

In addition to its publications, AASHTO performs or cooperates in research projects. One such project is the AASHTO 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), a division of the National Academy of Sciences, Engineering, and Medicine.

AASHTO re:source, formerly the AASHTO Materials Reference Laboratory (AMRL), accredits laboratories. 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 T 22, "Compressive Strength of Cylindrical Concrete Specimens," as the means of determining compressive strength. The laboratory performing T 22 will be required to be accredited in that test.

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

Standards
Current and withdrawn AASHTO standards include:


 * AASHTO TP10: Standard Test Method for Determining the tensile strength and temperature at fracture of field or laboratory compacted bituminous mixtures by measuring the tensile load in a specimen which is cooled at a constant rate while being restrained from contraction.
 * AASHTO T307: Standard Method of Test for Determining the Resilient Modulus of Soils and Aggregate Materials.
 * AASHTO T321/TP4: Test Standard for Determining the Fatigue Life of Compacted Hot-Mix Asphalt (HMA) Subjected to Repeated Flexural Bending.
 * AASHTO TP31: Standard Test Method for Determining the Resilient Modulus of Bituminous Mixtures by Indirect Tension
 * AASHTO TP62: Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures
 * AASHTO T321-03/TP8: Test Standard for Determining the Fatigue Life of Compacted Hot-Mix Asphalt (HMA) Subjected to Repeated Flexural Bending