Highway Statistics 2021
Annual Average Daily Traffic (AADT), an annual traffic count divided by the number of days in the year or a short-term traffic count annualized by factors to account for seasonality, etc.
Daily Vehicle-Miles of Travel (DVMT), the mileage traveled by all vehicles on a road system over an average day in a year.
Federal-Aid Highways, public roads eligible for Federal-aid highway funds.
Federal Highway Administration (FHWA), an agency within the U.S. Department of Transportation.
Highway Capacity Manual (HCM), a TRB publication that contains concepts, guidelines, and procedures for estimating the capacity and quality of service of highway facilities.
Highway Performance Monitoring System (HPMS), an annual compilation of data about the state of the Nation’s highway system.
Highway Trust Fund (HTF), the source of funds for the Federal-Aid Highway Program.
International Roughness Index (IRI), a statistic used to estimate the amount of roughness in a measured longitudinal profile.
Metropolitan Planning Organization (MPO), policy-making organization in the United States that is made up of representatives from local government and governmental transportation authorities.
National Highway System (NHS), approximately 160,000 miles (256,000 kilometers) of roadway important to the nation's economy, defense, and mobility, which includes these subsystems: Interstate, Other Principal Arterials, STRAHNET, major strategic highway network connectors, and intermodal connectors.
Pavement Serviceability Rating (PSR), a subjective rating of pavement ride quality based on visual inspection of the pavement rated from 0 to 5, where 0 is totally impassable or failed pavement and 5 is a pavement in excellent condition.
Strategic Highway Network (STRAHNET), a system of public highways that provides access, continuity, and emergency transportation of personnel and equipment for national defense purposes.
Transportation Research Board (TRB), one of six major divisions of the National Research Council, which promotes and supports research in all aspects of transportation.
Vehicle-Miles of Travel (VMT), the mileage traveled by all vehicles on a road system over a period of time such as a year.