National Highway System
The National Highway System (NHS) consists of a network of over 178,000 miles of interconnected urban and rural principal arterials and highways serving major population centers, international border crossings, ports, airports, public transportation facilities, other intermodal transportation facilities and major travel destinations. Beyond the interstate segment, NHS consists mostly of existing two-lane roads. The 256,000 kilometers (km) of NHS include only 4 percent of the nation's roads, but they carry more than 40 percent of all highway traffic, 75 percent of heavy truck traffic, and 90 percent of tourist traffic. With some exceptions (STRAHNET, major STRAHNET connectors, and connections to major intermodal terminals), only principal arterials are eligible for inclusion on the NHS.

The National Highway System Designation Act of 1995 was signed by President Clinton on November 28, 1995. This act designates 160,955 miles of roadways as the National Highway System (NHS). The system includes the Interstate Highway System as well as other roads important to the nation?s economy, defense, and mobility. The NHS was developed by the United States Department of Transportation in cooperation with the States Departments of Transportation, Local Officials, and Metropolitan Planning Organizations. Included in the national system is a identification of major intermodal terminals (rail-truck terminals, maritime ports, airports, and intermodal passenger facilities) and the highways that provide connections between these intermodal facilities and the NHS. The NHS and the additional intermodal connector routes provides an integrated transportation system to support the nation?s economy.

National defense highway needs are generally accomplished under regular public highway programs. Title 23 of the US Code, administered by the Federal Highway Administration (FHWA), provides for a Federal Aid Highway Program to assist the States in highway construction and improvement. Title 23 allows the Secretary of Transportation to give priority consideration to including highway needs that are important to national defense into the Federal Aid Highway Program.

The Emergency Highway Traffic Regulation (EHTR) is a regulation that contains plans, routes, and schedule of the actual use of highways to help the orderly flow of traffic during a national emergency. This includes evacuation, regulating movement through dangerous areas, and clearing priority traffic over routes of limited capacity.