National Highway System

The National Highway System (NHS) consists of 160,000 miles of roadway that are important to the nation's economy, defense, and mobility. The National Highway System was created by the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). NHS includes the following subsystems of roadways (note that a specific highway route may be on more than one subsystem):

Interstate

The plan for a network of Interstate highways connecting cities with a population greater than 1,000,000 people became a reality when President Dwight Eisenhower signed the Federal-Aid Highway Act of 1956. The Interstate Highway system was constructed but not completed. The Eisenhower Interstate System of Highways retains its separate identity within the NHS. The Story of the US Interstate - American History

Other Principal ARterials

These are highways or local streets in rural and urban areas which provide access between an arterial and a major port, airport, public transportation facility, or other intermodal transportation facility.

Non-Interstate Strategic Highway Network (STRAHNET):

This is a network of highways which are important to the United States' strategic defense policy and which provide defense access, continuity and emergency capabilities for defense purposes. The ability to move troops and equipment via highways to airports, ports, rail terminals, and other bases for rapid deployment is essential to our national defense.

Major Strategic Highway Network connectors (SC)

These are state highways and local roads linking major military installations and other defense-related facilities to the Strategic Highway Network and highways which are part of STRAHNET.

Intermodal Connectors (IMC):

Highways or local roads that provide access between major intermodal facilities and the other four subsystems of the National Highway System are Intermodal Connectors. FHWA maintains an Official Intermodal Connectors Listing that is updated by Caltrans.

Caltrans' Deputy Directive #32, dated February 2004, outlines the importance of the National Highway System to the State of California.