California Department of Transportation

National Highway System (NHS)

NHS Summary

The NHS is composed of approximately 160,000 miles of rural and urban roads nationwide serving major population centers, international border crossings, intermodal transportation facilities, and major travel destinations. The NHS includes the following:

  • The Interstate System.
  • Principal Arterials:
    • On October 1, 2012, all existing principal arterials were grandfathered into the NHS.
    • After October 1, 2012, newly designated principal arterials must go through the update process outlined below to be added to the NHS.
  • Intermodal Connectors: Highways that provide motor vehicle access between the NHS and major intermodal transportation facilities.
  • STRAHNET (Strategic Highway Network): The network of highways important to U.S. strategic defense.
  • STRAHNET Connectors: Connectors to major military installations.

MAP-21 Legislation

FHWA Questions and Answers

Federal Highway Administration NHS Questions and Answers following the implementation of MAP-21:

NHS Data:

Caltrans Earth NHS Map

To view a map of the NHS, go to Caltrans Earth, then on the left column click "Highways", then "Map-21 NHS.".

NHS Additions or Deletions


Page Updated on September 30, 2015