National Highway System

The National Highway System includes the Interstate Highway System as well as other roads important to the nation's economy, defense and mobility.

The National Highway System (NHS) was developed by the Federal Department of Transportation in 1995 in cooperation with the states, local officials and metropolitan planning organizations (MPOs).

The NHS consists of NHS routes, intermodal facilities and intermodal connector routes where required for travel from the NHS routes to the intermodal facilities. Routes designated as Strategic Highway Network (STRAHNET) by the Department of Defense also form part of the NHS.

There have been only minor changes to the NHS until the Moving Ahead for Progress in the 21st Century Act (MAP-21) was authorized by congress and signed into law in 2012. MAP-21 resulted in the addition of 1,200 miles of Washington roads to the NHS.

Washington NHS routes are maintained in Washington’s Highway Performance Monitoring System (HPMS) and represented in Washington’s HPMS spatial network (GIS). Changes and updates to the NHS are reported to FHWA annually.

NHS documents

Washington State Highway NHS List (PDF 7.18MB)

Washington Local Agency NHS List (PDF 1.0MB)

2021 National Highway System Routes as reported to FHWA in HPMS
NHS Routes: Centerline Miles Lane Miles
State Highway (including Interstate) 3,576 11,416
Local Agency 979 3,329
Total 4,555 14,745
NHS Routes: Centerline Miles Lane Miles
Interstate only 764 4,020

Note: Mileages do not include proposed (unbuilt) NHS


Changes to Washington’s NHS

Changes to the NHS must meet the federal guidance criteria detailed in US Code, Title 23 Part 470 Highway Systems and involve WSDOT, affected local and regional officials, and metropolitan planning organizations and the FHWA WA Division Office. Formal approval of changes to the NHS is issued by the FHWA Office of Planning. Changes to Washington’s approved NHS are managed by the WSDOT HPMS Section.

NHS map and data download

View the current NHS routes in the WSDOT National Highway System (NHS) Map Viewer, or download a copy of the data from the WSDOT Open Data Portal:
WSDOT - National Highway System for State Routes
WSDOT - National Highway System for Non-State Routes


Slow down on ice and snow.

It's easier to skid or lose control traveling at higher speeds. Give yourself more time to stop.

Carry chains, practice installing them.

Winter conditions could mean chains are required on your route. Practice putting them on your vehicle ahead of time.

Pack your winter car kit.

Carry extra supplies like warm clothing, ice scraper and brush, jumper cables and other emergency items.