U.S. Route 12 in Washington

U.S. Route 12
US 12 highlighted in red
Route information
Maintained by WSDOT
Length	430.52 mi[1] (692.85 km)
Existed	1967–present
Tourist routes	Lewis and Clark Trail White Pass Scenic Byway
Major junctions
West end	US 101 in Aberdeen
Major intersections	SR 8 in Elma I-5 near Chehalis SR 7 near Morton SR 123 near Mount Rainier SR 410 near Naches I-82 / US 97 in Yakima I-182 / US 395 in Pasco US 730 near Wallula SR 125 in Walla Walla
East end	US 12 in Lewiston, Idaho
Location
Country	United States
State	Washington
Counties	Grays Harbor, Thurston, Lewis, Yakima, Benton, Franklin, Walla Walla, Columbia, Garfield, Asotin
Highway system
United States Numbered Highway System List Special Divided State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 11 → SR 14

U.S. Route 12 (US 12) is a major east–west U.S. Highway, running from Aberdeen, Washington, to Detroit, Michigan. It spans 430.5 miles (692.8 km) across the state of Washington, making it the second longest highway in the state. It is also the only numbered highway to span the entire state from west to east, starting near the Pacific Ocean, and crossing the Idaho state line near Clarkston. It crosses the Cascade Range over White Pass, south of Mount Rainier National Park. Portions of it are concurrent with Interstate 5 (I-5) and Interstate 82 (I-82), although the majority of the route does not parallel any interstate highway.

Although US 12 was not extended into Washington until 1967, portions of it have been part of Washington's state highway system since as early as 1905. The last part of the highway to open was over White Pass in 1951, although it was added to the state highway system by the legislature in 1931. Most of the route (except for the approximately 160 miles (260 km) between Elma and Naches) had been part of the U.S. Highway System since its inception in 1926 as part of U.S. Route 410. The portion between Napavine and Grand Mound was also designated a U.S. Highway in 1926 as part of U.S. Route 99.