ⓘ List of Interstate Highways in Washington. The Interstate Highways in Washington is a group of seven designated Interstate Highways within the state of Washingt ..


ⓘ List of Interstate Highways in Washington

The Interstate Highways in Washington is a group of seven designated Interstate Highways within the state of Washington in the Pacific Northwest region of the United States. The highways, totaling 764 miles and spanning the state, are owned and maintained by the Washington State Department of Transportation. They were designated and primarily funded by the federal government, with road standards and numbering handled by the Federal Highway Administration and the American Association of State Highway and Transportation Officials

These highways connect every city in the state with a population of over 100.000 as well as the state capital, Olympia.

Interstate 90 I-90 is the longest primary Interstate Highway in Washington, which connects Seattle to Spokane and the Idaho border, measuring 297.52 mi 478.81 km, while I-82, connecting the Oregon border city of Umatilla to Elensburg via Yakima, is the shortest at 132.57 mi 213.35 km. The longest auxiliary Interstate Highway in Washington is I-405, a bypass of Seattle through the Eastside, at 30.30 mi 48.76 km, and the shortest is I-705, a spur into downtown Tacoma, at 1.50 mi 2.41 km. One route, I-605, has been proposed over the years to form another Eastside bypass, however there are no plans to construct this fifth auxiliary route.


1. Primary Interstate Highways

After passage of the Federal Aid Highway Act of 1956, which formed the Interstate Highway System, the American Association of State Highway Officials had approved I-5 and I-90 across Washington on August 17, 1957. I-82 was approved on October 17, 1957, two months after I-5 and I-90, as part of a 1.102-mile-long 1.773 km addition to the Interstate Highway System.


2. Auxiliary Interstate Highways

I-205 and I-405 were first codified into Washington State Law in 1970, and I-182 and I-705 were codified in 1979.

I-705 was completed in 1990, after a series of federal budget cuts, and was the last Interstate Highway to be completed in the state of Washington.

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