List of Interstate Highways in Washington
Interstate 90 (I-90) is the longest primary Interstate Highway in Washington, which connects Seattle to Spokane and the Idaho border, measuring , while I-82, connecting the Oregon border city of Umatilla to Elensburg via Yakima, is the shortest at . The longest auxiliary Interstate Highway in Washington is I-405, a bypass of Seattle through the Eastside, at , and the shortest is I-705, a spur into downtown Tacoma, at . 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.
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 addition to the Interstate Highway System.
Alaska Highway
The Alaska Highway (also known as the Alaskan Highway, Alaska-Canadian Highway, or ALCAN Highway) was constructed during World War II for the purpose of connecting the contiguous United States to Alaska across Canada. It begins at the junction with several Canadian highways in Dawson Creek, British Columbia, and runs to Delta Junction, Alaska, via Whitehorse, Yukon. Completed in 1942 at a length of approximately , it is long. The difference in distance is due to constant reconstruction of the highway, which has rerouted and straightened out numerous sections. The highway was opened to the public in 1948. Legendary over many decades for being a rough, challenging drive, the highway is now paved over its entire length. Its component highways are British Columbia Highway 97, Yukon Highway 1 and Alaska Route 2.