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.
Transportation in Appalachia
The next great leap in transportation was the creation of the U.S. Highway system in 1926, replacing the auto trails. The longest primary US highway contained in Appalachia is US 11 traversing the eastern side. US 21 was another primary US highway, but much of its route has been decommissioned and replaced with Interstate 77. These make/made up the north-south routes. East-west routes include US 30, US 33, US 40, US 50, US 60, and US 70. Many spur routes such as US 220 and US 119 serve various parts of Appalachia.