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.
Interstate 10
Interstate 10 (I-10) is the southernmost cross-country Interstate Highway in the American Interstate Highway System. It stretches from the Pacific Ocean at California State Route 1 (Pacific Coast Highway) in Santa Monica, California, to I-95 in Jacksonville, Florida. Major cities connected by I-10 include (from west to east) Los Angeles, Phoenix, Tucson, El Paso, San Antonio, Houston, Baton Rouge, New Orleans, and Jacksonville. This freeway is part of the originally planned Interstate Highway network that was laid out in 1956, and its last section was completed in 1990. I-10 is the fourth-longest Interstate Highway in the United States, following I-90, I-80, and I-40. About one-third of its length is within the state of Texas, where the freeway spans the state at its widest breadth.