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 80
Interstate 80 (I-80) is an east–west transcontinental freeway in the United States that runs from downtown San Francisco, California, to Teaneck, New Jersey, in the New York City Metropolitan Area. The highway was designated in 1956 as one of the original routes of the Interstate Highway System. Its final segment was opened to traffic in 1986. It is the second-longest Interstate Highway in the United States, following I-90. The Interstate runs through many major cities including Oakland, Sacramento, Reno, Salt Lake City, Omaha, Des Moines, and Toledo, and passes within of Chicago, Cleveland, and New York City.