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.
U.S. Route 50
U.S. Route 50 (US 50) is a major east–west route of the U.S. Highway system, stretching just over from West Sacramento, California, to Ocean City, Maryland, on the Atlantic Ocean. Until 1972, when it was replaced by Interstate Highways west of the Sacramento area, it extended (by way of Stockton, the Altamont Pass, and the Bay Bridge) to San Francisco, near the Pacific Ocean. The Interstates were constructed later and are mostly separate from this route. It generally serves a corridor south of Interstates 70 and 80 and north of Interstates 64 and 40. The route runs through mostly rural desert and mountains in the Western United States, with the section through Nevada known as "The Loneliest Road in America". In the Midwest, US 50 continues through mostly rural areas of farms as well as a few large cities including Kansas City, Missouri; St. Louis, Missouri; and Cincinnati, Ohio. The route continues into the Eastern United States, where it passes through the Appalachian Mountains in West Virginia before heading through Washington, D.C. From there, US 50 continues through Maryland as a high-speed road to Ocean City. Signs at each end give the length as , but the actual distance is slightly less, due to realignments since the former figure was measured. US 50 passes through a total of 12 states; California, Nevada, Utah, Colorado, Kansas, Missouri, Illinois, Indiana, Ohio, West Virginia, Virginia, and Maryland, as well as the District of Columbia.