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 435
I-435, a loop route of I-35, is long and intersects with nearly every other interstate highway in the Kansas City area (except for I-635 and I-670). An additional near Kansas City International Airport is signed along with I-29 and U.S. Route 71 (US 71), making I-435 the second-longest complete beltway numbered as a single Interstate Highway in the U.S., and fifth longest in the world after Cincinnati, Ohio's I-275 at , Houston, Texas's Beltway 8 at , Berlin's Bundesautobahn 10 at , and London's M25 motorway at . The majority——of I-435 is within the state of Missouri, and most of that roadway lies within the city limits of Kansas City. The first/last exit is at I-435's parent route, I-35, in Lenexa, Kansas. Going clockwise around Kansas City, the next interchange is exit 1A for Lackman Road. The milepost numbers do not start over when I-435 crosses the state line, but where it shares the same roadway as I-29, the latter's milepost (and therefore exit) numbering takes precedence.