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 90 in New York
Interstate 90 (I-90) is a part of the Interstate Highway System that runs from Seattle, Washington, to Boston, Massachusetts. In the U.S. state of New York, I-90 extends from the Pennsylvania state line at Ripley to the Massachusetts state line at Canaan, and is the second-longest highway in the state after NY 17. Although most of the route is part of the tolled New York State Thruway, two non-tolled sections exist along I-90 (the first, situated outside of Buffalo, is included in the Thruway system; the second, situated in the Capital District, is not part of the Thruway system and links Albany and its eastern suburbs). Within New York, I-90 has a complete set of auxiliary Interstates, which means that there are interstates numbered I-190 through I-990 in the state, with no gaps in between. For most of its length in New York, I-90 runs parallel to the former Erie Canal route, New York State Route 5 (NY 5), U.S. Route 20 (US 20) and the CSX railroad mainline that traverses the state.