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.
Mexican Federal Highway 180
Highway 180 connects at the Mexico–United States border with U.S. Route 83, one of the longest north-south U.S. Highways in the United States at . Federal Highway 180 also connects to both Interstate 69E and U.S. Route 77 at the border. U.S. Route 83 (along with both Interstate 69E and U.S. Route 77) starts the northern terminus of Highway 180 in Brownsville, Texas, at the Veterans International Bridge on the Mexican border. After crossing the bridge into the United States, Federal Highway 180 continues as U.S. Route 83 in Brownsville which then runs northward to the U.S. highway's northern terminus, north of Westhope, North Dakota, at the Canada–United States border. From here, the highway continues further as Manitoba Highway 83 until it ends at Swan River, Manitoba. In total, the three highways total in length.