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.
Pan-American Highway (North America)
The Pan-American Highway unofficially begins in Prudhoe Bay, Alaska near Deadhorse. Traveling south to Fairbanks, Alaska, the Highway follows the length of the Dalton Highway (Alaska Route 11) and Alaska Route 2. (Dalton Highway was the subject of the BBC's first episode of "World's Most Dangerous Roads".) From Fairbanks, Alaska's third largest city, the Pan-American Highway and the Alaska Highway are one and the same, following Alaska Route 2 southeast to the Canada–United States border southeast of Northway, Alaska, and adjacent to the Tetlin National Wildlife Refuge.