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.
California
The state has been a pioneer in road construction. One of the state's more visible landmarks, the Golden Gate Bridge, was the longest suspension bridge main span in the world at between 1937 (when it opened) and 1964. With its orange paint and panoramic views of the bay, this highway bridge is a popular tourist attraction and also accommodates pedestrians and bicyclists. The San Francisco–Oakland Bay Bridge (often abbreviated the "Bay Bridge"), completed in 1936, transports about 280,000 vehicles per day on two-decks. Its two sections meet at Yerba Buena Island through the world's largest diameter transportation bore tunnel, at wide by high. The Arroyo Seco Parkway, connecting Los Angeles and Pasadena, opened in 1940 as the first freeway in the Western United States. It was later extended south to the Four Level Interchange in downtown Los Angeles, regarded as the first stack interchange ever built.