Interstate 90 in Washington

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Interstate 90 (I-90), designated as the American Veterans Memorial Highway, is a transcontinental Interstate Highway that runs from Seattle, Washington, to Boston, Massachusetts. It crosses Washington state from west to east, traveling 298 miles (480 km) from Seattle across the Cascade Mountains and into Eastern Washington, reaching the Idaho state line east of Spokane. I-90 intersects several of the state's other major highways, including I-5 in Seattle, I-82 and U.S. Route 97 (US 97) near Ellensburg, and US 395 and US 2 in Spokane.

I-90 is the only Interstate to cross the state from west to east, and the only one to connect the state's two largest cities, Seattle and Spokane. It incorporates two of the longest floating bridges in the world, the Lacey V. Murrow Memorial Bridge and the Homer M. Hadley Memorial Bridge, which cross Lake Washington from Seattle to Mercer Island. I-90 crosses the Cascades at Snoqualmie Pass, one of the busiest mountain pass highways in the United States, and uses a series of viaducts and structures to navigate the terrain. The freeway travels across various landscapes, including suburban bedroom communities in the Seattle metropolitan area, forests of the Cascade Range, and the high plains of the Columbia Plateau.

The crossing at Snoqualmie Pass was established as a wagon road in 1867 and incorporated into a cross-state auto trail, known as the Sunset Highway, in the early 1910s. The Sunset Highway was incorporated into the national highway system in 1926 as part of US 10, which I-90 replaced when it was designated in 1957. The first segments of the freeway, located in Spokane and Spokane Valley, opened at around the same time and the state government completed upgrades of US 10 to Interstate standards for most of the route by the late 1970s.

The section of I-90 between Seattle and I-405 in Bellevue was delayed for decades because of environmental concerns and lawsuits by local groups over the freeway's potential impact on nearby neighborhoods. A compromise agreement was reached by the federal, state, and local governments in 1976 to build a second floating bridge across Lake Washington and include extensive parks above tunneled sections of I-90, which were completed in the early 1990s. The new floating bridge opened in 1989 and carried bi-directional traffic while the original floating bridge was renovated. The old bridge's center pontoons sank during a November 1990 windstorm due to a contractor error and were rebuilt over the following three years, reopening to traffic on September 12, 1993, marking the completion of the transcontinental highway....