The whole project started after a 2001 earthquake damaged the Alaskan Way Viaduct, which has carried State Route 99 through Seattle since the 1950s, dividing the city’s downtown from the short of the Puget Sound. Fearing the double-decker roadway wouldn’t withstand another shake, city planners decided to replace it with a two-mile tunnel under the city, and at the same time reintroduce Seattleites to the water.
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