State Route 509 (SR 509) is a state highway in the U.S. state of Washington, connecting Tacoma in Pierce County to Seattle in King County. The highway travels north from Interstate 705 (I-705) in Tacoma to SR 99 south of downtown Seattle. It serves cities along the Puget Sound and west of Seattle–Tacoma International Airport in south King County, including Federal Way, Des Moines, and Burien. SR 509 is part of the National Highway System and is a limited-access highway near the Port of Tacoma and from Burien to its northern terminus in Seattle. Prior to the 1964 highway renumbering, the highway was part of Secondary State Highway 1V (SSH 1V) from Tacoma to Des Moines and SSH 1K from Des Moines to Seattle. SR 509 was re-aligned onto the Burien Freeway in 1968 and the Port of Tacoma bypass in 1997, coinciding with the opening of its interchange with I-705 and the cable-stayed 21st Street Bridge. A freeway extension of SR 509 within the city of SeaTac, connecting the Burien Freeway to I-5, is planned to be completed by 2028. Route description SR 509 begins as South 21st Street at a single-point urban interchange with I-705 in downtown Tacoma in Pierce County, providing access to the Tacoma campus of the University of Washington and the Tacoma Link light rail line on Pacific Avenue. The highway travels east over the Thea Foss Waterway on the cable-stayed 21st Street Bridge into the Port of Tacoma as a four-lane limited-access highway, intersecting Portland Avenue in a half-diamond interchange before crossing the Puyallup River. SR 509 continues east, parallel to a City of Tacoma rail line through a partial cloverleaf interchange with Port of Tacoma Road before the divided highway ends at Taylor Way. The highway turns northwest along the Hylebos Waterway as Marine View Drive through the neighborhood of Northeast Tacoma towards Browns Point. SR 509 passes through Dash Point and its state park along the Puget Sound into King County and the city of Federal Way. The highway travels east as Dash Point Road through Federal Way past Decatur and Federal Way high schools before a junction with SR 99 west of I-5. The concurrent SR 99 and SR 509 travel north as the Pacific Highway past Highline Community College to an intersection with SR 516 in western Kent. SR 509 turns west to form a concurrency with SR 516, heading