Washington State Route 509

State Route 509
SR 509 highlighted in red
Route information
Auxiliary route of I-5
Maintained by WSDOT
Length	35.17 mi[1] (56.60 km)
Existed	1964[2]–present
Major junctions
South end	I-705 in Tacoma
Major intersections	SR 99 in Federal Way SR 516 in Des Moines SR 518 in Burien
North end	SR 99 in Seattle
Location
Country	United States
State	Washington
Counties	Pierce, King
Highway system
State highways in Washington Interstate US State Scenic Pre-1964 1964 renumbering Former
← SR 508 → SR 510

State Route 509 (SR 509) is a 35.17-mile-long (56.60 km) 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.