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Washington State Route 599

State Route 599 marker

State Route 599
Map of King County in western Washington with SR 599 highlighted in red
Route information
Auxiliary route of I‑5
Defined by RCW 47.17.808
Maintained by WSDOT
Length: 1.75 mi (2.82 km)
Existed: 1971 – present
Major junctions
South end: I‑5 in Tukwila
North end: SR 99 in Tukwila
Location
Counties: King
Highway system
SR 548 SR 702

State Route 599 marker

State Route 599 (SR 599) is a state highway in King County, Washington. It extends 1.75 miles (2.82 km) from I-5 north to State Route 99 (SR 99), within the city of Tukwila. The route serves as a connector from I-5 into West Seattle, avoiding the West Seattle Bridge.

SR 599 runs 1.75 miles (2.82 km) from I-5 north to SR 99, within the city of Tukwila. The route links I-5 with West Seattle, avoiding the West Seattle Bridge. WSDOT has found that about 48,000 motorists use the road daily at the I-5 based on average annual daily traffic (AADT) data.

From I-5 to East Marginal Way, an elevated light rail line runs on the west side of SR 599, served by Central Link trains operated by Sound Transit.

SR 599 became a state highway in 1971, but has been part of Washington's older highway system (Primary and Secondary Highways) from 1957 to 1970. The highway, then known as PSH 1 WM, or West Marginal Branch, was built during the 1960s. When it was completed, around 1968, U.S. Route 99 (US 99) was about to be removed from the system, so when I-5 was completed up to Tukwila, US 99 switched to the route of SR 599. Later on, the current route of SR 599 became known as US 99T (Temporary) and later SR 99T in 1964. In 1971, the highway became SR 599.


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