The SR 509 Completion Project in King County is part of the Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. Together, these projects complete two of the Puget Sound region’s most critical freight corridors and improve access to I-5, the ports of Tacoma and Seattle and Seattle-Tacoma International Airport. The SR 509 Completion Project builds a new four-lane expressway between I-5 and SR 509's current end near Sea-Tac Airport, builds new I-5 ramps, improves I-5 interchanges in south King County and constructs new bridges. When complete, the project will create an important north-south alternative to the congested I-5 corridor between Seattle and south King County.
What to expect
I-5 in SeaTac closed overnight Friday, March 1 and Saturday, March 2
On Friday, March 1 and Saturday, March 2, crews will close one direction of I-5 to set 10 girders for the northern portion of the new South 216th Street bridge. Lanes begin closing at 8 p.m.
Southbound I-5 lanes will be closed at South 200th Street from 10 p.m. Friday, March 1 to 6 a.m. Saturday, March 2. The South 200th Street on-ramp to southbound I-5 will also be closed.
Northbound I-5 lanes will be closed at SR 516 from 10 p.m. Saturday, March 2 to 6 a.m. Sunday, March 3. The SR 516 ramps to northbound I-5 will also be closed.
Drivers will follow signed detours via SR 99 both nights. Travelers should also consider using SR 167 to bypass the closure if their destination is not within the local area.
Traffic eastbound on South 216th Street in SeaTac detoured for six months
Eastbound traffic on South 216th Street in SeaTac will follow a detour to cross I-5 for six months. During this time, crews will build the northern portion of the new South 216th Street bridge. This video explains the bridge work and detour route.
The SR 509 Completion Project builds three new miles of SR 509 and completes the unfinished SR 509 in south King County. This new four-lane highway will become an important north-south alternative to the congested I-5 corridor between Seattle and south King County. The new segment of SR 509 will be called an expressway and will be tolled at one electronic toll point (no tollbooths).