Project overview
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 the 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
Eastbound SR 516 at I-5 closed June 13-16
All eastbound lanes of SR 516 between SR 99 and Military Road will be closed from 10 p.m. Friday, June 13 to 4 a.m. Monday, June 15. Drivers will follow a signed detour. In addition, the northbound I-5 exit to SR 516 will be closed from 11 p.m. Saturday, June 14 to 3:30 a.m. Sunday, June 15. During the closure, contractor crews will pave and restripe the eastbound lanes for expanded intersection opening later this summer.
Public comment on toll rate setting
The Washington State Transportation Commission issued its toll rate proposal for the SR 509 and SR 167 expressways. A virtual public hearing on the proposed toll rate is scheduled for June 17. Registration to attend the meeting is required. Information on the toll rate proposal, how to register for the meeting or offer feedback via email, phone or mail is available on the transportation commission website.
Construction work near Des Moines Creek and Lake to Sound trails
Construction work around the Des Moines Creek and Lake to Sound trails began in March 2025. Work is expected to last through 2028. Spring 2025 work includes cutting down and removing trees along the trails. In summer 2025, crews will begin earthwork along the SR 509 corridor. This will require large construction vehicles, including trucks with trailers, near or frequently crossing the trails. Trail users will see advance warning signs. At times, flaggers may also be on site to direct trail users and construction vehicles.
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).
