SR 509 Completion Project - Map

A map of the stages of the SR 509 completion project

Project highlights

  1. Lake to Sound Trail final segment
    The Puget Sound Gateway Program will help fund a portion of the Lake to Sound Trail to mitigate the project’s impacts. The Lake to Sound Trail is a 16-mile non-motorized trail extending from Lake Washington to the Puget Sound shoreline. WSDOT is working closely with the City of SeaTac and King County to finish the final segment of the trail. The SR 509 alignment will cross over the trail near South 200th Street and South 189th Street.
  2. Southern Access to Sea-Tac Airport
    The SR 509 Completion Project design accommodates the Port of Seattle’s concept for a South Airport Expressway from SR 509 to Sea-Tac International Airport. The new southern access point will reduce traffic pressure on the airport’s northern access point, while also improving airport access for communities south of SeaTac. An interim South Access will be provided from 28th/24th Avenue South.
  3. Early Work in SeaTac: Connecting 28th/24th Avenue South
    The city of SeaTac just completed a WSDOT supported project connecting 28th Avenue South to 24th Avenue South. The new road completes the gap in the 28/24th Avenue South corridor and provides an alternative to SR 99 in the SR 509 Completion Project area. As part of the project, SeaTac constructed a new bridge and tunnel that will accommodate the future SR 509 corridor and the South Airport Expressway.
  4. Tolling SR 509
    WSDOT will toll all lanes on the new portion of SR 509. WSDOT will collect tolls using all electronic tolling at one toll point. There will be no tollbooths. The Washington State Transportation Commission will set toll rates by time of day – more during peak periods and less during mid-day, evenings and weekends. Toll rates for the new portion of SR 509 have not been determined. The Legislature authorized tolling on this corridor in the 2019 session. The Washington State Transportation Commission will oversee the rate-setting process, which will begin closer to when the project is completed. The Legislature directed $85 million from tolls will be used to construct the SR 509 Completion Project.
  5. Working with Sound Transit
    WSDOT is working closely with Sound Transit as we work to build infrastructure projects in the same area. Coordination is underway to work through shared property needs. Both teams are in close coordination at key locations where alignments intersect with each other, including the SR 99 crossing, the South 216th St. Bridge, retaining walls near the Mansion Hill Neighborhood, and the Southbound off ramp to SR 516.