SR 509 expansion

• Project typeFreeway extension
• Project scheduleIn progress
• Contractor nameWashington State Department of Transportation

About this project

This project extends SR 509 to Interstate 5 near our city and adds an access point just south of SeaTac International Airport. The expansion connects local industrial areas directly, keeping heavy traffic and trucks off I-5, SR 99, and neighborhood streets.

$1 billion in funding for this project comes from the Connecting Washington funding package, local contributions, tolls, and federal grants.

Stages 1a and 1b

This stage involves building:

• New freeway, with tolls, to connect SR 509 with 28th/24th Avenue South and I-5  
• Two lanes in each direction, with truck climbing lanes, between South 188th Street and 28th/24th Avenue South
• Two lanes in each direction between 28th/24th Avenue South and I-5

Stage 2

This stage involves building:

• New freeway, with tolls, to connect where SR 509 ends (at South 188th Street/Des Moines Memorial Drive South) with 28th/24th Avenue South 
• Two lanes each way, with a full set of on- and off-ramps at South 188th Street/Des Moines Memorial Drive South

Project benefits

• Improved regional travel and economic growth
• New South 216th Street overpass with pedestrian and bike access
• Improvements to South 208th Street
• New street (34th Avenue South from South 204th Street to South 208th Street)
• Funding for part of the Lake to Sound Trail from our city to Burien

Key documents

• Construction Presentation(PDF, 4MB)