# SR 509 Completion Project construction

> Live situation record from CLSTR: https://clstr.news/situations/sr-509-completion-project-construction
> Updated: 2026-09-04T21:44:00.000Z. Sources: 4. Developments: 2.

The Washington State Department of Transportation (WSDOT) has scheduled a series of nighttime road closures in South King County to support the SR 509 Completion Project.

Initial closures announced for late August through early September included nightly work on South 200th Street in SeaTac to facilitate soil transport, alongside southbound lane closures on I-5 for drainage work. 

Subsequent scheduled closures for the second week of September involve continued drainage repairs on I-5 and new construction activities on SR 509, including landscaping, sign structure construction, and the nightly closure of the South 188th Street and South 160th Street on-ramps. The project aims to establish a three-mile tolled highway between I-5 and South 188th Street, with the final two miles expected to open in July 2028.

## Timeline

### 2026-09-04: WSDOT announces road closures on I-5 and SR 509

WSDOT will implement nighttime lane and ramp closures on I-5, SR 509, and local roads in Burien, SeaTac, and Kent from Sept. 8 to Sept. 11 for the SR 509 Completion Project.

3 sources. https://clstr.news/cluster/wsdot-announces-road-closures-on-i-5-and-sr-509

### 2026-08-28: WSDOT announces nighttime road closures for SR 509 project

WSDOT has announced nighttime closures on South 200th Street in SeaTac and southbound I-5 in South King County from August 31 to September 4 for the SR 509 Completion Project.

3 sources. https://clstr.news/cluster/wsdot-announces-nighttime-road-closures-for-sr-509-project

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Cite as: SR 509 Completion Project construction. CLSTR, https://clstr.news/situations/sr-509-completion-project-construction