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I live in, work in, or travel through Des Moines, SeaTac, and southern Burien

Des Moines Memorial Drive/South 188th Street

The new SR 509/South 188th Street interchange will now have access to all directions of travel.  To accommodate this change in traffic patterns and improve safety, WSDOT will rebuild the interchange by adding roundabouts. For southbound SR 509 traffic, the SR 509/South 188th Street interchange will be the last exit before continuing onto the tolled section of the expressway.

Crews expect to begin construction in this area as soon as the summer of 2025, starting with temporary ramps to create the new work zones. If you live near, work near, or travel through the SR 509/South 188th Street interchange, expect the noise, dust, and traffic pattern changes typically associated with road construction. Local access to businesses will be maintained.

New SR 509 Expressway

The new SR 509 Expressway will continue south from the SR 509/South 188th Street interchange, passing over the Lake to Sound Trail, under South 192nd Street, over Des Moines Memorial Drive, and over South 200th Street and Des Moines Creek Park before connecting with the new section of the SR 509 Expressway near 24th Avenue South.

If you use the Lake to Sound Trail: The trail will remain mostly open during construction. Crews may close the trail to set bridge girders or allow construction equipment to cross the trail. In these instances, there will be flaggers and traffic control measures to direct trail users. Expect noise typically associated with construction and heavy machinery.

If you use South 192nd Street: The road will close to all traffic for approximately nine months, starting as soon as 2025, while crews build a new South 192nd Street bridge that the future SR 509 Expressway will cross under. We’ll share more information about when community members can expect this closure once we have a final South 192nd Street bridge construction schedule.

If you use South 194th Street: The South 194th Street connection to Des Moines Memorial Drive will close permanently. This closure will happen after the South 192nd Street bridge has been completed and is open to travelers.

If you live near South 194th Street: The new SR 509 Expressway will pass through this area. Most work will occur during the day, and some nighttime construction activities will be scheduled as needed. Expect some daytime noise and dust typically associated with heavy construction.

If you use Des Moines Memorial Drive, between South 200th Street and South 192nd Street: Some nighttime closures will be scheduled to set bridge girders and perform other construction activities.

If you use the Des Moines Creek Trail: The trail will remain open during construction. Crews may close the trail to set bridge girders or allow construction equipment to cross the trail. In these instances, there will be flaggers and traffic control measures to direct trail users. Expect noise typically associated with construction and heavy machinery

If you use South 200th Street: South 200th Street will remain open during the day throughout construction and will not be rerouted. Frequent nighttime closures will be scheduled to build the elevated expressway.

You can learn more about what WSDOT has planned at each of these locations by visiting the  SR 509 Expressway interactive map.

Contractors are required to meet local noise variances and will take steps to minimize noise and potentially disruptive construction activity. Best practices for managing noise and construction near neighbors and businesses include:

  • Providing nearby residents with notices in advance of noisy nighttime work
  • Wetting down the ground to prevent dust
  • Lining truck beds to help dump material and limit tailgate slamming

If you have questions or concerns about construction at any time, you can always contact our team at our 24-hour hotline, 206-225-0674, or SR509Construction@wsdot.wa.gov.