SR 509/24th Avenue South to South 188th Street New Expressway

Welcome

WSDOT is starting construction on the State Route 509/24th Avenue South to South 188th Street New Expressway project in 2024. This project is the final, fully-funded stage (Stage 2) of the SR 509 Completion Project.

How to participate

This online open house provides information about the areas where project construction work will occur and the schedules for completing the project’s most visible activities. Please visit the following pages to learn more about the project and then share your questions on the Keep in Touch page.

You may access the online open house through Oct. 25, 2024.

What is this project?

The SR 509/24th Avenue South to South 188th Street New Expressway project is the final stage of the SR 509 Completion Project improvements, which connects SR 509 to I-5 in SeaTac. Once the project is complete in 2028, people traveling through the area will be able to bypass SR 518 and local streets when traveling between I-5, Sea-Tac Airport, the Port of Seattle and population centers in south King County. Community members will experience fewer container trucks on local roads as freight drivers will have a new route to reach their destinations. The new portion of SR 509 will be tolled. Throughout construction and after completion, people will still be able to use their current access points to SR 509 and I-5, and people will not pay tolls on the roads they use today.

What’s included in the project?

The SR 509/24th Avenue South to South 188th Street New Expressway project includes:

• Over two new miles of expressway.
• An additional lane on southbound I-5 between SR 516 and South 272nd Street in Kent.
• Roundabouts at South 160th Street in Burien and South 188th Street in SeaTac.
• New noise walls.
• Restoring natural areas within the project corridor.

Project timeline

Early construction activities include vegetation clearing throughout the project area. Heavier construction work will begin in fall 2024. Check out the work zones in the following pages to learn what to expect in the areas you live, work and travel.

The SR 509 Completion Project is already under construction. Stage 1a opened to traffic in 2022, Stage 1b is expected to open to traffic in 2025, and Stage 2 is expected to be open to traffic in 2028.

Work zones and schedules

Construction crews will perform work in four different cities: Burien, Des Moines, SeaTac, and Kent. We’ve provided details for each construction area so you know what to expect whether you are traveling through the area or living or working nearby.

Select links below to learn more about the construction updates in that area.

• I live in, work in, and travel through Burien.
• I live in, work in, or travel through Des Moines, SeaTac, and southern Burien.
• I live in, work near, or travel through the Barnes Creek area.
• I live in, work in, or travel through Kent.

I live in, work in, or travel through Burien

South 160th Street

To accommodate changes in traffic patterns and improve safety, WSDOT will rebuild the SR 509/South 160th Street interchange by adding roundabouts.

SR 509/South 160th Street interchange design

If you live near, work near, or travel through the SR 509/South 160th Street interchange, expect noise, dust, and traffic pattern changes typically associated with road construction.

Work on the SR 509/South 160th Street interchange began in summer 2024, starting with drainage construction work. Work at the SR 509/South 160th Street interchange will require weekend closures of South 160th Street. We’ll share more information once closure dates are decided. Local access to businesses and residences will be maintained.

Roundabouts

Studies have shown that roundabouts are safer than traditional stop-sign or traffic-signal-controlled intersections. To learn more about how to travel through roundabouts as a pedestrian, cyclist, or driver, check out WSDOT’s roundabout traffic safety webpage.

Noise walls

One noise wall will be built southwest of the SR 509/South 160th Street interchange alongside the southbound SR 509 on-ramp. The second noise wall will be built northeast of SR 509/South 160th Street interchange between Fourth Avenue South and northbound SR 509.

South 160th Street/SR 509 interchange design

If you live right next to one of the planned noise walls around the SR 509/South 160th Street interchange, you should expect survey crews to reach out to you before construction starts. During construction, crews will use machinery to dig noise wall foundations, compact the soil, pour concrete for the noise wall foundations, and install the new concrete panels. Construction on the noise walls is expected to last six to nine months depending on site conditions.

A noise wall the project team completed in Stage 1b of the SR 509 Completion Project

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.

Questions or concerns?

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.

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 summer 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 permanent closure will happen shortly after South 192nd Street closes.

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.

Questions or concerns?

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.

I live in, work near, or travel through the Barnes Creek area

Barnes Creek wetland mitigation

A large wetland improvement project is planned at Barnes Creek in Des Moines. The area extends from Kent-Des Moines Road to South 220th Street. The Barnes Creek restoration site enhances habitat for plants native to the region.

If you use the Barnes Creek Nature Trail, expect the trail to close periodically while crews work in the area. Crews will post signs ahead of trail closures.

If you live near the Barnes Creek mitigation site, expect some noise from construction machinery during daytime construction hours. Most work will be performed with hand tools and small construction machines.

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

Questions or concerns?

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.

I live in, work in, or travel through Kent

Southbound I-5 between SR 516 and South 272nd Street

WSDOT is making improvements to I-5 to help traffic transition between SR 509 and I-5. A new southbound lane between SR 516 and South 272nd Street will add capacity to I-5 for traffic traveling from SR 509 to the Kent Valley and Federal Way. Crews expect to begin work as soon as winter 2024.

If you use southbound I-5, expect frequent shoulder closures and periodic night and weekend lane closures. All construction work will take place behind temporary concrete barriers, but the traveling public should always slow down when traveling through work zones and watch for trucks entering and exiting work areas.

McSorley Creek near South 259th Street

A culvert under I-5 at McSorley Creek, located north of South 272nd Street, will be replaced with a larger culvert to maintain the water flow and keep I-5 resilient. Crews will access the construction site from South 259th Street.

If you live near or travel through South 259th Street, expect construction traffic and periodic lane and shoulder closures at this location.

Noise wall extension

WSDOT will extend the existing noise wall east of 32nd Place South in Kent to the north by 230 feet. A construction schedule for this has not yet been set.

If you live right next to the planned noise wall near 32nd Place South, you should expect survey crews to reach out to you before construction starts. During construction, crews will use machinery to compact the soil, pour concrete for the noise wall foundations, and form the new concrete panels.

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

Questions or concerns?

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.

What's next?

Construction is ramping up

Our contractor began construction on the Barnes Creek mitigation site in summer 2024, followed by work at the South 160th Street/SR 509 interchange and southbound I-5, between SR 516 and South 272nd Street. In 2025, crews will begin building the new SR 509 Expressway between 24th Avenue South and the South 188th Street interchange.

You may see our crews drilling, clearing vegetation, surveying, and working on utilities at any location throughout the project corridor before the end of 2024. The best way to stay up to date on construction activities is to follow WSDOT’s social media platforms and subscribe to our quarterly English-language newsletters, available in other languages on request.

If you have any questions at any time, you can always reach out to our team at 206-225-0674 or SR509Construction@wsdot.wa.gov.

What’s not included in Stage 2?