SR 509 Completion Project - Common questions

What will this project do?
This project will ease congestion on I-5, add a southern access point to Sea-Tac International Airport and improve service between industrial centers by allowing general-purpose traffic and trucks to bypass I-5, SR 99 and local streets.

The new portion of SR 509 will be four lanes, two in each direction with connections at 188th, 28th/24th, I-5 and SR 516 in Kent.

Why is this project needed? 
The purpose of this project is to reduce travel time and improve mobility for people and freight between Tacoma/South King County, Sea-Tac International Airport and Seattle's industrial area and port. Some specific needs are:

  • Improve throughput and lower levels of congestion on the new SR 509 corridor
  • Reduce travel times in the region
  • Improve economic vitality
  • Support local and regional land use planning and development
  • Reduce the number of serious injury and fatal crashes

How will the project benefit me?
As presently designed, the project will provide:

  • Travel time savings between urban and manufacturing/industrial centers, allowing freight shippers, businesses and people to spend less time traveling between south King County and Seattle.
  • South King County will be a better place for existing businesses and an attractive location for new ones—bringing jobs to the area.
  • People traveling from the south on I-5 will have a more direct connection to Sea-Tac Airport.
  • The Des Moines Creek Park multi-use path will be connected to the Lake to Sound Trail by this project.

When will construction get started?
Construction is presently scheduled to begin in 2021. Some earlier work, associated with the Sound Transit Federal Way Link Extension project will begin in the area beginning in 2019.  

After construction begins, how long will it take to build this project?
Construction will be done in stages. The first stage, from SR516 to 28th/24th will begin in 2021 and last until 2025. Stage two construction from 28th/24th to 188th will begin in 2025 and be completed in 2030. 

What is the plan for buying property?
Before improvements can be made to State transportation facilities, the Department of Transportation must acquire right-of-way. Right-of-Way is the term given to the land right that the State purchases, either by easement or by ownership, to place or improve public roads.

Owners of property needed for the project will be offered just (fair and equitable) compensation for the required right-of-way. Just compensation is based on the Department’s valuation of the needed property and estimate of any damages to the remaining property. Department procedures are guided by State and Federal regulations that have been designed to protect impacted owners of properties as well as taxpayers by managing public resources competently and efficiently while providing improvements to essential transportation services. The valuation process will be conducted by experienced and qualified independent appraisers under contract to the Department and in some instances by staff appraisers.

How can I find out if my property will be impacted and needed for the project?
For additional information, you may contact Jeff Nakken, the Right of Way Project Manager, at or 206-440-4195.

Additional questions and answers can also be found in our brochure.

Will noise levels increase as a result of this project?
Construction activities will result in short-term noise impacts. Contractors will take many steps to minimize noise, such as turning off idling equipment and confining work to daytime hours whenever possible.

Where will you build noise barriers?
WSDOT is presently evaluating noise levels along the proposed alignment. WSDOT will install noise barriers at areas where residents would  be affected by traffic noise and where construction of barriers is justified.

Will this project have an impact on traffic on the SR 99/First Ave. S Bridge?
Travel models indicate there will be some shift of traffic from the SR 599 corridor to the SR 509 corridor south of the bridge, but peak-hour traffic on the First Ave. S Bridge will increase only slightly as a result of this project.

Traffic on the bridge may increase more during non-peak hour travel times, as drivers will find that they can reduce their travel times by taking the improved SR 509 route as an alternative to I-5.

Why has it taken so long to fund and complete this project?
While the SR 509 Completion Project has been planned for the region for decades, it wasn't fully funded until 2015. Also, given that the Connecting Washington Funding Package releases portions of the funding every two years, design and construction activities stretch over the 16 year funding period.

How do trips in and out of the airport shift with the new SR 509?
The completion of SR 509 including the 28th/24th interchange as well as the interim airport south access will allow airport trips to and from the south to use this new connection to 509 and I-5. This will reduce some trips on the 188th corridor as well as SR 518 which connects to the airport north access.

Why are we tolling airport trips?
The legislative intent is for the project to be tolled to help fund construction. Airport trips are one of the major users and will be treated the same as other trips choosing to use the new SR 509 corridor. There will remain toll-free options to and from the airport.

What effects will the project have on the local environment?
In the long term, this project will have a number of positive effects on the local environment. The project will:

  • Reduce air pollution on local streets by diverting traffic to the new expressway.
  • Contribute to the Des Moines Creek Basin capital improvement projects that will improve water quality and stream health.
  • The Des Moines Creek Park multi-use path will be connected to the Lake to Sound Trail by this project
  • Improve facilities for storm-water management on I-5.

 As the project is built, environmental impacts typical of a construction project will occur. WSDOT and its contractors will use best management practices and comply with all state and local regulations designed to minimize effects on the environment.
For detailed information see the final environmental impact statement for the project.

Are you doing any further environmental analysis since the FEIS?
Yes. We are currently taking a fresh look at some of the potential environmental impacts associated with the project. This is called a “re-evaluation” of our FEIS. We anticipate having the results of our re-evaluation in the fall/winter of 2017.