I-5 - Steilacoom-DuPont Rd. to Thorne Lane - Corridor Improvements

Project news

  • Sign up for project updates
  • Read about construction progress on this project on the WSDOT Blog.
  • Construction is underway at the I-5/Berkeley Street interchange. View the latest ramp and lane closure schedule on the Pierce County construction webpage.
  • View the bicycle detour map.
  • Read the news release announcing the start of construction on this project. 
  • View the latest project photos on the WSDOT Flickr account.
  • Atkinson Construction has completed installing girders on the new Berkeley Street overpass and one of two new Thorne Lane overpasses. The second overpass at Thorne Lane will have girders installed sometime in the fall of 2019.
  • This project funded in the 2015 Connecting Washington transportation revenue package.

Needs & benefits

Why is WSDOT rebuilding the Berkeley Street and Thorne Lane interchanges and adding a lane in each direction on Interstate 5 between DuPont and Lakewood?
To relieve chronic traffic congestion and improve mobility along I-5 in the vicinity of Joint Base Lewis-McChord, WSDOT is rebuilding the interchanges at Thorne Lane and Berkeley Street and adding lanes to I-5.

The End Result
The changes would reduce chronic traffic congestion through the JBLM corridor. New interchanges that incorporate roundabouts and grade separation from the rail line improves traffic flow and reduces the potential for collisions.

Project Benefits
Congestion Relief:

  • Adding one lane in each direction of I-5 between Steilacoom-DuPont Road in DuPont and Thorne Lane in Lakewood will add additional capacity and improve traffic flow.
  • Auxiliary lanes are being added on northbound I-5 between Berkeley Street and Gravelly Lake Drive, and on southbound I-5 from Gravelly Lake Drive to Thorne Lane, and from Berkeley Street to JBLM Main Gate, providing a supplemental lane for vehicles entering and exiting I-5.
  • Benefit-Cost Analysis Report (pdf 695 kb)


  • The new interchanges are grade-separated from the existing rail line, reducing conflicts with trains.
  • Builds roundabouts at Thorne Lane interchange. Roundabouts are shown to reduce injury crashes by 75 percent at intersections where stop signs or signals were previously used for traffic control.

What to Expect

  • Narrowed and shifted lanes on I-5 and ramps in the project limits.
  • Overnight ramp and lane closures with signed detours.
  • Occasional weekend ramp closures and one extended closure of the Berkeley Street on-ramp to northbound I-5. Dates will be announced once available.
  • Extended closure of Union Avenue at Thorne Lane. Dates will be announced once available.
  • Access to Joint Base Lewis-McChord and Madigan Army Medical Center will be maintained.


  • The Interchange Justification Report was published September 2016.
  • On May 23, 2017, the U.S. Department of Transportation Federal Highway Administration issued a Finding Of No Significant Impact (FONSI) for the Interstate 5 JBLM Congestion Relief Project Environmental Assessment.
  • Design-Build contract awarded to Guy F. Atkinson Construction, LLC on May 17, 2018.
  • Design-Build contract began mid-2018.
  • October 2018 - construction began at the Berkeley Street interchange.
  • February 2019 - construction begins at the Thorne Lane interchange.
  • April 2019 - widening of Interstate 5 begins.
  • Fall 2019 - new Berkeley Street interchange opens.
  • Summer 2020 - new Thorne Lane interchange opens.
  • Fall 2020 - traffic in final configuration
  • Summer 2021 - final paving and striping, and construction ends.


Financial Data for PIN 300503T
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $0
CWA $242,945
Total $242,945

In July 2015, the Washington State Legislature included $495 million to fund the I-5 Mounts Road to Thorne Lane Interchange - Corridor Improvements project, as part of the Connecting Washington transportation revenue package. The project is funded through a 10 year period, from 2015-2025.


Chuck Meade, WSDOT Project Engineer

Cara Mitchell
WSDOT Olympic Region Communications

Small map for I-5 Steilacoom-DuPont Road to Thorne Lane project.