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

Project news

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  • The weekend closure of the existing Berkeley Street overpass and all northbound and southbound I-5 ramps to and from Berkeley Street is scheduled at 8 p.m. Friday, Feb. 28 to 5 a.m. March 2. Detours for this closure are available on the detour map webpage.
  • At 5 a.m. March 2, the new Berkeley Street overpass and all new northbound and southbound I-5 ramps will reopen. The one partial ramp closure that will remain in place is the left turn to northbound I-5 coming from Tillicum/Camp Murray. Drivers can access northbound I-5 via the Thorne Lane interchange. This partial ramp closure will not impact travelers coming from the Madigan Gate, as they will be able to use the on-ramp to northbound I-5. The opening of the new Berkeley Street overpass means that the old overpass will officially be closed and no longer in use.
  • Weather permitting, both directions of I-5 at Berkeley Street will close during overnight hours starting at 10:30 p.m. March 6 and 7, with all lanes reopening by 5:30 a.m. on Saturday and 6:30 a.m. on Sunday. During the overnight closures, traffic will be diverted up and over the Berkeley Street off- and on-ramps. The closure is necessary so crews can remove the old Berkeley Street overpass, so crews can continue widening I-5.
  • 146th Street Southwest at Murray Road will close for two weeks starting Sunday, March 15 while crews build the curbs and sidewalks on the new alignment of Murray Road as it leads to I-5. During the closure, a signed detour will be in place. Two-way traffic will be maintained on Murray Road.
  • Read the latest blog about the work taking place at the Berkeley Street and Thorne Lane overpasses.
  • View the latest ramp and lane closure schedule on the Pierce County construction webpage.
  • View the bicycle detour map.
  • View the latest project photos on the WSDOT Flickr account.
  • 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.
  • Winter 2020 - 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 $243,098
Total $243,098

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.


Brian Whitehouse,
WSDOT Project Engineer

Cara Mitchell
Media Relations
WSDOT Olympic Region

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