I-5 - Mounts Rd. to Steilacoom-DuPont Rd. - Corridor Improvements

Project news

  • View the proposed design on the project photos page. All designs are subject to change.
  • The Supplemental Environmental Assessment (SEA) is available for review.
  • Thank you to all who participated in the online open house. WSDOT is reviewing the comments. Responses will be published in the final environmental decision document. 

Needs & Benefits

To relieve chronic traffic congestion and improve mobility along I-5 in the vicinity of Joint Base Lewis-McChord, WSDOT is proposing to rebuild the interchange of Steilacoom-DuPont Road (Exit 119) and adding HOV lanes to I-5. This will support congestion relief on I-5 during peak traffic periods while maintaining access to neighboring communities and JBLM. The proposed build alternative also includes grade separation of the roadway over the railroad.

Why do you have to rebuild the interchange?

  • At the Steilacoom-DuPont Road interchange, the existing 1957 bridge over I-5 has openings that limit the potential to add lanes to the interstate. In addition, the existing overpass is classified as "poor condition" and does not meet current vertical clearance standards from I-5. A new interchange will be built to current design standards and allow for additional lanes of I-5 in both directions.
  • Current traffic flow is constrained by the close proximity of the ramp intersections, JBLM’s DuPont Gate, the railroad line, and the intersection of Wilmington Drive and Barksdale Avenue.


  • Determine build alternative: Mid 2016 through 2017. In May 2017, WSDOT reinitiated discussions with stakeholders to define a reconfiguration of the Steilacoom-DuPont Road (Exit 119) interchange that meets the project purpose and need. These efforts have resulted in the linked feasibility report (pdf 4.28 mb).
  • Environmental Studies: 2018 to spring 2021
  • Acquire Right of Way:  Summer 2021 to spring 2022
  • Design-Build Contract begins for final design and construction: Spring 2022
  • Construction complete: 2025


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 package. This project is funded through a 10 year period, from 2015-2025.


Bill Elliott
WSDOT JBLM Project Manager

Cara Mitchell
WSDOT Olympic Region Media Relations

I-5 Mounts Road to Steilacoom DuPont Road small project map