I-5 – Mounts Road to Steilacoom-DuPont Road Corridor Improvements

Background

The Washington State Department of Transportation is in the third phase of a series of projects that widen Interstate 5 from Mounts Road near DuPont to Gravelly Lake Drive in Lakewood. Southbound I-5 currently narrows down from four lanes to three, just past 41st Division Drive. This project extends the existing southbound I-5 HOV lane to Steilacoom-DuPont Road. The northbound HOV lane will extend from Mounts Road to the existing HOV lane at 41st Division Drive.

At the Steilacoom-DuPont Road interchange (exit 119), a new overpass will be constructed. The new overpass creates enough space to extend the I-5 HOV lanes further south into DuPont and provides increased vertical clearance over the interstate to meet current standards.

The aerial shows where southbound I-5 narrows down from four lanes to three, just past 41st Division Drive.

Current traffic flow in the area is constrained by the proximity of the I-5 ramp intersections, Joint Base Lewis-McChord’s DuPont Gate, the railroad, and the intersection of Wilmington Drive and Barksdale Avenue. Building a new Steilacoom-DuPont Road interchange will provide increased distance between the intersections while maintaining access to neighboring communities and JBLM. Once the new interchange is constructed, the existing bridge at exit 119 will be removed.

Design changes and benefits

Improvements include an extended HOV lane in both directions of I-5. Crews will build a partial diverging diamond interchange at the new Steilacoom-DuPont overpass and a roundabout. There also will be improved access to and from JBLM.

This project features a number of design changes around the Steilacoom-DuPont Road interchange that will result in improved access and reduced traffic congestion. The changes and benefits include:

• Extending the HOV lanes in both directions of I-5. The northbound HOV lane will start at Mounts Road. The southbound HOV lane will be extended from 41st Division Drive south into DuPont.
  • Increases capacity in this section of I-5 and reduces chronic traffic congestion.
• A new Steilacoom-DuPont Road overpass and a partial Diverging Diamond Interchange (DDI).
  • The new overpass will cross over the railroad, eliminating the current at-grade crossing. The DDI will reduce vehicle conflict points and improve efficiency with fewer traffic signals.
• Barrier-separated shared-use path on the new Steilacoom-DuPont Road overpass spanning I-5.
  • Improves pedestrian access by connecting JBLM to communities west of I-5 for people who walk, bike, or roll.
• Roundabout connecting the new overpass and Steilacoom-Dupont Road.
  • Improves efficiency for all users on the west side of I-5.
• Dedicated lanes at the reconstructed interchange that separate traffic traveling to either the JBLM DuPont Gate or the communities on the west side of I-5.
  • Improves efficiency through the interchange.
  • Check out the video below for a detailed look at improvements happening east of I-5 near JBLM.

What to expect

Construction will require lane shifts on I-5, overnight lane reductions and overnight and weekend ramp closures. Drivers, pedestrians and bicyclists should expect detours in the vicinity of Steilacoom-DuPont Road at various points of the project. All detours will be clearly signed.

Bicycles are not permitted on I-5 between 41st Division Drive and Center Drive. Travelers should be aware that access is restricted to JBLM property bordering the route.

Construction along this stretch of I-5 began in early August 2023 and will continue through 2026. The completed project will improve mobility along I-5 in the vicinity of Joint Base Lewis-McChord.

Construction

Keeping you moving throughout construction

Construction crews will shift traffic in stages to build the project. Each traffic shift will last for several months. Crews will remove existing infrastructure and build new features.

At the Steilacoom-DuPont Interchange, three travel lanes on both directions of I-5 will remain open. Bike and pedestrian detours will be clearly marked.

Crews will complete Stage 2 of the project in April 2025. In Stage 2, crews shifted northbound I-5 lanes to new pavement and created a work zone between southbound and northbound traffic. Closed sections of northbound I-5 were widened and abutments were constructed for the future Steilacoom-DuPont Road overpass. Work continued at the future roundabout on Steilacoom-DuPont Road and the I-5 bridge over Pendelton Avenue was partially removed. Crews will begin Stage 3 in late March 2025.

New Steilacoom-DuPont Road ramp to northbound I-5

Travelers likely noticed the new on-ramp has a raised concrete island. It created a curve on the ramp to northbound I-5.

The new Steilacoom-DuPont Road ramp to northbound I-5 is a piece of a larger puzzle. The puzzle piece you don’t see yet is the new bridge across all lanes of I-5.

The raised island will serve a future purpose. It will help separate traffic coming from JBLM and DuPont when the new bridge opens.

The new span will open as a diverging diamond interchange in 2026.

So why was this change made now? The raised concrete island was built before the ramp opened to travelers. If crews built it later, the ramp would need a series of closures.

Bird’s eye view (left) shows new on-ramp. Design visualization (right) shows how chicane will fit into the overall plan.

Stage 3: March 2025 – early 2026

In late March, crews will shift southbound I-5 lanes towards the median and create new work zones on the shoulder. These temporary lane shifts allow crews room to advance the work on the project. During stage 3, crews will:

• Build the Steilacoom-DuPont Road roundabout.
• Construct the new Steilacoom-DuPont Road overpass.
• Build the roadway between the roundabout and the new Steilacoom-DuPont Road I-5 overpass.
• Activate the traffic signal at Mounts Road.
• Widen northbound I-5 between Clark Road and the future Steilacoom-DuPont Road overpass.
• Partially remove the existing I-5 bridge over Pendleton Avenue.

The graphic shows work completed as of February 2025 and where the new bridge girders will be installed during two weekends of night closures in April. The girders for the new overpass will be installed north of the current Steilacoom-DuPont overpass.

The graphic shows work completed as of February 2025 and where the new bridge girders will be installed during two weekends of night closures in April. The girders for the new overpass will be installed north of the current Steilacoom-DuPont overpass.

The first picture below is a rendering of future improvements. The second is an aerial photo showing progress as of February 2025. In Stage 3, crews will construct the roundabout and the road to the new overpass.

New Mounts Road traffic signal

To improve travel time, WSDOT is installing a new traffic signal at the southbound I-5 exit to Mounts Road. The new signal will replace the existing all-way stop.

To prepare for the new signal, crews built a new wall between the Mounts Road exit and southbound I-5. The area creates space for the signal and electrical components. After workers complete this phase, activities will pause until parts for the signal can be manufactured and delivered. The new traffic signal is expected to be operational by late 2025.

What's next

As the project progresses, we will share updates about upcoming work and milestones, including:

• New roundabout opening in fall 2025, subject to change.
• Removal of the old Steilacoom-DuPont Road overpass in early 2026, subject to change.
• Opening of extended HOV lanes.

Please help keep road workers safe. When approaching a work zone, remember to:

• Slow down – drive the posted speeds for worker and traveler safety.
• Be kind –workers are out there helping to keep people safe and improve the roadways.
• Pay attention – both to workers directing travelers and surrounding traffic.
• Stay calm – expect delays, leave early or take alternate routes if possible; no meeting or appointment is worth risking someone’s life.

Stay connected

Travel conditions change quickly, we strongly encourage travelers to use the tools below to stay informed.

• View updates and upcoming closures on the project webpage
• Check real time travel conditions, view cameras and travel times
• Download WSDOT’s free smartphone app
• Sign up for email updates using GovDelivery