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

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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 keep people moving as the project reaches new stages. People will notice temporary changes to traffic patterns. The temporary changes will last at least several months.

The changes allow workers to continue building the new overpass and ramps while making way for the extended HOV lanes.

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

2025 in review: A new interchange takes shape

Stage 3 began in spring 2025. The stage is expected to be completed in late January 2026.

Over the last year, crews built a new Steilacoom-DuPont overpass that spans I-5 and the railroad tracks.

Workers also built new roundabout on Steilacoom-DuPont Road. The new roundabout opened two-way traffic between DuPont and Steilacoom.

The new roundabout will allow people to access the overpass which is currently under construction.

When the new overpass is completed, people will be able to access I-5 and Joint Base Lewis-McChord.

In Stage 4, access from the roundabout to the overpass will be available. Stage 5 will open two-way access over the overpass.

Crews also finished raising I-5 over Pendleton Avenue, adding additional clearance for vehicles driving under the highway.

The vertical clearance of the overpass was raised over four feet.

At the south end of the project, crews added a new traffic signal at the southbound I-5 exit to Mounts Road.

The new signal at Mounts Road replaced a 4-way stop.

Crews added new pavement on northbound I-5 between the new overpass and Clark Road. The widening will allow for a new northbound HOV lane to be constructed and opened in late 2026.

Crews worked behind concrete barrier to widen I-5.

How to get around, January 2026 – spring 2026

The new Steilacoom-DuPont Road overpass will partially open. The existing Steilacoom-DuPont Road bridge will be partially closed. The temporary changes allow crews to build out the new on-ramp to southbound I-5 without long-term closures.

From southbound I-5 to DuPont or JBLM

The southbound I-5 exit to DuPont will be located before the new overpass. The exit currently is located after it.

People heading to DuPont will use the right exit lane to travel toward the new roundabout. They will take the roundabout to head down Steilacoom-DuPont Road past Barksdale Village.

People heading to the JBLM/DuPont Gate will turn left onto the overpass. They will continue across the overpass before turning right toward the gate.

From northbound I-5 to DuPont or JBLM

If you travel north for DuPont or JBLM, your route does not change. People heading to DuPont will take a left turn at the end of the off-ramp and travel over the existing bridge to DuPont.

People going to the JBLM DuPont Gate will take a right at the end of the ramp and continue into the base.

From DuPont to southbound I-5, northbound I-5, and JBLM

If you leave DuPont for southbound I-5, your route does not change. Access the highway using the southbound I-5 on-ramp from the Wilmington Drive and Barksdale Avenue intersection.

To access northbound I-5, travel around the new Steilacoom-DuPont Road roundabout, over the new overpass, and take a left onto the on-ramp.

To reach JBLM, travel around the new Steilacoom-DuPont Road roundabout, over the new overpass, and take a right toward the base.

From JBLM to I-5 and DuPont

If leaving the JBLM DuPont Gate for northbound I-5, take a right from the gate and continue straight onto the on-ramp.

If leaving JBLM for southbound I-5, go straight from the gate and take a left at the end of the overpass.

To reach DuPont, go straight from the gate over the overpass.

Pedestrian and bicycle access

When traffic changes go into effect in January, bicyclists and pedestrians can begin using the pathway across the overpass. The shared-use path will provide a place for people who walk, bike or roll between JBLM and DuPont.

Spring 2026: Traffic changes and bridge demolition

In spring 2026, the interchange traffic flow will change again. Travelers will see that most of the interchange will be opened as a diverging diamond interchange. It will be similar to the diverging diamond interchange on Marvin Road in Lacey. Driving through a diverging diamond is as easy as following the signs and lane lines. Our diverging diamond webpage includes details about how to navigate the new layout.

When this phase is complete, both directions of traffic will flow across the new Steilacoom-DuPont overpass. With the new bridge open, crews will remove the old overpass. The bridge removal will require up to two weekend closures of I-5 with traffic detoured over the on- and off-ramps. WSDOT will announce when the demolition is scheduled.

Northbound I-5 traffic will be detoured up and over the Steilacoom-DuPont Road on- and off-ramps. Southbound traffic will exit, travel around the new roundabout, then return to southbound I-5 using the new on-ramp.

What's next

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

• Transition to Stage 5 and opening of the diverging diamond interchange.
• Demolition of the existing Steilacoom-DuPont Bridge at Clark Road.
• 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