Three-year project will bring HOV lanes and a redesigned interchange to DuPont and JBLM

By Joe Calabro

Exciting changes are coming to southwest Pierce County. Our contractor has begun construction that will widen Interstate 5 for High Occupancy Vehicle lanes between 41st Division Drive and Mounts Road in DuPont. This is the third in a series of projects that add HOV lanes to I-5 in the area. The existing HOV lanes will be extended in the following areas:

• On southbound I-5, the HOV lane will extend 1.7 miles from 41st Division Drive (exit 120) to the Steilacoom-DuPont interchange (Exit 119).
• On northbound I-5, the HOV lane will begin at Mounts Road (Exit 116) and continue north 3.5 miles to join the existing HOV lane near 41st Division Drive (Exit 120).

Southbound I-5 narrows down from four lanes to three just past 41st Division Drive. This project extends the existing HOV lane to Steilacoom-DuPont Road while the northbound HOV lane will extend from Mounts Road to the existing HOV lane at 41st Division Drive.

A new overpass and Diverging Diamond Interchange

To widen the interstate, crews must replace the 66-year-old Steilacoom-DuPont Road overpass. The new overpass will be built north of the existing bridge and include a partial Diverging Diamond Interchange (DDI). The partial DDI will include a traffic signal, like the new Marvin Road interchange in Lacey. Adding a DDI here improves mobility and safety between I-5, DuPont and JBLM. Pedestrians and bicyclists will have access to a shared-use path over the bridge.  

The new bridge over I-5 spans the railroad tracks, eliminating the need for DuPont travelers to stop for passing trains. This safety improvement will reduce travel times for all users of the overpass. Once the bridge is complete and open to traffic, work to remove the original overpass will begin, sometime in late 2025 to 2026. This work will likely require directional overnight closures of I-5. We will share details on the project webpage as construction progresses.

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 will also be improved access to and from JBLM.

A roundabout on Steilacoom-DuPont Road

A new roundabout will be installed at the junction of the new I-5 overpass and Steilacoom-DuPont Road. The roundabout will improve safety and reduce congestion for people traveling to or from DuPont and Steilacoom. The roundabout will accommodate vehicles of all sizes, including large trucks, emergency vehicles and buses. The shared-use path for pedestrians and bicyclists will extend from JBLM, over the new bridge, to the roundabout.

East of interchange: improved access at JBLM’s DuPont gate

Redesigning the interchange gives us the opportunity to improve how people access I-5. Improvements on the east side of the highway at JBLM’s DuPont gate (exit 119) include:

• Direct access between JBLM and both directions of I-5
• A dedicated northbound I-5 exit lane to DuPont and other communities west of I-5 via the new interchange
• Crosswalks and a pedestrian and bicycle path to the overpass

Auxiliary lane on northbound I-5 between Center Drive and Steilacoom-DuPont Road

Several years ago, we modified the Center Drive and Weigh Station on-ramp to northbound I-5 as part of the Stage 1 changes on the overall project. We are happy to share that the dedicated auxiliary lane is coming back, which will give all highway users more time to merge to mainline I-5. This addition, paired with the northbound I-5 exit lane to the JBLM DuPont Gate, will reduce how often drivers experience backups. 

New traffic signal at southbound I-5 and Mounts Road exit

Anyone who uses exit 116 to Yelm knows how backed up the Mounts Road exit gets during the afternoon commute. This project adds a traffic signal at the top of the ramp to help keep travelers moving.  

What travelers can expect

Lane and ramp closures are already underway. Three lanes of traffic will be maintained in both directions of I-5 throughout the project, keeping travel times similar to what they are now. Lane closures will generally occur overnight when traffic volumes are lower. Daytime work may be necessary to safely complete some of the construction. 

This project will occur in phases over three years. Each phase involves different types of work with various closures and detours. Be aware of temporary speed limit reductions and ramp closures. Give yourself extra time to follow detours if exiting or entering the highway in the area. You can learn more about the project phases and timeline at our online open house. We also encourage you to visit our project webpage and sign up for email alerts to track progress.