WSDOT extended the auxiliary lane south approximately 1.5 miles, so that it starts at the Mounts Road overpass. Trucks approaching the weigh station along with entering and exiting traffic use this lane while the majority of traffic uses the adjacent three through lanes.
To accommodate the auxiliary lane, northbound I-5 was widened into the center median. The final lane configurations includes three 11-foot-wide lanes, one 12-foot-wide lane and 8 feet on the inside shoulder.
An auxiliary lane is a supplemental or extra lane between interchanges. They are frequently used between closely spaced interchanges to allow for maneuvering of entering and exiting traffic, speed changes, weaving and truck climbing.
The extended auxiliary lane will ultimately become part of the HOV lane that is being built in the I-5 Mounts Road to Thorne Lane I/C Corridor Improvements project.
What to expect
The project is complete. Phase three construction that will widen I-5 to build an HOV lane from Center Drive to Steilacoom-DuPont Road is expected to begin in 2023.
New northbound I-5 auxiliary lane from Mounts Road to Center Drive in DuPont.