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I-5 JBLM Vicinity Congestion Relief Project, South Study Area: Supplemental Environmental Assessment and Online Public Meeting – Transportation

WSDOT evaluated existing and forecasted traffic for 2025 and 2040.

Two traffic scenarios were evaluated:

  • Traffic conditions assuming the project is not constructed 
  • Traffic conditions with the new lanes on I-5 operated as HOV lanes

HOV lanes currently do not exist in the vicinity of the project.  The new northbound and southbound lanes currently under construction in the North Study Area will be opened as HOV (2021). Once the new lanes in the South Study Area are completed, they would open as HOV lanes as well.

Travel Times and Freeway Operations

Construction of the project would reduce congestion and improve travel times. By 2040, I-5 would carry more people and accommodate more traffic with the project than without it. Travel time during the weekday PM peak hour between SR 512 and Mounts Road for HOVs would be 33 minutes faster for southbound trips in the 2025, and 26 minutes faster for northbound trips with the project. SOV travel times during the evening commute between these two interchanges would be 12 minutes faster in the southbound direction and 20 minutes faster in the northbound direction.

I-5 Southbound Cumulative Travel Time - 2025 PM Peak Hour SR 512 to Mounts Road
I-5 Northbound Cumulative Travel Time - 2025 PM Peak Hour Mounts Road to SR 512
I-5 Northbound Cumulative Travel Time - 2040 PM Peak Hour Mounts Road to SR 512
I-5 Southbound Cumulative Travel Time - 2040 PM Peak Hour SR 512 to Mounts Road

The project would improve mobility and safety conditions in 2025, and provide some operational benefits in 2040, especially for northbound traffic. Operation of the new lanes as HOV provides benefit for speed and reliability of transit, vanpools and carpools, particularly during the PM peak hour. 

Without construction of the project, traffic conditions would get worse, and most trips through the study area would take longer in the future than they do today.

Local Streets and Intersections

The new interchange at Steilacoom-DuPont Road would change how drivers access I-5 and local streets.  Local traffic would use the new Exit 119 B overpass to access local roads leading to DuPont, Steilacoom, and JBLM’s Integrity Gate. The ramp intersections with the local roads would be controlled by traffic signals. Drivers would experience very little delay at the new intersections. 

Drivers destined for JBLM via the DuPont Gate would use Exit 119A.  The ramps and overpass at Exit 119A would only serve the DuPont Gate. No access to local public roads would be available from this exit.  This design separates the traffic associated with JBLM from locally destined traffic and reduces congestion associated with JBLM security checks at the DuPont Gate.

Gravelly Thorne Connector Design Changes

A new road and shared use path called the Gravelly Thorne Connector (GTC) was originally included in the project.  The new road was designed to include a single southbound traffic lane and a shared use path between Gravelly Lake Drive and Thorne Lane.  The construction contract for the North Study Area improvements changed the design of I-5 to include a southbound auxiliary lane on I-5 between Gravelly Lake Drive and Thorne Lane.  This auxiliary lane will function as the southbound lane originally planned as part of the Gravelly Thorne Connector.  A shared use path constructed between Gravelly Lake Drive and Thorne Lane will also be designed to support use by emergency vehicles.

For More Information

To read more about the transportation analysis please see Section 3.3 of the Supplemental Environmental Assessment.