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February 5, 2024

National Finalist: Gold Award
Transportation

Photo from ACEC Washington
The project reconstructed two diamond interchanges with innovative roundabout-controlled interchanges spanning I-5.

Jacobs Engineering Group

Project: I-5 Steilacoom-DuPont Road to Thorn Lane corridor improvements
Client: WSDOT

The Interstate 5 Steilacoom-Dupont Road to Thorne Lane corridor improvements project undertaken by the Jacobs/Atkinson design-build team was a display of technical acumen and teamwork. The project involved widening 4.5 miles of I-5 and reconstructing two diamond interchanges, Berkeley Street and Thorne Lane, with innovative roundabout-controlled interchanges spanning I-5, and a Sound Transit rail line.

The project eliminated potential mainline traffic degradation by introducing a southbound connector roadway between Thorne Lane and Berkeley Street. This eliminated the need for a proposed auxiliary lane and avoided heavy weaving, enhancing traffic safety and flow.

Brain Whitehouse, Olympic Region assistant construction engineer for WSDOT said: “In an effort to save time and money, the team developed several WSDOT-approved alternate technical concepts to enhance the conceptual plan and to simplify any potential future widening in this area. This included redesigning the Thorne Lane interchange from a ‘dog bone’ bridge design (roundabouts at either end of a single bridge) to a two-bridge design. This solution simplified the structural design, eliminated grade-related safety issues, and improved traffic staging and local access during construction.”

The team also redesigned the Berkeley interchange from a similar “dog bone” design to a standard tight-diamond interchange, providing a new southbound barrier-separated connector roadway between Thorne Lane and Berkeley Street that eliminated the need for a proposed auxiliary lane that had the potential to degrade mainline operations.

The new traffic pattern provided a needed connection for the city of Lakewood and Tillicum, and the team coordinated with a multitude of stakeholders to address diverse project interests. Despite several owner-initiated change orders, the team successfully met the substantial completion date. The project has had positive impacts on the environment, local communities, traffic flow, military operations and traveler safety.


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