Interstate 5/State Route 161/State Route 18 Triangle Improvements | Federal Way, WA

After completing a corridor study for Washington State's DOT, WSP prepared detailed construction plans for one of the state's busiest interchanges. 


Location

  • Washington, USA

Client

  • Washington State Department of Transportation

Interstate 5/State Route 161/State Route 18 Triangle Improvements

The Washington State Department of Transportation selected WSP to complete a corridor study report for the Interstate 5/State Route 161/State Route 18 interchange. Considered state-of-the-art when constructed in the early 1960s, the four cloverleaf ramps are now considered a freeway relic, insufficient in managing the soaring traffic volumes resulting from population growth. The new interchange will offer significant traffic and safety improvements, while also yielding economic benefits for freight haulers and businesses relying on congestion relief at this pivotal location.

What began as just a “small study” is now a $235 million reconstruction program for one of western Washington’s most congested interchanges. Working with WSDOT and a team of eight subconsultant firms, WSP developed and studied 12 interchange alternatives and over three dozen alternatives to provide a new off-ramp connecting the freeway system to the City of Federal Way’s local street network. WSP’s engineers and scientists worked collaboratively to refine alternatives to reduce environmental effects. Detailed staging and traffic control plans were prepared to minimize disruptions during construction in this highly congested area. The project also included an extensive public involvement program that engaged local businesses; community groups; the general public; and two steering committees, a technical advisory committee and a public advisory committee.