Inslee and Local Leaders Launch Diverging Diamond Interchange Work to get I-90/SR 18 Traffic Moving

Gov. Jay Inslee joined other state and local representatives today to turn the first shovels of dirt, breaking ground on the Interstate 90/State Route 18 Interchange Improvements and Widening project. This interchange is one of the busiest in Washington. 

To keep traffic flowing and improve safety for freight and travelers, the Washington State Department of Transportation is building a diverging diamond interchange – only the second in the state – and widening SR 18 between the interchange and Deep Creek.

“We are investing in a transportation corridor that’s critical for moving travelers and products across our state while at the same time improving riparian and wildlife habitat and access,” said Inslee. “Together with cleaner fuels and more electric vehicles on the road, we are moving in the right direction for our people, our economy and our environment.”

Gov. Inslee was joined by U.S. Rep. Kim Schrier, Snoqualmie Tribal Chair Robert de los Angeles, state Sen. Mark Mullet, and state Reps. Bill Ramos, Lisa Callan, and local, county and business leaders.

WSDOT has contracted with design-builder Aecon on this $188 million project. Work begins in November and is scheduled to be completed in 2025. The project has several environmental benefits. Crews will remove old culverts and fish barriers so salmon and other native fish can access nearly 13 miles of streams. New four-lane bridges at Deep Creek and Lake Creek will allow wildlife to cross safely under the freeway. The project also adds a second two-lane bridge over the Raging River, doubling the lanes available to traffic.

“The Snoqualmie Tribe extensively advocated for this project and consulted on it, and we are pleased that Gov. Inslee, the state Legislature and WSDOT have treated this project as the urgent public safety priority it is,” said de los Angeles. “The Tribe supports the adoption of the innovative and safety-conscious diverging diamond interchange design because it will save lives and make the journey through our lands generally much safer.”

The project’s centerpiece is a diverging diamond interchange that lowers the potential for collisions by reducing the number of conflict points between vehicles from 26 to 14. In a diverging diamond interchange, through traffic and left turns to happen at the same time, eliminating the need for a separate left-turn phase and reducing the number of traffic lights.

James Harper, a WSDOT project engineer, said, “The widening project together with the diverging diamond interchange will keep traffic moving more freely, preventing backups at peak travel times.”

Secretary of Transportation Roger Millar discussed this project as a “home-grown highway project,” which is fully paid for with $183 million from existing gas tax funds and $5 million from the Connecting Washington funding package.

He continued by saying, “Washington has long been at the forefront of our expanding global economy, with millions of dollars in freight moving through our ports and to the rest of the nation every day. Our towns and cities are also growing, and the need to provide safe roads to travel on has never been higher. Our environment and our obligations to protect it have never been clearer.”

[Information provided by the Washington State Department of Transportation]

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