An example of the diverging diamond used in WSDOT’s explanation of the design. The Diverging Diamond design is planned to be implemented at the interchange of I-90 and SR 18. (Courtesy Photo)

An example of the diverging diamond used in WSDOT’s explanation of the design. The Diverging Diamond design is planned to be implemented at the interchange of I-90 and SR 18. (Courtesy Photo)

State route 18 interchange project still scheduled to break ground next year

The project would redesign the intersection and widen the highway.

A project to improve the I-90 and State Route 18 interchange is still scheduled to break ground next year, even amid the coronavirus pandemic.

The project is being driven by the Washington State Department of Transportation, which will build a new interchange at the intersection to improve traffic flow. Improvements will reconfigure the interchange to a diverging diamond structure, and widen 1.5 miles of State Route 18 to four lanes.

The interchange is one of the busiest in the state. Backups are common near the interchange during commuter hours and busy weekends.

An update on the project was delivered at the July 27 Snoqualmie City Council meeting by Mark Allison, a project engineer with the Department of Transportation.

Since the project design was selected a year ago, the state has been refining the project and hopes to send out a request for bids this fall. Construction is slated to begin in 2021 and wrap up in 2024. However, the Department of Transportation is expecting a $1.3 billion loss of revenue over the next three years due to the COVID-19 pandemic. It’s unclear which projects will be impacted by the budget cuts.

The state submitted an application for a federal grant, and is waiting to hear if it is approved.

The redevelopment plan initially included a weigh station for freight trucks. The former westbound weigh station near the interchange was closed to make way for the improvements. This was removed from the project, and will instead be located some 5 miles to the east near Tinkham Road. Construction on the weigh station is set to begin in 2022.

The interchange project was originally funded for $150 million, Allison said. The project now has a budget of around $146.5 million.

Improving the interchange is one way the state is trying to make State Route 18 safer. The winding, narrow road has been the source of numerous crashes as the population in King County has increased.

After a crash killed two in 2018, the Snoqualmie Casino even offered $1 million to accelerate safety projects along the corridor. From December 2017 to October 2018, there were six fatalities along a 7-mile stretch of the state route. Statewide during the same time, there were 38 deaths on state routes and interstates in King County.


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