WSDOT names contractor for State Route 18 intersection project

Construction to begin this year.

Map of construction area. Courtesy of WSDOT.

Map of construction area. Courtesy of WSDOT.

The Washington State Department of Transportation (WSDOT) has selected a contractor for the I-90/State Route 18 intersection project, one of the final steps before construction can begin on the decades-long $190 million project.

WSDOT announced Jan. 13 that Aecon Pacific Northwest Inc. had been selected to complete the design and rebuild of the interchange.

“This is a significant project and one the community has anticipated for a long time,” said WSDOT project engineer Mark Allison. “We look forward to working with Aecon to build an interchange that will serve people for many years.”

Improvements along SR 18, including at the interchange, has been a high priority item for Valley cities, the Snoqualmie Tribe and the SnoValley Chamber of Commerce for over a decade. The road is critical to the state’s economy and is one of the most dangerous in King County.

Nearly 23,000 vehicles use the road daily, including roughly 4,000 commuting to jobs in the Valley. Freight trucks also frequent the highway, transporting more than 10 million tons of freight annually, making it one of the state’s most used.

Construction at the intersection would build a diverging diamond interchange, which is expected to improve traffic flows at the highly congested intersection and reduce the number of traffic signals.

“It feels good to know that the life’s work of a lot of people has come to fruition,” said Kelly Coughlin, the executive director of the SnoValley Chamber, calling the project a huge victory for the local business community and those commuting on the road.

As part of the project, the highway will be widened to two lanes in both directions for about two miles from the intersection to Deep Creek.

The project will also construct a new four-lane bridge over Deep Creek, a new two-lane southbound bridge over Raging River and a dedicated turn lane from southbound Snoqualmie Parkway to westbound I–90.

Construction on the project is expected to begin later this year, tentatively set for May or June, and projected to finish in 2025.

The $190 million project was funded through a pre-existing gas tax and the 2015 Connecting Washington transportation fund — a $16 billion investment that enhances statewide transportation systems.

The project was delayed a year by the pandemic, with many fearful it would lose its funding, Coughlin said. After Aecon signs the contract for the project in February, it will represent the last major milestone before construction.

Although the project is expected to reduce traffic accidents and congestion, Coughlin said residents should expect some growing pains. WSDOT estimates construction at the interchange will require four full weekend closures alongside single-lane closures during the widening process.

As this project goes forward, the section of SR 18 between Issaquah-Hobart Road and Deep Creek, near Tiger Mountain, remains the last part of the highway in need of widening to four lanes.

This part of the highway has already received funding for the design phase, but needs additional funding to green-light construction. The 5th District’s state legislators are working to pass a state transportation package that would include funding for SR 18 during their 60-day legislative session that began Jan. 10.

State Sen. Mark Mullet (D-Issaquah) listed the transportation package as his top legislative priority. He said he hopes to fund the package through surpluses in the operating budget and federal support, without raising the gas tax.

“[The] revenue package will, among other things, provide the funds to finish Highway 18,” he said. “This deadly highway needs to be improved as soon as possible.”


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State Route 18 near Snoqualmie. Courtesy Photo.

State Route 18 near Snoqualmie. Courtesy Photo.

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