I-90 - SR 18 Interchange Improvements

Project news

  • WSDOT has selected a diverging diamond interchange as the preferred alternative for improvements.
  • We awarded a contract to build an auxiliary ramp from Snoqualmie Parkway to westbound I-90 to Road Construction Northwest, Inc. of Renton as part of this project.  
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  • View project photos on the WSDOT Flickr account

Needs & benefits

With rapid growth and development in Snoqualmie and surrounding communities, the I-90/SR 18 interchange is one of the busiest in the state. The interchange serves people who live in the area, in addition to freight haulers and cross state travelers. Backups near the interchange are common during peak periods and busy travel weekends.  In summer 2019 WSDOT selected a Diverging Diamond Interchange as the preferred alternative. In addition, this project will widen nearly 1.5 miles of SR 18 to four lanes from the interchange to Deep Creek. 

The westbound weigh station at the I-90/SR 18 interchange is now closed to make way for the interchange improvements. The weigh station was established over fifty years ago to weigh westbound logging trucks. Today, most freight is headed east, which means the weigh station was not used. WSDOT used this area to upgrade the SR 18/Snoqualmie Parkway on-ramp to westbound I-90. Crews upgraded the ramp so southbound Snoqualmie Parkway drivers now have a dedicated right turn and ramp lane using the old weigh station inspection lane. SR 18 to westbound I-90 drivers also have a dedicated ramp lane, using the existing on-ramp. Construction began in October 2019 and final ramp improvements will be completed in spring 2020. 

WSDOT is working with the Washington State Patrol to build a new Port of Entry weigh and inspection station on eastbound I-90 which will support weight and safety inspections of trucks headed east.

WSDOT will continue to monitor traffic in the area and make other low-cost improvements, when feasible, to manage congestion until the improved interchange is complete. Upcoming low-cost improvements include installation of advance warning signs on I-90 to notify drivers when they are approaching congestion on I-90 and “exit only” striping on the eastbound I-90 approach to the SR 18 exit.


2017: Design work initiated
2018: Jacobs (CH2MHill) selected to assist WSDOT in preparing the request for proposals
2018-2019: Community engagement, environmental and traffic analysis
September 2019: Announced diverging diamond interchange as preferred alternative 
December 2019: New auxiliary ramp from Snoqualmie Parkway to westbound I-90 open
2021: Interchange construction tentatively scheduled to begin
2023: New interchange opens


Financial Data for PIN 109070F
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $183,525
CWA $5,000
Total $188,525

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