I-90 - SR 18 Interchange Improvements

Project news

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. At this time a Diverging Diamond Interchange (DDI) is the leading concept, but WSDOT is conducting extensive community engagement, traffic and environmental analyses as an interchange design is developed and refined. 

The current, westbound weigh station at the I-90/SR 18 interchange will need to close to make way for the interchange improvements. The current weigh station was established over fifty years ago to weigh westbound logging trucks. Today, most freight is headed east, which means the existing weigh station is not frequently used.

With this project, 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 low-cost improvements, when feasible, to manage congestion until the improved interchange is complete. Upcoming low-cost improvements being made in winter 2018 and spring and summer 2019 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
2021: 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) $145,600
CWA $5,000
Total $150,600

Project area map thumbnail