I-90 - SR 18 Interchange Improvements

Project news

  • The I-90/SR 18 Interchange Improvements project is funded through Connecting Washington.
  • WSDOT awarded CH2MHill, Inc. a contract to assist WSDOT in conducting environmental planning, developing the preliminary design, and preparing the documentation needed for the Request for Proposals from contractors interested in completing the design of an improved interchange and widening of SR 18.

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. Well used by people who live in the area, freight haulers, and cross state travelers, backups on both routes during peak periods and busy travel weekends are common. At this time a Diverging Diamond Interchange (DDI) is the leading concept, but WSDOT will conduct extensive community engagement, traffic and environmental analysis as an interchange design is developed and refined.  

WSDOT will also conduct a detailed study to determine the optimal location for relocating the existing I-90 / SR 18 interchange weigh station, which is in the way of an improved interchange. WSDOT will analyze locations along eastbound I-90 that would support the Washington State Patrol commercial vehicle enforcement needs for eastbound freight traffic. 

Improving the interchange and widening SR 18 will provide better traffic flow and congestion relief. Other benefits include increased safety performance by eliminating weaving and improved travel times on I-90, SR 18, and Snoqualmie Parkway. Relocating the weigh station will also provide more truck parking and help reduce freight traffic on local city streets. 

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. Already planned for construction this year are advance warning signs on I-90 to notify drivers when they are approaching congestion on I-90. 


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) $145,000
CWA $5,000
Total $150,000

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