I-90 / SR 18 Interchange Improvements

The Interstate 90 / State Route 18 interchange is a problematic transportation challenge for Snoqualmie. Thankfully, after many years of meetings with the Washington State Department of Transportation and local leadership testimony in Olympia,  the Washington State Legislature approved $150 million to improve travel times and safety performance at the interchange. During the 2017 legislative session, the funding to design and construct interchange improvements was moved up by six years from 2029 to 2023. 

Project Description

The Washington State Department of Transportation (WSDOT) will conduct extensive community engagement, traffic analysis, and environmental analysis as an interchange design is refined. At this time a Diverging Diamond Interchange is the leading concept.  

WSDOT will conduct a detailed study to determine the optimal location for relocating the existing I-90 / SR 18 interchange weigh station to increase space available for the new interchange. WSDOT will analyze locations along eastbound I-90 that would support the Washington State Patrol commercial vehicle enforcement needs for eastbound freight traffic. 


  • Improved traffic flow and congestion relief
  • Increased safety 
  • Improved travel and commute times on I-90, SR 18, and Snoqualmie Parkway
  • Reducing freight traffic on local city streets by relocating the weigh station


2017: Design work initiatied
2018-2019: Environmental and traffic analysis; community engagement
2020: Construction scheduled to begin (tentative)
2023: New interchange opens

WSDOT will continue to monitor traffic in the area and make low-cost improvements, when feasible, to manage congestion until the new interchange is complete. Installation of advance warning signs on I-90 is planned for 2018. The signs will notify drivers when they are approaching heavy congestion at the interchange. 

  1. Daniel J. Marcinko

    Parks & Public Works Director
    Phone: 425-888-8009