I-90 / SR 18 Interchange Improvements

The Interstate 90 / State Route 18 interchange is a problematic transportation challenge for Snoqualmie. After many years of meetings with the Washington State Department of Transportation (WSDOT) and local leadership testimony in Olympia,  the Washington State Legislature approved $150 million to improve travel times and safety performance at the interchange.

Funding to design and construct interchange improvements was moved up by six years from 2019 to 2023 during the 2017 legislative session. 

As an interim solution to peak hour congestion, there is potential for a dedicated lane from Snoqualmie Parkway onto westbound I-90.*

Public Meetings

WSDOT will hold two public meeting to present designs and gather public input.

April 17, 6-8pm
Mount Si High School Freshman Campus
9200 Railroad Ave SE, Snoqualmie

April 18, 6-8pm
Twin Falls Middle School
46910 SE Middle Fork Rd, North Bend

*Interim Solution:
Dedicated  Lane from Snoqualmie Parkway onto Westbound I-90

Mayor Matt Larson, on behalf of the administration and staff, has been actively urging WSDOT to use a portion of the exit 25 weigh station as a temporary, designated on-ramp feeding from Snoqualmie Parkway onto westbound Interstate 90 during the interchange improvement project construction.

The overall investment would be approximately $1.2 million to be divided by a 50/50 match with the City of Snoqualmie. Senator Mark Mullet has secured WSDOT’s commitment to a $600,000 investment through a re-appropriation within the existing interchange project budget.

The Snoqualmie Tribe Impact Mitigation Committee has approved a contribution of $75,000 to the interim solution. The City of Covington's City Council approved a $50,000 contribution toward this project. Mayor Larson has also had positive conversations with the City of Maple Valley for a similar pending contribution.

The timeline for the dedicated lane is dependent on raising funds to be matched by WSDOT.

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. 


2017: Design work initiated
2018-2019: Community engagement, environmental and traffic analysis
2021: Construction tentatively scheduled to begin
2023: New interchange opens (anticipated)


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

More Information

Visit the
 WSDOT website for detailed information about this project.
  1. Daniel J. Marcinko

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