I-90 - SR 18 Interchange Improvements

Project news

  • During fall 2018 and through second quarter 2019, we are convening a Stakeholder Advisory Group and an Executive Advisory Group to bring together community representatives to discuss:
    • Ways the interchange functions poorly
    • SR 18 widening
    • Weigh/inspection station relocation
    • Design and construction constraints
    • Project priorities
    • Design concepts
  • Check back in early 2019 for information about our in-person and online open houses to gather community input on possible alternatives.
  • Sign up for project updates.
  • View project photos on the WSDOT Flickr account.
  • This project is funded through Connecting Washington.

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. 

WSDOT is conducting 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 the interchange improvements. WSDOT is analyzing 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 remove a source of congestion for the area and allow the Washington State Patrol to better enforce commercial traffic heading 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) $145,000
CWA $5,000
Total $150,000

Project area map thumbnail