Project Info

Budget Information

I-90 - SR 18 Interchange Improvements

Project news

  • The I-90/SR 18 Interchange Improvements project is funded through Connecting Washington.
  • Connecting Washington is a $16 billion investment in our state's multimodal transportation future.
  • This project was awarded to CH2M Hill, Inc.


The Washington State Legislature approved $150 million to improve travel times and safety performance at the Interstate 90 and State Route 18 interchange. The funding is part of the larger $16 billion Connecting Washington package.

The original timeline to begin the project was not scheduled until 2023. However, during the 2017 legislative session the funding to design and construct interchange improvements was moved up by six years.

Why is WSDOT making interchange improvements?
With rapid growth and development in Snoqualmie and surrounding communities, the I-90/SR 18 interchange is one of the busiest interchanges in our state. Local traffic, freight and other cross-state travelers are causing backups on both routes during peak periods and busy travel weekends.

At this time, a Diverging Diamond Interchange (DDI) is the preferred concept, as WSDOT believes it can provide improved traffic flow and congestion relief for all of the movements at I-90/SR 18. More than 80 have been constructed around the nation and WSDOT will soon be building its first DDI in Lacey at I-5 and SR 410. You can see how a diverging diamond interchange works by viewing this DDI video on WSDOT's YouTube channel.

Weigh station
As part of this project, WSDOT will perform a detailed study to determine whether the eastbound I-90/SR 18 interchange weigh station can be moved to a new location to better allow the Washington State Patrol to enforce weight and safety requirements for eastbound freight traffic.  
Past improvements
WSDOT has been keeping a close eye on this intersection and whenever possible, making low-cost improvements. WSDOT has already:

  • Widened the eastbound I-90 off-ramp to SR 18.
  • Changed the right lanes of eastbound and westbound I-90 to exit-only lanes.
  • Partnered with the city of Snoqualmie to change the lane configuration on southbound Snoqualmie Parkway by making the southbound right lane a right-turn only lane to the I-90 westbound on-ramp.
  • Adjusted traffic signal timing at the two signalized intersections to operate the interchange as efficiently as possible.

Upcoming improvements
WSDOT engineers will work to design interchange improvements to the area. In the meantime, travelers in this area can expect to see the following changes:

  • Installation of warning signs on I-90 in advance of the SR 18 interchange to guide through traffic to stay in the left two lanes. This will help keep the right two lanes of I-90 clear for the slow-moving vehicles destined for SR 18 or Snoqualmie Parkway.
  • Installation of no U-turn signs on SR 18 at the interchange to prohibit the U-turning movements that are causing congestion issues for the off-ramp traffic.

Community Engagement
As we near the design phase of this project WSDOT will thoroughly communicate with those who travel the interchange. A key goal during the construction phase will be to keep communities and neighborhoods in the area well informed about upcoming work and the impacts construction could have on the traveling public.  All constituents who travel this interchange are encouraged to attend open houses and share feedback with WSDOT through email, social media, phone calls or in person.


The End Result
This project will increase capacity at the interchange to better serve the thousands of commuters, freight industry workers and general travelers who use it each day.

Project Benefits
The $150 million Connecting Washington investment into the I-90/SR 18 interchange will improve safety performance and travel times on I-90, SR 18 and Snoqualmie Parkway.

What is the project timeline?
While construction on the interchange is not likely to begin until 2020, the advancement of the funding allowed WSDOT to start the design portion of the project in October 2017. This project is part of the Connecting Washington transportation package.

Financial Information

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) $124,500
CWA $3,500
Total $128,000
  • The 2015 Connecting Washington transportation funding package is expected to provide up to $150 million for this project.
  • The funding will go towards an environmental study of the area, engineering, right-of way acquisition, and construction.


How can I get more information?

Kris Olsen

Harmony Weinberg