• Project

I-90 – SR 18 Interchange Improvements

Both directions of State Route 18 will close under the I-90 bridges from 9 p.m. Thursday, May 15, to 5 a.m. Wednesday, May 21, for construction of the diverging diamond interchange. People can detour using eastbound and westbound I-90 and using adjacent interchanges to loop around -- exit 20 (High Point Way) or exit 22 (Preston-Fall City) to the west of SR 18 and exit 27 (Southeast North Bend Way) to the east of SR 18. Please expect delays, especially during peak travel times. Detour maps are in the maps and drawings tab on this page, and more information is available in a news release about the closure as well as our blog post for the 5-day closure.

Project overview

Growth in Snoqualmie Valley has made the I-90/SR 18 interchange one of the busiest in the state, causing backups during peak times and busy travel weekends. To improve traffic flow, WSDOT is building a diverging diamond interchange and adding two lanes on SR 18 between the interchange and Deep Creek.

Timeline
2022 - 2025
Project status
Construction
Funding
$188 million
Project hotline

What to expect

Building the diverging diamond interchange and widening SR 18 will be accomplished through several stages of construction during which travelers can expect traffic shifts, speed reductions and intermittent lane and ramp closures throughout the life of the project.

Congestion will increase during construction, so people should plan extra time for trips or find alternate routes.

Five-day SR 18 closure (May 15-21)

Starting Thursday night, May 15, both directions of SR 18 at the I-90 interchange will close around the clock for five full days, reopening Wednesday morning, May 21. This extended closure allows our contractor to complete critical work that would otherwise take months using the more common approach of overnight or weekend closures. Our crews will complete a major phase of work on the southern portion of the new diverging diamond interchange, including:

  • Installing new drainage and electrical crossings
  • Removing the existing SR 18 pavement, then rebuilding and paving the diverging diamond alignment south of the I- 90 bridges
  • Constructing concrete islands and curbs
  • Creating a left-turn lane from westbound SR 18 onto Southeast 104th Street
  • Installing a signalized U-turn so eastbound SR 18 drivers can head westbound toward Auburn

People can detour using eastbound and westbound I-90 and using adjacent interchanges to loop around -- exit 20 (High Point Way) or exit 22 (Preston-Fall City) to the west of SR 18 and exit 27 (Southeast North Bend Way) to the east of SR 18. We expect delays, especially during peak travel times. Please plan ahead, leave early and consider alternate routes if possible. Real-time traffic updates are available via the WSDOT app and travel map.

Reconstructing the I-90/SR 18 interchange will improve safety performance and travel times on I-90, SR 18 and Snoqualmie Parkway.