• Project

I-90 – SR 18 Interchange Improvements

Both directions of SR 18 will close under the I-90 bridges from 7 p.m. Thursday, July 17, through 5 a.m. Friday, July 25. During this eight-day closure, the diverging diamond interchange will be finished and traffic shifted into the final configuration. People can detour around the closure using eastbound and westbound I-90 and looping around and nearby interchanges.

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.

The southern end of the new interchange was built during a five-day closure of SR 18 under the I-90 bridges in late May and early June. A similar closure is expected to build the northern end and switch traffic into the final diverging diamond configuration. That closure has not yet been scheduled, but it is expected after the Fourth of July holiday weekend.

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

Eight-day SR 18 closure (July 17-25)

Starting Thursday night, July 17, both directions of SR 18 at the I-90 interchange will close around the clock for eight days, reopening Friday, July 25. 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 construction on the new diverging diamond interchange, including:

  • Placing new drainage and electrical crossings
  • Building concrete islands and curbing
  • Positioning and setting timing for new traffic signals
  • Completing the new I-90 on-ramps
  • Installing temporary lane striping and new signs to guide people through the interchange
  • Switching SR 18 traffic into the diverging diamond traffic pattern

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.