Good news: After nearly a decade of planning and design - and almost 20 months of construction - the new I-90/SR 18 Diverging Diamond Interchange will open Friday morning, July 25, 2025. To reach this project milestone, another round-the-clock, multi-day full closure of SR 18 underneath I-90 is needed, which starts Thursday night, July 17, 2025.

From 9 pm, Thursday, July 17, through 5 am, Friday, July 25, traffic will not be allowed along either direction of SR 18 beneath the I-90 bridges. People traveling through the I-90/SR 18 interchange during the closure should expect delays, especially during peak travel times, and follow signed detours.

Snoqualmie drivers are encouraged to plan detour routes ahead of time and add extra travel time to their commutes as many other drivers will be using those same detour routes.

Drivers can detour around the closure using eastbound and westbound I-90 and loop around at nearby interchanges – Preston/Fall City (exit 22) or Highpoint Way (exit 20) to the west and SE North Bend Way (exit 27) to the east. Exits 22 and 27 can also be used to access SR 202 as alternative routes into Snoqualmie. 

Some of the work needs dry weather and may need to be rescheduled if it rains.

Navigating the Interchange During Closure
Eastbound and westbound I-90 traffic will not be affected during most of the closure, but people traveling through the area should be aware that:

• Vehicles will not be permitted on either direction of SR 18 beneath the I-90 bridges.
• Traffic on the eastbound and westbound I-90 off-ramps will only be able to turn right.
• Eastbound SR 18 traffic must use the eastbound I-90 on-ramp and follow a detour.
• Southbound traffic on Snoqualmie Parkway must use the westbound I-90 on-ramp and follow a detour.

Before the closure
To help prepare for the switch to the diverging diamond pattern, crews need to install a permanent barrier along two of the four ramps that will remain open during the eight-day closure. To allow for this, travelers should expect ramp closures on the nights leading up to the extended closure:

• SR 18 on-ramp to eastbound I-90: Closes from 9 pm, Tuesday, July 15, until 5 am, Wednesday, July 16. People should detour using westbound I-90 and loop around to eastbound I-90 at Preston/Fall City (exit 22).
• Westbound I-90 off-ramp to SR 18: Closes from 9 pm, Wednesday, July 16, to 5 am, Thursday, July 17. People should continue on westbound I-90, loop around at Preston/Fall City (exit 22) and use the eastbound I-90 off-ramp to SR 18.

All four ramps also need to be restriped for the diverging diamond traffic pattern during the first night of the eight-day closure. People traveling through the area between 10 pm, Thursday, July 17, and 5 am, Friday, July 18, should expect a series of rolling slowdowns along eastbound and westbound I-90, and 10-minute traffic holds on eastbound SR 18 and southbound Snoqualmie Parkway approaching the interchange. Crews will update the striping on each ramp, one at a time.

After the closure
When SR 18 reopens Friday, July 25, SR 18 traffic will use the diverging diamond traffic pattern, where northbound and southbound traffic cross to the left side of the highway to go under the I-90 bridges before crossing back over. This eliminates vehicles turning left in front of on-coming traffic, allowing for fewer traffic signal phases and improving traffic flow. It also reduces the number of places where vehicles could possibly collide in the interchange from 26 to 14, improving safety.

• WATCH: Learn how a diverging diamond interchange works. 
• More info: I-90/SR 18 Interchange Improvements Project

In addition to building the new interchange, the project is widening more than 2 miles of SR 18 south of I-90 to two lanes in each direction and removing six barriers to fish passage. SR 18 widening is expected to finish later this fall.