SR 18 to close for eight days for construction at I-90

The new I-90/SR 18 interchange opens next week after nearly two years of construction, but drivers have eight days of pain to endure before that happens.

SR 18 will close under I-90 in Snoqualmie at 9 p.m. Thursday for construction. You will not be able to travel under I-90 until next Friday, July 25. A similar closure in June only lasted a few days.

“There’s a lot more work that’s involved this time,” David Rasbach, communications coordinator for the Washington Department of Transportation (WSDOT), said. “There’s a lot of electrical work to get the traffic signals set up, get some cameras set up, some drainage, more islands to build, more paving to do, getting the on ramps to I-90 set and everything like that.”

Drivers will still be able to access I-90 from SR 18, but only in very limited ways.

“If you’re going on eastbound SR 18, you’re going to have to take eastbound I-90,” Rasbach said. “And it’s the same thing coming from Snoqualmie, you have to get on westbound I-90.”

You will only be able to make a right turn from SR 18 to I-90. The simplest thing to do is to get on I-90 and go up one exit and make a U-turn. The traffic was manageable during the closure in early June.

“Expect delays, add extra time,” Rasbach said. “Leave early if you need to be somewhere on time, or just expect delays. We realize this is a big closure to close SR 18 under the bridges.”

What comes after the eight-day closure

After this eight-day closure, drivers will be using the new diverging diamond interchange, but the work isn’t finished. There will still be work around the interchange and on SR 18 toward Tiger Mountain.

“We still need to widen SR 18 to two lanes in each direction down to Deep Creek,” Rasbach said. “It’s currently only one lane in each direction. We’re getting close to that. Probably this fall we’ll open that, and that’s when we really think you’re going to see the diverging diamond shine.”

This will be the second diverging diamond interchange to open in Washington. The first was in Lacey.

What makes a DDI unique is that you drive on the left side of the road. This cuts down on the possible conflict points where cars and pedestrians can interact. It’s really designed to cut down on making left turns in front of oncoming traffic. It will seem strange at first, but drivers will adjust quickly.

“It’s really as easy as following the lines and signs,” Rasbach said. “They’re clearly marked with lines, arrows, signs that point you in the right direction, so you just follow that.”

WSDOT chose to do a full eight-day closure to get the project finished as fast as possible and cut down on multiple weekend and overnight closures.

Chris Sullivan is a traffic reporter for KIRO Newsradio. Read more of his stories here. Follow KIRO Newsradio traffic on X.

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