SR 18 under I-90 closes for 5 days: Major detours start Thursday

It’s one of the busiest and most congested interchanges in the state, and you won’t be able to use it for about a week.

State Route 18 (SR 18) closes at 9 p.m. Thursday and won’t reopen until 5 a.m. next Wednesday. That’s slightly more than five days of frustration for drivers who just want to use SR 18 under I-90 in Snoqualmie.

“If you’re heading northbound on SR 18, you’re going to have to get on eastbound I-90, and if you’re headed southbound on Snoqualmie Parkway, you’re going to have to get on westbound I-90,” said David Rasbach, the construction communicator for the Washington Department of Transportation (WSDOT).

Westbound I-90 drivers will not be able to access southbound SR 18. Eastbound I-90 drivers will not be able to head up Snoqualmie Parkway. You will have to go to the next exit and loop around.

“Definitely expect extra time, plus you’ve got to factor in the little extra distance you have to travel for the detours looping out to the next interchanges,” Rasbach said.

And this might not be the only major full closure of SR 18 in this area. The contractor still needs some extended time to build the north end of the interchange.

“That is still to be determined,” Rasbach said. “That will either be another longer closure or a series of shorter closures. We’re still determining what will be the best way for that.”

The entire interchange, which is a diverging diamond configuration, is on schedule to open this summer. The widening of SR 18 just south of I-90 should wrap up in the fall.

Big changes are coming over next few weeks

“We are anticipating moving traffic onto the new Deep Creek and Raging River bridges in the next few weeks, early June, perhaps, so that will be a big milestone for this project,” he said.

And a big change is coming for drivers. This will be the second completed diverging diamond interchange in the region, and it should make a huge difference.

“The whole reason we’re building the diverging diamond interchange is to improve traffic flow through this busy corridor, which is one of the busiest interchanges in the state.”

Once this work is complete, WSDOT will start on the widening and paving of SR 18 down the west slope of Tiger Mountain to the Issaquah-Hobart Road.

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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