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Southbound I-5 near Mountlake Terrace to close as Sound Transit goes over freeway

Another milestone for Sound Transit should be reached this weekend, as the Lynnwood extension begins its journey over I-5.

The light rail extension from Northgate to Lynnwood travels on the east side of I-5 all the way to the Snohomish County line, but the Lynnwood station is on the west side of the freeway. The light rail tracks will cross the freeway just north of the transit center in Mountlake Terrace. This weekend, the work on the connection over the freeway begins.

“It’s a lot of work, and it can’t be done when the freeway is open, for obvious reasons,” Sound Transit’s John Gallagher said.

Contractors must close the freeway to get this work done, so the southbound lanes of I-5 will be closed Friday, Saturday, and Sunday nights.

“That’s to construct falsework,” Gallagher said. “Falsework is a temporary steel column system that’s used to support the construction of the concrete deck, on top of which the light rail trains are going to travel.”

All southbound drivers will be forced to exit I-5 at 220th. The detour takes you south on Highway 99 to Highway 104 where you can rejoin the freeway. The closures begin at 11 p.m. each night, and the freeway should be open by 6:30 a.m. the next morning.

Southbound commuters Monday morning will be driving under this falsework structure for the first time. Sound Transit’s Gallagher said northbound drivers will have a similar series of nighttime closures coming up.

“In early 2021, we’ll be doing the same thing for the northbound lanes,” he said. “We’ll be giving people plenty of notice when we have that date nailed down.”

It’s been about a year and a half since Sound Transit started clearing the trees to make room for the Lynnwood extension, and the construction has been moving at a brisk pace ever since.

“We’re about 20% done with the civil construction,” Gallagher said. “Anyone who drives along I-5 can see that the landscape is changing, the columns are going up, the girders are going in, and you can really see what the shape of the alignment is going to be.”

The extension to Lynnwood is expected to open in 2024, the same year that light rail should open to Redmond. There are four stations along the route, and Sound Transit says it should take you about 30 minutes to get from Lynnwood to downtown Seattle.

Check out more of Chris’ Chokepoints.

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