Tunnel off-ramp to tame one of worst chokepoints on Eastside

Dec 14, 2023, 5:51 AM | Updated: 4:24 pm

eastside chokepoint...

(Photo: Chris Sullivan/KIRO Newsradio)

(Photo: Chris Sullivan/KIRO Newsradio)

A new tunnel off-ramp opens Thursday, which is designed to tame one of the worst chokepoints on the Eastside. Anyone who travels around State Route 520 between Bellevue and Redmond knows this spot is a nightmare.

It’s 148th Avenue Northeast. It crosses 520 just south of the Microsoft campus, and it provides access to Bel-Red Road. It serves neighborhoods. It serves Microsoft. It serves business parks and strip malls.

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To take 148th Northbound from Eastbound 520 is relatively simple. You get off, take a loop ramp  and take a right at the signal. No biggie.

But to head southbound is a lot more challenging because of where many drivers want to go from that off-ramp. They want to want to head east, or take a left turn at NE 24th Street. The problem is that the street is only 600-feet from the off-ramp. There’s just not enough room.

“The left-turning traffic at the 24th/148th intersection would back up north and block off the ramp, and the ramp traffic was backing up onto the freeway,” Washington State Department of Transportation (WSDOT) Project Manager Tom La Bolle said.

To fix this daily backup, WSDOT split the off-ramp from Eastbound 520 to Southbound 148th and put in a tunnel that provides a way around that signal at 24th.

The left side will go up to 148th for the southbound movement, and the right side ramp splits off and goes underneath 148th through the tunnel,” La Bolle said.

If you are familiar with this spot, the tunnel puts you behind the strip mall which houses a Safeway. Those who want to head east from there can do it without clogging 148th. The tunnel should open before noon Thursday, and La Bolle said there will be a learning curve for drivers.

“It’s pretty well signed and, with time, we’re confident people will understand what the routes are and how to go about doing it,” he said.

There is a roundabout at the end of the tunnel to help distribute the traffic.

This is another example of WSDOT using its existing footprint to find ways to solve congestion.

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“Because of the existing infrastructure and especially with the construction of the Sound Transit guideway a more traditional flyover ramp was not an option,” La Bolle said. “The only direct way to address it was with a direct access ramp, and the only real feasible way to do that was through a tunnel.”

The new ramp and roundabout were designed with future growth in the neighborhood in mind.

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