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Washington’s first diverging diamond interchange opening soon in Lacey


The state’s first diverging diamond interchange is about to open.

What makes this interchange so different? It’s more efficient, it’s safer, and it moves more people. It also puts drivers on the opposite side of the road as they cross the freeway overpass. Diverging Diamond Interchanges have been popping up around the country for about a decade, but the Marvin Road overpass of I-5 in Lacey will be the first one in Washington when its scheduled to open in about a week and a half.

What makes these interchanges so unique is that drivers go the wrong way across the overpasses. You are shifted into what would normally be the oncoming traffic lanes as you cross the freeway, and one direction of traffic goes at a time. So people who want to get on the freeway no longer have to wait for oncoming traffic or a second traffic signal.

The Washington Department of Transportation’s Doug Adamson said it might seem odd at first, but it makes a lot of sense.

“There’s absolutely nothing new to learn,” Adamson said. “You follow the signs and lines.”

Just follow the car in front of you. If you’re first in line at the light, just follow the road. You will be channeled into the proper lanes so it’s nearly impossible to make a mistake.

“There are raised barriers through there, and really, you are funneled through there, kind of like water flows through a creek,” Adamson said.

As the contractor moves into this final phase, drivers in Lacey can expect a lot of lane closures and other traffic disruptions, both on the freeway and surface streets. The entire interchange will be closed for the last weekend of the month.

This is just the first of several diverging diamonds on the drawing board in Washington. It’s how the state plans to overhaul the Highway 18 and I-90 interchange in Snoqualmie. Construction there is set to begin next year.

Phase 2 of Lacey's diverging diamond set to begin

Major I-5 construction is set to begin as early as April 1 in Lacey as our first diverging diamond interchange project enters its next phase. Work will take place at I-5 and Marvin Road and temporary changes will mean anyone who uses the overpass should add plenty of extra time to their trips. There will also be around-the-clock lane reductions on the Marvin Road overpass itself as it is converted into a diverging diamond interchange.

Posted by WSDOT on Tuesday, March 19, 2019

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