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Diverging Diamond interchange taking shape in Lacey


We’re about a year into construction on Washington’s first “diverging diamond” interchange, and I-5 drivers in Lacey are about to get their first benefits of the project.

Drivers have been dealing with construction delays and closures for more than a year, but next week they should be getting a new ramp.  The new ramp from Marvin Road to southbound I-5 is expected to open next week.

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Doug Adamson, with the Washington State Department of Transportation, said this should smooth out that transition and ease congestion.

“A lot of people go through every single day, including this new ramp, which will serve 14,000 vehicles a day,” Adamson said.

The one question I get about this project right now is “what’s with the new paved road just to the right of this new ramp.” There is a freshly-paved and unused stretch of road that extends from this ramp.

The new ramp will eventually provide access to new developments that the City of Lacey has planned in the future. Instead of building this frontage road later, WSDOT decided to put it in now.

“When the City of Lacey is able to build the connecting streets, then they’ll be able to connect in,” Adamson said.

So drivers are just going to have to stare longingly at that unused lane until Lacey is ready.

As for an update on the diverging diamond interchange itself, Adamson said they are on track to get it open in about a year. The overpass has been widened by eleven feet, and now the focus is on building the new on- and off-ramps.

I know there are still questions about driving through a diverging diamond interchange because it forces drivers into the opposite lanes of traffic as they cross the freeway, but if you can follow traffic lights, you will be fine.

“The great thing about a diverging diamond interchange is there is nothing new for you to learn,” Adamson said. “You come up to the stop sign and you wait for the green and you go.”

By driving on the opposite side of the road, it allows drivers to take free left turns without worrying about cross-traffic. It is more efficient and safer than a traditional freeway interchange.


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