Traffic

Coming soon to Lacey: This bizarre-looking interchange, the first of its kind in Washington

Diverging Diamond Interchange coming to Lacey

WSDOT will build the state’s first diverging Diamond Interchange (DDI) at I-5 and State Route 510 in Lacey in 2018. DDI’s are a proven way to move more people and reduce the potential for collisions by reducing conflict points.
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WSDOT will build the state’s first diverging Diamond Interchange (DDI) at I-5 and State Route 510 in Lacey in 2018. DDI’s are a proven way to move more people and reduce the potential for collisions by reducing conflict points.

The state’s first so-called diverging diamond interchange will be constructed on Marvin Road at Interstate 5 in the Hawks Prairie area of Lacey starting this summer.

The $72 million project is scheduled to be completed in 2020.

Transportation officials say don’t let the crisscrossing lanes scare you. The design keeps traffic moving by eliminating left turn lights: Once completed, drivers turning left from Marvin Road onto I-5 won’t have to stop at a light.

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Courtesy Washington State Department of Transportation

“Picture how often you as a driver sit waiting at a highway interchange for a left turn light to get on the highway,” said Doug Adamson, spokesman for the Washington State Department of Transportation.

The interchange is at the center of one of the fastest growing areas in Lacey. Since 2000, average daily traffic on the north side of the interchange has quadrupled, according to Roger Schoessel, city engineer for Lacey.

“It's going to keep growing, there's no doubt,” Schoessel said.

Last year the city widened part of Marvin Road and is now rebuilding Hogum Bay Road to accommodate more traffic.

As part of the interchange work, WSDOT will add a frontage road on the north side of I-5. The city expects that area to be developed in the near future.

There also will be safety improvements for cyclists and pedestrians on the interchange and turn lanes added to nearby Quinault Drive for drivers turning onto Marvin Road.

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Courtesy Washington State Department of Transportation

Most of the disruption during construction will be on Marvin Road, Adamson said. As much work as possible will happen at night, though there will be daytime lane closures, ramp closures and detours.

Two total closures of the interchange will happen toward the end of construction.

While the diverging diamond design is new to Washington, there are dozens of them across the country, according to WSDOT, including in Oregon, California and Idaho.

As for the look of it, Adamson said drivers will be fine as long as they follow the lines and the signs.

“Many people don’t actually realize they're in the diverging diamond interchange until they’re through it,” he said.

More on the project

WSDOT will hold two open houses in Lacey this month to talk about the project.

May 15: 5 to 7 p.m. at Nisqually Middle School, 8100 Steilacoom Road SE

May 22: 5 to 7 p.m. at Salish Middle School, 8605 Campus Glen Drive NE

Abby Spegman: 360-704-6869, @AbbySpegman
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