Local Information

Milestone decisions for I-90/SR 18 interchange improvement project near Snoqualmie

Thursday, September 19, 2019 - 13:24

Kris Olsen, communications, 206-440-4704

SNOQUALMIE – Three major advancements have pushed the I-90/SR 18 interchange improvement project in Snoqualmie into the next phase of development. This includes decisions about the interchange, an improved on-ramp to westbound Interstate 90, and a new weigh/inspection station.

Preferred alternative for interchange improvement
The Washington State Department of Transportation has selected a diverging diamond interchange to improve traffic flow and reduce congestion. A diverging diamond interchange moves more cars and reduces conflict points among vehicles compared to traditional diamond interchanges.

“There are more than 60 diverging diamond interchanges around the country and they consistently show collisions decrease,” said WSDOT Engineering Manager John Chi. “Our traffic models show this new interchange will prevent the backups that occur every day, and get more highway users on and off the highway in a safe and efficient manner.”

WSDOT will be conducting interchange design, environmental investigation and analysis along with more community engagement through 2020. Construction is scheduled to begin in 2021 with the new interchange opening in 2023.

The state’s first diverging diamond interchange is under construction on the State Route 510 intersection with I-5 near Lacey.

New inspection/weigh station
WSDOT is taking a fresh look at locations for a Washington State Patrol freight inspection station farther east of North Bend. Following guidance from local agency, county, and city representatives and extensive community feedback, WSDOT will work with the Washington State Patrol to continue the search for other viable sites.

The $150 million interchange improvement and weigh station project is funded through the 2015 Connecting Washington transportation program.

New on-ramp to westbound I-90
Next month, contractors will begin upgrading the existing ramp from Snoqualmie Parkway to westbound I-90. WSDOT awarded the contract to Road Construction Northwest, Inc. of Renton. The decommissioned westbound weigh station property will be used to create a second on-ramp lane for highway users. Construction is scheduled to begin next month.

“We are very pleased that this much-needed temporary designated on-ramp project is now moving forward and is projected to be completed before the end of the year,” said Snoqualmie Mayor Matt Larson. “It will provide immediate morning traffic congestion relief three years prior to original projections.”

The modifications include:

  • A dedicated right turn lane with no traffic signal for southbound Snoqualmie Parkway to westbound I-90 drivers, along with a dedicated ramp lane.
  • A dedicated ramp lane for eastbound SR 18 drivers turning west onto I-90.
  • A retimed traffic signal for SR 18 to westbound I-90 to provide a longer green light for drivers.
  • Traffic meters for both ramps.

The additional ramp lane and retimed signal will result in shorter backups and improved traffic flow at this intersection. This $1.2 million project is funded by WSDOT, the cities of Snoqualmie, Covington, Maple Valley, and the Snoqualmie Tribe. The on-ramps will be modified again and connected to the new I-90/SR 18 interchange prior to its opening in 2023.

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