Construction Ramps Up at the I-90/SR 18 Interchange

Major construction for the Interstate 90/State Route 18 interchange improvement project begins in late spring. In the meantime, people traveling near the I-90 and SR 18 interchange should plan for increased congestion in the coming weeks as contractor crews install work zone signs and clear trees throughout the project area.

Aecon, the Washington State Department of Transportation’s contractor for this project, will build a new diverging diamond interchange, the second in this state. This will improve traffic flow and safety for people who use this busy corridor. Improvements to SR 18 include widening the highway to two lanes in each direction from the interchange to about two miles south.

Additionally, crews will build three new bridges to improve habitat for native fish species and area wildlife. The project is expected to be completed in 2025.

A separate project still in design will finish widening SR 18, where the last project left off, creating two lanes in each direction to Issaquah-Hobart Road. Crews are conducting geotechnical drilling along SR 18 to collect information for the design process. This project could begin as early as 2025.

Tree removal and landscape improvements
Crews will continue to clear trees along SR 18 through March to make room to widen the highway. When construction is finished, they will plant 14,000 new trees in the project area and 3,040 trees along I-90 between Issaquah and North Bend.

At least 382 felled trees will remain onsite and be used to improve fish and wildlife habitat. Six culverts, now barriers to fish passage, will be removed, opening up access to 13 miles of fish habitat essential for salmon and steelhead.

What travelers can expect
There will be intermittent lane and ramp closures for the safety of travelers and construction crews as work progresses. Travel lanes will also shift as crews move through the stages of construction at the interchange and along SR 18.

Online open house planned
In late March, WSDOT will host an online open house to share more details about the project and what to expect during the stages of construction. Stay informed by subscribing to project update emails or following WSDOT on social media.

Home-grown project
During the groundbreaking ceremony in September 2022, state Secretary of Transportation Roger Millar described this project as a “home-grown highway project,” which is fully paid for with $183 million from existing gas tax funds and $5 million from the Connecting Washington funding package.

[Information provided by the Washington State Department of Transportation]

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