Curious about the heavy traffic on Highway 18 over Tiger Mountain? The answer lies in its crucial role as a major thoroughfare linking South King County to I-90. With the rapid urban sprawl in the Northwest, this route has become vital for countless commuters. Unfortunately, the Tiger Mountain pass has proven perilous for Washington drivers, leading to frequent accidents, some of which have been tragic. The combination of these collisions and typical rush hour usage results in significant traffic delays that can persist for hours.

The SR 18 Improvement Project aims to address the growing traffic congestion and backups at the I-90/SR 18 interchange, which has become one of the busiest in the state due to the rapid growth in Snoqualmie Valley. To improve traffic flow, the Washington State Department of Transportation (WSDOT) plans to construct a diverging diamond interchange and add two lanes on SR 18 between the interchange and Deep Creek. The project is expected to be carried out from 2022 to 2025 and has a budget of $188 million.

The construction process will be divided into three stages, each lasting six to nine months. During these stages, traffic will be shifted to accommodate various work zones, resulting in intermittent lane and ramp closures overnight throughout the project’s duration. This is likely to cause increased congestion, prompting travelers to plan for extra time or seek alternative routes.

The first stage of construction began in April 2023, with contractor crews clearing trees in the project area to make way for the new interchange and highway widening. Currently, from 8 p.m. to 5 a.m. Mondays through Thursdays, lane reductions are in effect, with flaggers alternating traffic at the SR 18 interchange. However, this work is currently on hold and scheduled to resume on Monday, Aug. 7.

The project includes the removal of the old weigh station near the westbound I-90 on-ramp from Snoqualmie Parkway, installation of new utilities, and construction of a drainage pond at the interchange. Additionally, two full weekend closures of SR 18 between I-90 ramp intersections are planned for summer 2024 to facilitate the transition to the new diverging diamond configuration.

According to the WSDOT, the diverging diamond interchange is a proven traffic management solution that enhances safety by reducing potential collision points. By reducing the number of conflict points from 26 to 14, the diverging diamond interchange decreases the opportunity for collisions by 50 percent. It allows through-traffic and left turns to occur simultaneously, eliminating the need for a separate left-turn phase.

As the project progresses, WSDOT encourages people to stay informed through their email updates and plan ahead for potential delays caused by construction. Once completed, the reconstructed interchange and widened SR 18 are expected to improve safety performance and travel times on I-90, SR 18, and Snoqualmie Parkway, benefiting both commuters and wildlife by improving habitat connectivity.

Have you been injured in a Car Accidents on Highway 18 on Tiger Mountain?

If you are involved in a collision on SR 18, don’t delay—reach out to us today at 206-497-4357 to schedule a free consultation. Washington Auto Law is a trusted and dedicated personal injury law firm that fights tirelessly for auto accident victims. We will guide you through the recovery process, help you get your vehicle repaired or replaced, deal with the insurance companies, help you find the right medical care, and reach a fair money settlement. Remember, we work on a recovery guarantee or no fee basis.

Read “What to Do After a Car Accident in Washington”>

Learn More about the WSDOT I-90 – SR 18 Interchange Improvements>

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