The Washington State Department of Transportation (WSDOT) has installed signs on eastbound Interstate 90 near Snoqualmie to warn drivers of traffic backups at the Highway 18 interchange.

The two lighted signs alert drivers to slow or stopped vehicles ahead in the right lane as heavy traffic exiting onto Highway 18 backs up onto the freeway.

The signs, which automatically activate depending on traffic conditions, were installed on I-90 at exit 22, 2 miles ahead of the Highway 18 interchange, and at exit 25, about 1 mile ahead.

Traffic Lab is a Seattle Times project that digs into the region’s thorny transportation issues, spotlights promising approaches to easing gridlock, and helps readers find the best ways to get around. It is funded with the help of community sponsors Alaska Airlines, CenturyLink, Kemper Development Co., NHL Seattle, PEMCO Mutual Insurance Company and Seattle Children’s hospital. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

The signs cost $594,000 and are paid for through state transportation funds.

From May 2016 to this past Friday, 266 crashes were reported on I-90 both eastbound and westbound, and at its interchanges, between mileposts 22 and 26, WSDOT said.

Of those crashes, 192 occurred on the main corridor and 74 occurred at onramps and offramps.

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No fatalities were reported, but 156 people were injured.

WSDOT has been planning to make safety improvements to the Highway 18 interchange. Design work began in 2017. Construction is scheduled to begin in 2021, and work is expected to be finished in 2023. The project, funded through a gas-tax increase approved in 2015, will cost about $150 million.

In the meantime, WSDOT is planning what it calls additional low-cost improvements.

In the next few months, WSDOT will extend the “exit only” striping more than 1 mile back on the eastbound I-90 approach to the Highway 18 exit. The work has been added to a paving project at no additional cost.