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UW scientists trying to quiet 520 bridge noise impacting neighbors

(Photo: Matt Pittman, MyNorthwest)

It’s hard to tell a bridge to keep it down when it’s noisy. But residents in the Medina, Clyde Hill, and surrounding neighborhoods are hearing a grating “ka-think” noise every time a vehicle runs over the metal expansion joints. Since that happens thousands of times a day, it’s becoming a major problem.

Stretching from Interstate 405 to Interstate 5, the new $4.6 billion 520 corridor was never intended to be a loud bridge, reports The Seattle Times. Its sound-muffling technology includes a grooved pavement that minimizes tire noise and adjacent sound-reducing walls. The expansion joints remain a problem, despite installed steel plating around them to contain the sound.

Hundreds of neighbors have complained about the noise since the bridge opened in 2016, and because drivers will not be taking another route just to keep it down, the city is having to take action.

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This past fall, University of Washington scientists set up microphones on the bridge in order to find potential solutions to the ongoing noise. According to the Times, different sized vehicles produce a unique sound as they cross over the expansion joints, with wide tires on buses creating a low bass, and sedans generating a high-pitched buzz.

It’s been noted that the sound tends to be worse at night when cars are traveling faster, which has disturbed residents during dinner and when they’re trying to sleep. The UW team found sounds in the range of 75 to 80 decibels at its peak. A previous WSDOT study found the bridge stayed under the U.S. government’s 67-decibel limit, though that data was based on a 15-minute average.

Results from the $181,000 Legislature approved study will be discussed with Medina city leaders Dec. 13, and WSDOT will give a report to lawmakers by early January.

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