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Overzealous application of de-icer was to blame for a series of crashes on the West Seattle Bridge on Dec. 2, officials said in a report to the Seattle City Council Tuesday.

But it wasn’t only that the city applied de-icer while the temperature was a balmy 43 degrees. A worker also put on twice as much as was necessary, creating man-made slippery conditions that caused as much a mess as ice might have.

It was an effort to stay ahead of the freeze that backfired on the Seattle Department of Transportation (SDOT). In a report to the council, SDOT officials said the problem wasn’t that the roadway was too warm, as they initially thought. The main problem was the city spread the salt solution on the road at twice the proper rate, making the bridge too slick to drive on before temperatures were anywhere near freezing.

At least three minor-injury crashes occurred before the city closed the bridge to put sand over the de-icer.

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The department was responding to an icy forecast, trying to get ahead of the chill before rush-hour and “Monday Night Football” traffic started flowing across the bridge.

“We were trying to be pro-active and get ahead of what various forecasts were telling us,” Steve Pratt, SDOT director of street maintenance, told a City Council committee Tuesday. ”We always try to err on the side of caution.”

But the department’s analysis left no question, he said: “There was no two ways about it. We made a mistake.”

Indeed, there was no ice when an SDOT operator started spreading magnesium chloride on a troublesome bend around noon. It was 43 degrees. The roadway was 38 degrees, and anything below 40 degrees should have been fine, Pratt said.

Seattle is particularly sensitive about salt solutions, which the city resumed using in 2009 after ice took days to thaw during a stretch of cold weather in 2008. Then-Mayor Greg Nickels was criticized for his handling of the storm, especially an environmental policy that had disallowed the use of salt.

SDOT spokesman Rick Sheridan said the city has a claims process people involved in the crashes can use to potentially pay for damage or injuries.

Emily Heffter: 206-464-8246 or On Twitter: @EmilyHeffter

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