SEATTLE -- The major snowstorms of the past two weeks that have left many side streets still covered in snow days later has prompted the city of Seattle to rethink its snow removal policy.

Seattle mayor Greg Nickels, facing criticism from many frustrated residents over the lack of snow removal, has ordered the Seattle Department of Transportation to begin using salt as a tool to clear major arterials during future snowstorms.

Salt will be used if more than 4 inches of snow is on the ground or predicted, if ice is predicted, or if extreme cold is expected to last longer than three days. Its use will still be restricted to hilly roads, major arterials, major bus routes, and primary routes to hospitals and other emergency facilities and any other roads deemed critical by the DOT.

"People were frustrated, and so was I," Nickels said.

It had been city policy to use sand and Geomelt de-icer instead of salt. The city says the de-icer, which contains only a small amount of salt, has proven effective in normal weather patterns of trace to 4 inches of snow lasting 1-3 days.

Nickels said the city's decision to use sand instead of salt was done with environmental impacts in mind, trying to keep salt from entering the city's freshwater streams and prevent corrosion on the city's infrastructure. He said in normal Seattle winters, the practice has worked well, but this storm dumped 14 inches of snow in many spots, making it the greatest snow in the city since 1996, and the snow and ice remained on the ground longer than any storm in the past 20 years.

The city says Boeing Field reported 357 consecutive hours of snow on the ground -- just short of 15 days.

In the short term, Nickels said he has hired two private contractors to help with the five city crews out sweeping the streets to get rid of the sand.

On Christmas Eve, Nickels gave the city response a "B" grade. He stood by that grade on Wednesday.

"I thought our crews did an outstanding job," he said. "They were out 24 hours a day, 7 days a week for two weeks and they did a good a job as possible. I think we can always do better and that's what we're going to try and do.... We're going to do better, but the people involved in this did the very best job that they could, and I'm very proud of them.

"We kept our residents safe. That is our highest calling and our greatest accomplishment but as I have said, we could do better."