By Matt Gephardt

This winter has brought it all: Record snow, record colds, record smog and now frozen rain can be added to the list. Thursday, the rare phenomenon coated the Wasatch Front in a thin layer of ice which led to hundreds of accidents.

"It's really unusual," said Utah Department of Transportation spokesperson John Gleason. "This is not typical Utah weather."

The U.D.O.T. is charged with keeping the state roadways clear and they have hundreds of massive snow plows to get the job done. The plows giant blades push aside the snow as the trucks dump tons of salt behind. But it is not always salt. Sometimes the plows drop sand, or a mixture of salt and sand. Why the difference? It's a good question.

Gleason says it all depends on the conditions.

"At a certain point, salt becomes less effective, he said.

The function of salt is to warm the road so that falling snow won't stick to the pavement. But when the temperatures drop below about 20 degrees, Gleason says the salt can't keep the roads warm enough, so on those days they will lay down sand to assist motorists.

Sand helps create traction so drivers don't just slide off the road," Gleason said.

And Gleason says there is another reason the U.D.O.T. avoids sand except in extreme conditions. When the snow melts, the sand turns to dust and that dust will pollute the air. To avoid added pollution, state law says that any sand dropped has to be cleaned up within three days.

Because of the added labor, Gleason says using sand is more costly than using salt alone and that's why, unless it's an emergency, they avoid it.

That law does not just apply to the U.D.O.T. If you put sand or other grit down on the sidewalks around your house to keep from slipping, legally, you're supposed to sweep it up afterwards.

(Copyright 2013 - Sinclair Broadcasting Group)Good Question: Why do Plows Sometimes Drop Sand not Salt?