Why can highways be kept clear of snow more easily?

Q. Your recent column on the who's who of snow plowing was informative. I have a related question: On a snowy day that closed all the schools in our area, I was driving on I-88 at about 1 p.m., and it was clear and dry.

There were no snow piles along the roadway like on local side streets. How does the tollway get down to dry pavement so quickly? I don't think they truck snow away since that would cause back-ups during rush hour, and I didn't see evidence of snow being pushed down embankments either. Is it just that the traffic doesn't allow much snow to settle there?

--J. B., Lisle

A. The Illinois State Toll Highway Authority gets snow off their roads faster than municipalities can clear local roads.

"Because our vehicles plow at 30-to-35 mph -- much faster than the local plows are usually able to go--that helps each plow throw snow farther away from the road and have it spread over a wider area on the side of the road rather than being piled high right off of the road surface," said Jan Kemp, assistant press secretary with the tollway authority.

"Your average local street doesn't have a huge parkway to plow the snow onto like the tollway does."

Additionally, two, three or four trucks often work in tandem during a heavy snowfall, and plow side-by-side to maximize removal of snow and slush.

"When the trucks are working in tandem, it allows them not only to clear the snow from the travel lanes, but also from the lane lines in-between," Kemp said.

During an average eight-to-12-hour storm, tollway authority plows may plow as many as six to eight times with applications of salt as needed.

"Once a salt-and-water brine is formed on the pavement, the movement of car tires on the road reduces further accumulations of snow to water or slush," Kemp said.

"When the storm subsides, heavy traffic accelerates the evaporation of moisture, and helps dry out the pavement."

The tollway authority occasionally does truck away excess snow build-up on bridge decks with narrow shoulders, or from toll plazas where the accumulation might impact travel lanes.