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There’s nothing like a new toy, and the scores of workers who clear snow from runways at O’Hare International Airport finally got to try out the new, state-of-the-art snowplows that hadn’t been of much use during this mild winter.

With snow falling at an average of up to 3 inches an hour for part of Thursday morning, workers pulled out a small fleet of high-powered plows that also sweep and blow snow from the runways, said city Department of Aviation spokeswoman Monique Bond. The new plows were among the 200 pieces of equipment used to combat the 12 inches of snow that fell at the airport.

The weather forced airlines to cancel about 30 percent of the Thursday morning flights out of O’Hare and Midway Airport, which got 10.7 inches of snow. The flights that did get out were delayed up to 2 hours, Bond said.

Though the plow drivers at O’Hare were enjoying their “toys,” thousands of schoolchildren got the day off Thursday as many private schools in the city and most schools in the suburbs closed their doors.

City public schools stayed open because classrooms “are the best place students can be,” said schools CEO Arne Duncan. Still, only about 70 percent of the seats were filled, down from 92 percent on a normal day, school officials said.

The snow made driving difficult Wednesday night and Thursday morning, even though the predicted freezing rain mostly failed to materialize.

“We had a challenging [morning] rush hour,” said Streets and Sanitation Commissioner Al Sanchez at a City Hall news conference. “When snow falls at that rate, it is challenging to keep up with it.” But by mid-morning, enough progress had been made in plowing and salting arterial streets that crews were able to begin working on side streets, he said.

Sanchez expressed optimism that streets would be in good shape by Friday’s morning rush, but he issued no guarantees, with light snow or freezing drizzle expected to develop late Thursday and continue into Friday morning.

“This is Chicago,” he said. “Mother Nature does her own thing.”

The snowy weather was blamed for one fatal heart attack and a rash of accidents, including two Wednesday night that killed three people.

Julie Anderson, 36, of Naperville and her son, William Jr., 12, were killed in a crash about 9:55 p.m. Wednesday on Book Road near 75th Street when the car they were riding in skidded into an oncoming sports-utility vehicle and was hit broadside, the DuPage County sheriff’s police said.

Bad conditions in Des Plaines also caused a two-car collision that killed Stephen Cyriac, 62, of the 10100 block of Holly Lane, Des Plaines, said Des Plaines police spokesman Chris Terrazzino.

Cyriac’s car was turning left from Rand Road onto Golf Road about 10 p.m. when his vehicle started to skid in the slush and slammed into an oncoming car, Terrazzino said.

Though the weather was a factor, the driver of the other vehicle, Slawomir Wojcik, of the 200 block of Pinehurst Drive in Des Plaines, was cited with driving under the influence and failing to reduce speed to avoid an accident, Terrazzino said.

Wylie Nelson, 58, of Wauconda, died apparently of a heart attack while shoveling his home, police said.

The Chicago Transit Authority’s rail system operated well in the morning rush, but buses moved more slowly than normal, said CTA President Frank Kruesi.