About 200 snowplows salted and cleared streets in Chicago throughout Thursday night as freezing rain changed into snow, causing slippery conditions on roads and sidewalks.

The city’s Department of Streets and Sanitation dispatched 199 snowplows to work on residential streets overnight after main streets, like Lake Shore Drive, had been cleared, according to a department statement.

“The City encourages motorists to drive according to conditions and be cautious of the road,” the statement said.

The Illinois Tollway deployed its full fleet of 182 plows Thursday afternoon, according to a release. The plows will patrol the 286 miles of toll road in 12 counties in northern Illinois.

Since Thursday evening, the city saw a little more than an inch of snow, according to the National Weather Service, but up to eight inches of snow was expected to blanket far northern suburbs in Lake and McHenry counties.

Weather conditions are expected to improve overnight, the weather service said.

The weather service warned residents not to over exert themselves while shoveling the heavy “heart attack snow.”

On Thursday, airlines canceled more than 225 flights at O’Hare International Airport, where delays averaged 60 minutes, according to the city Department of Aviation. Midway International Airport reported “a dozen” flights delayed 30 minutes or more with minor cancellations.