The deaths of an Elgin woman and her dog after their vehicle plummeted from Route 53 onto Route 14 in Palatine Monday night represented the worst possible consequence of one of winter's least visible safety concerns -- black ice.
Illinois State Police Tuesday confirmed slick road conditions were a factor in the deaths of 34-year-old Julie Allard and her dog, Cinnamon.
The basic cause of black ice is wet spots forming on parts of roads that don't drain properly or are vulnerable to drifting snow, said John Yonan, director of the Cook County Department of Transportation and Highways.
While there are likely locations and conditions for the presence of black ice, there are inevitably other situations in which it's more easily identified as the cause of an accident after the fact, Yonan said.
"It's hard to see when something is iced over," he said.
Some of the more likely places to expect black ice are elevated ramps where melting snow has been flowing downward, or on bridges that receive no warming from ground below.
But low spots where water can collect and refreeze aren't always easy to identify in advance on every single road, he said.
While black ice requires below-freezing temperatures, the current crop is due more to the recent heavy snowfall than the arctic blast that followed it, Yonan said. As the effectiveness of road salt diminishes at very low temperatures, it's more important to get roads properly plowed than salted to prevent black ice, he said.
As many problems as black ice has caused this week, it's actually less likely at these low temperatures than when the air is hovering right around the freezing mark, said Roy Lucke, director of transportation safety programs at the Northwestern University Center for Public Safety.
Black ice is not impacted snow like regular ice is but thawed water immediately before it became a roadway hazard, Lucke said. It's called black ice because it's thin to the point of invisibility.
"And of course it's always worse at night," Lucke said. "If you're paying attention, you can kind of see it during the day. After salt has turned a road white, ice will be darker than the road."
Police officers on patrol are often on the lookout for black ice when conditions are right and will often ask the public works departments from their own municipalities to take care of any they find, Lucke said.
Although roads throughout the region are overseen by municipal, state and county jurisdictions, the local public works departments are often able to be the quickest to address an identified problem, he said.
Northwestern's Center for Public Safety also runs the region's Traffic Safety School, and Lucke said exercising defensive driving -- particularly driving slowly -- is probably the best way for motorists to protect themselves.
While four-wheel-drive vehicles are helpful for driving through snow, they're of no help at all when hitting a patch of frictionless ice, Lucke said.
Illinois Transportation Secretary Ann L. Schneider also released a statement this week urging awareness of black ice and driver caution. Offramps, bridges, intersections and shady areas are all more prone to black ice and motorists should approach these slowly, she advised.