Among the many threats facing drivers during winter is the most dangerous of them all: Slippery, hard-to-spot and potentially deadly black ice.

“The biggest danger [with black ice] is that you are at the mercy of your vehicle and the ice until your car passes over it,” said Julie Lee, vice president and national director of AARP Driver Safety.

Black ice forms most often when it’s raining and air is at or below 32 degrees Fahrenheit at the surface. The low ground temperature causes the precipitation to freeze upon impact, thus creating ice. Sleet and the refreezing of runoff from melting snow can also generate black ice.

The thin nature and complexion of black ice makes it extremely difficult to spot, but using a car thermometer as an initial gauge may be helpful in determining the road conditions. Black ice gets its name from its ability to blend in with its surroundings.

A car thermometer, like any digital thermometer, tries to find the air’s ambient temperature. So, if a vehicle’s thermometer is close to freezing, the driver should take extra precaution behind the wheel.

While driving on black ice is similar in some regards to driving on snow, the biggest difference between the two is the amount of traction the vehicle retains. Ice causes no traction until the car has passed over the icy spot.

Due to a vehicle’s lack of traction on ice, the basic rule for driving on black ice is to stay calm and let the vehicle pass over it.