Black ice is thin, nearly clear ice that forms on roads. It is referred to as black ice because it is so thin and transparent that the black pavement is visible and seemingly safe. Black ice can be even more dangerous to drivers than snow or thick patches of ice because it doesn't have the typical visual warning signs, so drivers aren't as likely to take proper precautions.
Sudden temperature differences after a winter storm are a major factor in black ice formation. When the road temperature is below freezing (32 degrees F) and the air outside is above freezing, there is a risk of black ice. Pavement doesn't always raise its temperature as quickly as the air due to factors such as heavy traffic, amount of shade, tunnels and overpasses. These factors can block the sun from warming the pavement as it warms the air.
Once the pavement's temperature drops below freezing and the air stays above freezing, any type of moisture on the road can turn into black ice. Even light rain or snow can become dangerous because as soon as it comes into contact with the pavement, it freezes. Since it freezes so quickly, the ice forms a layer that is so thin, it's nearly transparent. The times after a winter storm has cleared up is when black ice is most likely to occur because the warmer air temperature melts the snow, but when the moisture comes into contact with the still freezing pavement, it freezes immediately.
To prevent accidents due to black ice, drivers should never assume that driving conditions are safe, especially if there has been any recent drop in temperature or increase in moisture, such as after a snow storm. Black ice is also susceptible to forming in the early morning when the pavement has not began to warm up. Black ice isn't completely undetectable. There are some visual warning signs, such as ice on windshield wipers or trees. Drivers can also spot black ice more easily in shaded areas, such as apartment parking lots or areas with many trees. Knowing what conditions cause black ice formation can keep drivers informed and safe.
