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What is Black Ice?

Tires often slide on black ice.
Black ice is usually transparent, which makes it dangerous for drivers.
Black ice often causes slide offs.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 14 December 2014
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Black ice is a deposit of ice which forms in a way which causes it to be transparent. Because the ice is totally clear, it is often invisible, which makes it very dangerous. Motorists are often at risk from these deposits because they don't see them on the roads, but they can still skid on them. Pedestrians and cyclists aren't immune to the dangers of black ice, as anyone who has fallen on seemingly safe pavement in the winter can tell you.

The formation of black ice begins when rain, fog, or mist deposits ice on pavement in cold weather. The latent heat of the pavement slows the freezing rate, so these droplets of water run together before they freeze. As a result, the air bubbles in the water are forced out, and the frozen sheet of ice which forms is almost completely clear. The ice often blends in with deposits of rain on a road, and it can also form with a matte appearance which makes the road surface look clear and dry.

Due to tricks of the wind and winter weather, black ice can form when temperatures are above freezing. In extremely cold regions, frozen ground and roadways can freeze when ambient temperatures are above the freezing point. It can also form on bridges and elevated walkways, because the wind cools these surfaces from both sides, making them much colder than the rest of the road.

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Because black ice forms in a single sheet, it is extremely slick. Cleated shoes and tires can still slide on it, as they may have difficulty grabbing hold to get the necessary traction. These ice deposits form commonly in the morning and early evening, and can melt away as quickly as they form. Some winter traffic accidents are blamed on black ice which has done just that, when all the evidence suggests that a car encountered a patch of ice, even though the ice may have vanished by the time responders arrive on the scene.

Some regions are more prone to black ice than others, and motorists in these areas may be aware of this. In some cases, signs are posted to alert people to the danger. There isn't much that drivers can do, other than driving slowly in cool weather, since this ice blends in with the roadway perfectly. If you do encounter a patch of black ice while driving and you skid, take your foot off the gas and steer in the direction of the skid until you regain control of the vehicle.

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anon325411
Post 5

Years ago when I went to traffic school, while serving in the military, black ice wasn't formed by water. The asphalt would become so cold that it would constrict the oil out of it that was deposited from cars. Thus, this oil would form on the top of the road as "black ice" plus the temp had to drop below -20c.

anon144995
Post 4

if ice freezes the same way on gray concrete,is this called gray ice. If ice freezes on grass is this green ice?

anon130911
Post 3

please explain the criteria of black ice.

colemanl
Post 2

Can you explain why it feels as if you have been shot out of a slingshot when you hit black ice even though you are driving at a slower it rate?

anon21913
Post 1

What you define as "black ice" is actually "dew ice". The term "Black Ice" came from the truck drivers explanation of the ice that formed near coal mine roads due to the coal dust blowing off the loaded trucks sticking to the moisture on the roadway and freezing, therefore causing the ice to become invisible and very slippery.

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