What is Black Ice?

While definitely a real phenomenon, “black ice” may be cited as the cause of a car crash, in fact, the real root cause may have been excessive speed, inattention, or some other fault on the part of the driver.

January 17th 2006 in Chicago, Illinois – 49 vehicles sat crumpled and mostly lifeless in two pileups on Halsted Street on an overpass in Riverdale Tuesday night.

From semi tractors to SUV’s to vans, whatever cars were there at the time, they were just bouncing off each other like bumper cars,” said Deputy Police Chief Mike Ryan. About 15 people were taken to the hospital, none life threatening injuries, police said.

It seemed no one-not even emergency responders-could keep from slipping and sliding on the ice rink that was Halsted Street. A couple of medical workers fell as they tried to reach victims, and police had to work to keep their balance.

Black ice is a term used to describe the frozen stuff on a blacktop road. That makes the ice all but invisible to motorists, who are only able to see the dark-colored pavement. There are a lot of variables in black ice formation: It is usually deposited by freezing rain, mist or fog. Because it contains relatively little entrained air in the form of bubbles, black ice is transparent and thus very difficult to see ( as compared to snow, frozen slush, rime ice, or other typical roadway forms of ice.) In addition, it often has a matte appearance.

Black ice also refers to the slick layer that forms on roadways from a light rain after a period without any precipitation. The water mixes with the road dust and oil but doesn’t wash away. This leaves the road surface as slick as ice, slicker than just being wet with water. This type of road hazard can occur any time of year, but especially in mostly dry summer months.

What people need to realize is that even though it looks like a clear day out there, the roads could be slippery. Drivers should always drive with caution and follow the speed limit especially during the winter season. A couple of degrees can make all the difference in the world.

Braking on Black Ice will cause a slight melting of the surface layer of the ice, producing a very thin layer of water. Water on ice is a lot more slippery than just ice. The problem in winter is that you will quickly break traction with the wheels. Once you do, your chances of remaining straight on the road are minimal. Reserve the limited traction of the wheels solely for steering..

If you own four winter snow tires for your automobile you still want to avoid braking on black ice.

When there is snow around, the snow will often provide more traction than ice. Even light snow directly on top of Black Ice may provide better traction than just the Black Ice.

Once melting starts, snow can add to the slipperiness of the underlying ice, giving you a good idea of the traction below.

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