Can you tell me about Black Ice?
- Barbara, Glenville
Answered by Justin Caudell
Barbara, I would be happy tell you about black ice. One of the most commonly
encountered dangers in the winter, black ice is an unseen and often misunderstood
hazard.
Also known as “glare ice” or “clear ice,” black ice typically refers to a thin coating of
glazed ice on a surface, often a roadway. While not truly black, it is transparent,
allowing the usually-black asphalt/macadam roadway to be seen through it, hence the
term. It also is unusually slick compared to other forms of ice on roadways.
Black ice is usually deposited by extremely cold rain droplets, mist or fog. The
process of freezing is slowed down due to latent heat given off in sublimation, allowing
the rain droplets to flow and merge together on the surface, forming a film before
freezing into clear ice. Nevertheless, because it contains relatively little entrapped 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 forms of ice on the roadways).
In addition, it often has a matte appearance rather than the expected gloss; and
often, it is interleaved with wet pavement, which is identical in appearance. For this
reason, it is especially hazardous when driving or walking because it is both hard to see
and extremely slick.
Black ice can form even when the ambient temperature is several degrees above
the freezing point of water (32 degrees). This occurs typically – and treacherously –
when terrain contours and or prevailing winds cause a local steep differential of
atmospheric pressure or temperature, or when the atmosphere has warmed up after a
prolonged cold spell that leaves the temperature of the ground and roadway well below
the freezing point.
Here are a few simple rules and tips to remember when you might encounter black
ice or other forms of ice on the roadway this upcoming winter:
Know your vehicle – Not all cars respond to the same icy, slipper roads. For that
reason, knowing how to handle your vehicle and how it responds in various weather
conditions is important. America’s Automobile Association (AAA) recommends that
motorists practice slow-speed maneuvers on an empty snow or ice covered parking lot.
You should also flip through your owner’s manual, familiarizing yourself with your
vehicles braking system and tire traction.
The distance factor – The most important thing to remember when driving on slick
roads is that you must travel, steer and brake more slowly than usual. The distance
needed to stop on ice is twice as long as that you would need to brake under normal
driving circumstances. This means you should keep at least a three-car distance form
the vehicle directly in front of you.
Locations to watch for – Certain areas of roadways, because of location or lack of
direct sunlight, are almost always more hazardous than others. Use extra caution when
driving on bridges, overpasses and through tunnels.
Sliding and skidding – The biggest problem facing most winter drivers is skidding on
slick, icy or snow covered roads. It is possible to steer out of a skid, however. Once you
feel your car begin to skid, slowly remove your foot from the accelerator until you feel
your wheels regain traction control. Do not attempt to brake! Though you don’t want to
over correct, turning your steering wheel in the direction of the skid will help regain
control of the vehicle.