Winter weather can bring about countless driving hazards. From heavy snow, to ice, to whiteout conditions, getting from point A to point B in winter can be a difficult endeavor. Sadly, there is one hazard that can even arise when there's not a raging snowstorm or blizzard outside. This threat is known as black ice, and can be one of the most dangerous aspects of winter driving.
First off, black ice is actually not even black. It is, in fact, much closer to clear. It gets its name from the blacktop road surface on which it often forms. On concrete surfaces, it looks slightly darker, but even then it tends to blend in well with its surroundings. There is very little air inside this type of ice, which creates this clear, chameleon-like transparency. Black ice is almost invisible to the naked eye, and often looks like simple, wet pavement.
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Black ice can form in several different ways. The temperature must be below 32 degrees, but from here, the meteorological setups can vary greatly. The most common way it is created is through the melt/freeze process of the snowpack. Typically, black ice will form at night and into dawn when the temperature dips below freezing and the previous day's temperatures have warmed up enough to melt the surrounding ice/snowpack. This meltwater then runs onto the surface of the road where it refreezes as a very thin layer of ice. This is why black ice often gives the appearance of wet pavement.
Frost and fog can also trigger black ice formation, but these tend to be less likely. However, these scenarios can be just as dangerous, as the ice layer tends to be even thinner, and thus less likely to spot.
Black ice can crop up just about anywhere and at any time, but it tends to be more prevalent in certain places and at certain times of day. As discussed earlier, it tends to form during the night and into the dawn hours when temperatures from the previous day dip back below freezing. Even on days when there is no melting, black ice can form during the nighttime/dawn hours when moisture from the air (fog) condenses and freezes to the road surface. Oftentimes, extreme cold can trigger black ice because it takes very little moisture in the air to condense and then freeze to roadways.
Bridges and overpasses also tend to be more susceptible to black ice formation. Cold air can seep underneath these structures, making their temperatures colder than a typical roadway, and thus the moisture on them is more likely to condense and freeze.
Image via NOAA
Black ice has a certain "surprise factor," which is what makes it so dangerous. However, there are ways to safeguard yourself against it. The main point is to be vigilant. Know, or at least have a good idea of, the current temperature when you're driving. Many cars now have thermometers that give dashboard readouts. If you're anywhere near the 30° mark, black ice is a possibility. Also, make sure to keep an eye out for wet looking pavement, as this is the most tell-tale sign of black ice.
If you happen to encounter any black ice, take your foot off the accelerator and refrain from making any sudden steering movements. If you start to slide, apply the brakes; hold them down if you have anti-lock brakes and pump if you do not. Unfortunately, all-wheel/4-wheel drive will not help you avoid or stop on black ice. This can only be done by slowing down and braking. Black ice can be one of the most dangerous hazards of winter driving, but with a little preparation and vigilance, accidents can be avoided.