Mental Floss
WEATHER WATCH

What Is Black Ice, And Why Is It So Dangerous?

Ellen Gutoskey
Wet or frozen?
Wet or frozen? / ollo/iStock via Getty Images
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Despite what its name suggests, black ice isn’t actually black—it’s clear. So clear, in fact, that it appears to be the color of whatever surface is beneath it. Since that’s often a black asphalt road, we call it “black ice.”

The transparent nature of black ice is because it’s much thinner than other ice, which also makes it more hazardous.

How Does Black Ice Form?

Picture a road blanketed by snow that fell during the morning. The sun comes out in the afternoon and melts the snow. But the road is still wet when the sun sets, and as the temperature drops below freezing, that water solidifies into an almost imperceptibly thin layer of ice. That’s black ice. As The Weather Channel explains, the same thing can happen if the temperature drops below freezing after a rain shower has left surfaces wet or after dew or fog condenses to form ice.

The main reason black ice is so dangerous is because it’s difficult to see. If you’re approaching a patch of thick, opaque ice—while driving or walking—you’d likely try to avoid it altogether, or at least decrease your speed considerably and proceed with the utmost caution.

With black ice, on the other hand, you may not know it’s there until it’s right under you. And if you do manage to see it beforehand, you might mistakenly think the surface in question is simply coated with water, not ice. Since cars and feet alike can handle wetness without too much trouble, you might not see the need to slow down or alter your path.

How to Avoid Black Ice

The most effective way to avoid black ice is simply to stay home if there’s a winter weather advisory for icy driving conditions. If that’s not possible, you can try to avoid—or at least be extra careful in—areas where black ice is especially common: bridges, overpasses, and shady stretches of pavement. In general, when temperatures are around or below freezing, don’t assume a wet patch is just a wet patch.

Here are some more helpful driving tips to keep you safe during the winter.

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