Q: You often hear the term "black ice." What is it?
A: It's not really black, but it is ice that is extremely dangerous, says Brent McRoberts of Texas A&M University. Black ice is ice that appears to be very dark or even black because it is transparent – it is reflecting the color of the asphalt on the road. "Black ice is a thin layer of ice on the road and it often looks wet, not especially icy. So it can be hard to notice from a distance, and for this reason it is dangerous to drive or walk on," McRoberts explains.
Q: Is it more dangerous than regular ice?
A: It is almost always more dangerous, McRoberts reports. "Black ice often forms at night and early in the morning, when temperatures are low but traffic is high," he adds. "Sunlight can often melt it because it is such a thin layer of ice, but black ice can last longer on roads that are protected by shade. One study in Sweden a few years ago showed that there are five times more accidents on roads that have black ice than on dry roads and twice as many accidents as on roads that had packed snow. That's why sanding crews are always important when an ice storm is about to hit."