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Accuracy • Independence • Integrity

February 23, 2019   |   Ithaca, NY

ColumnsScience Culture

Slow and steady wins the race with black ice

Having learned how to drive in wintry conditions in my hometown in Maine, one of the things I think about when driving in the winter is black ice. While ice in general poses a threat, the danger of black ice is due to its invisibility on the road. I wonder: What’s the difference between black ice and regular ice?

The secret disguise of black ice lies in its formation. Since it doesn’t have any air bubbles trapped inside, it freezes nearly perfectly clear, which allows you to see through it to the black pavement underneath. Regular “white” ice, on the other hand, has many swirls and air bubbles, making it more visible on roadways.

There are three conditions that need to be met in order for this illusive ice to form. For starters, there must be a source of gently falling water, such as a fog, mist or light rain. Even slowly melting slush or ice would work. The second condition is that there be no wind. Wind or heavy rain would cause air bubbles to be caught in the ice, which would form white ice. The third requirement may go without saying, but ground temperature must be at or below freezing: 32 degrees Fahrenheit or 0 degrees Celsius.

I said that a lack of wind was required, however, an exception includes bridges. Roads are insulated by the ground below it, making it slower to temperature change. Without this benefit of insulation, a bridge is exposed to wind that can cool the structure quickly. So while the surrounding road may be safe and clear, bridges can harbor black ice. Other typical places where black ice forms are dark or shaded areas, such as under trees or overpasses.

Other odd conditions can lead to black ice as well. As long as the road pavement is at a freezing temperature, even a sunny day can create dangerous ice. Imagine piles of snow on the side of the road. The sunlight can slowly melt the snow, which refreezes clear on the road. Seemingly warmer air temperatures in winter don’t always mean that the road surface is warm as well.

So is there a way to see black ice? Although it’s usually transparent, black ice can sometimes be spotted. As a thin, smooth layer, it can appear shiny or glossy compared to the dull, black pavement around it. But the majority of the time, black ice lurks unseen.

And what do you do if you encounter black ice, or ice of any kind, when driving? The most important thing to remember is to drive cautiously and to not panic. There’s no one rule since every situation is different, but any sudden movements, such as accelerating, braking or turningcan cause you to lose control of your car. Further, your vehicle can’t get any traction on ice, and it’s important to be cautious no matter what you’re driving — even if you have a four-wheel drive vehicle, no traction means no traction.

Finally, some words of wisdom to my fellow winter drivers: Slow and steady wins the race!