Today’s Wonder of the Day was inspired by Grace. Grace Wonders, “How does black ice form?” Thanks for WONDERing with us, Grace!
What are some of your favorite things to do in winter? When the weather turns cold and snow begins to fall, you probably look forward to a snow day off from school and some sledding on your favorite hill.
If you're an adult, though, that weather brings with it a special headache that most people would rather avoid: driving in snow and ice. The things you take for granted under normal conditions, like steering your car exactly where you want and stopping quickly, can be tricky and hazardous during the winter.
Even when there's no snow on the ground, driving can still be tricky if a special type of driving hazard presents itself. You can be driving along and see something on the road ahead that looks like wet pavement. When your car hits it, though, you can be spinning out of control before you know it.
What did you run into? Weather experts call it black ice. The name is a bit deceptive. Black ice isn't actually black in color. It's also not milky white like regular ice. Instead, it's almost completely clear. Since you see right through it to the pavement below, it often seems to be black, thus the name "black ice."
Black ice needs the right conditions to form. First, water must collect on the road in a very thin layer without splashing or wind. Regular rainfall on a windy day might freeze, but it would contain air bubbles and swirls that give regular ice its white color.
Black ice is almost perfectly clear, so the source of water usually comes from fog, exhaust condensation from vehicle tailpipes, gentle, misty rain, or melted snow and slush. It is so thin that it can form when the surface temperature of the road is freezing even if the air temperature is above freezing.
Cold, sunless early winter mornings are a prime time to find black ice on the roads. Black ice often forms overnight when temperatures drop.
It also tends to form on bridges and overpasses, since those structures freeze before roadways. Drivers should also watch out for spots on the road that are shaded by trees or other objects, since shady areas are perfect spots for black ice to form.
What should you do if you're driving and you hit a patch of black ice? The immediate temptation is to hit the brake pedal, since you want the car to stop if you feel it sliding out of control.
However, experts recommend removing your foot from the gas, keeping your steering wheel straight, and waiting just a couple of seconds until your tires regain some traction before trying to apply the brakes to stop. This sounds easy, but it can be difficult to remember when you hit a patch of black ice.
Experts also suggest that drivers not use cruise control if black ice is possible. Turning off cruise control gives the driver more control over acceleration and braking in case black ice is encountered.