Black ice: the dangers for road users
Black ice can be lethal. And scary. Probably not in that order.
The leading winter-related causes of death is car accidents. Although fatal accidents actually are more common in summer and fall, people are far more likely to die in a snow- or ice-related car accident than due to exposure or hypothermia.
Nearly 20% of all traffic accidents every year are attributed to winter conditions, meaning snow or ice. Consider for a moment that most parts of the country don’t see more than a little snow each year, and some states don’t even get below freezing, and that number seems huge.
We all know to go slow when the roads are covered in the white stuff, though often we still don’t go slow enough. You can limit your chances of a winter weather-related accident with a set of winter-specific tires. Packing a set of tire chains for travel in the mountains is also a good idea.
A frightening cause of accidents, and one that is harder to prepare for, is suddenly driving across a patch of black ice on road. With snow, you expect less traction. You see it and prepare for it. But sheet ice (glare ice, clear ice, black ice, etc) can look like a regular wet spot. The stealthy nature of this ice is made worse by just how slick it is to create an often dangerous combination.
What is black ice?
All it takes to create an icy surface with little to no traction is a small amount of water and a cold surface. Even when the ambient temperature is above freezing, ice can sometimes form in deadly patches. Here’s a rundown of where it catches people by surprise most often:
- Underpasses - Areas of the road that don’t get direct sunlight, such as the shady underpass under a road, can have a surface temperature much lower than the surrounding area. As an added hazard, lower lying areas tend to collect moisture too.
- Shaded Areas - Just like an underpass, areas shaded by trees or tall buildings can often hide a nasty patch of ice. Luckily, patchy ice is much less dangerous than a solid sheet, but one particularly slippery section can upset a car enough to make regaining traction impossible on a wet road. Don’t panic, let the car slip off of the ice before trying any steering corrections or braking.
- Bridges and Overpasses - If you have ever seen a lizard lay on a rock that has been in the sun, you know some materials absorb heat more than others. Those signs the say “Bridge freezes before road” are to remind you of just that. You can be cruising down a winter road as the sun goes down, with ambient temps just beginning to fall, and find the overpass is a solid sheet of ice. Bridge surfaces just don’t hold heat the way the surrounding countryside does.
When does black ice form?
Black ice is most likely to occur just as the sun is setting or coming up, and most common when the thermometer is around freezing. If you are on your way home from work, and the sun has just gone down, and it is 35 degrees (or less) outside… WATCH OUT!
Another scenario that can lead to a sudden sheet of ice is a sudden rain shower. In the winter, precipitation can form of snow, if the air and temperature are just right. Freezing rain or sleet falls when there is a warm layer of air above a cold layer, which freezes the drops into little balls. If the warm air is close to the ground, but the ground itself is below freezing, the drops can hit the ground before freezing solid, forming sheet ice.
What to do when driving on black ice
The best thing to do when you hit black ice when driving a car is nothing at all. Typically a car on a sheet of ice has so little traction that no steering, braking or accelerating input is going to have any effect and will likely make things worse.
The best bet is to let the car keep going in the direction it is going until you hit pavement again. Even applying or letting off the brakes or throttle can make things worse. If you happen to hit a patch mid-corner and start to skid, you should treat it like any other skid, and try to aim the front wheels in the direction the car is skidding; if the wheels are rolling you have much more control than if they are sliding.
But driving on a traction-compromised surface is much too complicated to get into here. The best advice is just to just slow down whenever the conditions are such that you may encounter ice. Once the thermometer drops below 40 degrees, you should be extra careful out on the road.