How Dangerous Is Black Ice?

Article summary

• Black ice is a thin, nearly invisible layer of ice that can look like wet pavement and cause tires to lose traction.
• It often forms overnight or early in the morning, especially on shaded roads, bridges and overpasses.
• Reduce your risk by slowing down, increasing following distance, avoiding unnecessary lane changes and staying home when conditions are unsafe.

Precipitation and freezing temperatures can make the winter months a risky time for motorists to be behind the wheel. According to data from the Federal Highway Administration, approximately 12 percent of vehicle crashes—nearly 745,000 collisions—are weather-related, meaning they involve events like rain, snow, sleet, hail and fog. While most weather-related crashes happen during periods of rain or mist, about 18 percent occur during freezing precipitation.

One of the more treacherous weather-related road hazards is black ice. This article explains all you need to know about the hazard, including what it is, how it forms, where to look for it and the best way to react when you encounter it.

What is black ice?

The thin, almost invisible layer of ice that forms on a roadway is called black ice. There are three things that make it particularly dangerous:

1. It’s hard to spot. Pavement with a patch of black ice appears dark and wet rather than frozen.
2. It can be very slippery. Tires can’t get traction on the smooth surface.
3. It catches drivers off guard. A motorist traveling at normal speed on what seems like a clear roadway may unexpectedly encounter a lone patch of black ice.

What does black ice look like on the road?

Because the thin layer of ice forms without trapping a lot of air bubbles, it lacks the white appearance that most icy roads have. Pavement with black ice will be a little darker and duller than the rest of the road surface. 

When and how does black ice happen?

Black ice usually forms overnight or in the early morning hours when there’s no sunlight to warm the pavement. Snow or ice that’s melted but hasn’t completely evaporated can refreeze into a thin, almost invisible layer when temperatures drop below freezing. It can also form in periods of freezing rain—a condition where light rain falls onto a very cold surface and then freezes.

Black ice vs. sleet

Unlike black ice (where moisture collects on a cold surface and then freezes into a slick, transparent layer), sleet is precipitation that freezes in the air as ice pellets and collects on road surfaces as frosty or white ice granules. Black ice and sleet are both serious driving hazards, but frozen pellets of sleet are usually easier to see.

What places are likely spots for black ice?

Black ice commonly forms on highly shaded areas, infrequently traveled roads and on surfaces like bridges and overpasses where there is no insulation beneath the pavement.

Expect the unexpected

If you notice ice forming on any objects, you should assume that there will be patches of ice on the roadway as well. Here are some things you can do to reduce your risk:

• Stay home. It’s better to avoid taking unnecessary chances than to risk a crash.
• Reduce speed and anticipate delays. Most snow and ice-related crashes happen when vehicles travel at speeds faster than weather conditions allow.
• Leave extra space between vehicles. Increasing your following distance from the car in front of you allows more time to react to unexpected events.
• Avoid unnecessary lane changes. Ice that’s built up between lanes could cause your tires to lose traction.
• Buckle up. The proper use of restraints is the most effective way to keep all vehicle occupants safe on the roads.

AAA to the rescue

If you find yourself in the middle of a winter weather mishap, it’s likely AAA can help. Roadside assistance (available by phone, text, the AAA Roadside Assistance website or by using the AAA Mobile app) can resolve issues like these:

• Dead battery. Cold weather significantly reduces a car battery’s output and efficiency.
• Vehicle crashes/slides off the road. Ice increases the risk of skidding and can cause a car to slide off the road or crash into another vehicle.
• Empty gas tank. Running out of gas in freezing temperatures puts you at risk. AAA advises to never let your gas tank drop below a quarter of a tank in inclement weather, but if you do run out of gas, AAA Roadside Assistance includes 24/7 emergency fuel delivery to members.
• Frozen locks. Whether you’ve locked your keys in the car or you can’t open the door because the locks have frozen, AAA can help.

Are there other risks from black ice?

While you should always watch for black ice when you’re behind the wheel and conditions are conducive for it to form, roadways are not the only place you might encounter the hazard. Stay safe and watch for black ice when you’re walking on steps, walkways and driveways as well.