Roads can be slippery and dangerous even above freezing

Beware of black ice on bridges and similar hazards

22 Oct 2021

Accident experts at DEKRA warn drivers to again be prepared for sudden slippery road conditions in the fall. Parts of roads through wooded areas and on north-facing slopes, bridges, and high plains can become surprisingly dangerous.

  • Prepare for unexpected slippery roads in fall
  • Stay alert, adjust your speed, and keep a greater distance
  • Watch out for signs indicating slippery road conditions
DEKRA accident researcher Stefanie Ritter warns that “patches of black ice on roads during the fall take drivers by surprise time and time again. The most common time for this to happen is when the temperature is just a few degrees above freezing and most of the road surface still looks like it provides a good grip.”
However, in some places on the road, the temperature can drop below freezing sooner than in the surrounding areas. Those often affected include cool wooded areas, shady north-facing slopes, windy high plains, depressions in which cold air gets trapped, and even bridges, where cold air blows against the underside. If rain or dew freezes, or frost settles on the road, this can turn into dreaded areas of black ice.
“It is important to be on your guard and not get taken by surprise. When the temperature outside drops, drive more carefully, lower your speed, and keep a greater distance,” advises the expert. “One indication that the roads might be icy is when a thin layer of ice forms on the windows of vehicles parked outside overnight.”
Take warning signs seriously
It is vital to heed any warning signs that indicate slippery conditions from snow and ice. In several countries, “snowflake” signs warn drivers that they are about to drive over a section of road that is easily susceptible to the formation of black ice. A large number of modern vehicles also have technology that alerts drivers to this risk, with a warning appearing on the display and a sound given when the outside temperature drops to a critical range – below around 4°C (around 39°F).
If a vehicle starts to slip on ice, the driver should try to regain control by releasing the clutch, carefully counter-steering, and performing an emergency brake if necessary. For vehicles that have an antilock braking system (ABS), drivers need to press down firmly on the brake pedal to engage the full braking power. But for older vehicles without ABS, continuous braking will only prevent the driver from being able to continue steering. Drivers of these vehicles should try to get the vehicle back under control by releasing the clutch and braking intermittently.
Hydroplaning and dangerous slippery mud
Ice is not the only problem at this time of year. The frequent rain showers in the fall can also cause roads to become slippery in next to no time. Dirt that falls off agricultural vehicles and then turns into slippery mud from the rain can be just as dangerous as actual ice. If water remains on the road and does not drain away quickly enough, this can put vehicles at risk of hydroplaning. This is when a film of water forms between the tires and the road, causing the tires to lose contact with the road and the driver to lose their ability to steer the vehicle.
Hydroplaning tends to occur from speeds of around 80km/h (50mph). However, if the tires have a low tread depth, or the water level is higher, such as in ruts, the car could already start to hydroplane at lower speeds. If this happens, drivers should remain calm, make sure they continue steering straight ahead, take their foot off the gas, and brake with caution.