Driving with poor visibility

Automatic headlamps are often not enough in foggy conditions

Oct 11, 2021

More and more often when the weather gets cold, road users are driving through fog. When it comes to driving with poor visibility, DEKRA’s experts have some advice to offer: maintain a good distance, adjust speed, and turn on the low beams.

  • Stay well back instead of tailgating the vehicle in front
  • Make sure you can stop within visible area ahead
  • Fog lights have the advantage of casting a wider beam
The experts advise against relying on the use of automatic headlamps when driving in foggy conditions. “In modern vehicles, it’s better to switch on the low-beam headlamps manually,” says Luigi Ancona, an accident researcher at DEKRA. “If the light switch is set to ‘auto,’ the vehicle will usually just activate the daytime running lights during daylight, as the lighting systems only differentiate between light and dark.”
As a result, the rear end of the vehicle will remain dark while the daytime running lights are on, and the headlamps will also be dimmer. This makes the vehicle more difficult to see from both behind and in front in poor-visibility conditions, practically guaranteeing dangerous situations when the weather is foggy.
Fog lights help drivers see better
Fog lights have the advantage of casting a wider beam of light than the normal low-beam headlamps as well as better illuminating the pavement immediately in front of the vehicle. And if the low beams are left switched off, this will also reduce the level of glare for the driver. When driving in foggy conditions in the dark, it can be useful to switch back and forth between fog lights and low beams to find the best compromise between road illumination and glare. High beams should always be avoided in these situations, as they are strongly reflected by the fog and will only worsen visibility.
Seeing and being seen
Another way to improve visibility is to keep the windshield wipers running in the intermittent setting. This will wipe away droplets of fog that settle on the windshield. It is also a good idea to regularly clean dirt from the headlamps, which can significantly reduce visibility, especially on wet and dirty roads.
It is not just good vision that counts in the fog – more than ever, being seen in time is also crucial. The high-intensity rear fog lights make it possible to warn drivers behind. However, they must only be used when they are necessary. In Germany, for example, they are only to be activated when visibility is below 50 meters in fog – and vehicles in these conditions then must not travel faster than 50 km/h. German drivers can use the roadside guide posts, which are usually set up at this exact interval, to help them navigate these situations. If the fog clears up, the rear fog lights must be switched back off to avoid dazzling drivers behind.
Keep an assured clear distance in foggy weather
“As a rule, when the weather is foggy, the approach should be to keep an assured clear distance,” Ancona explains. This means that drivers should stay within a speed range that allows them to stop inside the visible stretch of road ahead. “First and foremost, it’s important not to be tempted to ‘tailgate’ vehicles in front,” he warns. “When someone fails to keep the safe distance that’s needed, there’s a real risk of a rear-end collision. And it’s also important to refrain from overtaking in foggy conditions – drivers should be extra-attentive and prepared to brake.”