In poor visibility, the rule of thumb is that distance should equal speed
Whenever visibility is severely restricted, German traffic regulations stipulate that headlights should be used on low beam – even in daytime. This applies equally in the case of fog, snow, and rain. By contrast, daytime running lights are entirely unsuitable for use in fog. In such conditions, the use of fog lights is also permitted. As soon as visibility improves, fog lights should be switched off again. However, drivers should also be aware that many vehicles with automatic headlights do not switch to low beam in fog so they must deploy the light switch themselves in such conditions.
Greater safety is provided by the correct use of rear fog lights. However, in Germany, they are only permitted in fog or if visibility is less than 50 meters (55 yards), also in built-up areas.
The brightness of rear fog lights makes vehicles more visible to following drivers in thick fog, thus reducing the risk of a rear-end collision. For this reason, they should be switched on as early as possible
explains Thomas Gut, a DEKRA accident analyst.
Fog lights must be switched off again when the fog lifts and visibility increases to more than 50 meters. Their brightness may dazzle other road users and hide a vehicle’s brake lights. Any infringement may result in a fine of 20 euros. It is also important to remember that a maximum speed of only 50 kilometers (30 miles) per hour is permitted if visibility is less than 50 meters. Outside built-up areas in Germany, drivers can use the roadside guide posts, which are usually set up at this exact interval, to help them navigate these situations.
When visibility is poor, another requirement is for drivers to keep their distance. In normal visibility, the rule of thumb is that the distance should be half the speed. “However, this does not apply in fog. Here, the distance must be considerably larger,” says Gut. The expert
recommends applying the rule of distance equals speed – at a speed of 50 kilometers per hour, the distance to the vehicle ahead should be increased to around 50 meters.