What must you do on encountering sudden dense fog driving at daytime?

In conditions of sudden dense fog during daytime, it is crucial to adapt your driving to ensure safety. First, reducing speed is essential because visibility is significantly compromised, making it difficult to judge distances and react on time. Second, turning on dipped headlights is important for making your vehicle visible to others and for improving your own visibility as well.

According to German traffic regulations, specifically the Straßenverkehrs-Ordnung (StVO), use of headlights in poor visibility conditions is mandatory to enhance safety on the road. Parking lights are not adequate because they do not provide sufficient illumination or visibility to other drivers. Thus, adapting speed and using dipped headlights are the correct and necessary actions to take when encountering such road conditions.