When driving a bus in heavy snowfall or dense fog where visibility drops below 50 metres, what driving behavior is required?

1. Increase the following distance substantially, reduce speed, and use dipped headlights with the rear fog lamp (Nebelschlussleuchte) where visibility justifies it
2. Follow the tail lights of the vehicle ahead closely, so as not to lose the line of the road
3. Switch to main beam, which throws light further into the fog
4. Keep to the normal cruising speed but switch on the hazard warning lights