Darkness, fog, heavy rain can severely limit visibility - this can be particularly dangerous for motorcyclists. Road users should always adapt their speed to visibility conditions.
In heavy rain or fog - i.e. when visibility is particularly poor - the Institute for Two-Wheeler Safety (ifz) recommends driving slowly. The same applies in the dark: You must be able to stop your vehicle within the area of the road that is illuminated by the dipped beam. If obstacles and the course of the road are clearly visible thanks to guidance devices with reflectors and external light, this obligation does not apply either.