The thing is expectations and boundaries. As a participant of traffic you need to be able to feel secure, regardless of day or night. So in your example (and I

The thing is expectations and boundaries. As a participant of traffic you need to be able to feel secure, regardless of day or night. So in your example (and I live near a school and 30 km/hour street near it), if there is hardly any traffic at night you don't expect anyone either. Which might make someone driving 50 km/hour even more dangerous than when everyone is driving too hard constantly during day.