How far ahead should you scan the road when looking for hazards?

As far as you can. You should constantly scan far ahead, to the sides, close by and in between Don't let your gaze linger to long in one place, see what is a head and make up scenariOS. "There is a car parked by the side of the road ahead, is there a driver that might step out suddenly" "There are some kids playing, do they have a ball that might roll into the street?" "It is getting dark, is there any animals starting to move around here?"