Why do you hear the sound of the horn of an approaching car before the car reaches us?

Thanks for the question. This phenomenon may have something to do with the fact that you may be in the approaching car's way, and they may want you to get out of the way. If the horn sounds only as the approaching car reaches you, it may be too late for anything to be done - hence most people opt for a sounding of the horn at some distance away.

You hear the sound before the car reaches you because sound travels faster than the car is travelling.