I think that most cases of road rage could be eliminated if cars could express body language. If it was possible to tell from a long way away that someone is in a hurry or a bad mood, people might stay out of their way. Conversely, if someone made a mistake while driving and their "oops" was clearly visible, people might be more likely to forgive them.
Perhaps future technology will make this possible - a couple of cameras mounted in the dashboard connected to a holographic display on the roof might just do the trick. Though by the time we have that technology hopefully cars will be driving themselves.