Road Rage seems to me to be a symptom of drivers' inability to communicate with each other. All you have are your lights and your horn. The usual methods for defusing conflicts are impossible - when in a car, you can't make requests of, apologize to, or even say "thank you" to another driver. There's no room for politeness in the system, and the lack of standard social feedback makes people feel like others are treating them with contempt, which in turn makes them angry.

On a side note, the earliest description of what might be called "road rage" occurs in the Ancient Greek tragedy Oedipus the King; Oedipus and his biological father, neither knowing the other's identity, get into a fight over whose chariot has right-of-way.