I have a theory:  Road rage is actually a neurological condition caused by a lack of oxygen in the brain. 

It's safe to assume all vehicles produce at least some amount of carbon monoxide.  It would be naive not to think even a small portion of that gas entered the interior of the vehicle directly behind each moving vehicle.  As people breathe in carbon monoxide, I would assume it displaces (or replaces) oxygen in their blood and brain.  I have no evidence concerning this, but perhaps one of the symptoms of decreased oxygen levels in the brain is irritability.  Now take a person who either has a naturally lower amount of oxygen in their blood or who is just normally irritable.  Add some carbon monoxide which increases that person's irritability, and bam.  You have that guy in the pickup truck with the big tires who drives like his butt is on fire. 

I have a solution:  Equip vehicles with oxygen tanks.  One of the effects of breathing pure oxygen is a feeling of euphoria.  I would think that a good way to cure irritability is with euphoria.  Of course there's the added issue of having a container of highly reactive oxygen in an otherwise dangerous vehicle that's powered by a highly flammable fuel, but that's for the engineers to figure out. #travel