Many things can cause road rage. Even trivial and unintentional moves can lead to an act of behind-the-wheel violence. All drivers have their own "driving personality" when they drive. One attitude that drivers depict is carelessness. More accidents are caused by careless drivers than anyone else. These irresponsible drivers are often not watching or paying attention to their surroundings, making dumb mistakes that could easily make someone upset.
Another attitude is recklessness. Many reckless drivers are often teenagers; they haven't had their license that long so they don't know how to make the right decisions when it comes to driving. When people act reckless, they feel as if they can do anything and they won't get caught.
A third attitude is temper. While I am not aware of any statistics many of the people I have helped with road rage report being angry all or most of the time while driving. When in an agitated state your brain's sense of judgement and impulse control are dramatically compromised and your instincts take control. Even the smallest mistake made by another driver can drive you around the bend (sorry about the bad pun).
More on this tomorrow!