I think the problem is a combination of poor education of cyclists and motorists (and let's face it many of us fall into both categories since many of us drive and cycle). It doesn't help that there has been poor urban/suburban planning and over congestion of most urban/suburban roadways. I quit trying to ride on the street while living in suburban D.C. and ended up buying a mountain bike and driving it to trails to ride. Now that I'm retired to a rural area, I can ride the roads again. I'm cautious, but there's no real congestion here and people tend to be more laid back and courteous as a result. Road rage was such a significant issue by the time I left D.C., I had come to hate getting on the capitol beltway. A sign of the times is the fact that several years ago the lead violist with the national symphony was shot and killed driving the beltway at night. His mistake was to pass a car with a harried, angry driver who took being passed as an insult, had a gun and pulled along side the car of the violist and shot him. It's a sad sign of the condition of the human state, but not surprising. In the 70's, when human over population was not a verboten topic, there were a number of scientific studies about the affects of over crowding, using rats, one of the major affects observed was violent aggression.