>Another potential factor: left lane highway driving. I drove in a 3rd world country this summer and they were very consistent about driving in the right lane and only passing in the left lane. No one at all drove in the left lane. I think left lane driving in the US leads to more risky maneuvers and road rage responses.

I try to stay in the right lane at all times, but according to truckers it's safer to stay in the left lane, as vehicles merging onto a highway from the right act poorly.