There's that famous video of people dancing, where a person in a gorilla suit enters and leaves the action, and at the end, people don't remember seeing the gorilla.

I think drivers are creatures of habit, especially in heavy traffic on a familiar route such as their daily work commute. They are not really in complete control of their cars -- certainly if traffic is heavy enough that nobody is following at a safe distance. Now throw distractions into the mix.

I'm also an experienced urban cyclist, and I believe that route choice is a major safety factor. I have some rules of thumb for roads to avoid, and am extremely lucky that I live in a town that is fairly cycle- and pedestrian-friendly. I have a hunch that car drivers in my town have gradually adapted to the presence of cyclists, for the better.

I do ride on 55 mph roads in the countryside, but only ones with very little traffic, and the region has quite friendly drivers. Stories from cyclists living in other states suggest to me that straightforward aggression is a factor in a lot of the close passes and other antics that they experience.