Ignorance of rules seem to be part of the issue. Using bike lanes (in Cambridge!), I've had turning drivers honk or yell nasty things at intersections as I went straight through, not knowing they are required to yield. Drivers are trained to be forgiving to pedestrians and the crazy jay-walking that happens in Boston, but still treat bikes like aberrations.

I drive as well, and admit it felt very unnatural at first at check behind me for bikes when turning right.