In some places it might be. In most, it's probably distraction -- phones, eating, etc. -- or alcohol, but if those are less common and hostility is high, the latter could probably overtake.
People will pass very fasts and very close when they're angry at the cyclist for being on the road and "in their way". I've actually had someone try to run me off the road before. (I've had plenty of people try to merge into where I was, but this was someone trying to do it because he wanted me on the sidewalk "where I belonged". We stopped and argued at a light right afterwards.)
If that behavior were common, cycling would be vastly more dangerous. Maybe in Philadelphia it was.
People will pass very fasts and very close when they're angry at the cyclist for being on the road and "in their way". I've actually had someone try to run me off the road before. (I've had plenty of people try to merge into where I was, but this was someone trying to do it because he wanted me on the sidewalk "where I belonged". We stopped and argued at a light right afterwards.)
If that behavior were common, cycling would be vastly more dangerous. Maybe in Philadelphia it was.