Originally Posted by
caelric
No, sir, you are incorrect. Wearing headphones cuts down on your SA, whether you think so or not. Also, most state laws (if not all, I am not fully aware of all state laws) prohibit the wearing of headphones by car drivers; as I understand, bicycle riders have all the same rights and responsibilities as car drivers, where applicable. So, in addition to being unsafe, it is most likely illegal, though I admit I am unsure on the illegal part.
Headphones without a doubt will diminish your SA as, generally speaking, any distraction does. That said, as far as headphones "being unsafe", I can't think that it's an inordinate risk. Are you seriously biking down the street evading into the ditch everytime you hear something growl? I understand that it provides you a little more sensory input, but between the wind and all the road noise it's next to impossible to get all that much useful information from your ears while biking (knowing that the vehicle coming up behind you is a truck isn't useful unless that actually causes some reaction, which I'm guessing isn't the case).