I can't hear cars well enough no matter what I have in my ears. In traffic, the noise of the car(s) that just passed me mask any sounds of the cars coming up behind me. If I'm near a bus or a truck, I can't hear anything else.

If I'm going to cross lanes, I need to do it with enough space that I'm not going to startle a vehicle coming up behind me (because, as I'm sure you're all aware, not every driver is even looking out their windshield). That means that I need several seconds' worth of space, which translates to thirty yards or more depending on the speed of traffic. There's no way in hell I'm going to be able to hear far enough behind me with wind noise and other noises flooding my ears.

So, IMNSHO, the sense of hearing while riding in traffic is about as useless as it is to a deaf person. Listening to music can't make it worse. Riding in traffic, then, requires me to do just two things -- get visual confirmation of every hazard, and NOT ride like a dumbass.