Hmm if I lived in LA I'd probably recommend against confronting motorists, an acquaintance told me he did and the driver pulls a gun out of the glove box (of course he ran away quickly at this point!)

In Toronto where I don't fear getting shot at for confronting a motorist, I still don't feel any good can come of it. Usually if they are a prick enough to try to run you off the road, then they are going to be even more of a prick when confronted. The exception where it might be useful is for someone who was unaware of you rather than actively aggressively towards you. But still human nature being what it is nobody likes to be confronted Once, and only once, a driver rolled down their window (without me confronting them first) and said sorry...

So I usually just stick with funny faces, or knocking on the car if it passing me close enough for me to do that. I also just like catching up with them because they usually know what they've done and if the light is red they usually fear retribution. They seem in an awful hurry not to have to wait beside you.