Having a light (not a laser, just a light...) mounted on your helmet that you can flash them with helps too. The idea is not to blind them, that would be dangerous, but to give them a quick flash the same way an oncoming car might. I have a pretty bright little LED flashlight that I rubberband to my helmet when I expect to be riding in the dark. Not only does it help alert cars to my presence - I also use it to flash drivers who might otherwise try to pull out in front of me - it helps light my own way when it is very dark. I like the flashlight because it is not heavy and lasts a long time and it is not blindingly bright. My regular head light is a a bit awkward for helmet mounting.