Try driving to Boston on Route 2 going the 55mph posted speed limit; you'll get yourself killed. So I've given up on that, go with the flow of traffic, and figure as long as I'm not the fastest thing around I'll be all set.

As for flashing your lights as a warning, I've been aware of it for as long as I remember. My first thought is "You've got a light out!" but I've seen it used for other things as well. I also remember my Dad constantly warning me that cops aren't happy if you warn speeders about them, but I never could figure out how the cop would know. Though I'd rather the speeders get caught anyhow.