I've read about some places where a rural highway leading into a town will narrow to ten foot lanes, waking drivers out of their daze because the driving environment is about to become much more complex. I wish I could remember where this was.
I can't give figures on the effectiveness of this, but as a driver you instinctively slow down when the road appears narrower. It seems to me more effective than a sign on the side of the road.
[0]: http://www.rediweldtraffic.co.uk/media/9186/RediPaveHeader.j...
That will guarantee that car accidents and deaths drop dramatically.
Historical evidence suggests that there would indeed be fewer accidents but more car drivers would die (because even quite trivial bumps would be fatal), though pedestrians and cyclists would be safer. As someone who chooses not to drive, that sounds pretty good to me.