Rumble Strip

A strip of raised bumps running along the verge of a road, or between lanes. Their primary purpose is to make a loud vibrating noise if you drift too far to the edge of the road. (i.e. falling asleep). Most commonly found on motorways/expressways along the shoulder/verge.

Also used here in the UK in urban areas to inform drivers they are exceeding the speed limit -- DavidPostill (07 Sep 2003)

In the USA there are several ways this is done. Round domed "dots" about two or three inches in diameter, rectangular ones with reflectors pointed down the highway which are sometimes put in indentantions in the road so snowplows don't knock them loose, and of course just alterations of the pavement surface itself. -- RobertField