The ol' pothole trick

 I  don't know about you, but this would slow me  down!  People slow down

 and try  to "straddle" the hole, then breath a sign of  relief they

 completely clear it!  

 This is actually a speed control device that  is in use in various

 places in the U.S.   Scroll down and look at all three  pictures. And it is much cheaper than  speed enforcement cameras

  Very  clever, especially if moved around each  day.