Automatically control speed limits

  Have something put on every city block that emits a signal that tells the car what speed it can go up to in that area. Also have all the cars in the U.S equipped with a "receiver" and some kind of a governor that adjusts according to the signal received. To make sure the chip in the car isn't messed with you could have them checked every time you get your emissions checked. Also make sure the emitters installed on every street checked and also have them pick up the cars that don't have a chip installed and report them.