A game: the more distance you keep from other cars on the freeway while adhering to the speed limits, the more points you earn. With networked vehicles reporting data, you can compete against your friends, anonymous neighbors, etc. Higher points (less breaking) could equal rewards at businesses from drive-through restaurants to gas stations.
A hypothesis: if this game became popular, freeway traffic would flow more smoothly, average speeds would increase and there would be less crashes as well as the resulting jams; all without the need of self-driving vehicles.