Actually, they already have it (and have for the last couple of years of car models). It's called OBDIII. Your car literally broadcasts a signal giving out the same information that OBDII gives when you plug in. It also broadcasts things like how fast you are going, how many passengers are wearing their seat belts, etc.
One state has conducted experiments showing that with OBDIII they can track eight lanes of traffic doing 100 mph. You could literally get speeding tickets in the mail because your vehicle told them, at a tracking point, that you were doing 45 in a 35. You could also get "environmental" tickets because your check engine light is on and it is telling you that you have a bad oxygen sensor.
And then there are the seat belt tickets...
Needless to say, because every car broadcasts its own ID with the signal (which is how they know it is you), they could also track where you go at all times and just refer to the historical data when necessary.
Just another reason to keep my 1984 Landcruiser running.