Why?
It is already technologically possible to know where a modern car is - simply by collating traffic camera data, or by getting the data from the owner's cell phone, or the car's GPS anti-theft device (which more and more cars have today).
The state will know where your car is, whether or not your car is driverless - because the technology exists today to cheaply observe anybody who is in public, and then collate and analyze the data. Because the public doesn't see anything wrong with this (in the US), this data will inevitably be collated. Certainly at least in the cities and suburbs, where most people live.
Driverless cars offer getting rid us of:
1. Driver licensing and its attendant nonsense. (I am not driving, why do I need a permit?)
2. DUI laws and their attendant nonsense. (I am not driving, why does it matter if I am drunk?)
3. Texting laws and their attendant nonsense (I am not driving why does it matter if I am texting?)
4. Taxi medallions and their attendant nonsense.