[PhantomGremlin]

Article doesn't mention license plate readers, which are quite common nowadays.

Also, in addition to plates, wouldn't it be possible to monitor cellphone metadata in real time? Every phone is constantly checking into a base station, whether it is currently in use or not.

After a while it would be easy to build up a very useful database that not only kept track of cars but also kept track of the cellphones associated with those cars.

I can't see how to prevent any of this from happening.

For all I know, Homeland Security already does all this. About the only thing keeping them from doing it is that some external contractor would probably charge them $billions to design and integrate this, and maybe they just haven't spent the money yet.