Comment Quite a bit different than NSA tracking (Score 5, Insightful) 201
Tracking the movements of vehicles is quite a bit different than tracking cell phone conversations. There is no expectation of privacy when driving a vehicle on public roads. Operating a vehicle (at least in the US) is heavily regulated, requiring registration of the vehicle, insurance, and licensed operators. In my area, in addition to the traffic cameras there are license plate scanners on most police vehicles. They scan and record the plates of vehicles as the police drive around town, popping up an alert if they get a "hit" on a vehicle with issues (suspended registration, insurance, or involvement in a crime).
You're also tracked via tolls (EZ Pass in my area) and gasoline purchases (credit card data), but the police don't have easy access to that data without a subpoena.