Who says they can't, right now, just use GPS to track and record the locations of all vehicles, at all times?

US plan to track drivers went much wider, new documents reveal

Federal agencies tried to use vehicle license-plate readers to track the travel patterns of Americans on a much wider scale than previously thought, with new documents showing the technology was proposed for use to monitor public meetings.

The American Civil Liberties Union released more documents this week revealing for the first time the potential scale of a massive database containing the data of millions of drivers, logged from automatic license plate readers around the US.