How many miles is an unmarked vehicle allowed to follow closely behind a car on the interstate in order to find some reason or traffic violation (e.g. illegal lane change)? Isn't there some case law that states an unmarked vehicle can't follow for too long because some traffic infraction is bound to occur?

  • Besides the fact that you are wrong about the police having a time limit, the very premise "some traffic infraction is bound to occur" is absurd. That's like saying, "Police shouldn't be able to investigate a homicide for more than two weeks, because I'm bound to kill someone sooner or later." You have to follow the law at all times, not just when the police are watching.
    – SegNerd
    Aug 6, 2016 at 18:26

1 Answer 1


Until it runs out of gas.

With the caveat that I can't prove a negative: No, there is no such statute or case law restricting how long a police or law enforcement vehicle can follow someone on a road.

However, law enforcement officers can be subject to investigation and sanction under "stalking" or "harassment" laws, which typically require a pattern of documented misbehavior in the absence of good cause for said behavior.

  • There was some discussion in US v Jones in which the defense conceded that the police could devote personal resources for 24 hour surveillance and following on public roads.
    – user3851
    Aug 6, 2016 at 4:22
  • 1
    Oh, not just the oral argument. It made it into the opinion: "Thus, even assuming that the concurrence is correct to say that traditional surveillance of Jones for a 4-week period would have required a large team of agents, multiple vehicles, and perhaps aerial assistance, our cases suggest that such visual observation is constitutionally permissible."
    – user3851
    Aug 6, 2016 at 4:27
  • 1
    Also, p 40-42 of oral argument. Council for the defendant was asked "the police could have had round-the-clock surveillance on this individual for a whole month or for 2 months or for 3 months, and that would not have violated anything, would it?". He answered, "no", and later adds, "A tail -- if they can -- if they want a tail, if they want to commit the resources, that's fine."
    – user3851
    Aug 6, 2016 at 4:35

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