A person's word that an infraction has been comitted does, however, reach the status of being able to ask the suspected vehicle to pull over and expect the driver to answer at least one question, which probably would have only amounted to "have you had anything to drink tonight?", perhaps with a caveat that they had received a report about the vehicle so that the driver understands the reason for the question.
Not in my state. Here, the police can only pull you over based on probable cause of an infraction (or worse). "Reasonable suspicion" is not sufficient grounds.