because the chance of it being an impostor is vastly outweighed by the probability it is a LEO.
Sorry, R1145, that doesn't pass the reason test. The possible consequences of stopping for a police impersonator far outweigh those or refusing to stop for a real cop in an unmarked vehicle. Many years ago, this issue was addressed by a Virginia court, which ruled the defendant, a state representative, had no duty to stop for an unmarked vehicle and was justified in not doing so. That's Virginia. Could be different elsewhere. But I wager it can be successfully challenged anywhere in the U.S.