It is now established that a detention which occurs during a motor vehicle stop by the police constitutes a seizure within the meaning of the Fourth and Fourteenth Amendments to the United States Constitution. The question remains whether there is a requirement for the police to inform motorists of their Miranda right to remain silent during a motor vehicle detention. This question was answered in the US Supreme Court decision of Berkemer v. McCarty, 468 U.S. 420 (1984). The court held that the requirements of Miranda v. Arizona apply even in those situations where the defendant is arrested for a minor motor vehicle violation. If the police wish to conduct a custodial interrogation of the defendant, they must first inform him of his constitutional rights.
What about a motor vehicle detention that does not result in an arrest? Although there are many similarities between a motor vehicle detention and an arrest, the Court found two significant differences between a formal arrest and a roadside motor vehicle detention. First, the Court found that most traffic stops are usually temporary and brief. Driver’s have an expectation that this short stop may result in a summons being issued and then they will be free to go on their way. The court found this strikingly different from a stationhouse interrogation where the questioning is usually prolonged and the defendant is often aware that the questioning will continue until the police obtain a confession. The second key difference the court emphasized is that during a typical traffic stop a motorist may not feel as though they are completely at the mercy of the police officer. The public nature of the stop reduces the ability of a police officer to use illegitimate means to elicit self-incriminating statements and also diminishes the driver’s fear that if he does not cooperate, the police officer may become abusive.
As a result, the court ruled that individuals who are temporarily detained during an ordinary traffic stop are not in custody for purposes of Miranda. There is no requirement that police inform detained motorists of their Miranda rights unless or until the police place a given motorist or vehicle occupant under arrest and wish to conduct a custodial interrogation.