The Carroll Rule

The Carroll Rule

The automobile exception takes its shape from a Prohibition-era stop on a Michigan highway, and the facts of that stop explain most of what the rule demands. In Carroll v. United States, federal prohibition agents had posed as buyers in a Grand Rapids apartment on September 29, 1921, and negotiated with George Carroll and John Kiro for three cases of whiskey, which the two men agreed to deliver and never did.¹ A week later the agents saw the defendants' car heading toward Detroit and tried to follow it, but lost it near East Lansing. On December 15 the agents recognized the same car and the same two men traveling from the direction of Detroit toward Grand Rapids. They stopped the car about sixteen miles outside Grand Rapids, searched it without a warrant, and found sixty-nine quarts of whiskey hidden in the back of the seat.²

The defendants moved to suppress the liquor as the product of an unconstitutional search, the trial court refused, and the Supreme Court affirmed the convictions. Chief Justice Taft wrote for six Justices, with McReynolds and Sutherland dissenting.³ The holding is that the Fourth Amendment does not forbid a warrantless search and seizure of an automobile on a public highway when the officer has probable cause to believe the car is carrying contraband.⁴ The defendants had argued that a car should be treated as a "house" and so protected as a house is. The Court found the analogy poor: a house is a permanent structure, while a car is a movable object, and a search on the open road is not a break-in of the home or an invasion of the privacies of life.⁵ The reasoning behind that contrast gets its own section next, but the practical point is already visible. A car can be driven out of the locality or jurisdiction where a warrant would have to be sought, so a rule that demands a warrant first would often mean the search never happens.⁶

The ordinary warrant requirement assumes that an officer with probable cause can go to a magistrate, wait for approval, and come back to find the evidence where it was. That assumption holds for a store or a dwelling, which stays put while the paperwork is done. It fails for a car on the road, which means the officer's real choice is often between searching now and not searching at all. The Carroll rule resolves that choice by letting the officer's own probable cause stand in for the magistrate's judgment. Taft stated the test this way: a warrantless search and seizure is valid if it is made "upon probable cause, that is, upon a belief, reasonably arising out of circumstances known to the seizing officer, that an automobile or other vehicle contains that which by law is subject to seizure and destruction."⁷ Today the exception is stated more broadly than the liquor in Carroll: probable cause that the vehicle holds contraband, fruits, instrumentalities, or evidence of a crime is enough.

The measure of legality is the officer's cause to believe the car holds something seizable, and the occupants' arrest has no role in it. The Court said so directly, in language later repeated in Chambers v. Maroney: the right to search and the validity of the seizure are not dependent on the right to arrest, and depend instead on the reasonable cause the officer has to believe the car's contents offend against the law.⁸ That independence matters on the facts of Carroll itself, because the agents had no basis for an in-presence misdemeanor arrest of the occupants before the search turned up the liquor.⁹ A search incident to arrest requires a lawful arrest first. The car search under this exception requires only probable cause about the car, and it reaches the vehicle rather than the people in it.¹⁰

Because the magistrate's check has been removed, probable cause carries the whole justification, and the case shows how much work it does. The agents did not act on a hunch. They had bargained with these very men over whiskey, had seen the same car on the road, and later recognized both car and occupants returning from Detroit. The two dissenting Justices thought the agents had acted on suspicion rather than probable cause, and that disagreement shows where the contest in these cases lies. Once probable cause exists the warrant is excused; where it is missing, the search fails however mobile the car is.

The distinction between goods in a dwelling and goods in a vehicle is older than the automobile. In Carroll the Court relied on early federal statutes from the First, Second, and Fourth Congresses, which authorized warrantless searches of ships and the seizure of concealed goods subject to duties. Those laws treated goods hidden in a dwelling house or similar place differently from goods being carried in a movable vessel, where they could readily be put out of reach of a search warrant.¹¹ That history shows the contrast between fixed and movable places was familiar when the Fourth Amendment was adopted. It does not say why movability or the road should matter, and later decisions gave two different answers to that question, which the next section takes in turn.