The Supreme Court ruled that the subjective motivations of police officers were irrelevant when stopping a car based on probable cause of a traffic violation, however minor.

Plainclothes District of Columbia officers working in a “high drug area” in an unmarked vehicle noticed a truck occupied by two young African Americans waiting at a stop sign for an unusually long period of time. The truck then turned without signaling and left the intersection at what the officers called an unreasonable speed. When the officers stopped the truck, presumably to warn the driver about possible traffic violations, they observed plastic bags that seemed to contain cocaine. The occupants of the truck were arrested and later convicted of violating federal drug laws. At trial, the defense lawyers unsuccessfully tried to have the evidence suppressed. They pointed out that the officers did not have probable cause, or even reasonable suspicion, to think that the truck contained contraband. Based on these circumstances, they argued that the justification for stopping the truck, given the circumstances, appeared to be pretextual. To prevent the police from using a very minor traffic violation as a pretext to investigate the possibility of other crimes on the basis of a vague suspicion, the defense lawyers asserted that the Fourth Amendment test for automobile stops should be whether an officer, acting reasonably, would have stopped the vehicle for the reason given.

The Supreme Court unanimously found that the police were justified in stopping the vehicle in the circumstances of the case. Delivering the opinion of the Court, Justice Antonin ScaliaScalia, Antonin;Whren v. United States wrote that “the decision to stop an automobile is reasonable where the police have probable cause to believe that a traffic violation has occurred.” He referred to precedents in which the Court had refused to entertain Fourth Amendment probable-cause challenges based on the subjective motivations of police officers. Although Scalia acknowledged that the U.S. Constitution prohibits selective law enforcement based on considerations such as race, he saw “no realistic alternative to the traditional common-law rule that probable cause justifies a search and seizure.”

Civil libertarians worried that the Whren ruling was inconsistent with the spirit of the Fourth Amendment. They argued that the broad scope of ruling would allow the police to use traffic stops to investigation individuals without being able to articulate any reasonable cause, which might encourage practices such as “racial profiling.” They noted that the police, after having made a stop, may frisk occupants for weapons based on reasonable suspicion, investigate suspicious containers in plain view, request consent searches without explaining the right to refuse, and use dogs to detect drugs without reasonable suspicion of any kind.

Automobile searches

Bill of Rights

Exclusionary rule

Fourth Amendment

Scalia, Antonin

Search warrant requirement