To stop a vehicle, police normally must have reasonable cause to believe the driver has broken the law. Otherwise, a roadside detention violates the Fourth Amendment’s prohibition against unreasonable searches and seizures. It doesn’t take much to justify a stop—even something minor like a taillight out will suffice. But what if police are just using a traffic or equipment violation as an excuse to stop a motorist? Do the subjective motivations of an officer matter?
The U.S. Supreme Court answered these questions in Whren v. U.S., 517 U.S. 806 (1996).
In Whren, undercover police officers stopped a motorist with reasonable cause of a traffic violation. However, there was evidence suggesting the officers really made the stop to investigate the driver for drug dealing. During the detention, the police observed bags of crack cocaine inside the vehicle.
In court, the defendant argued the drug evidence should be thrown out because the stop was illegal. (Evidence obtained during an unlawful detention is normally inadmissible in court per the “exclusionary rule.”) His theory was that police weren’t genuinely concerned with the traffic violation—they just used it as an excuse to pull him over.
The Supreme Court rejected the pretext argument. The basis of the ruling was that an officer’s subjective motivations don’t matter. According to the Court, a traffic detention is lawful so long as—viewed objectively—there’s a legitimate reason for the stop.
(This article is about the U.S. Constitution as interpreted by the U.S. Supreme Court. Keep in mind that your state’s laws might offer more protections.)