The 6-3 decision limits the increasingly common practice whereby officers stop a car for a traffic violation and then call for a drug-sniffing dog to inspect the vehicle.
The justices, both liberal and conservative, agreed that it was an unconstitutional "search and seizure" to hold a motorist in such cases.
"Police may not prolong detention of a car and driver beyond the time reasonably required to address the traffic violation," said Justice
The decision applies the 4th Amendment's ban on "unreasonable searches and seizures" and covers all the police--local, state and federal.
Ginsburg said police officers who stop a car for speeding or another traffic violation are justified in checking the motorist and his driver's license. But a traffic stop does not give officers the authority to conduct an "unrelated" investigation involving drugs, she said.
"The tolerable duration of police inquiries in the traffic-stop context is determined by the seizure's 'mission' --to address the traffic violation that warranted the stop and attend to related safety concerns," she explained in Rodriguez vs. United States. "Authority for the seizure thus ends when tasks tied to the traffic infraction are--and reasonably should have been--completed."
Tuesday's ruling marks one of the few times the high court has invoked the 4th Amendment to limit police conducting traffic stops.
Two years ago, the justices ruled police may not use drug-sniffing dogs around the front door of a home without a search warrant, stressing the privacy expectations of a home.
The justices now expand that to prevent traffic stops from becoming a pretext for stopping cars and conducting drug searches.
The case decided Tuesday began when a Nebraska police officer saw a vehicle run onto the shoulder of a highway and then jerk back on to the road. It was after midnight on March 27, 2012.
Two men were in car, and driver, Dennys Rodriguez, said he had driven off the road to avoid a pot hole. The officer checked his license, registration and insurance, and also checked the passenger. A few minutes later, he decided to write Rodriguez a written warning.
Once the traffic stop was "out of the way," the officer asked Rodriguez for permission to search his vehicle with a drug-sniffing dog. The driver refused, but the officer told him he may not leave until a second officer arrived.
About five minutes later, a second officer arrived and the dog was used to search around the car. The animal alerted to the presence of drugs. Acting on that alert, the officers found a bag of methamphetamine.
Rodriguez was prosecuted in federal court for the drug violation, but he challenged the seizure of evidence on the grounds it violated the 4th Amendment. The judge and the 8th Circuit Court of Appeals ruled that a minimal extra detention of 7-10 minutes was reasonable, and Rodriguez was sentenced to five years in prison.
The high court reversed the 8th Circuit's decision and said it was not reasonable to prolong the traffic stop so the dog could sniff around the car.
Justices Clarence Thomas, Samuel Alito and Anthony Kennedy dissented. They said the stop itself was legal, and it was reasonable to hold the motorist because the officer suspected they may be carrying drugs.