Given the danger posed by drunk or reckless drivers, police should follow up on information — even information from an anonymous source — that a vehicle might be careening down a street or threatening other motorists and pedestrians. If they confirm that is the case, they should stop the vehicle.

But that isn’t what happened in a California case decided by the Supreme Court last month. The court’s ruling makes it too easy for police to stop motorists on the basis of an anonymous tip.

In 2008, a 911 dispatch team in Mendocino County received a report that a pickup truck had forced another vehicle off the road, giving rise to a concern that the driver might be drunk. California Highway Patrol officers followed the truck for five miles but observed no sign of drunken or erratic driving. They pulled the car over anyway and, after smelling marijuana, searched the vehicle and found 30 pounds of the drug.

The occupants of the truck argued that the police lacked the “reasonable suspicion” required for a traffic stop. But, writing for the majority, Justice Clarence Thomas concluded that the stop was reasonable because the tip was reliable given the “totality of circumstances,” including the fact that the caller identified the truck and its license plate.

In a scathing dissent, Justice Antonin Scalia, joined by Justices Ruth Bader Ginsburg, Sonia Sotomayor and Elena Kagan, said that the majority had undermined precedents holding that anonymous tips must be corroborated before police can act on them. Scalia warned that motorists could now be stopped (and searched) “based upon a phone tip, true or false, of a single instance of careless driving.”

That’s not the only problem. In a 1990 case in which the court upheld a stop based partly on an anonymous tip, Justice John Paul Stevens worried that a police officer who stopped a suspect might falsely testify that he was acting on anonymous information. Fabrication will be an even greater temptation after last month’s decision.

We hope Scalia proves to be an alarmist and that lower courts will insist that anonymous tips be extremely detailed and convincing before accepting them as justification for traffic stops that lead to searches and criminal charges. But this case should have gone the other way.

Editorial by the Los Angeles Times