Cases involving the Fourth Amendment’s proscription on unreasonable searches and seizures are the sleepers of every Supreme Court term. Unless the justices are confronted with new technologies or particularly invasive government practices—like body-cavity or thermal-imaging searches—these decisions rarely grab headlines, leaving only prosecutors, defense attorneys, and law professors to ponder their significance.

But this can’t be the norm—not in the wake of Ferguson, with heightened awareness of abusive policing. Today more than ever, an understanding of what limits the Constitution places on police and the Supreme Court’s interpretation of those limits should be essential knowledge. Anything less, to borrow the words of Justice Sonia Sotomayor, would simply reduce the Fourth Amendment “to a useless piece of paper.”

Because at the root of Rodriguez v. United States, decided Tuesday by the Supreme Court, lies one of the most common, and perhaps the only, interaction law-abiding citizens will ever have with law enforcement: traffic stops. Being pulled over is so mundane, I wondered in February whether Chief Justice John Roberts had ever been inconvenienced by the practice, perhaps as a result of driving with a broken taillight—the kind of infraction that triggered the killing of Walter Scott in South Carolina earlier this month.

When Rodriguez was argued in January, Roberts asked how exactly traffic stops go down in real life, saying lightheartedly, “Usually, people have told me, when you’re stopped, the officer says, 'License and registration.'” That drew laughs from the courtroom—the implication being that Roberts wouldn't admit to ever having broken the law—but it also suggested that perhaps he doesn’t quite grasp how humiliating these encounters can be. This prompted a rebuttal in open court from Sotomayor, who told the chief that she’d been stopped and that the experience of being kept longer than the time required to give her a ticket was “annoying as heck.”

Whether Roberts eventually grasped as much is unclear, but he did join the six-justice majority that agreed that police can’t extend the length of a traffic stop beyond the time necessary to inquire into the alleged traffic violation. In a triumph for citizens’ rights, the Supreme Court ruled that “a police stop exceeding the time needed to handle the matter for which the stop was made violates the Constitution’s shield against unreasonable seizures.”

That’s a big deal, if only because a lot can happen whenever police extend a traffic stop, even for a few minutes longer than necessary. To be sure, police already have wide latitude to stop anyone who is observed violating traffic laws; if probable cause exists that you’re not obeying the rules of the road, police are justified in stopping you. But what if, during the course of the stop, police also suspect you’re up to no good? Can they just hold you while they call in the dogs, as happened in Rodriguez, or for backup to conduct a wider criminal investigation? The lower courts that originally considered Rodriguez thought so, reasoning that a stop lasting, say, seven to ten minutes longer than necessary “was not of constitutional significance”—that the annoyance merely amounted to a “de minimis intrusion” on a motorist’s freedom of movement.

The Supreme Court didn’t buy that argument. “Authority for the seizure... ends when tasks tied to the traffic infraction are—or reasonably should have been—completed,” wrote Justice Ruth Bader Ginsburg for the majority. The court focused exclusively on the true “mission” of traffic stops—incidentals such as “checking the driver’s license, determining whether there are outstanding warrants against the driver, and inspecting the automobile’s registration and proof of insurance.” All of these things are well and good when the initial stop is valid.

The problem arises when a well-meaning officer turns the traffic inquiry into a prolonged, crime-fighting one. Such unrelated “detours” away from the original traffic mission, the court observed, are unconstitutional without independent, reasonable suspicion that an actual crime has taken place. A cop’s “large hunch” about criminal wrongdoing won’t do.

That’s a commonsense approach—no one should be stopped for even a moment longer than absolutely necessary. But will the ruling deter police from trying other dilatory tactics? Rodriguez, for one, doesn’t explicitly forbid officers from, say, taking their sweet time while running your license plate or from engaging in “friendly” small talk aimed at eliciting consent. These end-runs are still largely acceptable, and only time will tell what other methods cops will employ to bide their time and divine suspicion where initially there was none.

Until then, the Supreme Court should be commended for making the right call and delivering a ruling that, though far from a blockbuster, should encourage anyone who cares about the continued vitality of the Fourth Amendment. In post-Ferguson America, there’s just no other section of the Constitution that matters more—the power of policing rises and falls with every pronouncement on it.