Concept
Traffic Stops
Terry stop and frisk
Traffic Stops
A traffic stop is the setting where most people actually meet the Terry rules, and the Court treats it as a close relative of the street stop. Most traffic stops resemble the brief detention that Terry authorized in both duration and atmosphere: the encounter is short and unfolds at the roadside.1 The Court has also recognized that traffic stops are especially dangerous for officers, and the reasons are specific enough to be worth stating, because they explain the rules in every section below.
The Court's account of the danger rests on both numbers and structure. In 1994 alone there were 5,762 officer assaults and 11 officers killed during traffic pursuits and stops. The structural explanation is that an officer approaching a stopped car faces occupants who may have access to weapons hidden in the passenger compartment, each additional occupant adds another possible source of harm, and the risk of violence comes from the chance that a routine stop will uncover evidence of a more serious crime, which gives any occupant a reason to resist, a passenger as much as the driver.2 A speeding ticket alone rarely provokes a fight. The hidden possibility of something worse does, and an officer cannot know at the window which stops carry it.
Because the officer cannot tell in advance which stop will turn dangerous, the Court's response is to let officers take firm control of the scene. The risk of harm to police and occupants alike is minimized, the Court has said, when officers routinely exercise "unquestioned command of the situation."3 Control measures can be imposed without suspicion about a particular occupant because the liberty side of the balance is light. Reasonableness under the Fourth Amendment depends on weighing the public interest against the individual's right to personal security, officer safety is a legitimate and weighty public interest, and an occupant of a car that is already lawfully stopped suffers only a minimal added intrusion from being told to step out.4 A frisk sits on the other side of that balance. It adds a physical search of the person that the stop itself does not involve, so the rules keep it tied to individualized suspicion.
Arizona v. Johnson organizes the whole topic around Terry's two conditions. The first is that the stop be lawful, and the second is that, to move from a stop to a frisk, the officer reasonably suspect that the person stopped is armed and dangerous.5 In a traffic stop the first condition is met whenever police may lawfully detain the automobile and its occupants pending inquiry into a vehicular violation, and the police need not have additional cause to believe any occupant is involved in criminal activity.6 The second condition does not relax. To frisk a driver or a passenger, police must harbor reasonable suspicion that the person is armed and dangerous, just as with a pedestrian.7 Three earlier decisions built that structure: Pennsylvania v. Mimms allowed officers to order a driver out of a lawfully stopped vehicle, Maryland v. Wilson extended that rule to passengers, and Brendlin v. California held that a passenger is seized from the moment the car stops, so a passenger may challenge the stop.8 Each receives its own treatment below.
Students lose points here by carrying the relaxed standard for control measures over to the frisk. An officer who may order everyone out of the car without suspicion still needs reasonable suspicion for each person frisked. The frisk standard also asks a narrower question than students expect. It does not ask whether the passenger is suspected of the traffic violation or of any other crime; a passenger may be frisked on reasonable suspicion of being armed and dangerous even without suspicion of criminal activity unrelated to the stop itself.9
The sections below follow a stop in the order it unfolds: how the stop begins, who it seizes, what officers may order the occupants to do, when they may frisk, and how long the stop may last before an added investigation outruns its original purpose. The first question is what justifies stopping the car at all.
Initiating the Stop
A traffic stop begins with the car, so the first Terry condition asks whether the officer was entitled to pull it over at all. Stopping a car detains everyone inside it, and the Court treats even a brief roadside detention for a limited purpose as a seizure of persons, which means the stop must be reasonable under the circumstances.11 As a general matter, the decision to stop an automobile is reasonable where police have probable cause to believe a traffic violation has occurred. Probable cause here means facts that would lead a reasonable officer to conclude the violation actually happened.12 In Whren v. United States the Court added the point that decides most exam problems: as long as officers have that probable cause, the stop is reasonable regardless of the officer's subjective motives or any pretextual desire to investigate other crimes for which the officers lack sufficient cause.13 The rule therefore has two parts, an objective trigger and the irrelevance of motive, and each has its own reason.
The facts of Whren show both parts operating. Plainclothes vice-squad officers in an unmarked car were patrolling what they regarded as a high-drug area when they passed a Pathfinder truck with temporary plates that sat at a stop sign for more than 20 seconds, its driver looking down into the passenger's lap. When the officers turned their car around, the truck turned right without signaling and sped off at an unreasonable speed, and the officers overtook it at a red light.14 An officer approaching the driver's window saw two large bags of what appeared to be crack cocaine in an occupant's hands.15 At the suppression hearing the occupants argued that nothing justified suspecting drug dealing and that the stated reason for approaching, a warning about traffic violations, was a pretext.16 Whether that account of motive was true did not matter, because the district court had found probable cause to believe the traffic code was violated, and that finding made the stop reasonable and the drugs admissible.17
The two halves of the rule rest on different reasons. The requirement of probable cause protects drivers from stops on whim, because the officer must be able to point to something that happened on the road, such as a missed turn signal. The indifference to motive does subtler work. A court ruling on a suppression motion can test whether a car turned without signaling through the officer's testimony, a dashcam recording, or another witness, but an officer's private reason for wanting the car stopped is visible only through the officer's own say-so. A test that turned on motive would make the officer's account of the officer's own mind the decisive evidence, and every suppression hearing would become an inquiry no court could check. Tying legality to objective facts means the result depends on what a judge can verify.
The Court gave further reasons for staying with the traditional rule. It performs a balancing of the individual's interests against the government's only when a search or seizure is carried out in an extraordinary manner, such as deadly force, unannounced entry into a home, or penetration of the body, and a traffic stop made by officers out of uniform does not qualify, so the usual rule applies that probable cause outweighs the private interest in avoiding police contact.18 The occupants also argued that traffic codes are so numerous and so hard to obey perfectly that nearly every driver is guilty of something, which lets police single out whomever they like. The Court found no principle for deciding when a code becomes so expansive that a violation stops being the ordinary measure of lawful enforcement, and no standard for deciding which provisions are important enough to enforce, so it kept the rule that probable cause justifies a seizure.19 The remedy for a driver who believes police enforced the code selectively against a disfavored group lies in the Equal Protection Clause, which asks about discriminatory purpose, and the Fourth Amendment analysis of the stop is unaffected.20
The stop in Arizona v. Johnson shows that the violation does not have to be serious. Officers on Arizona's gang task force were on patrol near a neighborhood associated with the Crips when a license plate check showed that a car's registration had been suspended for an insurance-related violation, and they pulled the car over.21 Under Arizona law that violation was a civil infraction warranting a citation, and the officers had no reason to suspect anyone in the car of criminal activity.22 The stop still satisfied the first Terry condition, because in the traffic setting that condition is met whenever police may lawfully detain an automobile and its occupants pending inquiry into a vehicular violation, with no added cause to believe any occupant is involved in criminal activity.23 A suspended registration is an observable, checkable fact, and it supplied the objective basis that Whren requires, whatever the task force's broader interest in gangs.
The only fact that moved the result is the observed violation, and the officer's desire to find drugs was identical in both versions. Students lose this issue when they treat a pretextual motive as a defect in the stop, since the objective test asks whether the violation was observed and leaves the officer's purpose out of the Fourth Amendment inquiry.24 A stop with no observed violation can still be lawful if the officer has independent reasonable suspicion of criminal activity, so the analysis has a second route that the hunch in the first version of the hypothetical fails to reach.
Who Is Seized
The preceding section asked whether officers were entitled to pull a car over. A prior question faces anyone who wants to contest the answer: was that person seized at all? The Fourth Amendment guards against unreasonable seizures, so a person who was never seized has no claim that a stop was unlawful, however baseless it was. A person is seized when an officer, by physical force or a show of authority, terminates or restrains the person's freedom of movement through means intentionally applied, and a show of authority seizes only if the person actually submits to it.26 When police conduct is ambiguous or the person simply goes along, the test asks whether a reasonable person would have believed that leaving was not an option, or, for a person who had no wish to leave anyway, whether a reasonable person would feel free to decline the officers' requests or otherwise end the encounter.27
That a traffic stop seizes the driver had long been settled, even though the stop is brief and its purpose limited.28 The passenger's position was less clear, because the officer's claim of authority rests on the driver's apparent fault, and the Court had said many times in passing that a stop seizes everyone in the vehicle without ever squarely deciding the point.29 In Brendlin v. California the Court decided it: when police stop a vehicle, the driver and the passengers are all seized, so a passenger may challenge the legality of the stop and seek suppression of the evidence it produced.30 The facts show why the question mattered. Deputy Brokenbrough and his partner pulled over a Buick to verify that its temporary operating permit matched the car, although nothing about the permit looked unusual, and the State later conceded that the police had no adequate justification for the stop.31 The passenger, Bruce Brendlin, turned out to be a parole violator with an outstanding warrant, and the searches that followed produced a syringe cap on his person and methamphetamine-making materials in the car.32 The State's only answer to his suppression motion was that a passenger is not seized by a stop of the car and so cannot complain of it.33
The Court rejected that answer by asking whether a reasonable person in the passenger's position would have believed it possible to end the encounter, and it concluded that any reasonable passenger would understand the police to be exercising control to the point that no one in the car could depart without police permission.34 Each step of the reasoning rests on how a stop actually feels from the passenger seat. A stop curtails the travel the passenger chose just as much as it halts the driver, and the police intrusion does not distinguish between the two. An officer who orders one particular car to the roadside acts under an implicit claim of right based on some fault, and a sensible person would not expect the officer to let people come and go from the focal point of that investigation. Even when only the driving is in question, a passenger expects some scrutiny, and an attempt to walk away would so obviously draw an objection that no passenger would try it. The Court added that its rule in Maryland v. Wilson, allowing officers to order passengers out of a lawfully stopped car, reflects a social expectation of unquestioned police command that fits poorly with any notion that a passenger could leave without advance permission.35
The van's occupants differ from the pedestrian in one respect: the officers exercise authority over the vehicle that carries them, and they cannot leave it without police permission.36 Students lose this issue when they reason that a passenger suspected of nothing has no basis to complain about the stop, because the seizure follows from the stop of the car and does not wait on any suspicion about the passenger.37
The same fact sets up the frisk analysis in the sections ahead. Because a stop seizes every occupant, the first Terry condition, a lawful investigatory stop, is met for the driver and each passenger whenever it is lawful for police to detain the car and its occupants pending inquiry into a vehicular violation, and officers need no added cause to believe any occupant is involved in crime.38 In Arizona v. Johnson the car was lawfully stopped for a suspended registration and officers had no reason to suspect anyone inside of criminal activity, yet the back-seat passenger was seized by a stop that satisfied the first condition.39 Wilson supplies the reason: passengers may give police no independent ground to stop them, but as a practical matter they are already stopped by virtue of the stop of the vehicle.40 The seizure of passengers therefore has two consequences. It lets a passenger challenge an unjustified stop, as Brendlin did, and it makes a justified stop of the car a justified stop of everyone in it, as in Johnson, so that the remaining question for a given occupant becomes whether that person may be frisked.
Exit Orders
The preceding section showed that a traffic stop seizes every occupant of the car, and that fact raises the next practical question: what may officers do with the people they have seized? The mildest power concerns where those people stand. During a lawful traffic stop, an officer may order the driver and the passengers out of the vehicle for safety, and the officer needs no individualized suspicion that any of them is dangerous.42 The rule was built in two steps, one for drivers and one for passengers, and both steps rest on the same balance between the officer's safety and the occupant's liberty.
The driver rule comes first. As the Court summarized it in Arizona v. Johnson, Pennsylvania v. Mimms held that once a motor vehicle has been lawfully detained for a traffic violation, officers may order the driver to get out without violating the Fourth Amendment.43 The balance favored the officer because the government's interest in officer safety was legitimate and weighty, while the added intrusion of making an already-stopped driver stand outside the car was de minimis.44 The safety interest carries that much weight because most traffic stops resemble Terry stops in duration and atmosphere, and traffic stops are especially fraught with danger to police officers.45 The intrusion counts as small because the driver has already lost the freedom to drive away, so the order changes only where the driver stands in relation to the car.
Whether that reasoning reaches passengers was the question in Maryland v. Wilson, and the Court held that it does.46 A Maryland trooper saw a car on I-95 traveling 64 miles per hour in a 55 zone with no regular license tag, only a torn paper rental-company notice dangling from the rear.47 The car continued for another mile and a half after the trooper signaled it to stop, and during that stretch the two passengers repeatedly ducked below sight level and reappeared.48 The driver was trembling, and the front-seat passenger, Jerry Lee Wilson, was sweating and extremely nervous. While the driver searched for the rental papers, the trooper ordered Wilson out, and a quantity of crack cocaine fell to the ground.49 The Maryland courts suppressed the drugs on the theory that the driver rule did not apply to passengers, and the Supreme Court reversed, holding that an officer making a traffic stop may order passengers to get out of the car pending completion of the stop.50
The Court reached that result by running the same two-sided balance for passengers. On the safety side, the interest is the same whether the occupant is driving or riding, traffic stops are dangerous (the Court noted 5,762 officer assaults and 11 officers killed during traffic pursuits and stops in a single year), and each additional occupant adds a possible source of harm to the officer.51 On the liberty side, the passenger's case is in one respect stronger than the driver's, because probable cause exists as to the driver's violation while nothing gives police a reason to detain a passenger.52 The Court answered with a practical observation: passengers are already stopped by virtue of the stop of the vehicle, so the only change an exit order works is that they stand outside the car rather than sit inside it, where they are cut off from any weapon hidden in the passenger compartment.53
The absence of an individualized-suspicion requirement follows from where the danger comes from. The risk of violence in a traffic stop seldom arises from an ordinary motorist's reaction to a speeding ticket. It arises because evidence of a more serious crime might surface during the stop, and a passenger's motive to use force to avoid apprehension for that crime is as great as the driver's.54 An officer cannot see in advance which occupant is hiding such evidence, so a rule demanding suspicion of danger before the order would force the officer to establish the very fact the order exists to guard against, at the moment the officer knows least. A categorical rule avoids that problem, and the small size of the intrusion makes a categorical rule tolerable. The Court also relied on the idea that the risk of harm to both police and occupants is minimized when officers routinely exercise unquestioned command of the situation.55
The facts of Wilson contained some warning signs, since the passengers kept ducking out of sight and the front passenger was sweating, but the rule announced does not depend on them. Brendlin v. California later described the holding as allowing an officer to order a passenger out as a precaution, without reasonable suspicion that the passenger poses a safety risk.56 That same societal expectation of unquestioned police command is what led Brendlin to conclude that no passenger would feel free to leave a stopped car.57
An exit order is a different and smaller intrusion than a frisk, and the exit-order rule does not stretch to cover the second. Moving a person from the seat to the roadside changes where the person stands, while a pat-down is a touching of the person's body and clothing. For that reason, justifying a pat-down of a driver or a passenger during a traffic stop requires reasonable suspicion that the person subjected to the frisk is armed and dangerous.58 The two powers therefore operate separately, and when the officer lacks grounds for a frisk, the officer may still require the driver or passenger to get out.59
Students lose this issue when they demand individualized suspicion for the exit order itself, or when they assume that a valid exit order carries a pat-down along with it. Each mistake merges two questions that the cases keep apart, since the order asks only whether the stop was lawful and the occupant is already seized, while the frisk asks whether this particular person may be armed and dangerous.
Two conditions frame the exit rule. The stop must itself be lawful, because the driver rule applies once a vehicle has been lawfully detained for a traffic violation,60 and the passenger order lasts only pending completion of the stop.61 An order given during an unjustified stop therefore draws no support from the rule. Whether the officer may go further and frisk a particular occupant is the question the next section takes up.
Frisking Occupants
An exit order settles where an occupant stands, but it authorizes no touching, and the frisk is the power that does. During a lawful traffic stop, an officer may frisk the driver or a passenger if the officer reasonably suspects that the person to be frisked is armed and dangerous, and the officer need not also suspect that person of criminal activity unrelated to the stop.63 The rule comes from Arizona v. Johnson, which carries the two conditions of Terry v. Ohio into the car: the investigatory stop must be lawful, and to move from the stop to a frisk the officer must reasonably suspect that the person stopped is armed and dangerous.64 The traffic setting alters only the first condition. Because a stop of the car seizes everyone in it, that condition is met whenever it is lawful for police to detain the automobile and its occupants pending inquiry into a vehicular violation, while the second condition stays exactly as it is for a pedestrian on a sidewalk.65
The facts show how little the officers knew when they began. Three members of a Tucson gang task force pulled a car over after a license plate check showed that its registration had been suspended for an insurance-related violation, which under Arizona law was a civil infraction warranting a citation, and they had no reason to suspect any of the three occupants of criminal activity.66 Officer Trevizo attended to Lemon Montrea Johnson, the back-seat passenger, and noticed that he kept his eyes on the officers as they approached, wore a blue bandana and other clothing she considered consistent with Crips membership, and carried a scanner in his jacket pocket that struck her as highly unusual.67 Johnson gave his name and date of birth, said he had no identification, volunteered that he came from Eloy, a town Trevizo knew to be home to a Crips gang, and told her he had served time in prison for burglary and had been out for about a year.68 Trevizo asked him to get out of the car so she could question him away from the front-seat passenger about the gang, and he complied; suspecting from what she had seen and heard that he might have a weapon, she patted him down as he exited and felt the butt of a gun near his waist.69 Johnson was charged with possessing a weapon as a prohibited possessor, the trial court denied his motion to suppress after concluding that the stop was lawful and that Trevizo had cause to suspect he was armed and dangerous, and a jury convicted him.70
The Arizona Court of Appeals reversed the conviction without disputing that the stop was lawful. It accepted that Johnson was seized when the officers stopped the car, but it reasoned that by the time of the frisk the detention had evolved into a separate, consensual encounter arising from Trevizo's unrelated inquiry into his possible gang affiliation, and that without reason to believe he was involved in criminal activity she had no right to pat him down, even if she had reason to suspect he was armed and dangerous.71 The theory therefore had two links: the questioning ended the seizure, and with the seizure gone a suspicion of danger could not justify a pat-down. Judge Espinosa, dissenting below, found it highly unrealistic to conclude that Trevizo's courtesy and Johnson's cooperation had turned a continuous chain of events into a consensual encounter within a few moments, and he stressed that Johnson remained seized as part of a valid traffic stop throughout.72
The Supreme Court reversed, and it broke the first link. A traffic stop communicates to a reasonable passenger that he or she is not free to end the encounter with the police and move about at will, and nothing in the record conveyed to Johnson that, before the frisk, the stop had ended or that he was otherwise free to depart without police permission.73 The Court added that Trevizo was not constitutionally required to give him a chance to leave the scene after he stepped out of the car without first making sure she was not letting a dangerous person get behind her.74 The inquiry looks to what the officers' conduct communicates to a reasonable passenger, so a friendly tone does not release anyone. A rule that treated polite questioning as the end of the seizure would also strip the officer of protective authority at the moment of closest contact, and it would give officers a reason to avoid talking with passengers at all. Johnson stayed seized from start to finish, which means the first Terry condition was still satisfied when Trevizo frisked him.
The Court then explained why the officer needs no suspicion that a passenger has committed some other crime. The first condition is met whenever it is lawful to detain the car and its occupants pending inquiry into a vehicular violation, and the police need not have, in addition, cause to believe any occupant is involved in criminal activity.75 The reason traces to where the danger in a traffic stop comes from. On the Court's account in Maryland v. Wilson, the risk of violence stems from the chance that evidence of a more serious crime will be uncovered during the stop, and a passenger's motive to use force to avoid apprehension for that crime is every bit as great as the driver's.76 A requirement that the officer first suspect a separate crime would tie protection to a question that has no bearing on whether the person in front of the officer has a gun. Johnson also completes a line of decisions: Pennsylvania v. Mimms allowed a driver, once out of the car, to be patted down if the officer reasonably concludes that the driver might be armed and presently dangerous, and Wilson and Brendlin v. California then extended the exit-order power and the seizure to passengers, so the same footing now applies to anyone in the car.77
None of this relaxes the second condition. A lawful stop does not by itself authorize a frisk, because the two are separate intrusions with separate purposes: the stop gives the officer time to inquire, and the frisk protects the officer while the inquiry goes on.78 A pat-down touches the person's body and clothing, so the justification has to attach to the individual who is frisked, and without that limit a lawful stop of any car would license a routine search of everyone inside at the officer's discretion. The showing required is modest. The test is objective, and it is enough that there is a substantial possibility the person is armed, without the quantum of evidence that would justify an arrest for carrying a concealed weapon; the nature of the crime under investigation, a bulge in clothing, a sudden movement toward a pocket, or knowledge that the person was armed on an earlier occasion can supply it.79 In Johnson the trial court found that Trevizo's observations (the bandana, the scanner, the gang-associated hometown, and the burglary prison term) gave her cause to suspect he was armed and dangerous, and the Supreme Court held the patdown consistent with the Fourth Amendment.80
In a traffic stop the first two steps usually resolve quickly, which leaves the individualized suspicion of the third step as the point on which most problems turn. A passenger who is fully seized can still be a person the officer has no right to frisk.
Students lose this issue in two directions. Some demand suspicion of unrelated criminal activity before a passenger may be frisked, which Johnson rejects because the lawful stop of the car already satisfies the first condition for every occupant. Others reason that a seized passenger may be patted down simply for being in the car, which skips the second condition entirely. Johnson also shows the order in which the two powers operate: Trevizo's request that Johnson step out needed no showing of danger, and the frisk that followed rested on her separate suspicion that he might have a weapon.84
Extending the Stop
A traffic stop draws its authority from the violation that prompted it, and that same source of authority fixes how long the stop may last. The earlier sections here asked who may be seized and touched during a stop. This one asks how long the seizure may run and what officers may add to it while it does. Illinois v. Caballes answers the question for the most common addition, a drug-detection dog. A sniff of a vehicle during a lawful traffic stop is not a search and needs no reasonable suspicion of drug activity, so long as the stop is not prolonged beyond the time needed to handle the matter for which it was made.86
The facts show how the rule works in practice. An Illinois trooper, Daniel Gillette, stopped Roy Caballes for driving 71 miles per hour in a 65 zone. A second trooper from a drug interdiction team heard about the stop on the radio and, although Gillette had asked for no help, came to the scene with a dog.87 Gillette had checked the license and run a warrant check, and he was still writing the warning ticket when the dog arrived, walked around the car, and alerted at the trunk, where the troopers found marijuana.88 The Illinois Supreme Court ordered the evidence suppressed. It reasoned that the dog converted a lawful traffic stop into a drug investigation, and that the shift in purpose lacked any reasonable suspicion of narcotics.89 The Supreme Court accepted the state court's conclusion that the length of the stop was entirely justified by the traffic offense and the ordinary inquiries that go with it, and it held that a sniff does not change the character of a stop that was lawful at its start unless the sniff itself infringes a protected privacy interest, which it does not.90
Two separate ideas hold the rule together, and each has its own reason. The first concerns the seizure. The traffic violation justifies detaining the driver for as long as it takes to deal with the violation, so a sniff performed within that time adds no detention to what the violation already supports. A stop stretched beyond that point is a different seizure, one the violation no longer justifies.91 The second idea concerns privacy. Government conduct that compromises no legitimate privacy interest is not a search, and no one has a legitimate interest in possessing contraband, so a procedure that reveals only whether contraband is present intrudes on nothing the law protects.92 Because the sniff is not a search, the Fourth Amendment attaches no suspicion requirement to it, and the Illinois court erred by treating the dog as the cause of a constitutional violation when the stop itself was proper from beginning to end.
The same privacy reasoning appears in United States v. Place, which involved luggage rather than a car. Police there could briefly detain a traveler's bags on reasonable suspicion that they held contraband, and exposing the bags to a trained narcotics dog was not a search, because the sniff discloses only the presence or absence of contraband and no other private information.93 Yet the Court found a 90-minute detention of the luggage in an airport unreasonable when it rested only on reasonable suspicion, because a detention of this kind must be limited in scope and duration.94 The two holdings answer different questions. One asks whether the sniff is a search, and the other asks whether the detention that made the sniff possible lasted too long. Read together with Caballes, they place the constitutional question on the length of the detention, since the sniff itself, revealing only contraband, raises no privacy problem.
The dissenting opinions in Caballes show the competing view, which clarifies how narrow the majority rule is. Justice Ginsburg would have applied the two-part Terry test to the traffic stop. Terry requires that the stop be justified at its inception and that the officer's action be "reasonably related in scope to the circumstances which justified the interference in the first place."95 She read scope to cover the manner of the seizure as well as its length, and she concluded that bringing in a drug dog broadened the stop even if it added no time.96 Justice Souter treated the sniff as a search and argued that police may not use a suspect's immobility to look for evidence unrelated to the reason for the detention.97 The majority rejected both positions for a sniff that leaves the length of the stop unchanged. What survives of the dissenters' concern is the duration limit, which keeps an officer from stretching a stop beyond the time its purpose requires.
Students go wrong on this point in two directions. Some demand reasonable suspicion of drug activity before any dog sniff during a traffic stop, which Caballes rejects for a sniff that fits inside the stop. Others treat Caballes as approving every sniff and forget that the holding is conditioned on the sniff not prolonging the stop, so that time added to the stop is the fact that flips the analysis. The rule does not say that an officer may hold a driver for a dog. It says that a dog arriving while the traffic matter is still being handled adds nothing to the seizure.
Step three does most of the work on an exam, because the facts usually tell the student exactly when the ticket was finished and when the dog arrived.
The duration limit here is the traffic-stop form of a principle that runs through this chapter. A Terry stop is justified as a brief detention tied to a limited purpose, and the line between a stop and an arrest marks the point at which a detention has grown past that purpose. Place and Caballes apply the same logic to time. Once the purpose of the seizure has been served, the justification that supported it has run out, and whatever the officer does afterward needs support of its own.