U.S. Supreme Court’s Early Direction on Police Conduct During Traffic Stops

In my initial post on this topic I raised the issue of how the Fourth Amendment applies to police use of force, particularly deadly force in the traffic stop context. Maybe the Fourth Amendment should provide protection in a way that some of the recent tragedies in the news—particularly instances in which police have shot and killed someone as a result of an initial traffic stop—could have been avoided?

The U.S. Supreme Court has repeatedly implied that the Fourth Amendment restricts police conduct during traffic stops. It did so by analogizing traffic stops to Terry stops, as it did in Pennsylvania v. Mimms (1977) and in Berkemer v. McCarty (1984), in which it wrote that “the usual traffic stop is more analogous to a so-called ‘Terry stop,’ than to a formal arrest.” The Court later reaffirmed this Terry analogy in Knowles v. Iowa (1998) and Illinois v. Caballes (2005).

Further, the Court has expressly extended Terry to traffic stops. For example, in Michigan v. Long (1983) it ruled that the vehicle itself could be frisked if reasonable suspicion existed. It also ruled in United States v. Arvizu (2002) and United States v. Cortez (1981) that Terry’s reasonable suspicion standard (a standard lower than the Fourth Amendment’s probable cause standard) justifies traffic stops, though this is a tricky extension to justify. Terry embraced a reasonable suspicion threshold as a compromise:  a lower suspicion threshold would be applied to promote police discretion—with the goal of improving officer and public safety and controlling crime—but based on a trade-off in which the police intrusion was to be more limited than if it had been justified by the more demanding probable cause standard. Though Terry allowed one intrusive search—the frisk—that search was not automatic. It could only occur if there was a reasonable suspicion of danger (not all suspected crimes are accompanied by a reasonable suspicion of danger, something like shop lifting being a classic example). And under Terry that frisk could only come after an initial investigative search—an oral inquiry (part of the “stop” in stop-and-frisk) in which police can seek information such as what the suspect is doing in the area, identification, etc. Thus, the Court explained in the Berkemer traffic stop case that in a typical Terry encounter “the officer may ask the detainee a moderate number of questions to determine his identity and to try to obtain information confirming or dispelling the officer's suspicions. But the detainee is not obliged to respond. And, unless the detainee's answers provide the officer with probable cause to arrest him, he must then be released.” However, as I will explain in a future post, the Court later indicated that it would not be as restrictive about police discretion in traffic stops as Terry arguably implies should be the case.

In any event, these earlier Supreme Court Terry invocations in traffic stop contexts led numerous state courts to conclude that, similar to how Terry imposes Fourth Amendment constraints on what police may do during a stop-and-frisk encounter, applying a Terry analogy in traffic stop cases means that search and seizure law should also impose constraints on police during traffic stops. I will describe this state court approach in my next post on this topic.