The killing of Tyre Nichols has raised questions about the use and risks of a routine part of U.S. policing: the traffic stop.

Nichols died in the hospital on Jan. 10, 2022, from injuries sustained in a beating by five officers three days earlier. The violence occurred after the 29-year-old Black man was pulled over while driving in Memphis, Tennessee. The officers, all of whom are also Black, have since been fired and face charges of second-degree murder.

While not all traffic stops result in violent encounters – indeed studies suggest that relatively few do – the case of Nichols highlights that such encounters can become sites of police violence. And this isn’t an isolated incident. Before Nichols came Patrick Lyoya, Philando Castile and Sandra Bland, to name just a few high-profile cases. All were killed by police in incidents that began with a traffic stop.

We have analyzed a data set of more than 20 million traffic stops as part of research into the effectiveness of this routine part of police life. What we have found is that, even by its own standards, the return on this high-contact form of policing is slim – it rarely leads to criminal charges or convictions. Moreover, the negative consequences are far-reaching. Law enforcement traffic stops are prone to racial bias and cause harm to communities and individuals disproportionate to any benefit that they bring, our research suggests.

Traffic stops represent the most common nonvoluntary interaction between citizens and police officers in the U.S. Every year, around 20 million stops are recorded.

Some of these stops are for legitimate public safety reasons – drunken drivers, for example, are an obvious risk to other road users. But police officers have huge discretion when it comes to conducting traffic stops for a whole slew of driving infractions, from a broken taillight to speeding. They can also, in most states, initiate a traffic stop as the pretext to investigating other crimes. This right was confirmed by the Supreme Court in 1996 in Whren vs. United States. The ruling stated that it is not unconstitutional for officers to use any traffic violation, no matter how minor, as a reason to search the vehicle for other suspected crimes – for example, the possession of illegal drugs – if they have reasonable cause.

These pretextual stops, stopping cars for minor infractions as an opportunity to look for evidence of drug-related or violent crime, can be thought of as the roadside equivalent to “stop and frisk” – the practice of allowing officers to search someone on the streets if they have “reasonable” suspicion of criminal activity.

Both form part of what is called the “broken windows” theory of policing. This idea, which rose to prominence in the 1990s, holds that minor instances of disorder in a neighborhood create an environment that will eventually lead to more serious instances of crime, and that by focusing on smaller infractions police can root out more serious offenses.

The SCORPIAN unit that pulled over Nichols exemplifies the type of high-contact, proactive, and aggressive policing that often characterizes broken windows tactics. The officers who killed Nichols gave him more than 70 orders in just a few minutes.

Broken windows policing has long been debunked by many criminologists who find that it fails to achieve its objectives, at the detriment of communities. Our research suggests that traffic stops yield few results when it comes to serious crimes. Analysis of 9.5 million traffic stops in North Carolina between 2013 and 2019 shows that just 1.2% led to felony charges. The felony conviction rate resulting from pulling over a driver was 0.23%.

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