Study Finds ‘Persistent’ Racial Bias in Police Traffic Stops and Searches

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Photo by Chris Yarzab via Flickr

Police decisions to stop and search motorists are affected by “persistent racial bias,” according to a study published in the Nature Human Behaviour journal.

The authors of the study constructed a national dataset of approximately 95 million traffic stops conducted by 21 state patrol agencies and 35 municipal police departments between 2011 and 2018. The data showed that comparatively fewer Black drivers were stopped after sunset—when it’s assumed to be difficult for police officers to identify motorists by race.

“If Black drivers comprise a smaller share of stopped drivers when it is dark and accordingly difficult to determine a driver’s race, that suggests Black drivers were stopped during daylight hours in part because of their race,” the authors said.

Moreover, after being stopped, Black and Latinx drivers were searched on the basis of less evidence than their white counterparts, the study found. This was the case for searches carried out by both state patrol agencies and municipal police departments, according to the article.

The authors argued that their findings suggest “decisions about whom to stop and, subsequently, whom to search are biased against Black and Hispanic drivers.”

The authors also studied the effects of drug policies on racial disparities in traffic stops.

The legalization of recreational marijuana lowered the number of searches of white, Black, and Hispanic drivers; however, the evidentiary standard for searching minority drivers remained lower than that for white drivers, the study found.

This led the authors to conclude that the problem of racial disparities in traffic stops is solvable: the legalization of recreational marijuana is one of many policy interventions that could reduce such bias.

Although the study’s results stem from a comprehensive study of traffic stops, “they only partially capture the wider impacts of law enforcement on communities of color,” warned the study’s authors.

The authors explained: “If, for example, officers disproportionately patrol Black and Hispanic neighborhoods, the downstream effects can be injurious even if individual stop decisions are not directly affected by the color of one’s skin. Similarly, enforcement of minor traffic violations, like broken tail lights – even if conducted uniformly and without animus – can place heavy burdens on Black and Hispanic drivers without improving public safety.”

More research, data collection, and data analysis is needed in these areas, wrote the authors.

The study’s authors were Emma Pierson, Ph.D., assistant professor at Cornell Tech; Camelia Simoiu, Ph.D. candidate at Stanford University; Jan Overgoor, Ph.D. candidate at Stanford University; Sam Corbett-Davies, Ph.D. candidate at Stanford University; Daniel Jenson, engineering student at Stanford University; and Amy Shoemaker, data scientist at the Stanford Computational Policy Lab.

Other authors were Vignesh Ramachandran, producer at ProPublica Illinois; Phoebe Barghouty, data journalist at the Stanford Open Policing Project; Cheryl Phillips, professor at Stanford University; Ravi Shroff, assistant professor at New York University; and Sharad Goel, assistant professor at Stanford University.

Additional information about the study’s methodology can be found here.

The full study can be accessed here.

Michael Gelb is a TCR News Intern.

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