Police officers speak to Black drivers less respectfully, study finds. Here's why it matters

Police officers communicate in a friendlier, more respectful way to white drivers than Black drivers during routine traffic stops, and these routine interactions can erode police-community trust, a new study found.

Study author Nicholas Camp, an assistant professor at the University of Michigan, has previously found that officers use less respectful language with Black drivers, but the peer-reviewed study published this week in the Journal of Personality and Social Psychology reveals differences not in what police say but how they say it. 

“Racial disparities in cues as subtle as an officer’s tone of voice can shape citizens’ trust in the police and alter their interpretation of subsequent encounters,” researchers wrote.

Researchers asked more than 400 people to listen to 250 short audio clips from body camera footage of routine traffic stops of men in an unnamed mid-size city. The audio was edited so participants could only hear the officer's tone of voice but couldn't understand what they were saying.

Listeners rated the cop's tone of voice as significantly less friendly, less respectful and more tense in audio taken from traffic stops of Black drivers. This finding was consistent regardless of the officer's and listener's race or gender. 

"I was surprised that we observed disparities in such a subtle cue," Camp said. "And that these interpersonal cues had an influence on citizens trust even though our results are supported by past research."

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More than 20 million Americans are stopped by police each year, and Black drivers are 20% more likely to get pulled over than white drivers, according to a study from the Stanford Open Policing Project. 

Recent high-profile cases including the killing of Daunte Wright and Philando Castile highlighted that these routine stops are more likely to be fatal for people of color. The Washington Post reported that Black people accounted for a disproportionate share of traffic-stop deaths in 2015, citing its database of police shootings.

Camp and his colleagues found that racial disparities in routine interactions can also negatively impact police-community trust. American's trust in police fell to an all time low in the weeks following the murder of George Floyd and the subsequent nationwide protests against systemic racism and police brutality, driven in part by a growing racial divide on the issue. 

In a follow-up experiment, people who listened to clips of police interacting with Black drivers said they would be less trusting and supportive of the department. Participants who felt they had been previously treated unfairly by police generally judged the clips more harshly.

"There's a cycle where disparities can reduce institutional trust and in turn that trust or lack of trust shapes how you interpret the next encounter you have with law enforcement," Camp said.

Camp found that body camera footage could be used not just as evidence in cases of police misconduct but to identify other patterns in the thousands of daily interactions with the public and change them to break this cycle.

He said law enforcement has shown interest as they've discussed the study's findings and he is conducting more research on the impact of training on officer communication.

"Officers receive a lot of training on use of force ... I would argue that officer's should also receive a lot of training on communication," he said. "These every day interactions these encounters are common but also really consequential."

Follow N'dea Yancey-Bragg on Twitter: @NdeaYanceyBragg