A large-scale study of traffic stops across the U.S. found significant black-versus-white disparities in how often drivers were stopped and searched by police, as well as evidence of racial bias behind those disparities.
Researchers looked at data for nearly 100 million traffic stops from 2011 to 2017, carried out by 21 state patrol agencies, including in California, New York and Texas, as well as 29 municipal police departments, including Denver; Tampa, Florida; and Fort Wayne, Indiana.
The researchers also sought to dig beyond the disparities themselves to assess whether there was evidence of racial discrimination motivating the different rates of stops and searches.
For stops, they conducted a “veil of darkness” test, meant to assess if the disparity was less after nightfall, when it would be harder to detect a driver’s race. They, in fact, did find a drop in the proportion of black drivers stopped after dark, suggesting racial bias was a factor.
In terms of searches, the study found that, although police were more likely to find drugs, guns or other contraband in stops of white drivers, black drivers were still searched about 1.5 to 2 times as often.
The analysis “reveals evidence of widespread discrimination” in law enforcement’s decisions to stop and search drivers, the study said.
“I see the work we’re doing as opening the door and starting the conversation with local journalists, policymakers to start doing a deeper dive to understand what’s driving the discrimination,” said Stanford data scientist Amy Shoemaker, who worked on the study. “And have conversations with police departments about how to make policy changes addressing these disparities and about the impact on communities of color.”
The study’s findings on racial disparities in policing echo some previous research, including The Washington Post’s analysis of Department of Justice survey results from 2011 showing black drivers were about 31 percent more likely to be pulled over by cops than were white drivers.
The Stanford study sought to go beyond such statistics by performing certain tests to assess if there was evidence of racial discrimination behind the disparities in police stops.
Besides the “veil of darkness” test, researchers also looked at the rate at which drivers were searched and the likelihood that these would turn up contraband, and they found evidence that the bar was lower for searching black and Latino drivers than for searching whites.
Specifically, black and Latino drivers who were stopped were searched more often than whites on average. In the 16 states for which they had the necessary data, state patrollers searched black drivers at a rate of 3.8 percent, Latino drivers at a 3.6 percent rate, whites at 1.6 percent.
To test if the search rates were the product of discrimination (and not the result of black and Latino drivers hypothetically possessing contraband at higher rates), the researchers assessed how often searches were “successful” in finding drugs, alcohol, guns or other illegal materials. Across state patrol stops, searches of white drivers led to finding contraband 36 percent of the time, while for black drivers it was found in 32 percent of the searches and for Latino drivers 26 percent of the time.
Additionally, the researchers sought to examine the effects of legalizing recreational marijuana in Colorado and Washington states on the rates of stops and searches. According to their findings, while legalization reduced the overall number of searches for both white, black and Latino drivers, the bar for searching black and Latino drivers was still lower than for whites.
The study’s findings provide broader context behind some of the high-profile stories of police stops and searches that have led to violence against black Americans in recent years. Sandra Bland, for instance, was a 28-year-old black driver who was pulled over by a Texas state trooper in 2015 for, as the officer said, failing to signal when she changed lanes. After refusing to get out of the car, the trooper arrested her ― and within 65 hours she was dead. The coroner said she’d hanged herself with a noose made from a garbage bag.
The study also provides data backing up the everyday experiences of black Americans, who often face such discrimination in policing in their everyday lives and interactions with officers.
“I was heading home one night, and the Miami-Dade County police felt that I took too many turns, and that’s the reason why they stopped me in my own driveway,” McKenzie Fleurimond told HuffPost for its Existing While Black project last year.
“Even with giving them my license and them seeing that the house that I was in front of was in fact my house, they proceeded to run my plates… to verify that the car was in fact mine,” she added. “It was a very demeaning experience, especially being in front of your house.”