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Black Drivers Stopped by Police More than Ticketed by Speed Cameras in Chicago

Nebiyou Tilahun, Associate Professor of Urban Planning and Policy

Black drivers in Chicago are stopped by police officers at higher rates than they are ticketed by automated speed cameras, according to new research. They also were stopped by police at a disproportionately higher rate than what would be expected given the proportion of Black drivers on a road. The opposite was true for white drivers, who were ticketed at disproportionately lower rates.

While this confirms previous research on racial bias in policing, the comparison of officer stops to cameras offers a clearer picture than police data alone.

“The difference in rates between automated and non-automated systems paints a stark picture,” said Nebiyou Tilahun, an associate professor of urban planning and policy at the University of Illinois Chicago and a coauthor on the study.

The research, published in the Proceedings of the National Academy of Sciences, used a database that estimates the racial composition of drivers on roadways based on cellphone GPS data to determine the racial makeup of drivers on specific Chicago roads. Researchers compared that data with the race of drivers who were stopped by police or received an automated speed ticket on those roads. For police stops, the driver’s race is listed in the police report; for the cameras, the researchers used the U.S. Census tract that the ticket was mailed to as a predictor of the driver’s race.

The researchers found that Black drivers were ticketed at slightly higher rates by cameras than would be expected given their share of drivers on a particular road. Tilahun said it’s not clear why this happened — there may have been a confounding factor, such as driver age, which the researchers didn’t examine.

What was clear was that police issued tickets to Black drivers at rates well above what would be expected given Black drivers’ share of the road. For example, on roads where Black drivers made up 50% of drivers, they comprised, on average, 70% of police stops.

The opposite was true for white drivers. When they made up 50% of the drivers on a road, they comprised, on average, fewer than 20% of police stops. And white drivers, on average, accounted for a smaller share of police stops than automated tickets whether they made up a higher or lower share of drivers.

The results draw attention to racial disparities in police stops, Tilahun said. While these results aren’t necessarily a surprise, they eliminate some of the factors that could be blamed for muddying the data when looking only at police stops, such as the argument that police are more likely to patrol areas with a high percentage of Black drivers.

“Before, you might be able to say, ‘Well, there are confounding factors. We really can’t be sure.’ I think this makes it much clearer and puts it on the agenda for all involved that roadway stops need to be more racially neutral,” he said.

The study’s coauthors are Sajad Askari, a PhD student at UIC, and researchers from Cornell University, Rutgers University and the University of Sydney.