Cops in Cook County among worst, huge study of traffic stops across U.S. finds


If you are black and were driving in Evanston in 2014, it was seven times more likely that if police officers stopped your car they would search you than if you are white.

Researchers at the University of North Carolina documented that disparity as part of what may be the largest study of traffic stops ever collected, analyzing 55 million stops based on data from 132 different agencies in 16 states. Across the board, researchers found that stops by law enforcement officers led to searches if the drivers are black and Hispanic far more commonly than if they are white. But four law enforcement agencies stand out in the study: the Cook County Sheriff’s Department, the Evanston Police Department, the Chicago Police Department and the Palatine Police Department.

The study examined, by race, what percentage of traffic stops turned into searches year by year as far back as 1999, though data was not available for every year for every agency. The study lists the 10 agencies that, in any single year, had the most disproportionate stops.  For stops comparing white drivers and black drivers, the Evanston Police Department took up six of those 10 spots, having a strikingly disproportionate ratio each year between 2009 and 2014.  (see Table 1). The Chicago Police Department was listed in three of the four remaining spots.

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For searches of Hispanic drivers compared to their white counterparts, the Cook County Sheriff over a four-year period between 2008 and 2011 had the four most disproportionate ratios of any studied agencies. In 2009, the worst single year, it was more than 18 times more likely a Hispanic driver than a white driver would be searched after a stop by Cook County sheriff deputies.  All ten agencies with the worst ratios were Illinois departments; in addition to the repeated listings of the Cook County sheriff, the Palatine police department also was on the list four times, and the Evanston police and DuPage Sheriff each were listed among the 10 worst ratios once. (see Table 2).

Table 1: Highest Black-White search rate ratios by agency by year

RankAgencyYearBlack:White Search Rate Ratio
10Evanston PD20116.07
9Chicago PD20086.26
8Chicago PD20096.28
7New Lenox PD20136.41
6Evanston PD20126.61
5Evanston PD20147.08
4Chicago PD20107.21
3Evanston PD20137.63
2Evanston PD20107.77
1Evanston PD20097.96

“The high numbers did surprise me,” said Cmdr. Joseph Dugan, spokesman for the Evanston Police Department. “Historically I think we’ve had good relationships with communities of color but there’s always room for improvements— things that can be improved upon, things that can be enhanced.”

The study comes less than a year after Chicago’s Police Accountability Task Force published a report detailing distrust between CPD and communities of color in the city. According to that report, Hispanic and black drivers stopped by CPD were searched approximately four times as often as white drivers in 2013, while white drivers were found to have contraband twice as often.

The UNC team compiled data from eight states with laws requiring agencies to report traffic stops in efforts to identify any racial discrimination, as well as agencies from eight other states that voluntarily published data at least some years.

Political science professor Frank R. Baumgartner, the lead researcher, said the disparity could result from the rise of aggressive policing tactics to crack down on crime in particular neighborhoods, which would point to what he identifies as “a systemic bias that’s different than a personal animus of any officer.”

Table 2: Highest Hispanic-White search rate ratios by agency by year

RankAgencyYearHispanic:White Search Rate Ratio
10Dupage Co. Sheriff20128.99
9Evanston PD200911.26
8Palatine PD200912.28
7Palatine PD201012.33
6Palatine PD201112.52
5Palatine PD200813.51
4Cook County Sheriff201113.64
3Cook County Sheriff201015.13
2Cook County Sheriff200816.44
1Cook County Sheriff200918.14

“Racially segregated communities might have more of an issue because a lot of the disparate policing is related to neighborhoods,” Baumgartner said in an interview. “A lot of what we’re seeing is… officers in certain neighborhoods being very aggressive and not as aggressive in others.”

Dugan said that the Evanston Police Department uses a geomapping system to determine where to deploy officers, part of a program instituted in 2014 called Data-Driven Approaches to Crime and Traffic Safety. This approach is based on “the theory that most often crimes are committed with assistance of a motor vehicle,” according to the Evanston Police Department website, and deploys officers to areas with high concentrations of crime and traffic violations.

“We do deploy resources into particular areas,” said Dugan.

But as Baumgartner and his coauthors wrote, “investigatory stops were always a blunt instrument for stopping crime because drug dealers and violent criminals do not have any strong systematic driving tendencies that distinguish them from innocent motorist.”

While law enforcement agencies in Illinois often were often found to have comparatively high racial disparities, the state is one of eight with laws requiring the reporting of traffic stops by law enforcement. The Illinois law was enacted in 1998 and extends through 2019, requiring law enforcement agencies to report statistics on the racial breakdown of traffic stops to the Illinois Department of Transportation each year.

“Illinois has to be given credit for making this data available,” Baumgartner said.