Illinois Traffic Stops

Racial Disparities in Illinois Traffic Stops

Across the state of Illinois, Latinx and black drivers are searched and subjected to dog sniff testsStatewide, Latinx drivers are subjected to dog sniff tests at a lower rate than white drivers. However, in the agencies with statistically significant differences between white and Latinx dog sniff rates, dogs are used in stops involving Latinx drivers at higher rates. This is explained in more detail below. at significantly higher rates than white drivers when stopped by Illinois law enforcement. Yet when officers search cars, minority drivers are no more likely to actually have contraband than white drivers.

Clearly, there is a problem. We hope this report will serve as a resource to help law enforcement agencies make informed improvements around racial disparities for the good of their officers and the people they serve.

Since 2004, the Illinois Traffic and Pedestrian Stop Statistical Study Act has required Illinois law enforcement to document and report traffic stops to the Illinois Department of Transportation. The data reveal the effectiveness and unintended consequences of law enforcement tactics and allow agencies to compare themselves to each other.

Traffic Stops

In 2017, over two million traffic stops occurred in Illinois. After each stop a law enforcement officer filled out this form, recording the details of the traffic stopSome law enforcement agencies did not submit data to the Illinois Department of Transportation. Only agencies that submitted data are included below., including:

  • The driver's race
  • The reason the driver was stopped
  • Whether or not the officer conducted a search
  • Whether or not contraband (illegal drugs, weapons, etc.) was found during the search
  • What action resulted (e.g. a citation/ticket, written warning, verbal warning)

in 2017. Shading changes in this plot do not indicate significance, but rather highlight a subset of the data and puts the metric into context of the whole population. Each square represents ~ stops.

Filter charts and text by selecting an agency.

conducted traffic stops involving black, Latinx, Asian, or white drivers in 2017.American Indian / Alaska Native, Native Hawaiian, and Pacific Islander are also listed on the traffic stops form. These races were left out here, not because they were seen as less important, but because the counts reported for these races were mostly too small to check for any sort of significance. Of these stops:

  • () involved a black driver,
  • () involved a Latinx driver,
  • () involved an Asian driver, and
  • () involved a white driver.

People often want to compare the demographics of those stopped by law enforcement to the demographics of the residential population to calculate a "stop rate".Stop rate would refer to the metric calculated by dividing a race's stopped population by its driving population (assuming driving population were known). Assuming the driving population mirrors the residential population, an unbiased department should stop people of each race at about the same rate they appear in the population. However, this approach is not as straightforward as it may seem. First, the actual driving population, as well as the associated demographics, are unknown. Second, race is recorded differently on the traffic stop form than on the census, making comparisons difficult. In short, a "stop rate" is impossible to calculate accurately.

Black Latinx Asian White
Stop Count
Stop PercentageStop percentage refers to the percentage of the total stops that involved a driver of this race.

Traffic stops by all Illinois law enforcement agencies with corresponding population information.

In order to focus on metrics that are directly measurable—rather than guessing at demographics tracked using different systems and criteria—we compare the outcomes by race for people who have already been stopped. By choosing this focus, we do not mean to suggest that there are no racial disparities in who gets stopped. Agencies, especially those with high stop counts, should still consider their residential population when examining their data for bias.

Every traffic stop can produce several possible outcomes. For example, the officer may or may not search the driver. Officers may record different reasons to justify searches. They may receive consent from the driver to conduct a search, or they may establish probable cause, including through a dog sniff alert. During a search, the officer may or may not find contraband. The officer could also give a verbal warning, a written warning, or a citation.

We explore some of these outcomes below. Select an agency above and follow along.

Consent Searches

During a traffic stop, an officer may ask permission to search your car. If you agree, this is called a "consent search." Unlike other searches that require officers to identify some suspicion of a crime, the decision to conduct a consent search is left to the subjective judgment of the officer. Supervisors and courts do not review those decisions. These subjective, unreviewed decisions raise concerns about racial bias, whether conscious or unconscious.

Some argue that the rate at which drivers are searched (or asked to be searched) is not necessarily an indicator of discrimination because officers may base their decisions on evidence that the driver has contraband, and individuals in different racial groups may carry contraband at different rates. So let's compare the rates at which contraband was found (from now on referred to as "contraband hit rates") by Illinois law enforcement agencies during consent searches.

First, are minority drivers any more likely to be found with contraband? Darker bubbles represent agencies where the difference in hit rates are statistically significant. (Find an explanation of statistical significance and how we've chosen to display it here.) As you can see below, the minority contraband hit rates of most agencies do not significantly differ from white contraband hit rates.

Hint: click a bubble to select its corresponding agency.

Consent search hit rates for black, Latinx, and Asian drivers compared to white drivers for each Illinois law enforcement agency, 2015 through 2017. The exact location of circles on this plot and following rate plots have been adjusted to reduce overlap and enable visibility of each agency circle; this may result in some circles being represented in a location that is slightly off their intended value. The exact value can be viewed by hovering over the circle.

Consent search hit rates by race searched by , 2015 through 2017.

The contraband hit rate data provides no evidence that any agency should search minority drivers more than white drivers. In fact, when minority hit rates do differ significantly from white rates, they are lower. In other words, for departments with statistically significant differences, officers are more likely to find contraband on white drivers than black or Latinx drivers.

Dog Sniffs

The next outcome we explore is whether there are there racial disparities in officers' decisions to use a dog to sniff a vehicle during a traffic stop.

Dog sniff rates on black, Latinx, and Asian drivers compared to white drivers for each Illinois law enforcement agency, 2017.

Dog sniff rates by race for , 2017.

An officer's decision to use a dog during a traffic stop is another subjective decision and, as with consent searches, officers are more likely to use a dog during stops of black drivers. Across the state, Latinx drivers are subjected to dog sniff tests at a lower overall rate than white drivers, but in the agencies with statistically significant differences between white and Latinx dog sniff rates, dog sniffs are used in stops involving Latinx drivers at higher rates.

These patterns in the use of consent searches and dog sniff tests illustrate the disparate impact of policing on minority communities.


A traffic stop generally results in one of three outcomes:

  1. Citation / ticket
  2. Written Warning
  3. Verbal Warning

In an ideal world, officers would issue tickets or warnings at approximately equal rates among racial groups of people who are stopped. However, interpreting discrepancies in these rates requires nuance. In the aggregate, patterns of issuing tickets to black and Latinx drivers, but not white drivers, may indicate racial discrimination. On the other hand, patterns of officers frequently stopping minority drivers but finding nothing to ticket may indicate racial profiling.

Drivers themselves would likely prefer that an officer give them a warning rather than a ticket. But high rates of officers only issuing warnings could be an indication that officers are using potential violations of traffic laws as pretext to pull people over. These stops result in fewer tickets because the real motivation behind the stop is to look in the car or conduct a search. Read more on this this practice here.

Citation rates for black, Latinx, and Asian drivers compared to white drivers for each Illinois law enforcement agency, 2017

Citation rates by race for in 2017.

There are often stark racial differences in the decision to issue a ticket or a warning. These disparate outcomes—whether more tickets are issued to white drivers compared to black and Latinx drivers—warrant further investigation.

This website is an ongoing project. We are continuing to analyze this data, and will soon update this site with other metrics.

Key Takeaways

Across Illinois:

  • When law enforcement officers search a car, they are typically no more likely to find contraband on a minority driver than a white driver.
  • Yet, Latinx and black drivers are searched at higher rates than white drivers.
  • Black drivers are also more likely to be subjected to dog sniff tests than white drivers.
  • In the agencies with statistically significant differences between white and Latinx dog sniff rates, dog sniffs are used in stops involving Latinx drivers at higher rates.
  • Across Illinois, citation rates are mixed. There are patterns of both very low and very high citation rates for black and Latinx drivers, with a large number of law enforcement agencies citing minority drivers at significantly higher rates than white drivers.

Further Analysis and Data Collection

The Illinois Traffic and Pedestrian Stop Statistical Study Act is set to expire in July of 2019. This session there will be a bill introduced to continue collection of this data. We urge you to support the continuation of this data collection by calling your representatives.
UPDATE: We're very happy to announce that a new bill that will require the permanent continued collection of this data by law enforcement was signed into law by Governor Pritzker in June 2019!

This website does not explore all the information packed into this data, much of which is quite nuanced. We hope to continue to expand this website with new, explorable plots as the latest data becomes available.

If you'd like to explore the full data set, you can find it here. Please feel free to reach out to us if you find anything interesting.