About Us

Traffic Stop Study

Our departments partnered with CR Research Group LC to analyze data on discretionary traffic stops. We requested the review as a proactive step to evaluate whether or not racial disparities existed in traffic stops and outcomes, including written warnings, citations and arrests.

The independent review found “negligible evidence of racial bias” by Ames and Iowa State University police officers when conducting traffic stops. The report that follows provides greater detail, but here are a few important findings:

  • There is little evidence that officers stopped a greater proportion of people of color compared to white drivers. The disproportionality index (the measurement used to assess racial disparity)
    for both departments was almost always lower than .05, which is described in the reports as a low confidence indicator of disproportionality.
  • In 2017‐2018, the Iowa State review (which included three years of data) found people of color were more likely to receive a citation during a traffic stop, while white drivers were more likely
    to receive a warning. In 2019, there were no differences based on race.
  • In 2018, the Ames review (which included two years of data) found no differences between people of color and white drivers. In 2019, white drivers were more likely to receive a citation and people of color were more likely to receive a warning as the result of a traffic stop.
  • There was racial disparity in arrests for both departments, but nearly all of the arrests were for nondiscretionary offenses, which means officers were required to make an arrest. 

Disproportionality is one way to assess potential bias or discrimination, but as the researcher explains in the report it may also indicate differences in driver behavior, vehicle condition or driver‐license status. We also note that many of the findings for citations and warnings were not statistically significant, and the study did not control for other factors that may influence traffic stops and outcomes.

As stated above, nearly all of the arrests were for nondiscretionary offenses, which means the officer is required to make an arrest. This includes arrests for operating while intoxicated, driving while barred or existing warrants. Arrests also include “cite and release” charges, such as driving under suspension, which did not require the driver to go to jail, but promise to appear for a later court date. For these reasons, it is difficult to make definitive conclusions about all outcomes of traffic stops.

As with any study, there are limitations, but this is one tool that allows us to evaluate our performance over time. We will continue to examine traffic stops as part of our internal reviews. Our departments also provide ongoing bias‐based training for officers, publish monthly reports on police activity and engage in conversations within our departments and the community about race.

We are committed to strengthening the relationships we have within our communities and improving transparency and appreciate your partnership in this effort.


Chief Geoff Huff, Ames Police Department

Chief Michael Newton, Iowa State University Police Department

Please find the full study here.