Traffic Stop Data Analysis
Stonewall Analytics, LLC 2
Executive Summary
This report analyzes nearly 160,000 traffic stops conducted in Suffolk County, New York, in
2023, with the goal of assessing whether racial or ethnic disparities exist in stop and search
practices. The study applies two key statistical tests: the Veil-of-Darkness test to evaluate racial bias in stop decisions and the Hit Rate test to examine search outcomes across different racial and ethnic groups. The data were obtained through the Suffolk County Police Department. The data were cleaned and standardized to ensure consistency across the reporting period of calendar year 2023.
The Veil-of-Darkness test compares traffic stops made during daylight and nighttime hours,
under the assumption that officers are less able to discern a driver’s race at night. Logistic
regression models were used to assess whether minority drivers were stopped more frequently
in daylight than at night, controlling for various factors such as officer command type. The
results showed no statistically significant relationship between daylight stops and the likelihood
of stopping minority drivers, as compared to White drivers. The odds ratios for minority drivers
remained close to 1.0, indicating that racial bias did not appear to be a significant factor in
initial stop decisions.
The second component of the analysis focused on traffic stops with searches using the Hit Rate test, which assesses whether searches yielded a positive result, which is defined as a search yielding illegal drugs, illegal weapons, or other contraband or evidence. Although the data revealed variation in hit rates across racial and ethnic groups, with White drivers having the highest positive result rate, statistical tests found no significant difference in hit rates between White drivers and Black or Hispanic drivers across geographic areas. While White drivers were more likely to have positive result searches, the difference was not statistically significant, suggesting that variations in search outcomes may be influenced by other factors rather than bias in policing practices.
Overall, the study found no evidence of racial bias in traffic stop decisions based on the Veil-of-Darkness test and no statistically significant differences in search hit rates between minority
and White drivers. However, the findings highlight the importance of ongoing monitoring and
refinement of data collection practices to ensure transparency and fairness in law enforcement
activities. Future research should explore additional variables that may contribute to disparities
in post-stop outcomes and continue evaluating traffic stop data over time to detect any
emerging patterns or policy impacts.
Get the report HERE
Future of Policing 