Racial disparities in traffic stop outcomes are widespread and well documented. Less well understood is how racial disparities may be amplified or muted in different contexts. Here we focus on one such situational factor: whether the initial traffic stop was related to a traffic safety violation or a (broadly defined) investigatory purpose. This is a salient contextual characteristic as stop type relates to different levels of assumed discretion and purpose. While all traffic stops involve some officer discretion, investigatory stops are more easily used as justifications to conduct a search based on an officer's diffuse suspicion; traffic safety stops are more often just what they seem. Using millions of traffic stops from several states, we show that black male drivers are more likely to be searched and less likely to be found with contraband and that this relationship is amplified where the initial stop purpose is investigatory. One implication of this is that one path to alleviating disparities in traffic stops for agencies is emphasizing traffic safety, rather than using stops as a supplemental investigatory tool.

Evidence that racial minorities are targeted for searches during police traffic stops is widespread, but observed differences in outcomes following a traffic stop between white drivers and people of color could potentially be due to factors correlated with driver race. Using a unique dataset recording over 5 million traffic stops from 90 municipal police departments, we control for and evaluate alternative explanations for why a driver may be searched. These include: (1) the context of the stop itself, (2) the characteristics of the police department including the race of the police chief, and (3) demographic and racial composition of the municipality within which the stop occurs. We find that the driver's race remains a robust predictor: black male drivers are consistently subjected to more intensive police scrutiny than white drivers. Additionally, we find that all drivers are less likely to be subject to highly discretionary searches if the police chief is black. Together, these findings indicate that race matters in multiple and varied ways for policing outcomes.

This paper provides evidence of racial variation in traffic enforcement responses to local government budget stress using data from policing agencies in the state of Missouri from 2001 through 2012. Like previous studies, we find that local budget stress is associated with higher citation rates; we also find an increase in traffic-stop arrest rates. However, we find that these effects are concentrated among White (rather than Black or Latino) drivers. The results are robust to the inclusion of a range of covariates and a variety of model specifications, including a regression discontinuity examining bare budget shortfalls. Considering potential mechanisms, we find that targeting of White drivers is higher where the White-to-Black income ratio is higher, consistent with the targeting of drivers who are better able to pay fines. Further, the relative effect on White drivers is higher in areas with statistical over-policing of Black drivers: when Black drivers are already getting too many fines, police cite White drivers from whom they are presumably more likely to be able to raise the needed extra revenue. These results highlight the relationship between policing-as-taxation and racial inequality in policing outcomes.