Traffic Stops Research Articles

Contact and Context: How Municipal Traffic Stops Shape Citizen Character

Previous research shows that how the state conducts itself influences citizen attitudes and behaviors through direct and proximal contact; we show the actions of state agents ripple out even further. Joining bureaucratic data on a publicly observable state behavior—racial disparities in investigatory traffic stops—with survey data, this article shows that residing in a place with extreme racial disparities in traffic stops is associated with depressed confidence in the police even in the absence of more direct forms of contact. This relationship does not extend to participatory behaviors, however, in which only personal stop history and proximal contact are predictors. Racially disparate policing practices, then, may undermine law enforcement legitimacy in a community as a whole, but mobilization to change policy appears limited to individuals who more directly experience the carceral state.

Racial Demographics Explain the Link Between Racial Disparities in Traffic Stops and County-Level Racial Attitudes

Disparities in the treatment of Black and White Americans in police stops are pernicious and widespread. We examined racial disparities in police traffic stops by leveraging data on hundreds of U.S. counties from the Stanford Open Policing Project and corresponding county-level data on implicit and explicit racial attitudes from the Project Implicit research website. We found that Black–White traffic-stop disparities are associated with county-level implicit and explicit racial attitudes and that this association is attributable to racial demographics: Counties with a higher proportion of White residents had larger racial disparities in police traffic stops. We also examined racial disparities in several poststop outcomes (e.g., arrest rates) and found that they were not systematically related to racial attitudes, despite evidence of disparities. These findings indicate that racial disparities in counties’ traffic stops are reliably linked to counties’ racial attitudes and demographic compositions.

Racial Bias in Police Traffic Stops: White Residents’ County-Level Prejudice and Stereotypes Are Related to Disproportionate Stopping of Black Drivers

Racial disparities in policing are well documented, but the reasons for such disparities are often debated. In the current research, we weighed in on this debate using a regional-level bias framework: We investigated the link between racial disparities in police traffic stops and regional-level racial bias, employing data from more than 130 million police traffic stops in 1,413 U.S. counties and county-level measures of racial bias from more than 2 million online respondents. Compared with their population share in county demographics, Black drivers were stopped at disproportionate rates in the majority of counties. Crucially, disproportionate stopping of Black drivers was higher in counties with higher levels of racial prejudice by White residents (rs = .07−.36). Furthermore, county-level aggregates of White people’s threat-related stereotypes were less consistent in predicting disproportionate stopping (rs = .00−.19). These observed relationships between regional-level bias and racial disparities in policing highlight the importance of the context in which police operate.

Deprogramming Bias: Expanding the Exclusionary Rule to Pretextual Traffic Stop Using Data from Autonomous Vehicle and Drive-Assistance Technology

As autonomous vehicles become more commonplace and roads become safer, this new technology provides an opportunity for courts to reconsider the constitutional rationale of modern search and seizure law. The Supreme Court should allow drivers to use evidence of police officer conduct relative to their vehicle’s technological capabilities to argue that a traffic stop was pretextual, meaning they were stopped for reasons other than their supposed violation. Additionally, the Court should expand the exclusionary rule to forbid the use of evidence extracted after a pretextual stop. The Court should retain some exceptions to the expanded exclusionary rule, such as when there is a major public safety concern. In the semi-autonomous world, the Court has the opportunity to adopt a more expansive vision of Fourth Amendment protections and, in doing so, help remedy the issue of racial profiling in traffic stops.

Racial Bias in Traffic Stops: The City of Charlotte

This study analyzes the traffic stops data published by the City of Charlotte in the years 2016-2017 and 2019-2020 to determine if there was any racial bias in the policing. R was used to examine 213,475 stops that involved Black and White drivers. The analysis showed that Black drivers were more likely to be searched, and more likely to be let off with a lighter consequence (e.g., verbal warning). White drivers were more likely to get a citation while Black drivers were more likely to get arrested. When restricted to stops with searches, White drivers were more likely to be given a citation or arrested while Black drivers were more likely to be let off without action. These results are further skewed against Black males between the ages of 18-25. Implications are discussed. The R script and dataset are made available to facilitate reproducible research. Keywords: traffic stops, police bias, statistics, dataset

Comparing Systemic and Individual Sources of Racially Disparate Traffic Stop Outcomes

Abstract The deaths of George Floyd and Breonna Taylor brought discussions of race and policing to the forefront in the summer of 2020 in the United States, spurring protests and calls for policing reform. However, enacting successful reforms curtailing racially biased policing requires understanding whether bias is widespread, likely tied to systemic sources, or the work of a few racist officers. This study elaborates on these perspectives by drawing on theories of systemic and individual bias that may arise when bureaucrats have ample discretion. Using millions of traffic stops, I construct two measures to evaluate whether disparities are widespread—as indicated by the first perspective—or confined to a few officers—as suggested by the second. This study finds widespread racial disparities in who is searched following a traffic stop and that banning consent searches would alter policing patterns more than eliminating outlier officers in a set of paired t-tests.

Disrupting the Traffic Stop–to-Deportation Pipeline: The New York State Greenlight Law’s Intent and Implementation

This article analyzes the traffic stop–to-deportation pipeline in New York State, how it harms children of immigrants, and how New York’s Greenlight Law seeks to disrupt it but has been hobbled by an implementation gap. It first establishes the phenomenon of the traffic stop–to-deportation pipeline by documenting how traffic stops are a key cause of deportations in New York State. Second, it analyzes how the pipeline harms (mostly US citizen) children of undocumented immigrants in New York State, who are more than 7 percent (more than 300,000) of New York State’s children. The pipeline makes these children fear and mistrust the police; harms their educational, social, and brain development; and consumes family income with the Mexican driver tax (costs incurred because parents could not get a driver’s license). Third, the article analyzes how the Greenlight Law should help remedy these harms, and how an implementation gap leaves many parents and children vulnerable to the pipeline. The implementation gap is partly due to the pandemic, but also driven by political and other factors that could be addressed by policy. Finally, the article analyzes how variation in implementing the Greenlight Law could leave the pipeline undisrupted and lead to unequal protection of the law by place in New York State. The article makes policy recommendations for stronger enactment to reduce the pipeline’s harms.

Racial Prejudice and Police Stops: A Systematic Review of the Empirical Literature.

A police stop must be based on founded suspicion: an officer's ability to correctly discriminate suspicious behavior. However, police stops can be influenced by negative attitudes toward Black individuals. We conducted a systematic review of empirical articles published from 2014 to 2019 that investigated the relationship between racial prejudice and police stops on PsycInfo using keywords such as "race," "ethnic," "police stop," "traffic stop," and "stop and frisk." Results included 16 studies conducted in the United States, England, Wales, and the Netherlands and showed that Black men were the most frequent targets of police stops; that many individuals who have been stopped by the police reported negative perceptions of the police force; that the Stop, Question, and Frisk strategy used by some U.S. police departments proved to be a type of stop that favors racial selectivity; and that traffic stops were favorable environments for racially biased actions by officers. We conclude that institutional racism in police stops proves to be a problem shared by several countries, including Brazil. We suggest more investigations to characterize institutional racism in the police force and in other settings and interventions aimed at reducing individual biases and collective racist practices.

Do Female Officers Police Differently? Evidence from Traffic Stops

AbstractPolitical scientists have increasingly begun to study how citizen characteristics shape whether—and how—they interact with the police. Less is known about how officer characteristics shape these interactions. In this article, we examine how one officer characteristic—officer sex—shapes the nature of police‐initiated contact with citizens. Drawing on literature from multiple fields, we develop and test a set of competing expectations. Using over four million traffic stops made by the Florida State Highway Patrol and Charlotte (North Carolina) Police Department, we find that female officers are less likely to search drivers than men on the force. Despite these lower search rates, when female officers do conduct a search, they are more likely to find contraband and they confiscate the same net amount of contraband as male officers. These results indicate that female officers are able to minimize the number of negative interactions with citizens without losses in effectiveness.

Stigmatization and Stops: Power Threat Theory and Traffic Stop Statistics in North Carolina

The power threat theory (PTT) in criminal justice, as well as traffic stop studies, has been well documented; especially in within Black populations. Through the use of reported traffic stop data between 2010-2019, the purpose of this study is to determine 1) the extent to which racial disparities exist as a result of traffic stop decisions and 2) whether traffic stops decisions are consistent with the power threat thesis. Results reveal that Blacks, compared to other racial categories, are significantly more likely to experience traffic stops, thus supporting PTT. Areas of further research, limitations, and policy implications are identified.

Brief of Professors of Criminal Law and Criminal Procedure as Amici Curiae in Support of Petitioner in Carlisle V. Kentucky

Abstract Mr. Carlisle was a passenger in a vehicle stopped by a police officer for suspected vehicle equipment violations. The officer lacked reasonable suspicion, let alone probable cause, to suspect Mr. Carlisle was armed and dangerous, or that he was guilty of engaging in any criminal conduct. All that the officer knew was that Mr. Carlisle, a black man, was a passenger in a vehicle stopped for a minor traffic violation. Despite the absence of any fact-based justification for doing so, the officer demanded that Mr. Carlisle provide identification and ran a criminal background check. The Supreme Court of Kentucky held that police officers are automatically entitled to demand that a passenger like Mr. Carlisle provide identification and then to conduct background investigations of them merely because the passengers were riding in a motor vehicle stopped for a minor traffic violation. This approach—allowing police unregulated discretion to conduct criminal history checks of every vehicle occupant at every traffic stop, permits precisely the sort of arbitrary and unjustified government intrusions prohibited by the Fourth Amendment. By failing to impose even minimal Fourth Amendment standards, the Kentucky Supreme Court grants officers arbitrary authority to subject people to a seizure and search based solely on a hunch. In the absence of facts creating at least reasonable suspicion that passengers are engaged in criminal conduct, or reason to believe that they pose a threat to officer safety, requiring mere passengers to identify themselves and running criminal background checks on them unnecessarily extends the length of detention (a seizure for Fourth Amendment purposes) and exceeds the mission of a valid traffic stop. If allowed to stand, the Kentucky Supreme Court’s decision would permit officers to exercise arbitrary and unjustified authority in more than 1.5 million traffic stops conducted every month.

Driving While Black and Brown in Vermont: Can Race Data Analysis Contribute to Reform?

Many states now require law enforcement to collect race data on traffic stops, but there has been little research on the use of that data to inform public policy or reform efforts at the agency level. This article addresses that lacuna by presenting results from the first statewide analysis of Vermont traffic stop data. Racial threat theory, a subset of stratification theory, would predict that policing in a predominantly white state like Vermont would exhibit lower racial disparities than states with a more racially diverse population because the “threat” to white dominance is less. The results contradict that prediction. Vermont, despite its reputation as a liberal state, is not different from other states in exhibiting wide racial disparities in policing. And yet, analysis and dissemination of race data in policing, by providing an evidentiary basis for citizen claims of racial bias, contributed to action on the part of the state legislature and government to address racial discrimination not only in policing but also in the broader criminal justice system. We report on those reform efforts and on the actions taken by three reform-minded law enforcement agencies to reduce and eliminate unjustifiable racial disparities in policing.

At the intersection: Race, gender, and discretion in police traffic stop outcomes

AbstractRacial 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.

“Driver’s License, Military ID, and Proof of Registration and Insurance, Please”: Officer Discretion Surrounding Traffic Stops On an Air Force Installation

Officer discretion is an oft-debated topic in American culture today. A plethora of research has been conducted on how local, county, and state law enforcement officers use their discretionary authority specific to enforcement of moving violations and the initiation of traffic stops, however to date, no such work has been conducted on a policing entity within the United States military. Through observational ride alongs and unstructured discussion with participants, this study breaks that barrier and assesses how one particular Air Force installation’s law enforcement officers exercise their authority.Â

Discretion in Traffic Stops: The Influence of Budget Cuts on Traffic Citations

AbstractIn traffic enforcement, officers have a broad range of discretionary power. They decide whether to initiate a stop. They also decide whether to write a ticket or to give a warning. Various factors affect officers' discretion, such as a driver's race, gender, and neighborhood characteristics. This study examines the influence of budget cuts to the sheriff's department on a county's traffic fines revenue. This study applies a difference‐in‐difference approach to analyze traffic citations issued by two groups of traffic enforcement officers—California's county sheriff deputies and California Highway Patrol (CHP) officers. Results show that deputies raised more traffic fines after their department experienced budget cuts in the previous years. In contrast, the number of tickets issued by CHP officers who do not receive financial benefits from the county government is not affected by a county's fiscal condition changes. This study provides evidence that traffic enforcement is under financial influence.

Deputize and Deport: The Effect of Immigration Enforcement on Policing

Does expanding the role of the police to include immigration enforcement reduce their effectiveness? I use a regression discontinuity design and daily data on over 17 million traffic stops to evaluate the effect of a policy directive increasing Texas Department of Public Safety (DPS) Highway Patrol presence near the border in the predominantly Latinx counties of Hidalgo and Starr for the purposes of anti-human and drug trafficking. I find the directive substantially increased the number of traffic stops in its area of operations, increased the rate of unnecessary stops, and decreased the stop-and-search hit rate for recovering relevant contraband (e.g. drugs, weapons). Moreover, the directive appears to have had limited effectiveness in detecting human smuggling, finding undocumented immigrants, and reducing crime. These effects are not driven by an influx of inexperienced troopers, but rather lower thresholds for initializing a traffic stop motivated by the directive, consistent with qualitative accounts of profiling and unwarranted policing in the South Texas region.

Public perceptions of police behavior during traffic stops: logistic regression and machine learning approaches compared

Prior research on citizen perceptions of police has taken a wide-angle lens approach to the topic, with only a few studies investigating public perceptions of particular types of citizen–police encounters. In the current study, we make use of archival data on police traffic stops drawn from four waves of the BJS police–public contact surveys (PPCS) conducted in 2005, 2008, 2011, and again in 2015. In addition to employing conventional logistic regression, we make use of random forest classification to analyze survey data from a machine learning perspective. We use conventional logistic regression as a tool of explanation and random forest classification as a tool of prediction. We compare the findings generated by these two distinct analytical approaches. Substantive findings are quite similar for the explanatory and forecasting approaches. Driver’s belief that a traffic stop is legitimate is a major factor in how he or she evaluates police behavior in traffic stops, and whether the police use or threaten force during traffic stops may be the second most important factor. We draw out the implications of our work for our understanding of traffic stop dynamics, for the theory of procedural justice, for the theory of negativity bias, and for the enhanced use of machine learning in criminal justice.

Determinants of Citizens’ Perceptions of Police Behavior During Traffic and Pedestrian Stops

A large body of research has examined public perceptions of police behavior. Many of these studies have raised concerns about perceptions of unequal treatment of citizens by law enforcement and the effects such disparate treatment might have on police–community relations. This scholarship has largely examined global perceptions of police behavior rather than asking about actual encounters with officers. Relying on global opinions of police, however, tends to distort perceptions as it tends to illicit prejudiced and stereotypical views about law enforcement rather than lived experiences. This article offers a more precise approach to measuring police behavior during encounters with citizens by assessing views of those who have had recent contact with law enforcement. Specifically, we examine how perceptions of police behavior during both traffic stops and street stops of pedestrians might vary according to a citizen’s sociodemographic background and geographic location and how such factors might influence perceptions of the legitimacy of their encounter with the officer. Results from our multivariate analyses suggest that youth, African Americans, the poor, and those living in large urban areas are significantly more likely than others to believe they were treated outside of the scope of acceptable police conduct. Furthermore, ethnic minorities, the poor, and those in urban areas are much more likely to perceive the stop as illegitimate. Our results suggest that much of this might be explained by differences in police behavior according to the size of the place and across different social groups.

Are Constitutional Rights Enough? An Empirical Assessment of Racial Bias in Police Stops

This Article seeks to empirically test the conventional wisdom that a permissive constitutional standard bearing on pretextual traffic stops — such as that held by the Supreme Court in Whren v. United States — contributes to racial disparities in police officers’ decisions to initiate stops. To gain empirical traction on this question, we consider a natural experiment afforded by variations in constitutional law in the State of Washington. Following Whren, the Washington Supreme Court took a more restrictive stance than the U.S. Supreme Court, prohibiting pretextual stops by police officers. Thereafter, in December, 2012, the Washington Supreme Court reversed course and returned to a lax standard effectively equivalent to that of Whren. We investigate the effect of this latter change in the law — i.e., the 2012 retreat to a Whren-like standard — on the degree of racial disparities in traffic stops in Washington. For these purposes, we use a dataset of over 7 million traffic stops from 2010 to 2015 and employ a range of empirical techniques — including the estimation of difference-in-difference models and triple-differences models — that are designed to isolate the effect of the change in Washington constitutional law and account for both observable and unobservable factors that may also impact racial disparities in traffic stop rates. In particular, we employ a novel methodological approach designed to separate the effect of the change in constitutional standards in Washington from the effect of Washington’s contemporaneous legalization of recreational marijuana. Across our deep dive into these matters, we fail to find evidence that supports the conventional wisdom that Whren intensifies racial bias in officers’ decisions to initiate stops. On the contrary, our results suggest that constitutional standards, at best, have little to no impact on the gap between the stop rates of non-white and white drivers (or between black and white drivers). Racial disparities in traffic stops are an undeniable problem. And to best address this problem, we need to understand which legal tools do and do not work in regulating officer behavior. We suggest that the rejection of the conventional wisdom implied by our findings may be due to certain inherent weaknesses in the way in which the relevant constitutional standards are enforced — i.e., via the exclusionary rule. To the extent an officer’s decision to initiate a traffic stop is heavily driven by factors other than the remote possibility that any evidence obtained during a pretextual stop will be suppressed, it is unlikely that a constitutional-rights-based approach will meaningfully reduce racial disparities in traffic stop rates in practice. Instead, we propose several extra-constitutional approaches to this critical problem, including the use of administrative disciplinary systems that evaluate an officer’s aggregate pattern of behavior, not their behavior in individual cases — i.e., approaches designed to bolster a deterrent channel — along with the development of technologies that rely less on officer discretion in the first place.

Race, Place, and Context: The Persistence of Race Effects in Traffic Stop Outcomes in the Face of Situational, Demographic, and Political Controls

AbstractEvidence 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.