Traffic stops in the United States

Millions of traffic stops occur each year in the United States. They are one of the most common interactions between police officers and citizens in the country and influence public perceptions of law enforcement. The authority that police have regarding traffic stops in the United States has increased significantly since the early twentieth century when motor vehicles first became widely used. Some believe that traffic stops increase public safety by reducing dangerous driving and giving officers more opportunities to arrest those suspected of criminal activity. However, others contend that traffic stops are mostly unnecessary, and officers have too much discretion in deciding when to conduct them. Opponents argue that traffic stops are particularly harmful because research suggests that racial bias influences which citizens are pulled over and what outcomes occur.

Overview

In the United States, state and local governments are responsible for traffic stops and enforcing traffic code violations. The US federal government does not have jurisdiction over traffic stops, although the federal government does influence traffic stops and policing in general. The Department of Transportation is part of the Executive Branch of the US government and includes the National Highway Traffic Safety Administration (NHTSA), which offers guidance about best practices for policing and traffic stops. The US Supreme Court has an even more significant role in shaping traffic stops in the United States, as the Court’s decisions have helped determine when and why police officers can conduct traffic stops. The Court has jurisdiction over these decisions because they relate to citizens’ constitutional rights.

State and local governments have been involved in traffic stops and monitoring traffic code violations since motor vehicles were first on roadways in the twentieth century. As they became more common, they replaced horses, wagons, and other modes of transportation. Motor vehicles were a threat to public safety because they were more dangerous than other forms of transportation and increased deaths and injuries along the roadways. States and local governments reacted by creating new laws to regulate their operation, tasking law enforcement with enforcing them. By the 1920s, police officers had already begun to use traffic stops to enforce traffic laws and other laws if they suspected illegal behavior. In 1925, the Supreme Court decided the case of Carroll v. United States, in which police detained a vehicle because they had probable cause to believe the individuals inside were selling liquor, which was illegal during Prohibition. The Supreme Court found that vehicles could be searched if the officers had probable cause. This decision and its implications would have a significant impact on policing in the United States, as it gave law enforcement officers a great deal of discretion in choosing when to make traffic stops. Since the 1920s, traffic codes and traffic stops have changed based on continued clarification of citizens’ rights through Supreme Court cases, changes in motor vehicle and roadway technology, and social changes.

State and local law enforcement organizations conduct traffic stops in the United States. Based on jurisdiction, different groups of officers can conduct traffic stops in various areas. Traffic stops begin with a police officer deciding to stop a particular vehicle. Most often, officers stop vehicles because the driver committed a driving violation (e.g., driving above the speed limit), the driver is guilty of an equipment violation (e.g., the headlights on the vehicle are burned out), or the officer has reasonable suspicion to suspect the occupants are involved in criminal activity. Officers can make traffic stops for other reasons, however. Sometimes officers use low-level traffic offenses (e.g., hanging an object from the rearview mirror) to conduct traffic stops. Officers may make such stops to further investigate a vehicle or its occupants even if they have no other legal justification for doing so. Such stops are controversial. Officers may also randomly “run,” or research, vehicles’ license plate numbers to identify stolen vehicles or owners with outstanding warrants.

Officers who initiate traffic stops then follow their law enforcement organization’s procedures. Often, an officer begins a stop by sending their organization basic details—such as the location of the stop, the state of the vehicle’s registration, the license plate tag number, and a description of the vehicle. The officer then “pulls over” the vehicle being stopped. Generally, an officer accomplishes this by turning on the emergency lights and following the targeted vehicle. The driver of the targeted vehicle is generally required by law to pull over to the right side of the road when an officer initiates a traffic stop in that way. An officer may “run” the license plate number of the vehicle at this point if it was not researched earlier. Such a search can help an officer determine if the stop is likely to be high risk. If this is the case, the officer will most likely follow a different procedure (e.g., the officer may call in and wait for backup officers to arrive before approaching the targeted vehicle).

During a routine traffic stop, the officer will next park behind and slightly farther to the left of the other vehicle. Parking closer to traffic helps protect the officer who is vulnerable to oncoming traffic during a traffic stop. The vehicle’s driver and occupants are expected to follow certain rules during the traffic stop. They are expected to pull over and stop the vehicle when they notice an officer’s intent to stop them. They are also expected to turn on an interior light, keep their hands on the steering wheel, and provide information (e.g., driver’s license, proof of insurance, etc.) requested by an officer. Furthermore, drivers and other occupants are expected to stay inside their vehicles unless an officer asks them to exit.

The officer should then explain the reason for the stop. He or she can ask the vehicle’s occupants questions, but they are not required by law to answer them. The officer can continue to ask questions, but the questions should be related to the traffic stop unless the officer has probable cause for believing criminal activity is taking place. The officer can require the driver to exit the car and pat down the driver to search for contraband or weapons. However, the officer needs a warrant to search the vehicle unless he or she sees something in plain sight that provides probable cause. Occupants other than the driver are not required to leave the vehicle unless the officer has probable cause or a warrant. Occupants may ask the officer if they are free to leave and may exit the vehicle if the officer permits this. The officer returns to the police vehicle to conduct record checks and prepare any citations. He or she is supposed to maintain visual contact with the vehicle and its occupants.

At the end of the traffic stop, the officer can give the driver a warning or a citation. The driver does not admit guilt by accepting the citation and can contest the citation in court. The officer can also end the stop by arresting the driver or other occupants if that officer has probable cause. After the traffic stop ends, the officer completes any necessary documentation. The officer should also ensure that the driver can enter traffic safely and resume normal travel.

Further Information

Even though the federal government does not participate in traffic stops in the United States, it has a significant influence on when and how officers conduct them. Legal experts have identified traffic stops as a type of seizure that is protected by the Fourth Amendment. The Fourth Amended states in part, “The right of the people to be secure . . . against unreasonable searches and seizures, shall not be violated.” This means police officers must conduct “reasonable” traffic stops. Since the definition of what is reasonable may be widely disputed, the Supreme Court’s decisions have helped define aspects of what is and is not reasonable behavior during those stops.

One of the most significant decisions by the Supreme Court was determining the legality of pretext stops. Pretext stops are those during which police officers use minor traffic violations (e.g., hanging something from the rearview mirror, driving with an expired plate, etc.) to stop vehicles when they suspect the people in the vehicles to be involved in criminal activity. In Whren v. United States (1996), the Supreme Court decided that a minor traffic violation was a valid reason for conducting a traffic stop, even when the officer conducted the stop in the hopes of identifying other types of criminal activity. In this case, a man, Brown, was driving a truck and saw an officer approaching. He turned without signaling and drove away from the officer at an unreasonable speed. The officer pulled over Brown because he failed to signal and found that a passenger, Whren, had crack cocaine in his hands. The Court found the traffic stop to be reasonable and allowable.

Some Supreme Court decisions indicate that the Court has balanced public safety with individual rights. In the 1980s, more police organizations began using sobriety checkpoints. At these checkpoints, officers interviewed all drivers who passed through a particular area on the road. The officers had no pretext for stopping the vehicles other than to check for people who were driving while drunk. In the case Michigan Department of State Police v. Sitz (1990), the Supreme Court decided that such sobriety checkpoints did not violate the Fourth Amendment because “the measure of the intrusion on motorists stopped briefly at sobriety checkpoints . . . is slight.” However, in the case City of Indianapolis v. Edmond (2000) the Supreme Court found that a checkpoint setup just to catch criminal behavior, such as drug possession, without a specific, targeted reason and purpose (e.g., having a checkpoint at night on a holiday when drunk-driving accidents are common) was not lawful and violated the Fourth Amendment. The Court made a similar decision in 1979 in Delaware v. Prouse. In that case, the Court decided that it was unlawful for officers to stop vehicles just to check driver’s licenses and registrations. In that case, police officers pulled over Prouse only to check his driver’s license and registration and found marijuana in the car. The Supreme Court said that the driver’s privacy was more important than identifying his behavior.

However, the court has ruled that officers can stop a vehicle based on reasonable assumptions. This was established in 2020 in Kansas V. Glover. In this case, an officer had run a check of the license plate and discovered the vehicle was registered to a man whose license had been revoked. Based on that information the officer stopped the vehicle and discovered the owner driving without a license. The truck owner, Charles GloverJr., argued the stop had violated the Fourth Amendment. The Supreme Court however ruled that an officer can stop a vehicle based on the assumption that the registered owner is the driver. Another case, Heien v. North Carolina (2014) gave officers further discretion by ruling that an officer can stop a vehicle based on a mistaken but reasonable understanding of the law.

Viewpoints

Most police organizations cite public safety as their goal for conducting traffic stops. Some believe that traffic stops contribute to public safety by reducing dangerous driving behaviors (e.g., driving above the speed limit, failing to signal before turning). According to proponents, stopping these behaviors reduces the number of vehicle crashes and the severity of crashes that do occur. Furthermore, some contend that traffic stops improve public safety by catching those who are driving while impaired by drugs or alcohol as well as those who are guilty of other crimes.

However, according to opponents, even if law enforcement groups have the goal of public safety with traffic stops, the stops cause more social harm than good. This is largely because police officers have a great deal of discretion when choosing when to conduct a traffic stop and what outcome occurs. All traffic codes in the United States are detailed and include hundreds or thousands of rules that vehicle operators must follow. Opponents of traffic stops argue that officers can find a reason to conduct pretext stops on nearly any vehicle.

Because finding pretext is easy, the officers who conduct the stops can choose to stop most vehicles. Some critics of policing point out that personal bias will most likely influence traffic stops since officers have so much discretion. Data also supports the idea that bias influences traffic stops. Research indicates that race plays an important role in which drivers are pulled over. For example, a largescale 2020 study indicated that Black motorists were less likely to be pulled over after dark when race was less noticeable to officers conducting stops (Pierson, et al 2020). Furthermore, the study indicated that White drivers were about 20 percent less likely to be pulled over than Black drivers. Minorities in the United States also supported these beliefs. For example, a 2019 Pew Research Center poll indicated that Black adults were about five times more likely than White adults to indicate that they were unfairly stopped by police (Desilver, Lipka, & Fahmy, 2020).

Some Americans believe that eliminating some traffic stops, particularly those for low-level offenses, could improve public safety. Supporters of such changes argue that low-level offenses, such as driving with an expired license plate tag, do not usually impact public safety. Therefore, the supporters assert that eliminating the contact between law enforcement and citizens is most likely good overall because numerous traffic stops can lead to injury and death. For example, in 2021 the city council in Berkeley, California, eliminated traffic stops for low-level offenses, such as driving without a seatbelt and driving with an expired license plate tag. The city council determined that these low-level offenses were often used for pretext stops, which are believed to be more likely to affect Black and Hispanic citizens than those of other races.

Traffic stops are also controversial because some police organizations use the stops as money-making tools. Often, people who incur driving citations must pay fines. Many police organizations rely on the money made from these stops to balance their budgets. Some people believe that police officers will increase their use of pretext stops just to increase the amount of money the organization makes from fines. Many people criticize this motivation for traffic stops. Opponents point out that officers whose purpose is to maintain public safety are engaging with members of the public while armed just to extract fines from citizens. These opponents also note that traffic stops can turn deadly and view such as actions as putting money above public safety.

Data about traffic stops are not systematically tracked in the United States. State and local law enforcement agencies report information about their traffic stops, but the United States does not have a specific governmental organization that collects and analyzes statistics about traffic stops. Some nonprofit organizations and other groups collect, publish, and analyze traffic stop data. For example, the Stanford Policing Project collects and publishes information from numerous state and municipal police organizations. Many people who advocate for police reform or abolition argue that collecting and publishing data about traffic stops is vital to public understanding of police-citizen interactions since traffic stops are the most common type of interaction.

Bibliography

Cases—Vehicles. (n.d.). Oyez. www.oyez.org/issues/229. Accessed 7 Feb. 2025.

Desilver, D., Lipka, M., & Fahmy, D. (2020). "10 things we know about race and policing in the U.S." Pew Research Center. www.pewresearch.org/fact-tank/2020/06/03/10-things-we-know-about-race-and-policing-in-the-u-s/. Accessed 7 Feb. 2025.

Kamin, Sam. "Unreasonable Traffic Stops."  William and Mary Law Review, vol. 65, no. 6, 2024, scholarship.law.wm.edu/wmlr/vol65/iss6/3. Accessed 7 Feb. 2025.

LaFave, W. R. (2004). The “Routine Traffic Stop” from Start to Finish: Too Much “Routine,” Not Enough Fourth Amendment, Michigan Law Review, 102(8), 1843–1905.

Liptak, Adam. "Supreme Court Rules on Traffic Stops and Age Bias." The New York Times, 6 Apr. 2020, www.nytimes.com/2020/04/06/us/supreme-court-traffic-stops-age-bias.html. Accessed 7 Feb. 2025.

McIntire, M., & Keller M. H. (2021, November 2). "The Demand for Money Behind Many Police Traffic Stops." The New York Times. www.nytimes.com/2021/10/31/us/police-ticket-quotas-money-funding.html. Accessed 7 Feb. 2025.

Mercer, M. (2020, September 3). "Police ‘Pretext’ Traffic Stops Need to End, Some Lawmakers Say." Pew Trusts. www.pewtrusts.org/en/research-and-analysis/blogs/stateline/2020/09/03/police-pretext-traffic-stops-need-to-end-some-lawmakers-say. Accessed 7 Feb. 2025.

Pelic, J. (2003). United States v. Arvizu: Investigatory Stops and the Fourth Amendment. Journal of Criminal Law and Criminology, 93(4), 1033–1056.

Pierson, E., Simoiu, C., Overgoor, J. et al. (2020). A Large-Scale Analysis of Racial Disparities in Police Stops Across the United States. Nature Human Behaviour, 4, 736–745. doi.org/10.1038/s41562-020-0858-1. Accessed 7 Feb. 2025.

Ravani, S. (Feb 24, 2021). Calif. City Adopts Police Reforms, Votes to Take Cops Off Some Traffic Stops. Police 1. www.police1.com/traffic-patrol/articles/calif-city-adopts-police-reforms-votes-to-take-cops-off-some-traffic-stops-Q0VMhHHkmbqAsZ8H/. Accessed 7 Feb. 2025.

Ryan, T. (2020, 6 April). "Supreme Court Clarifies Police Power in Traffic Stops." Courthouse News Service. www.courthousenews.com/supreme-court-clarifies-police-power-in-traffic-stops/. Accessed 7 Feb. 2025.

Seo, S. (2019). Policing the Open Road: How Cars Transformed American Freedom. Harvard University Press.

Traffic Stop. (n.d.). Cornell Law School Legal Information Institute. www.law.cornell.edu/wex/traffic‗stop. Accessed 7 Feb. 2025.