Whenever a new officer makes an arrest that resulted from a traffic stop, a veteran officer or supervisor is seemingly always nearby asking, “Where is your probable cause (PC) ticket?” or “What was your PC?” Although those are sometimes valid questions, in far too many agencies, they have become mandatory questions that the new officer better have an answer for. The veteran officers and supervisors simply lack a proper understanding of which standard is needed and when. In the state of Illinois, the answer is simple; if the reason for the stop can be found in the Illinois Vehicle Code (IVC), the probable cause standard is applicable. If the reason for the stop is found anywhere else in the Illinois Compiled Statutes (ILCS), the reasonable suspicion standard is applicable. For those of you outside of Illinois, it is equally as simple. Traffic stops for traffic violations require the officer to possess a probable cause belief that a traffic violation has occurred. Traffic stops made based upon the belief that a crime has occurred or is about to occur only require a standard of reasonable suspicion.

Back in 1968, we were handed down the one piece of case law almost every law enforcement officer knows of in Terry v. Ohio. This case establishes reasonable suspicion. It gives officers the power to detain someone and perform a limited pat-down based on nothing other than the fact the officer can reasonably articulate that they believe a crime has occurred or is about to occur. The case law does not state that the offender(s) must be on foot, and it does not state that this is not applicable if the offender(s) happen to be in a vehicle. Since 1968, there have been numerous other rulings that support traffic stops based on reasonable suspicion, probable cause and pretext stops. These pieces of case law articulate and define what we can and cannot do while conducting a traffic stop. 

In 1996, the courts gave us their decision on Whren v. United States. In this case, some Washington, D.C, tac officers wearing plain clothes in an unmarked car were driving around. They saw a sport utility vehicle driven by James Brown stopped at a stop sign for longer than usual. The vehicle then turned without signaling. The SUV ultimately drove away at a higher-than-average rate of speed.

The officers stopped the vehicle for a traffic violation (probable cause) and spoke with Brown and his passenger, Michael Whren. When the tac officers approached the car, they saw bags of crack in Whren’s hands and other drugs in plain sight. The tac officers arrested Brown and Whren and searched the car. The issue was raised that these tac officers were in a high drug area and had other reasons than the turn signal for stopping the car. The court held that the tac officers had a probable cause belief that a traffic violation had occurred. Once they observed the traffic violation, it did not matter if they wanted to stop the vehicle to investigate drug crimes or not. Justice Scalia even stated, “Such stops could be made regardless of an officer’s true intentions.”

In Kansas v. Glover (2020), a Douglas County Sheriff’s deputy was on duty and ran a registration check on a 1995 Chevy pickup truck. The registration returned to Charles Glover Jr. The Kansas Department Revenue database also showed Glover to have a revoked driver’s license. The deputy then initiated a traffic stop on the 1995 Chevy based on the assumption that Glover was driving. Glover was charged as a habitual traffic violator under Kansas law. Later, it was argued the deputy lacked reasonable suspicion. The court held that it was reasonable to assume the registered owner of the vehicle was driving the vehicle. However, the court stated, “When the officer lacks information negating an inference that the owner is driving the vehicle, an investigative traffic stop made after running a vehicle’s license plate and learning that the registered owner’s driver’s license has been revoked is reasonable under the Fourth Amendment, pp. 3–10” (SCOTUS Glover 1). This states that officers can stop a vehicle based upon nothing more than a suspended or revoked registered owner, provided we do not have any information showing the registered owner is not the driver. 

When looking at case law, it is also important to read the cases that tell us we cannot do something. In U.S. v. Pena Montes (2009), an officer in Albuquerque, New Mexico, spotted a vehicle driving without a registration tag. The officer stopped the vehicle and observed that the vehicle did have a valid dealer tag displayed. Even after the officer observed the valid tag, he continued to speak with the driver and the vehicle’s passenger, Jose Luis Pena-Montes. Pena-Montes gave a fictitious name and was subsequently arrested for concealing his identity. Once he was properly identified, it was learned that he was a previously deported felon, and he was charged with illegal re-entry into the United States. The court ruled that once the officer learned the vehicle was, in fact, displaying a valid registration, all further law enforcement actions became fruits of the poisonous tree. The officer neither had probable cause nor reasonable suspicion once he observed the dealer tag and, therefore, had no grounds to detain the occupants of the vehicle. 

As police officers, we took an oath to uphold the Constitution of the United States of America. We took oaths to uphold the state, county and possibly even local laws relative to the jurisdictions we serve. These oaths should not be taken lightly. If we are going to serve, protect and discharge our duties to the best of our abilities, then we need to fully understand that the United States Constitution, as well as our state and local law books, are living, breathing documents. They adapt and evolve, as does the population we serve. It is our responsibility to understand these documents and keep up with the changes that are coming our way. No one is going to force you to memorize each new piece of legislation that comes up, but it is your responsibility to make sure that as an officer of the law, you are following every legal way of doing things. After all, you owe it to yourself, your family and those you serve to keep up on these cases that literally change the way we do business.