Vehicle Stops

Fundamentals of Procedural Law by Adam J. McKee

Law enforcement officers often encounter situations that may necessitate a search of a vehicle during a vehicle stop. However, the Fourth Amendment of the U.S. Constitution provides protection against unreasonable searches and seizures. This includes vehicles. But are there circumstances where an officer can search a vehicle with less than probable cause? The answer is yes, under certain conditions, and we’ll explore those here.

It is important to realize that officers can’t stop a vehicle just because they feel like it.  They have to have a valid reason to interfere with a  person’s liberty.  Let’s examine some of the lawful reasons that a driver can be stopped in the first place.

When an Officer May Lawfully Stop a Vehicle

Law enforcement officers have the right to stop vehicles under certain circumstances. Traffic law violations are the most common reasons for vehicle stops. If an officer observes a vehicle committing a traffic violation—such as speeding, running a red light, failing to signal, or driving erratically—they have a legal basis to initiate a stop.

In addition to traffic violations, police officers may also stop vehicles based on reasonable suspicion of criminal activity. The U.S. Supreme Court decision in Terry v. Ohio (1968) established the concept of “reasonable suspicion.” This means that if an officer has specific and articulable facts leading to a suspicion that the driver or someone in the vehicle has committed, is committing, or is about to commit a crime, they can lawfully stop the vehicle. This could include a vehicle that matches the description of one used in a crime or suspicious behavior that suggests a crime might be occurring.

Moreover, sobriety checkpoints or roadblocks set up to identify drunk drivers are another instance where officers may stop vehicles. In these cases, vehicles are stopped without specific suspicion of wrongdoing. The U.S. Supreme Court in Michigan Department of State Police v. Sitz (1990) held these checkpoints to be constitutional.

It’s important to remember that while law enforcement has the right to stop vehicles under these conditions, any subsequent searches or seizures must also adhere to legal guidelines, primarily respecting the Fourth Amendment rights of individuals against unreasonable searches and seizures.

The Automobile Exception

The Supreme Court case Carroll v. United States (1925) established the automobile exception to the Fourth Amendment. This exception allows officers to search a vehicle without a warrant if they have probable cause to believe it contains evidence of a crime. However, what happens when there’s less than probable cause?

The Terry Stop: Application to Vehicles

Terry v. Ohio (1968) is a landmark case that provides some guidance. It allows officers to conduct a brief, investigatory stop when they have a reasonable suspicion of criminal activity. In the context of vehicles, an officer might stop a vehicle based on such suspicion. This could result from erratic driving, a traffic violation, or other suspicious behavior.

During a Terry stop, if the officer has a reasonable belief that the driver or passengers might be armed and dangerous, they can perform a protective frisk of the vehicle’s passenger compartment. This is a limited search for weapons, not a full search of the vehicle.

Consent Searches

Another circumstance where officers can search a vehicle with less than probable cause is when they obtain the consent of the driver. The Supreme Court in Schneckloth v. Bustamonte (1973) held that consent must be voluntary and not the result of duress or coercion. If the driver or owner of the vehicle freely gives consent, a search may be performed even without any suspicion of criminal activity.


Law enforcement officers can perform searches of vehicles with less than probable cause under certain circumstances. The Terry stop allows a limited search of the vehicle’s passenger compartment if there’s a reasonable belief that the driver or passengers might be armed.

Consent searches, on the other hand, can occur when the driver or owner voluntarily permits the search, even in the absence of any suspicion of criminal activity. It’s vital to note that these exceptions to the probable cause requirement aim to balance the need for law enforcement effectiveness with the protection of individual privacy rights.

Modification History

File Created:  08/07/2018

Last Modified:  08/07/2018

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This work is licensed under an Open Educational Resource-Quality Master Source (OER-QMS) License.

Open Education Resource--Quality Master Source License


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