Traffic stop

A traffic stop, colloquially referred to as being pulled over, is a temporary detention of a driver of a vehicle and its occupants by police to investigate a possible crime or minor violation of law.

A traffic stop is usually considered to be a Terry stop and, as such, is a seizure by police; the standard set by the United States Supreme Court in Terry v. Ohio regarding temporary detentions requires only reasonable articulable suspicion that a crime has occurred or is about to occur. Traffic stops can be initiated at any time during the detention and arrest process, ranging from stops prior to arrest or issuance of a ticket for violation based on probable cause.

Traffic stops date to the 1920s.

Traffic stops may be executed upon reasonable articulable suspicion that a crime has occurred, for example, an observation of a possible equipment violation or a suspicion of driving under the influence (DUI) based on driving behavior. In some jurisdictions, general roadblock checkpoints are applied for random checks of driver. A primary purpose of the traffic stop at this point is frequently to determine if the police have probable cause for arrest. At this stage, the police are not required to issue a Miranda warning, because a traffic stop prior to formal arrest is not considered to be custodial under Miranda, and will often ask questions intended to elicit the suspect to provide answers that may be used as evidence in the event of an arrest.

Non-evidentiary testing falls under this stage because implied consent laws in the US generally do not apply to Preliminary Breath Test (PBT) testing (small handheld devices, as opposed to evidential breath test devices). (For some violations, such as refusals by commercial drivers or by drivers under 21 years of age, some US jurisdictions may impose implied consent consequences for a PBT refusal,^{[citation needed]} but these are generally not considered to be a refusals under the general "implied consent" laws.) Participation in "field sobriety tests" (FSTs or SFSTs) is voluntary in the U.S..

Probable cause is the arrest stage in which sufficient evidence is available to sustain a warrant for arrest. Probable cause is a stronger standard of evidence than a reasonable suspicion, but weaker than what is required to secure a criminal conviction. In some cases, notably DUI stops, the "sufficient evidence" is used for requiring an evidentiary chemical test (e.g., evidential breathalyzer test) by invoking an implied consent request. While state terminology regarding whether evidentiary testing is an "arrest", such testing is constitutionally a "search incident to arrest".

A stop is usually accomplished through a process known as "pulling over" the suspect's vehicle. Police vehicles (except those used by undercover personnel) traditionally have sirens, loudspeakers, and lightbars that rotate or flash. These devices are used by the officer to get the attention of the suspect and to signal that they are expected to move over to the shoulder and stop. Failure to comply could result in citation of failure to yield to an emergency vehicle and possibly raise suspicion that the driver is attempting to flee.

Similar alerting devices are also typically equipped on other emergency vehicles such as fire trucks and ambulances, although police departments often use blue lights to signal drivers to pull over. In all cases, such signals and the laws requiring that other vehicles pull to the shoulder allow the emergency vehicles to pass other traffic safely and efficiently when responding to emergency situations. In the case of a traffic stop, the officer pulls the patrol vehicle behind the subject vehicle as it stops instead of proceeding past as they would during other emergency responses.