What is required for a police officer to initiate a traffic stop?

To initiate a traffic stop, a police officer must have reasonable suspicion that a law has been violated. This standard is a lower threshold than probable cause and is appropriate in situations where an officer observes behavior that suggests a traffic infraction is occurring or has occurred.

Reasonable suspicion is based on the officer's experience and specific observations, allowing for an immediate response to potentially unlawful behavior. Such behaviors may include erratic driving, failure to signal, or speeding, all of which provide sufficient grounds for the officer to stop the vehicle for further investigation.

In contrast, the other options listed, like requiring probable cause of a grave crime or a valid warrant, set higher thresholds that are not necessary for initiating a traffic stop. Additionally, witness testimony alone, while potentially helpful, does not typically constitute the reasonable suspicion needed by the officer to initiate a stop. It is the officer's observations and experience that primarily serve as the basis for this reasonable suspicion in traffic enforcement scenarios.