Probable Cause

The purpose of ‘probable cause’ laws is to give a police officer reasonable justification for arresting a driver suspected of being under the influence of alcohol or drugs (DUI or DWI). Its simple meaning is when circumstances indicate that a crime has been committed, is in the process of being committed, or is likely to be committed.

An officer flashes lights and siren to stop a driver. Perhaps the driver was weaving, driving too fast, seemed unsure as to where to go, or other behavior that was indicative of driver confusion. These minor infractions give the police officer ‘probable cause’ to think that the driver may be under the influence of drugs or alcohol and to detain him or her for further investigation. Based on probable cause for the detention in the original instance, the officer may then proceed to request the driver to perform standardized field sobriety tests to confirm suspicion that the driver is intoxicated.

These simple cognitive and/or physical tests provide further evidence if the driver is impaired. The results of these tests can give an officer further justification – called probable cause – to arrest the driver on suspicion of DUI. The driver would then be subjected to chemical testing (blood, urine, or breath). The breath test can be administered roadside, but blood or urine tests must be administered at a law enforcement detention facility or medical facility. Chemical testing is what provides the ultimate evidence upon which to base formal charges.

In circumstances other than drunk driving, if an officer pulls over a driver for a minor infraction and smells marijuana smoke or sees drug paraphernalia in plain sight, or if the driver’s or passenger’s behavior indicates that a crime may be in progress, the officer has probable cause to request permission to search the vehicle or may call for a drug dog to be brought to the scene to search for evidence.

Probable cause indicates stronger evidence than ‘reasonable suspicion,’ which is similar in meaning that a person has been or was about to perform an illegal act. Acting under reasonable suspicion, an officer may frisk a suspect for weapons but may not search for drugs.