Under the U.S. Supreme Court decision in Terry v. Ohio, a Virginia police officer can generally stop an individual for questioning, or pull a vehicle over, only if the officer has a reasonable suspicion a crime may have been committed. This means that with the notable exception of random DWI/DUI checkpoints, an officer cannot stop a car to check whether the driver is intoxicated unless the officer can articulate a reasonable suspicion of illegal activity.
Reasonable suspicion for a traffic stop can be based on the officer observing a moving violation, such as speeding or running a stop light. It can also be based on the officer’s observation of certain driving behaviors associated with drunk driving, such as weaving, leaving the roadway or driving at an excessively slow speed.
An officer’s reasonable and articulable suspicion will justify stopping a vehicle, but reasonable suspicion alone is not enough to justify an arrest. In order to arrest a person, the officer must meet the higher standard of probable cause. While reasonable suspicion means the officer has a basis to believe a crime may have been committed, probable cause requires a basis to believe a crime has probably been committed. In a DUI/DWI case, probable cause is typically established by field sobriety tests and a breath test for blood alcohol content.
A defendant facing DUI/DWI charges can challenge the legality of the traffic stop by arguing the officer did not have a reasonable suspicion to justify the stop. If this challenge is successful, the court can dismiss the charges.
Source: dui.findlaw.com, “What is Reasonable Suspicion for a DUI Stop?,” accessed March 6, 2017