What evidence is needed to arrest someone suspected of drunk driving?

Despite all of the TV shows in which the police always say “you are under arrest,” for purposes of a defendant’s rights under U.S. laws, an arrest may occur long before those words are uttered. The courts have concluded that an arrest occurs when a reasonable person would conclude that his or her freedom has been significantly limited and that the suspect reasonably believes he is not free to leave.

Generally speaking, there are four types of evidence that a police officer will consider and gather in a drunk driving investigation: gross observations of behavior in general; specific observations of what are known as “field sobriety tests” (FST); information obtained from questioning the suspect; and chemical test results of the motorist’s blood, breath or urine.

A police officer may arrest a motorist for drunk driving if the cumulative effect of the evidence convinces the officer that he has “probable cause” or “reasonable cause” to make an arrest. This is a far lower standard than the one the state must prove at trial where the case must be proven “beyond a reasonable doubt.” Although this is a high standard, it is met every day in courts all over the country.

Case Studies: Evidence for Arrest in Drunk Driving Cases

Case Study 1: Observations of Behavior

During a routine patrol, Officer Smith notices a vehicle swerving erratically and crossing the centerline multiple times. The officer pulls over the driver, observes slurred speech, bloodshot eyes, and the smell of alcohol on the driver’s breath. Based on these gross observations of behavior, Officer Smith determines there is reasonable cause to arrest the driver on suspicion of drunk driving.

Case Study 2: Field Sobriety Tests

Officer Johnson responds to a report of a possible drunk driver. Upon arrival, he observes a vehicle parked on the side of the road with the driver inside. Officer Johnson administers standardized field sobriety tests, during which the driver exhibits poor balance and coordination. These specific observations from the field sobriety tests, combined with the odor of alcohol on the driver’s breath, provide Officer Johnson with probable cause to arrest the driver for drunk driving.

Case Study 3: Questioning and Chemical Test Results

Officer Martinez conducts a traffic stop after observing a driver running a red light. During questioning, the driver admits to consuming multiple alcoholic beverages. Officer Martinez administers a breathalyzer test, which indicates a blood alcohol concentration above the legal limit. Based on the driver’s admission, along with the results of the chemical test, Officer Martinez determines there is reasonable cause to arrest the driver for driving under the influence.