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How do police determine if someone is drunk driving? 

On Behalf of | Jan 31, 2023 | OWI-DUI Defense

As you know, driving under the influence of drugs or alcohol is prohibited in the state of Indiana, like every other state. When police pull over someone in the belief they’ve been drunk driving, then they may charge them with an OWI/DUI. 

However, police can’t just perform a traffic stop on just anyone. Likewise, they can’t charge just anyone for an OWI/DUI without first having the right evidence. What do police need to determine if someone is drunk driving? Here’s what you should know:

Reasonable suspicion

First and foremost, the police need reasonable suspicion to perform a traffic stop on a possible drunk driver. This may mean an officer noticed a driver swerving, ran a stop sign or violated a traffic law. Then police may investigate a driver related to the alleged infraction that is supported by reasonable suspicion. 

Police may perform a traffic stop on someone who they’re unsure is drunk, such as someone who didn’t signal during a turn or has an expired license plate. When this happens police must develop reasonable suspicion of drunk driving within the reasonable investigation of the original basis of the traffic stop. This may involve observing bloodshot, watery eyes, possibly slurred speech or the smell of alcohol on the breath of the driver. These are questions of fact and credibility that may be challenged in a criminal case.

Standardized field sobriety tests

Following a traffic stop, the police may ask the driver to take sobriety tests, if they have reasonable suspicion of driving under the influence. These standardized tests involve several exercises, and are used in the investigation to move from reasonable suspicion to the higher standard of probable cause to arrest for drunk driving. 

Breath alcohol content testing

If the standardized field sobriety tests provide probable cause of alleged drunk driving, police may arrest the driver and request that the driver submit to an evidentiary breath test under the implied consent law. A breath test is used to collect evidence of the driver’s blood alcohol content (BAC). If a driver’s BAC is 0.08% or higher, then they may be charged with an OWI/DUI.