When police officers initiate a traffic stop for suspected drunk driving, the behavior of the driver could be what gives them probable cause. Someone swerving over the center line in the road, erratically breaking for no perceivable reason or responding strangely to changing traffic conditions could be a warning sign of impairment.
During a traffic stop, the officer will ask the driver questions and use both their answers and their behavior to either affirm or reduce their concerns. If they still think the driver may be under the influence of alcohol, they could request a field sobriety test followed by a chemical breath test.
Even if you pass the field sobriety test, you could wind up arrested if the chemical breath test shows that you are in violation of the purse they limit for alcohol in your bloodstream.
What does per se mean?
Like many modern legal terms, per se is a Latin phrase. It means “by itself.” In the context of impaired driving laws, the per se limit is the threshold for intoxication established by the government.
It has to do with the amount of alcohol in your body and not necessarily any signs of impairment. Having an alcohol level over the per se limit is a violation of the law, even if someone still thinks they can safely drive.
What is the per se limit on alcohol for drivers?
Researchers looked at how the human body responds to alcohol and set a limit based on what would likely impair most drivers. For most people, the per se limit to their blood alcohol concentration (BAC) is 0.08%.
However, many states also have zero-tolerance policies about alcohol for underage drivers, meaning that much lower BAC is can lead to drunk driving charges for those who are not yet 21. In South Dakota, that cutoff is 0.02%.
If someone is driving a commercial vehicle rather than a standard passenger vehicle, the per se limit for their BAC drops down to 0.04% because of how much more skill and focus those larger vehicles take to safely operate.
When you understand the terminology used in drunk driving charges, it will be easier for you to respond after an impaired driving arrest.