Before law enforcement arrests a driver for driving under the influence, the officer must have a reason to pull the driver over as well as reason to suspect that the person is under the influence of alcohol or drugs.

Police use three main identifiers in the process of determining whether or not someone may be guilty of DUI.

Signs of DUI

A police officer becomes aware of people driving under the influence through observation of certain signs. For example, the driver may be speeding, swerving, failing to yield, failing to stop or driving too slowly. How the driver pulls the vehicle to the side of the road may also indicate impairment.

Once drivers have pulled over and the officer can observe them directly, he or she then checks for other signs. These may include the smell of alcohol on the breath, bloodshot or glassy eyes, flushed face, difficulty exiting the vehicle and slurred speech, as well as a disheveled appearance or belligerent behavior.

Field sobriety tests

Field sobriety tests include having the driver stand on one leg, attempt to walk in a straight line and look from side to side without the eyes jerking noticeably. Police officers use these tests if they notice other signs of driving under the influence. Failing these tests might trigger additional testing or an arrest.

Chemical tests

Blood alcohol content tests measure the amount of alcohol in a person’s system through urine, saliva, breath or blood samples. Mathematical formulas determine the BAC from the sample. A driver who refuses to take a chemical test faces license revocation, and the prosecutor may use the refusal as evidence of intoxication.

If a breath test result is at or above the limit of 0.08%, the officer will arrest the driver for DUI. Even if the results are between 0.05% and 0.08% the officer may still arrest the driver.