Driving erratically
If an officer sees someone driving erratically, they can usually tell if someone is driving under the influence by using some of the following signs.
Driving erratically
Swerving Unnecessary stopping
Speeding or driving too slow
Running a red light
Reckless driving
Driving with a broken tail light
Witnesses
The police can find out if someone is committing DUI if they saw the act themselves, received a report through the radio, or a witness reported to them.
Observing behavior consistent with intoxication
If the police has stopped your car or is patrolling on foot, they will usually notice if someone is drunk, and determine if they are fit for driving.
Observing behavior consistent with intoxication
Failing field sobriety tests
Drowsiness Aggression
Slurred speech Unstable movement or posture
Incriminating evidence
The police use supporting evidence to claim that the driver is driving while intoxicated. Drivers can still be arrested if their BAC is over the limit within 2 hours after driving.
Incriminating evidence
Presence of alcoholic beverages
in the vehicle
In a location they can only reach by
driving
Social media Smell of alcohol or intoxicating substances
BAC Testing
A person cannot be charged if they just look drunk, they have to be intoxicated enough to be judged too inebriated to drive. Thusly, tests will be performed on the alleged drunk driver. If they also find that the driver is beyond the BAC limit, they can be charged with drunk driving.