A person who believes they have had too much to drink to safely or legally drive may sit, lie, or fall asleep in their vehicle in a parking lot or parking space outside of a bar or restaurant, or may pull off the road and park to “sleep it off.” When the police observe a person occupying or sleeping in a parked car they may investigate if the car is illegally parked (on the side of the road or elsewhere) or for the stated purpose of checking on the well-being of the occupant of the vehicle.

After knocking on the window and attempting to wake the occupant of the vehicle the police will typically ask if the occupant was recently operating the vehicle and whether the occupant has had anything to drink. Based in part on the occupant’s answers to these questions the police may request the occupant submit to a breath or blood test, perform field sobriety tests, and may ultimately arrest the occupant for DUI/DWI.

Laws defining DUI/DWI criminal offenses vary from state to state and often include a person who is in physical control of a vehicle as being within the definition of operating a vehicle. Based on such a broad statutory definition of operating a vehicle—and depending on other factors such as (1) whether the occupant was in the driver’s seat of the vehicle or the back seat or passenger seat; (2) whether the vehicle’s engine was running; (3) whether the occupant was awake or asleep; and (4) whether the key, if any, was in the ignition—the police may arrest the occupant for DUI/DWI.

In South Dakota, DUI (Driving Under the Influence) laws are codified under SDCL 32-23. A person may be charged with a DUI if they are in 'actual physical control' of a vehicle while under the influence of alcohol or drugs. This means that even if a person is not driving, but is in a position to start and operate the vehicle, they could potentially face DUI charges. Factors such as the person's location in the vehicle, whether the engine is running, the occupant's state of consciousness, and the location of the keys can all influence whether they are considered to be in actual physical control of the vehicle. If the police find someone in a parked car who appears to have been drinking, they may investigate to determine if the person has been driving or is in physical control of the vehicle. The police may conduct field sobriety tests and request a breath or blood test. Refusal to submit to a chemical test can result in immediate administrative penalties. If the evidence suggests the person was in actual physical control of the vehicle while intoxicated, they may be arrested for DUI, regardless of their intention to 'sleep it off.'