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 Alaska, a person found by police in a parked vehicle who is suspected of being intoxicated may be subject to an investigation to determine if they were operating the vehicle while under the influence. Alaska law considers a person to be 'driving' or 'operating' a vehicle if they are in physical control of it, which can include situations where the person is not actively driving but has the potential to drive, such as sitting in the driver's seat with the keys in the ignition, even if asleep. Factors such as the location of the person within the vehicle, whether the engine is running, the person's state (awake or asleep), and the location of the keys are taken into account when determining physical control. If the police have reasonable grounds to believe the person was operating the vehicle while intoxicated, they may request the individual to submit to a breath or blood test and perform field sobriety tests. Refusal to submit to a chemical test can result in penalties. Depending on the outcome of these tests and the circumstances, the individual may be arrested for DUI/DWI. It's important to note that simply being in a parked vehicle does not guarantee immunity from DUI/DWI charges if other factors suggest the person was in physical control of the vehicle while intoxicated.