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 Iowa, DUI/DWI laws can apply to a person who is in 'physical control' of a vehicle, even if they are not actively driving. This means that if someone is sitting, lying, or sleeping in their vehicle and exhibits signs of intoxication, they could potentially be charged with a DUI/DWI. The police have the authority to investigate if they find someone in a parked car, especially if the car is parked illegally or if there is concern for the person's well-being. During the investigation, if the police determine that the person has been drinking and is in physical control of the vehicle, they may conduct field sobriety tests or request a breath or blood test. Factors such as the person's location in the vehicle, whether the engine is running, the person's state of consciousness, and the location of the keys can all influence whether an arrest for DUI/DWI is made. It's important for individuals to understand that being in a parked vehicle does not necessarily protect them from a DUI/DWI charge if they are deemed to be in physical control of the vehicle while under the influence.