In a car crash or other incident involving multiple vehicles the police may investigate whether the driver of any of the vehicles is under the influence of or intoxicated by alcohol or drugs, and are not limited to investigating and arresting only the driver who was at fault in the accident, for example.
In California, when a car crash or other incident involving multiple vehicles occurs, law enforcement officers have the authority to investigate all drivers involved for potential intoxication or impairment due to alcohol or drugs. This means that even if a driver is not at fault for the accident, they can still be subject to investigation and arrest if there is reasonable suspicion or evidence of driving under the influence (DUI). California's Vehicle Code Section 23152 makes it illegal for anyone who is under the influence of any alcoholic beverage or drug, or the combined influence of alcohol and drugs, to operate a vehicle. The law does not discriminate based on fault in an accident, and police can arrest any driver who is suspected of DUI at the scene of a multi-vehicle incident.