Most states and even counties have very strict laws when a person is arrested for driving under the influence of alcohol or a controlled substance which includes impounding of the vehicle being driven for a certain period of time.The vehicle impounded is evidence pertaining to the arrest and as evidence it can be impounded essentially for as long it takes to resolve the alleged crime that it was an instrument of. It does not matter in whose name the car is registered in.Answer: It is legal for law enforcement to have your car impounded as evidence supporting the arrest of your son. You option is to request its release and see what happens.