Actually - I live in MD, its a good law.
The number of car thefts from driveways goes up in this here parts when people start up their cars and then leave them to go inside.
Since the law went into effect, the number of car thefts from driveways is about nil.
Did the number of thefts go down, or did it just change where they get stolen?
The number of reported (to the police) car thefts.
Start punishing the victims and the number of 911 calls will drop too.