PARKED AUTO ON GRAVEL PARKING LOT. THE DRIVE SELECT DID GO INTO THE PARK POSITION UPON SHUT-DOWN AND THE ENGINE DID NOT TURN OFF WHEN THE IGNITION BUTTON WAS DEPRESSED. NO ENGINE SOUND APPARENT DUE LOW RPM AND GOOD SOUND SUPPRESSION MATERIAL. EXCITED THE VEHICLE AND LOCKED CAR DOOR.THE CAR DID NOT MOVE AS I LEFT THE AREA.SUBSEQUENT TO MY DEPARTURE,THE TORQUE BUILT UP ENOUGH TO PROPEL THE CAR ACROSS THE PARKING LOT AND INTO A TREE IN FRONT OF A PRIVATE RESIDENT ADJACENT TO THE FAIR GROUNDS. *TR