I PARKED IN MY DRIVEWAY, WHICH HAS A SLIGHT INCLINE, PUT CAR IN PARK BUT LEFT IGNITION RUNNING AND HEADLIGHTS ON. I HAVE PARKED IN THIS SPACE SEVEN YEARS AND WAS NOT IN HABIT OF PULLING THE PARKING BRAKE. I HAD A VISITOR WHO NEEDED TO SEE DECK STEPS AS IT WAS NIGHTTIME. WE BOTH GOT OUT, WENT UP THE STEPS AND I RETURNED TO TURN OFF CAR. WHEN I LEAVE KEYS IN IGNITION I KEEP DRIVER'S DOOR AJAR TO PREVENT UNWANTED LOCKING. I OPEN DOOR, LEAN IN TO TURN OFF KEY. BEFORE I CAN REACH THE KEY, THE CAR STARTS ROLLING BACKWARDS. I THROW MYSELF SIDEWAYS TO AVOID CAR ROLLING OVER ME. BECAUSE OF INCLINE, CAR GATHERS SLIGHT SPEED AS IT ROLLS ABOUT 40-50 FEET DOWN DRIVEWAY (I LIVE ON A HILL AND DRIVEWAY INCLINE IS MORE PRONOUNCED FARTHER DOWN). IT VEERS SLIGHTLY TO LEFT AND I HEAR A "THUD." ENGINE STOPS, HEADLIGHTS GO OUT, AS BEST I RECALL. CAR WAS STOPPED BY A SIX-INCH DIAMETER TREE. WHEN I GET BACK IN, I HAVE TO ROCK THE STEERING WHEEL BACK AND FORTH TO GET THE IGNITION STARTED AND DRIVE CAR BACK TO PARKING SPOT. ODD THING IS THAT WHEN I GET IN THE CAR TO MOVE IT FROM TREE, THE GEAR IS IN "PARK." DAMAGE IS SUBSTANTIAL, NEARLY $10,000 BECAUSE OF WHERE IT HIT IN THE BACK AND INVOLVED THE EXPENSIVE EMISSIONS SYSTEM. I HAVE TRIED TO RECREATE THIS, PUTTING GEAR IN BOTH NEUTRAL AND REVERSE AT SAME PARKING SPOT. I STRONGLY BELIEVE IF I HAD UNKNOWINGLY LEFT IT IN REVERSE, IT WOULD HAVE IMMEDIATELY STARTED ROLLING BACKWARD; IF I'D LEFT IT IN NEUTRAL, THE WEIGHT SHIFT OF GETTING OUT OF THE CAR