THE CAR WAS IN PARK & I WAS SITTING IN IT ON THE TOP OF MY DRIVEWAY. I WAS ABOUT TO OPEN THE DOOR WHEN IT STARTED TO ROLL BACKWARDS WHILE STILL IN PARK. IT STARTED TO PICK UP SPEED & DID NOT STOP UNTIL IT HIT A TREE. I WAS SO SHOCKED BY WHAT WAS HAPPENING & THE FACT THAT I LIVE ON THE RIVER EVEN THOUGH NEARLY 900 FEET AWAY ALL I COULD THINK OF WAS IT WAS GOING TO ROLL STRAIGHT IN THE RIVER. I JUMPED OUT OF THE CAR & SEVERELY INJURED MYSELF WITH A CONCUSSION , CRACKED RIBS & A BROKEN NOSE. THE CAR WAS IN PARK & STARTED TO ROLL WHILE STILL IN PARK. WHEN IT FINALLY CAME TO STOP BY HITTING A TREE IT WAS STILL IN PARK. MY MECHANIC BELIEVES IT IS A PROBLEM WITH THE TRANSMISSION. GENERAL MOTORS SENT SOMEONE OUT TWICE & AT THIS POINT WE ARE IN LIMBO. THE CAR IS NOT DRIVEABLE - IF WE HAVE IT REPAIRED MY INSURANCE DOES NOT FEEL IT IS A SAFE CAR TO DRIVE WITH OUT KNOWING THE REASON IT ROLLED BACK. GM HAS NOT BEEN HELPFUL OR VERY FORTHCOMING. I HAVE MANY PICTURES BUT WAS HAVING A PROBLEM UPLOADING THEM. IF YOU NEED TO SEE THEM I CAN MAIL THEM IF I STILL CAN NOT UPLOAD THEM.