THE VEHICLE WAS STATIONARY ON AN INCLINE SUBURBAN CITY STREET. THE KEY WAS UNABLE TO BE REMOVED FROM THE IGNITION AFTER DRIVING AND PLACING GEAR IN THE PARK POSITION. I WAS ABLE TO REMOVE IT AFTER I PUT THE VEHICLE IN THE NEUTRAL GEAR POSITION. HOWEVER, THIS PRESENTED A HAZARD AND CAUSED AN ACCIDENT AS THE VEHICLE ROLLED BACKWARD AND SIDE SWIPED A STATIONARY VEHICLE. THIS HAS HAPPENED SEVERAL TIMES.