WHILE BACKING UP IN REVERSE, VEHICLE SUDDENLY ACCELERATED. OPERATOR HAD FOOT ON BRAKE BUT VEHICLE DID NOT RESPOND TO BRAKING TO STOP THE CAR AND VEHICLE CONTINUED TO ACCELERATE UNTIL CONTACT WITH A PARKED VEHICLE. BOTH VEHICLES SUSTAINED DAMAGE. POLICE OBSERVED SKID MARKS FROM ATTEMPTS TO BRAKE. EVENT OCCURRED ON JULY 24, 2018 AT APPROXIMATELY 4:00 P.M. IN A SMALL PARKING LOT AT A CONVENIENCE STORE IN FREMONT, NH.