CAR WAS PARKED IN A CARPORT ON FLAT GROUND. CAME OUTSIDE CAR WAS GONE .. ROLLED OUT OF THE CARPORT DOWN A 500 FT DRIVEWAY, TURNED INTO THE DRIVEWAY ACROSS THE HIGHWAY INTO A VEHICLE PARKED THERE.. ELECTRONIC BRAKING WAS APPLIED AND STILL ENGAGED.. PARKED THE CAR BACK INTO THE CARPORT AND TRIED PUSHING IT OUT OF THE CARPORT AND WOULDNT BUDGE... MY VEHICLE ROLLED ACROSS A BUSY HIGHWAY AND IF THE LADY DIDNT HAVE A VEHICLE PARKED THERE IT WOULD HAVE WENT INTO THE SIDE OF HER HOUSE...