UNIT DRIVING ON FLAT ROAD, LEFT FRONT DRIVES STARTED SMOKING WHILE DRIVING ON INTERSTATE BRAKES NOT BEING APPLIED, DRIVER STOPPED AND BY THIS TIME THE FIRE HAD SPREAD THRU THE UNDER SIDE OF TRUCK AND TRAILER, TOTAL LOSS OF TRUCK, TRAILER AND LOAD, BELIVED TO BE HALDEX BRAKE CAN FAILURE LEAKING AIR AND CAUSING BRAKES TO DRAG AND START ON FIRE