CARTAGE VEHICLE HAD LEFT PLANT AND ROLLED OVER ONTO ITS LEFT SIDE JUST BEYOND THE FIRST SHALLOW CURVE IN THE ACCESS ROAD ABOUT 0.7 MILE OUTSIDE THE PLANT ENTRANCE GATE. AT 3:00 AM IT WAS DARK BUT CLEAR AND DRY. NO KNOWN OBSTACLES WERE PRESENT ON THE ROADWAY. THE DRIVER'S SPEED IS UNKNOWN.