OPERATOR WAS DRIVING INTO PIT AT START OF SHIFT AND MOVED TO RIGHT DUE TO ONCOMMING TRAFFIC. OPERATOR MISJUDGED LOCATION OF CATCH BENCH RIDING FRONT TIRE ON BENCH. CAME OFF BENCH, CROSSED ROAD TO LEFT SIDE, RETURNED TO RIGHT SIDE AND RAN UP HIGHWALL. TRUCK PIVOTED WHEN CONTACTED WALL WITH HEADACHE RACK OR OTHER PART OF FRONT OF TRUCK. MOMENTUM CAUSED TRUCK TO ROLL OVER LANDING TOP.