August 12, 2011, a locomotive runaway has happened on the local railway named Xihe railway of a certain city, it led to a death of an older person and serious damage of four automobiles. The causing factors of the runaway accident have been comprehensively analyzed, which respectively include four aspects: human, machine, environment and management. By using the principle of fault tree analysis (FTA), the locomotive runaway accident fault tree has been set up after the accident investigation. Based on the corresponding formula, the authors have calculated the structure importance coefficient o...