Using fault tree analysis to identify the failures of level crossing protection devices

Level crossings are potential hazardous locations in a railway system. To reduce the risk of level crossings, several active protection devices such as flashing lights and barriers may be installed. Previous studies have proved that such protection devices are effective in decreasing the probability of accidents. However, these protection devices may be partially out of order or receive error signals. Once protection devices cannot operate correctly, they may deliver wrong information that confuses the users. As a result, the users may trespass a level crossing in a dangerous situation. To realize the causes of different types of wrong operations, this study categorized them into error warning, conflict warning, and no warning. Then fault tree analysis is employed to identify the failure types and the causes behind the wrong operations of protection devices, including the failures of flashing lights, boom barriers, train direction indicators, obstacle detectors, and emergency buttons. The results indicate that error warning is mostly due to the error messages of the track circuit. Conflict warning is caused by specific failures of the protection devices. Finally, the wiring error of the track circuit is the main cause leading to no warning.