Causes and Countermeasures of Train Emergency Braking Failures under DRB Turn-back Mode on Xi’an Metro Line 14

Objective Under the DRB (driverless return button) mode on Xi’an Metro Line 14, the train emergency braking will occur after the train automatically switching its head car on the turn-back line, resulting in the train turn-back failure. The failure happens rather frequently, so it is necessary to find out the causes of the failure and develop corresponding countermeasures. Method The operation process of the train turn-back under DRB mode is introduced, and the ATO/ATP (automatic train operation/automatic train protection) control principle under the DRB mode is expounded. In response to the actual situation of the train emergency braking failure under the DRB mode on Xi’an Metro Line 14, the causes of the failure are sought from three aspects, i.e. signal system, train traction system, and train braking system. Tests are conducted on the working conditions such as lifting the train starting level and improving the impact rate during the traction stage. The process of the train onboard signal head car switching is further analyzed. Causes of the train emergency braking failure under the DRB mode are identified, and corresponding countermeasures are developed. Result & Conclusion Under the DRB mode, when the train head car switching process completes in the train activation end, it is not completed in the on-board signal control. The inconsistency between the signal control end and the train activation end in the process of the train head car switching is identified as the failure cause. The operational data of the line indicates that the developed countermeasures prevent the reoccuring of the train emergency braking failure under DRB mode.