Risk analysis for the modification in automatic train control systems

The automatic train control system (ATC) is the safety critical system (SCS). Based on the revised parts of the ATC, this paper analyzes the risks which may be triggered by the parts of modification. The paper follows the international standard of railway function safety, and describes the relevant requirements and basic methods. From the basic structure of the ATC, the required safety integrity level (SIL) of each part of the system is discussed. The paper concludes the methods for risk analysis and evaluation in the modified system. They contain hazard identification, hazard validation, consequence analyzing, the methods for determining risk category, hazard severity, possible hazard frequency, stages for dividing risks and recommended management for eliminate and alleviate risks. Those results of the revised system were analyzed by using lists of hazard identification, hazard influence and hazard liber. And risk monitoring is implemented by using the hazard liber.