Hybrid Online Safety Observer for CTCS-3 Train Control System On-Board Equipment

The on-board equipment of Chinese Train Control System-3 (CTCS-3) plays a key role in protecting trains from over-speeding. Conventional over-speed protection methods monitor the speed at discrete time instants. However, the over-speed behavior between discrete time instants cannot be detected, which may cause potential risks. To address this problem, this paper proposes a hybrid safety observation method to monitor train speed throughout the operation. In the proposed method, the train behavior is modeled with a hybrid automata, which takes parameters that affect train movement into consideration. Train behavior in the next control cycles is predicted periodically by computing the reachable set of the model. The safety property set is obtained according to the runtime speed limits. The intersection check between the reachable set and safety property set is performed to decide whether train speed may exceed the speed limit in a short future period. A case study is presented to demonstrate the proposed method in action by using real engineering data from the Chinese railway industry. The results show that the observation method is feasible in verifying the violations of CTCS-3 on-board equipment safety properties.