Automatic Turn-back Scheme for City Railway Intervals Based on CTCS2+ATO Signaling System

［Objective］When there is a malfunction or temporary operation schedule adjustment under public transit operational scenarios，the train turn-back in intervals is required for city railways using the CTCS2+ATO (Chinese train control system level 2+automatic train operation) signaling system. To enhance the safety and efficiency of the interval turn-back operations in city railways, an automatic train turnback scheme is proposed. ［Method］By optimizing the existing local circuit wiring, interface communication protocols, and software control logic in CTCS2+ATO signaling system, and controlling the track circuit coding direction in the interval turn-back area independently, the proposed scheme can achieve signaling system automatic turn-back operations in city railway intervals through utilizing reserved fields in the existing interface communication protocols between the computer interlocking system, train control center, and centralized dispatching system to add turn-back route identifiers, refining the track circuit coding logic, balise placement and message transmission logic to increase normal/turn-back routes, interval directions, and multi-scenario combinations of track circuit coding protection logic. The feasibility of the proposed scheme is analyzed in terms of adaptability, operational efficiency, and safety. ［Result & Conclusion］The first application results of this optimized scheme in Shanghai City Railway Airport Line project, along with simulation results of the scheme based on partial site data, demonstrate that the interval automatic turn-back scheme meets the operational requirement of a typical 3-mintue tracking interval for city railways.