Reliability and Operational Impact of "CBTC plus TBTC" Dual-Signal Redundant Train Control System

"CBTC (Communication Based Train Control) + TBTC (Track-circuit Based Train Control)" is a dual-signal redundant train control system. The TBTC is the fallback mode, which is mainly implemented in the re-signaling program of the existing TBTC line. This study uses reliability block diagrams to quantitatively analyze the reliability of the dual-signal system and the time-colored Petri net of degraded operations to calculate the delay time caused by signal equipment failure leading to mode transition. These methods are applied to "CBTC + TBTC" re-signaling program of Shanghai Metro Line 2. The results show that the reliability of the new system is higher than that of the existing TBTC system and a single CBTC system, and the train delay caused by the fault leading to system fallback is minimized to 1 min. The analysis method also provides references for other multi-mode train control systems.