Moveable block signaling, commonly known as Communications-Based Train Control (CBTC), is a highly integrated system that combines train positioning, wireless communication, onboard computers, and central control systems.
The first major component is precise train location determination. The system must continuously know the exact location of every train operating within the territory.
Various technologies are used to determine train position, including transponders (balises), RFID tags, wheel speed sensors (tachometers), GPS systems, and inertial measurement units (IMUs). These technologies are often used together to improve accuracy and reliability.
Another critical component is the continuous communication system. Reliable two-way digital communication allows trains and central control to exchange information regarding train location, speed, movement authority, and system status in real time.
Communication technologies commonly used include wireless LAN (WLAN), ultra-wideband (UWB) systems, and cellular communication networks.
The central control system acts as the brain of the CBTC system. It receives information from all trains, calculates safe braking distances, issues movement authorities, monitors train performance, and responds to abnormal conditions.
Each train contains an onboard train control system. This onboard computer continuously determines train position, communicates with central control, receives operating commands, and monitors train performance.
The onboard system also performs Automatic Train Protection (ATP) functions, including overspeed protection, enforcement of movement authority limits, and collision avoidance.
Train operators may receive information through cab displays that provide speed commands, movement authorities, train status, and other operating data.
Although moveable block systems reduce dependence on traditional wayside signaling, some trackside equipment remains necessary. This may include zone controllers, transponders, communication equipment, and traditional interlockings that interface with the CBTC system.
Together, these components create a dynamic signaling system capable of continuously managing train movements using real-time train location and communication data.