Computer Based Train Control, commonly called CBTC, functions through a continuous loop of data acquisition, processing, communication, and action to ensure safe and efficient train movement.
Each train continuously determines its precise location using onboard sensors such as odometers and speed sensors.
The train periodically calibrates its position using fixed reference points such as balises or beacons.
Some CBTC systems may also use radar or Radio Frequency Identification, commonly called RFID, to improve location accuracy.
The train wirelessly transmits its real-time location, speed, direction, and other operational data to the central control center.
This communication is continuous or very frequent so that the control system always has current train information.
The central control system receives and processes data from all trains on the network.
Using advanced algorithms, the system considers track geometry, gradients, speed restrictions, interlocking status, and the movement of other trains.
Based on this information, the central system calculates the safe braking distance required for each train and determines the maximum safe speed and the extent of its Movement Authority, commonly called MA.
The central control system transmits the Movement Authority back to the train.
The Movement Authority tells the train how far it is safely allowed to proceed.
The system often also sends a speed profile, which gives target speeds for different sections of the authorized movement.
The onboard computer system receives the Movement Authority and speed profile from the central control system.
The Automatic Train Protection system, commonly called ATP, continuously monitors the train's actual speed and position against the received limits.
If the train exceeds the permitted speed or approaches the end of its Movement Authority without proper braking, the ATP system automatically applies the brakes to prevent overspeed or collision.
The entire CBTC process is dynamic and continuous.
As train positions change, train speeds change, or track and operating conditions change, the central control system continually recalculates and updates the Movement Authorities and speed profiles for all trains.
This allows trains to operate with tighter spacing and more efficient traffic flow than traditional fixed block systems.
CBTC systems often interface with other railway systems such as interlocking systems and traffic management systems.
Interlocking systems help with route setting and route protection at junctions, while traffic management systems help optimize the overall railway network.
This continuous cycle of localization, communication, centralized processing, and onboard control gives CBTC its advanced capabilities, increased safety, improved capacity, and enhanced operational efficiency.