In a moveable block signaling system, train movements are governed continuously by a central control system using real-time information received from every train operating within the territory.
Each train constantly transmits its location and speed through the communication network. This information is continuously updated and monitored by the central control system.
Using this information, the central control system calculates a safe braking distance for each train. The calculation considers train speed, braking performance, track gradient, and other operating conditions.
Based on these calculations, the central control system establishes a movement authority for each train. Movement authority defines the maximum distance a train is permitted to travel under current operating conditions.
Unlike traditional fixed block systems, the movement authority is not based on predetermined blocks of track. Instead, it is dynamically adjusted as trains move and conditions change.
The movement authority and any necessary speed commands are transmitted continuously to the train's onboard control system through the CBTC communication network.
The onboard train control system continuously compares the train's actual speed and position against the authorized limits received from central control.
Automatic Train Protection (ATP) functions are integrated into the onboard equipment. ATP continuously monitors train operation to ensure safe compliance with movement authority and speed restrictions.
If a train exceeds its authorized speed or approaches the limit of its movement authority, the ATP system can automatically intervene and apply the brakes to prevent unsafe operation.
As trains accelerate, decelerate, or change position, the central control system continuously recalculates safe braking distances and updates movement authorities in real time. This creates a moving safety envelope that travels with each train.
This dynamic process allows trains to operate safely with shorter headways, improving railway capacity while maintaining a high level of operational safety.