Computer Based Train Control, commonly called CBTC, can be categorized in several ways. These categories reflect system architecture, the level of automation, and the communication technologies used.
Understanding these classifications helps explain the flexibility and adaptability of CBTC in different railway environments.
In a centralized CBTC architecture, a central control center acts as the main processing hub.
The central system receives train location and status information from all trains, calculates safe Movement Authorities and speed profiles, and transmits these commands back to the trains.
This architecture depends heavily on a strong and reliable communication link between the trains and the central control system.
In a distributed CBTC architecture, more processing and decision-making capability is shifted to the trains themselves.
Trains may communicate directly with each other to help maintain safe separation and coordinate movements, reducing reliance on one central entity for some critical functions.
This approach can offer advantages in scalability and resilience.
CBTC is a major technology that supports different Grades of Automation, often called GoA, as defined by international standards such as IEC 62290.
In GoA 1, the driver is responsible for starting, stopping, speed control, and door operation while following signals.
CBTC in this case mainly provides train protection and real-time information to the driver.
In GoA 2, the Automatic Train Operation subsystem can automate train starting and stopping accurately at stations.
A driver is still typically responsible for door operation, handling emergencies, and possibly manual operation during degraded conditions.
In GoA 3, the CBTC system controls starting, stopping, and door operation automatically.
There is no driver onboard, but attendants may still be present to assist passengers, handle emergencies, and take manual control if required.
In GoA 4, the CBTC system fully automates train operation, including starting, stopping, door operation, and handling planned contingencies.
No onboard operating staff are required for normal train movement, and platform screen doors are often used for additional safety.
Reliable and continuous communication is essential for CBTC operation.
The most common modern CBTC systems are radio-based.
These systems may use Wi-Fi, cellular networks, or proprietary industrial radio systems. Coverage is often provided by radio base stations or leaky feeder cables installed along the railway.
Inductive loops and balises are not usually used for continuous high-bandwidth communication in full CBTC systems, but they can still be important for train positioning and for transmitting discrete data.
These devices help improve train location accuracy and support safe operation.
These CBTC categories are not mutually exclusive. A railway may use a centralized architecture, support GoA 4, and operate over a radio-based communication network all at the same time.
The most suitable type of CBTC system depends on the needs of the railway, such as whether it is an urban metro, mainline, or freight operation.