Computer Based Train Control systems can be categorized based on their architecture, the level of automation they support, and the communication technologies they use.
Understanding these categories provides a clearer overview of the different types of CBTC systems used in railway operations.
In a centralized CBTC system, a central control system manages train movements based on continuous communication with all trains operating within the controlled territory.
The central control system receives train location, speed, direction, and operating status information.
It then calculates safe Movement Authorities and speed profiles and transmits this information back to each train.
Centralized CBTC is a widely adopted architecture because it allows the railway to coordinate and supervise train movements from a central location.
In a distributed or train-centric CBTC system, more processing and decision-making functions are performed by the onboard train systems.
Trains may communicate directly with other trains for certain safety and train-separation functions.
This can reduce dependence on one central control point and may improve system scalability and resilience.
CBTC is an important technology that enables different Grades of Automation, commonly called GoA.
The Grades of Automation describe how much of the train operation is performed manually and how much is performed automatically.
In GoA 1, the driver operates the train manually.
The driver controls starting, stopping, speed, and door operation while the CBTC system provides train supervision and protection.
In GoA 2, starting and stopping can be performed automatically.
A driver is still normally present and is typically responsible for door operation, emergencies, and manual train operation during degraded conditions.
In GoA 3, starting, stopping, speed control, and door operation are automated.
There is no driver in the train cab, but an attendant may be onboard to assist passengers, respond to emergencies, or operate the train manually if required.
In GoA 4, train operation is fully automated.
Starting, stopping, speed control, and door operation are performed automatically without an operator or attendant onboard during normal operation.
Reliable two-way wireless communication is essential for CBTC operation.
The communication system allows trains and control equipment to continuously exchange train location, speed, Movement Authority, speed profile, and operating command information.
Radio-based communication is the most common communication method used in modern CBTC systems.
These systems may use Wi-Fi, LTE-R, cellular technology, or proprietary industrial radio systems.
Communication coverage can be provided through wayside antennas, radio base stations, or leaky feeder cables installed along the railway.
Inductive loops and balises may also be used in CBTC systems.
These devices are mainly used for train positioning and the transmission of information at specific points along the railway.
They are less commonly used as the primary method for continuous high-speed communication in a full CBTC system.
A specific CBTC system is usually described using a combination of its architecture, Grade of Automation, and communication technology.
For example, a railway may use a centralized CBTC architecture, operate at GoA 4, and use a radio-based communication network.
The type of CBTC system selected depends on the railway's capacity requirements, safety standards, operating environment, infrastructure, and desired level of automation.