Technical progress has made train control systems capable of supervising, operating and controlling the entire operational process. The key elements for this are:
- Automatic Train Protection (ATP) is the system and all equipment responsible for basic safety; it avoids collisions, red signal overrunning and exceeding speed limits by applying brakes automatically. A line equipped with ATP corresponds (at least) to a GoA1.
- Automatic Train Operation (ATO) insures partial or complete automatic train piloting and driverless functionalities. The ATO system performs all the functions of the driver, except for door closing. The driver only needs to close the doors, and if the way is clear, the train will automatically proceed to the next station. This corresponds to a GoA2. Many newer systems are completely computer controlled; most systems still elect to maintain a driver, or a train attendant of some kind, to mitigate risks associated with failures or emergencies. This corresponds to a GoA3.
- Automatic Train Control (ATC) performs automatically normal signaller operations such as route setting and train regulation. The ATO and the ATC systems work together to maintain a train within a defined tolerance of its timetable. The combined system will marginally adjust operating parameters such as the ratio of power to coast when moving and station dwell time, in order to bring the train back to the timetable slot defined for it. There is no driver, and no staff assigned to accompany the train, corresponding to a GoA4.
At Grade of Automation 4, ATC systems work within an overall signalling system with interlocking, automatic train supervision, track vacancy detection and communication functions.
FOUR LEVELS FOR A FULL-SIZED AUTOMATED TRAIN CONTROL SYSTEM
- The Operation Control Centre (OCC) supervises the overall train running and provides automatic train supervision (ATS) functions.
- The ATP, ATO and ATC functions are performed by on-board and wayside equipments which exchange data.
- Wayside level – providing automatic train protection (ATP), automatic train operation (ATO), electronic interlocking and track vacancy detection functions from the trackside
- Train borne level – providing ATP, ATO and human-machine interface (HMI) functions on board the trains.
- Various types of communication between track and train. Progress of Information and Communication Technology (ICT) means that traditional equipments such as induction loops or beacons are increasingly replaced by radio communication.