Railway City

"Automatic Train Protection" (ATP) system protects a train against excessivespeed, collision and other hazardous conditions that may arise during train movements.It operates by transmitting signals of maximum speed limits from the track to atrain and comparing continuously the actual train speed with these speed limits.If the train speed exceeds these speed limits, the system then applies emergencybrake to prevent the train from excessive speed. It also ensures that there is alwayssufficient unoccupied track in front of the train in the event of an emergency brakeapplication for the train to stop clear of any other trains to prevent collision.

"Automatic Train Operation" (ATO) system performs the driving of a train automatically. It controls the regulation of acceleration, coasting, braking and station stopping of a train according to the received signals but is guarded against excessive speed or collision continuously by the ATP ("Automatic Train Protection") system.

The signalling system is designed and operated under the "fail-safe" principle. The "fail-safe" feature ensures that, in the event of a signalling failure, the system will respond in such a way that it will cause no harm to other devices or danger to personnel. Very often, this will cause stoppage of trains and hence prevent the occurrences of hazardous conditions that may arise due to train movements. Hence, safety of passengers is always protected.

Both the Tung Chung Line and Airport Express Rail Link share common tracks at certain sections of the lines and they are installed with the same ATP ("Automatic Train Protection") system. The ATP system will only allow a train to enter the track of the Airport Express Line when the track is clear for train movement and hence ensure railway safety.

While the driving of a train is normally carried out by ATO ("Automatic Train Operation"), a Train Captain may assume the driving duty with the train set at the manual mode under certain circumstances. However, under manual driving, the train movement is still safeguarded by ATP ("Automatic Train Protection"). Even in case that the Train Captain fails to observe a red signal, the train will be caused to a stop by ATP within the safety buffer zone beyond the signal and hence ensure safety.