Railway signalling is the system used on railways to direct rail traffic and to keep trains a safe distance apart from each other, as well as to ensure trains run according to schedule.
Signalling ensures safe and smooth operation by separating trains, ensuring they have enough braking distance to stop, and also by routing trains down the correct tracks and platforms.
The ATC system automatically controls train movement, enforcing train safety and directing train operations via its two sub-systems, the ATP and ATO.
The system has trackside ATC and trainborne ATC working together to provide safe train separation by using train detection, localisation, and end of authority protection. It also provides safe train operation and movement by using train speed determination, monitoring, over-speed protection and emergency braking. The safety of alighting and departing passengers will also be provided by using a station interlocking system.
The ATP subsystem maintains protection against collisions, excessive speed, and other hazardous conditions by combining the following procedures: train detection, train separation and end of authority protection.
The ATP ensures safe train separation by using the ATP track circuit status and by location determination. In order to verify that the train is able to stop at required stopping point to protect the train ahead, the ATP monitors the speed of the train, keeping it to an allowable speed. In the event of overspeed, the train will initiate emergency braking to protect the train ahead.
The system also ensures a safe exchange of passengers at station by providing zero speed detection to prove train has stopped. Door opening permission is also provided only when the train has stopped at the correct position. It also prevents the train from departing when the train and station doors are not closed.
The ATO system drives the train automatically to achieve prescribed operational performance within the safety constraints imposed by ATP. The main function of the ATO is to drive the train, provide accurate stopping position at the station and to control the train and platform screen doors.
The trainborne ATO subsystem drives the train in automatic mode, providing the traction and braking control demands to the train rolling stock system. Upon approaching a station, the ATO adjusts its speed. After accurately stopping at the station, the ATO provides the control of opening and closing of train and platform screen doors.
The International Association of Public Transport (UITP) summarises automation of rail transport into five Grades of Automation.
|Grade of Automation||Type of Train operation||Setting train in motion||Stopping train||Door closure||Operation in event of Disruption|
|GoA 0||On-Sight Train Operation||Driver||Driver||Driver||Driver|
|GoA 1||ATP with driver||Driver||Driver||Driver||Driver|
|GoA 2 - STO||Semi-automatic Train Operation
(ATP and ATO with driver)
|GoA 3 - DTO||Driverless Train Operation||Automatic||Automatic||Train attendant||Train attendant|
|GoA 4 - UTO||Unattended Train Operation||Automatic||Automatic||Automatic||Automatic|
Table obtained from UITP
A speed signalled fixed-block system consists of several blocks that contains speed codes along the track. Each block can only be occupied by a single train at any given time. A train cannot enter the block directly behind the train ahead, providing a safe distance of at least one block. This ensures that the trains will have enough distance to apply the brakes if it bypasses the stop signal, thus preventing collision with the train ahead.
Trains are operated based on a displayed "target speed", which changes based on speed restrictions and the distance to the train ahead. Signalling information is transmitted to the train's cab and shown on the operating console.
|Line||System||Level of Automation*||Commissioned|
|Fixed-block Westinghouse FS2000 ATC||STO||1987|
|Bukit Panjang LRT||Fixed-block Bombardier CITYFLO 550 ATC||UTO||1999|
|Fixed-block Kyosan APM Signalling ATC||UTO||2003|
|Changi Airport Skytrain||Fixed-block Kyosan APM Signalling ATC||UTO||2006|
|Sentosa Express||Fixed-block Hitachi Digital ATP||GoA 1||2007|
Moving block signalling separates trains based on the train's absolute position and characteristics. The allowable speed of the train is not fixed and can vary based on the distance between the trains. The trackside ATC system computes the stopping point and braking curve based on the speed of trains.
Moving block enables the stopping point to be inside a track detection system, therefore reducing the distance between two subsequent trains without affecting safety. Together with the necessary safety margins and a continuous two-way digital communication between each train and the wayside system, the Limit of Movement Authority of the train is constantly updated based on the precise location reported from the train in front.
|Line||System||Level of Automation*||Commissioned|
|North East Line||Moving-block Alstom Urbalis 300 CBTC||UTO||2003|
|Circle Line||Moving-block Alstom Urbalis 300 CBTC||UTO||2009|
|Downtown Line||Moving-block Invensys Sirius CBTC||UTO||2013|
East-West Line (Tuas West Extension)
|Moving-block Thales SelTrac Convergence CBTC||UTO||2017|
|Sentosa Express||Moving-block Hitachi Wireless CBTC||DTO||2017|
|East-West Line||Moving-block Thales SelTrac Convergence CBTC||UTO||2018|
|Thomson-East Coast Line||Moving-block Alstom Urbalis 400 CBTC||UTO||Commissioning 2019|
ATS supervises the overall operation of the train service according to a prescribed timetable or train interval by de-centralised processing through a network of distributed computers involving the automation of train supervision, with the flexibility for manual intervention.
Functions of the ATS: