What is railway signalling

The concept of a digital railway hails from the s when we began to use computers to control the signalling. The loss of vital data, such as the exact position of trains or the status of the track ahead, results in delays because the system can only allow train movements when it knows it is safe to do so.

So, when a signalling system fails, is it possible to switch it off and turn it back on again? Sometimes, yes, but very often it is a component that needs to be located alongside the track which has failed. These failures require staff to physically access and repair the component, which all takes time. Signalling systems are also vulnerable to a wide range of risks ranging from flooding to lightning strikes.

These can cause failures that are difficult and time-consuming to resolve. Points failure: A fault with the movable pieces of track or their operating equipment that enable trains to change tracks. They often occur in places where our cables are older or have been stolen. Power failures can affect systems covering a very large area. Extreme heat: Very high temperatures can affect signalling systems, causing them to shut down.

They can also affect train detection systems. Faulty components: Faults in all types of electronic, electrical and mechanical components can result in a system failure. A complete system is made up of many thousands of individual components and duplication is not always possible. These different elements of a signalling system combine to minimise the likelihood of human failure:. Installing and maintaining rail signalling systems demands high levels of knowledge and skill in a discipline that crosses electrical, communications technology and information technology.

Entry to rail signalling Employment and employers Rail signalling tester roles Training options Recognition of existing skills. ATR subsystems adjust the performance of individual trains to maintain schedules.

Automatic Train Supervision ATS A safety within an automatic train control system which monitors the system status and provides the appropriate controls to direct the operation of trains in order to maintain intended traffic patterns and minimize the effect of train delays on the operating schedule. A track Inductor based system linked to the aspects of fixed lineside Signals.

The track mounted inductors are supplied as standard or extra strength. Axle Counter An axle counter is a device on a railway that detects the passing of a train between two points on a track. Track mounted equipment counts the number of axles entering and leaving a Track Section at each extremity.

A calculation is performed to determine whether the track section is Occupied or Clear. Balise A track mounted spot transmission unit that uses transponder technology. Berth A location where a Train Description may be displayed by the Train Describer and which is normally associated with a Signal. Braking Curve A graphical representation of the Braking Distance of a train in relation to the Gradient, the braking characteristics and speed of the train.

Braking Distance Emergency The distance in which a train is capable of stopping in an emergency. Braking Distance Service The distance in which a train is capable of stopping, from a given speed, at such a deceleration for a passenger train that the passengers do not suffer discomfort or alarm, or at an equivalent deceleration in the case of non-passenger trains. Cab Signal A display in the driving cab of a train, showing Permissible Speed or extent of Movement Authority, instead of or supplementing lineside Signals.

Communications-Based Train Control CBTC A railway signaling system that makes use of the telecommunications between the train and track equipment for the traffic management and infrastructure control.

By means of the CBTC systems, the exact position of a train is known more accurately than with the traditional signaling systems. Computer Based Interlocking CBI A generic term for a second generation processor based system for controlling the Interlocking between Points and Signals, as well as communication with lineside Signalling Functions.

Degraded Mode Conditions The state of the part of the railway system when it continues to operate in a restricted manner due to the failure of one or more components. Dispatcher An employee who supervises the train movements of a line or a certain area.

A dispatcher may also perform the duty of a Train Control Operator. Driverless Train Operation DTO A signal train operation where starting and stopping are automated but a train attendant operates the doors and drives the train in case of emergencies, or GoA3.

Dwell Time The total elapsed time from the time that a train stops in a station until the time it resumes moving. Emergency Release A device, usually sealed, to permit the operation of a Signalling Function in case of emergency or failure. Fail-Safe A design philosophy which results in expected failures maintaining or placing the equipment in a safe state. Fixed Block The section of track between two fixed points.

Flank Protection Protection from overrunning movements approaching on converging tracks, usually by additional Point Interlocking or Train Detection. Grades of Automation GoA There are various degrees of automation; these are defined according to which basic functions of train operation are the responsibility of staff, and which are the responsibility of the system itself. Hazard Any real or potential condition that can cause injury, death, or damage or loss of equipment or property.