Rail terminology

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Rail terminology
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2012-05-22 00:15:03
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  1. Automatic
    Train Control (ATC)
    • The system for automatically controlling train movements and directing train operations. ATC requires automatic train operation (ATO) and automatic train protection (ATP) subsystems and has features which
    • enhance operational safety, e.g., through the separation of trains by implementing a conflict free timetable, train detection and interlocking of routes. ATC allows the automatic control of trains throughout a railway network, obviating the need for train drivers. The
    • Docklands Light Railway in London provides a good example of this type of operation. (Australians use this acronym to describe automatic train protection.)UoS
  2. Automatic Train Monitoring (ATM)
    Subsystem to monitor the train service by means of train describers, track circuit occupation or balise based data collection. ATM is normally a subsystem of automatic train supervision (ATS) and is sometimes also referred to as train service monitoring.
  3. Automatic Train Operation (ATO)
    • The subsystem within the automatic train control (ATC) system which performs functions otherwise assigned to the train operator (driver). ATO is not generally considered to be safety critical since interlockings and automatic train protection (ATP) ensure that trains’
    • routes and movements cannot conflict. Driverless operation of trains requires the transmission of control data using track circuits, inductive loops, balises or radio signals. Radio signals can be diffused by broadcast or leaky cable feeders.
  4. Automatic Train Protection (ATP)
    The subsystem within the overall train control system which automatically ensures compliance with or observation of some or all speed restrictions or movement authorities’. Normally, the term ATP refers to the provision of failsafe protection against collisions, excessive speed, and other hazardous conditions which may arise during train movements by preventing trains from ignoring control commands. This definition covers what could be described as ‘Comprehensive ATP’ (see below). Less effective systems (such as TPWS, AWS and Trainstops) are sometimes also classified as ATP. As a result, the following hierarchy of functionality is proposed, with ATP as the ‘global’ term: Warning Systems ‘systems assisting observation of movement authorities, based upon manual activation’, e.g., the Driver Reminder Appliance (DRA); Automatic Warning Systems ‘systems automatically assisting observation of movement authorities’, e.g. the standard British AWS system; Automatic Train Stop ‘a system automatically enforcing compliance with the limits of movement authorities’; Partial ATP ‘a system automatically enforcing compliance with speed restrictions and movement authorities at some locations or for some vehicles’; Comprehensive ATP ‘a system automatically enforcing compliance with all speed restrictions and movement authorities (for all vehicles) within a given area’. This type of system is often divided into two subcategories, Intermittent ATP and Continuous ATP. There are many different types of implementation but all require the transmission of control data using track circuits, inductive loops, balises or radio signals. Radio signals can be diffused by broadcast or leaky cable feeders.
  5. Automatic Warning System
    Used to give advance warning to drivers of a signal aspect, a temporary speed restriction or a permanent speed restriction at least 30% slower than the previous limit.
  6. Automatic Warning System (AWS)
    British system for alerting the driver to a signal aspect which requires action (horn for danger) or indicating a clear signal ahead (bell for green). Based on a track-mounted permanent magnet with an electromagnet to cancel the warning.
  7. Calling-on Signal
    Used to indicate to a driver that he may proceed at caution speed because he is entering a section occupied by another vehicle or train. Normally used for coupling operations at station platforms.
  8. Diamond Crossing
    Point where two tracks cross without connection. Named after the shape of the track formation which occurs.
  9. Double Slip
    Track formation where two tracks cross and are connected across the obtuse angles through interconnecting point-work. Expensive to build and maintain and used only where space is very limited.
  10. Emergency Evacuation
    Regarded as essential for underground railways, emergency evacuation systems are now incorporated into all new railway designs which run in tunnels or elevated viaducts for long distances. The system usually requires either a floor level side walkway in the tunnel so that passengers can escape through side doors or a rapidly deployed end door to allow passengers to walk down to track level. The trouble with side walkways is that they require a wider tunnel than the train and this pushes up the cost of the tunnel construction. For a system very rarely, if ever used, this additional expense might be considered unnecessary by a prudent operator. Elevated structures require emergency exit systems.
  11. Headway
    • This is the name given to the elapsed time between trains
    • passing a fixed point in the same direction over the same track. It is usually expressed in minutes e.g. "trains were running at a 4-minute headway". Another way of expressing it is as trains per hour (tph).
  12. Impedance Bond
    A connection box, usually mounted between the rails, which provides continuity of return current for traction power supply circuits where rails have been divided into insulated sections for signalling track circuit purposes.
  13. Interlocking
    • In signalling, a system to prevent the setting up of conflicting routes. At first they were mechanical, then electro-mechanical. Now they are largely computerised using a two in three voting system or similar protocol. Also note the term SSI (solid state interlocking). In the US, the term Interlocking refers to an area where junctions and signals are under the control of a signal cabin or "Tower".
    • Points and signals at junctions must operate in harmony to ensure that no unsafe moves are set up.
  14. Line Capacity
    The maximum possible number of trains capable of being operated over a line in one direction. Usually expressed as trains per hour, it will depend on all trains running at the same speed, having equal braking capacity and on how the signalling is arranged.
  15. Overlap
    The safe braking distance beyond a signal provided in case the train fails to stop at the signal when it is showing a danger aspect.
  16. Overhead
    Generic term (as in "the overhead") referring to electric traction supply wires suspended over the track for current collection by trains. Also known as "overhead line", "OLE" (overhead line equipment), or catenary after the line suspension system. Current is collected by a pantograph on the roof of the train or locomotive.
  17. Route Locking
    The system in railway signalling whereby a route which has been set up for an approaching train is electrically and mechanically locked as the train approaches and while it passes through the route. The route is secured by the control system which prevents any conflicting routes being set up or signals being cleared. It is additionally secured by the passage of the train through the track circuits of the route concerned.
  18. Tamping
    The process by which ballast is packed around the sleepers of a track to ensure the correct position for the location, speed and curvature. Can be done manually or mechanically by special "tamping machines", usually independently powered track vehicles.
  19. Track Circuits
    Means by which the passage of trains is detected and the information used to control signals provided for train safety and control. The simple track circuit consists of a relay energised by a low voltage circuit fed through the running rails of a section of track. Each section is electrically isolated from others. The energised relay detects no train present and can be used to switch power to a green signal light. If a train enters the section, its wheelsets will short out the circuit, causing the relay to de-energise and switch off the green signal. The relay will now switch on the red signal light. The light remains red until the last wheelset of the train clears the section, allowing the track circuit to be restored and the signal to return to green.
  20. Traction Current
    Term used for electric power supply used on electric railways for trains. Normally supplied by overhead wire or third rail and collected by a pantograph on the roof of the train in the former case or by shoes attached to the bogies in the latter.
  21. Traction/Brake Controller
    Train control device provided for the operator in the driving cab in which the power application control and braking control is combined in the same handle.
  22. Third Rail System
    Traction current collection system which uses an additional rail to transmit the electrical supply and which is collected by shoes attached to the train.
  23. Route and Track Locking
    Once a driver has been given a clear signal indicating a route, it is essential that the route is not changed before the train has completed the manoeuvre through the route and it has completely cleared it. To prevent the route being changed once a train is committed to it, the section of track on the approach side of the signal becomes locked as the train reaches it to prevent the route being changed within the safe braking distance on the approach to the signal. In addition, the route between the signal and the points is "route locked". Once this track circuit is occupied the point control is locked and the points cannot be moved.

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