This page provides a modern list of terminology i.e., a glossary for the most common railway terms. You can download a copy of the following .pdf files: 

Acronyms and Abbreviations and

UK Railway Lexicon

prepared by the team at the Railway Research Centre at the University of Birmingham.



A wheel notation (not now common) for a locomotive with two 6-wheeled bogies where the outer axles of each bogie are powered and the centre axle is unpowered or trailing. 


Association of American Railroads. US body for determination of railway engineering standards, equivalent to the European UIC. 

Abnormal Heavy Road Load

Any road load which falls outside the scope of the Construction and Use Regulations because of its weight or weight distribution.RT


In UK railway signalling terms, 'acceptance' means the permission given by a signalman for a train to enter the section of line he controls. 

Acceptance (of rolling stock) 

Final part of the process to introduce new types of rolling stock, onboard systems or infrastructure components to the railway network managed by Network Rail.UoS

Accommodation Bridge

A bridge connecting two areas of land which were under common ownership but separated when the railway was built.RT

Active Suspension

A recent development in train ride control, active suspension uses microprocessor control to detect changes in track formation or direction and then signal changes in the suspension configuration. In this way, sideways movements can be used to stiffen hydraulic resistance in dampers or induce hydraulic jacking movement to adjust body tilt. 

Add Value Machines

Used in some automatic fare collection systems to allow passengers to increase the residual value of a stored value ticket. 

Adhesion Coefficient (m

The ratio of the tangential and normal forces that exist between the wheel and the rail at standstill and during motion. The adhesion coefficient for rolling motion is usually referred to as m R. Generally taken as 0.3 to 0.4 for dry rail, but can be as low as 0.01 for icy and greasy rail.UoS

Adhesive Weight

The total weight carried on the driving axles of a vehicle and therefore contributing to adhesion. 

Adjustment Switch

A device which allows longitudinal rail movement to dissipate thermal forces when CWR is adjacent to jointed track or other features not designed to withstand thermal forces. Adjustment switches are also used when thermal forces, additional to those in CWR, may be encountered such as at long under-bridges which are themselves subject to expansion and contraction (US term: Breather Switch). RT

Advanced Passenger Train (APT)

High speed tilting train, the development of which was abandoned by British Rail in the early 1980s. A version of the technology was later used by the Italians who produced a tilting train design known as "Pendolino". 

Air Bags

Hollow rubber vehicle suspension devices containing compressed air and controlled to ensure pressure, and therefore body level, is maintained constant. See air suspension and secondary suspension.

Air Brake

This is the most common type of train brake using compressed air. 

Air Dryer

A device provided to remove moisture from compressed air produced by a compressor. If moisture is allowed to pass into pipework, it collects in valves and systems, reducing efficiency and causing rust. Some older systems collected so much moisture than up to 20 gallons of water could be drained from a train. To remove it, an old oil drum was wheeled under the train and the main reservoirs drained directly into it. In days gone by, a main air reservoir under a vehicle could collect so much condensate (water) that a sharp frost could cause it to freeze and expand sufficiently to split the tank. 

Air Suspension

Also known as air springs, many modern passenger vehicles now employ a form of air suspension. The car body rests on a set of the rubber air cushions or bags, two being arranged on each bogie bolster. Compressed air is fed into the bags under the control of a levelling valve to ensure the correct pressure is maintained. Air bags are usually designed with a solid rubber core upon which the body will rest in the event of a burst bag. Normally the train can continue to run in this condition, usually at reduced speed. Air bags are also designed to allow for shear during transition through curves. 


The horizontal (line) and vertical (top) position of a railway track, described by curved track of horizontal radius R, tangent track where R =  , vertical radius and gradient.UoS

Alley (US)

A clear track in a switching yard. (UK: marshalling yard.)UoS


Rotating machine for generating alternating current. Normally found in a diesel-electric locomotive, where it is driven by the diesel engine to provide power for the electric motors and auxiliary services on the train. Also used, prior to the introduction of inverters, for providing auxiliary supplies on electric trains, where the machine was powered from the traction current supply. 

Anchor Length

The length of CWR track that is left clipped down during the stressing operation to ensure that no movement occurs at the fixed ends of the length being stressed.RT

Ancillary Movement

Movements of locomotives and rolling stock directly in association with normal day-to-day train services.RT

Angle Cock

A pneumatic isolating cock used on railway vehicles to shut off and/or drain air pipes (hoses) between vehicles. They are normally positioned at vehicle ends to allow the inter-connecting hoses to be isolated and drained of air before being uncoupled. Brake pipe angle cocks do not have bleed holes to drain hoses. 

AntiCreeper (US)

A device firmly attached to the base of a rail and bearing against a crosstie (sleeper), to keep the rail from moving longitudinally under traffic. (UK: Rail Anchor.)UoS

Approach Control

See Route Signalling Page

Approach Track

See Route Signalling Page

Arm Repeater

An electrical indicator which shows the position of a semaphore signal arm to the controlling signalman.RT


The core feature of a rolling stock design where two adjacent railway vehicle ends are mounted on one bogie. Nowadays much favoured by tramcar or light rail vehicle (LRV) designers. Also used on some European high speed train designs. It has the benefit of reducing the number of bogies required for a train. Generally only suitable for lighter weight vehicles since the load on each axle is proportionally increased. Usually requires special lifting systems to be provided in maintenance workshops. 


The visual indication of a colour light (or mechanical) signal as displayed to the driver.RT The signalling term meaning the indication given to the driver of an approaching train by a signal as in "the signal was showing a green aspect". It is said that a driver rarely 'sees' green aspects, only yellow and red ones. After all, he doesn't need to recognise a green signal, he can just carry on at normal speed. 

Associated Society of Locomotive Engineers and Firemen

Union, popularly known as ASLEF, which represents many train drivers.RT

Asynchronous Motor

Modern traction motor type using three phase electrical supply and now the favoured design for modern train traction systems. Can be used on DC and AC electrified railways with suitable control electronics and on diesel-electric locomotives. For more information see the Electric Traction Pages Page. 

Automatic Block Signal (ABS)

A train control subsystem based on a series of consecutive blocks governed by block signals which are controlled by the movement of trains and certain other conditions (e.g., detection of level crossing closure) rather than by a signaller or train describer driven route setting system. The installation includes automatic line side signals, cab signals or both, actuated by a train or light engine by means of axle counters or track circuits. This is a very basic form of automatic route setting (ARS) UoS. See also US Signalling, where the term ABS has a different meaning. 

Automatic Cab Signal System (ACS) (US)

A system that automatically operates a display of signal aspects in the cab of a train as well as the cab warning whistle.UoS

Automatic Code Insertion

The means by which, when a train terminates, the next working of its stock is automatically picked up by the signalling in IECC areas.RT

Automatic Coupler

An automatic coupler allows two vehicles to be attached to each other merely by pushing the two vehicles together. There are various types and systems in use, which range from a simple automatic mechanical coupler (like the 'buckeye coupler' of US origin) to one which is remotely controlled and can connect and secure air and electrical connections in one operation. In Europe only used for Multiple Unit trains and specialised types of rolling stock. The proposed UIC auto-coupler was shelved in the 1970s due to cost but Germany and France are currently carrying out trials of a traction only auto-coupler.UoS Careful specification and attention to design detail is required to ensure reliability.  One is mindful of problems suffered by MUNI in San Francisco on their Boeing LRVs and by Eurotunnel and London Underground, all of whom use complex automatic couplers. Good advice is not to use them unless you really have to and can spend the money on looking after them. Automatic couplers are expensive to repair after even minor collisions or 'rough shunts' as they are often called to reduce the operating manager's anger. 

Automatic Dropping Device (ADD)

Mechanism which causes a damaged or displaced pantograph to drop automatically to limit (further) damage to the overhead line equipment.RT

Automatic Fare Collection (AFC) 

A revenue collection system common on metros and urban railways which requires the passenger to buy a ticket and use it to release an entrance or exit gate to permit access to or exit from the railway. AFC reduces the need for ticket checking staff and reduces fraud by passengers and staff. 

Automatic Level Crossing

Includes AHB, ABCL, AOCL and AOCR level crossings plus those protected by miniature red/green warning lights. RT

Automatic Open Crossing (remotely monitored)

Now only one left on the Network Rail system (in Scotland.)RT

Automatic Railway Inquiry Systems

In Europe a prototype system to provide passenger timetable information.RT

Automatic Route Setting (System) (ARS)

Electronic or relay based system which sets routes using information from a train describer and the timetable without the need for intervention by a signaller.UoS

Automatic Signal

A colour light signal which operates automatically as trains travel onto and off track circuits ahead.RT

Automatic Stop Arm (US)

See (Automatic) Train Stop (UK).UoS

Automatic Systems

The hierarchy of the components of automatic assistance to the operation of trains is not clearcut. Different authors advocate different structures. The structure presented described in the following paragraphs is based on PhD work by D.Woodland. See also our Signalling Pages 

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

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.UoS

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.UoS

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.UoS

Automatic Signalling

A system whereby lineside visual signals for drivers are controlled entirely by the passage of trains using track circuits. Used where there are no junctions or turnouts, which require 'semi-automatic signalling'. 

Automatic Train Regulation (ATR)

Subsystem to ensure that the train service returns to timetabled operation or to regular, fixed headways, following disruption. ATR subsystems adjust the performance of individual trains to maintain schedules. ATR is normally a subsystem of automatic train supervision (ATS).UoS

Automatic Train Reporting

Electronic system for reporting train movements based on the passing of train identities using a signal panel train describer.RT+UoS

Automatic Train Stop

A wayside system that works in conjunction with equipment installed on the vehicle to apply the brakes at designated speed restrictions, block signals or on a dispatcher’s signal, should the driver not respond. Once actuated, the brakes are applied until the train has been brought to stop. See Train Stop.UoS

Automatic Train Supervision (ATS)

The top-level system in real time train control which regulates performance levels, monitors the trains in service and which provides data to controllers to adjust the service to minimise the inconvenience otherwise caused by irregularities. The ATS subsystem also typically includes automatic train regulation functions which are implemented through an automatic routing system (ARS). ATS requires automatic train monitoring (ATM) and service monitoring to be able to adjust the timings of trains appropriately. ATS supports automatic train control by managing the routes or network.UoS

Automatic Vehicle Identification

Semiautomatic mechanism for reporting of train movements based on the location of freight rolling stock and subsequent translation to actual train identities/activities reported to TOPS (generally limited to electricity coal services).RT

Automatic Vehicle Identification (AVI)

Transponder based system to identify the number and other useful information of any vehicle in a train using a trackside interrogating unit. The passive UIC standard system is low cost (about US$40 per unit for the hardware). AVI components are also being used for low cost ATP applications. UoS

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.RT

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.UoS

Autonomous Traction

A railway traction vehicle that does not rely on wayside power supply (e.g., electrification or linear motor) for propulsion, for example, a steam locomotive or a diesel locomotive.

Auxiliary Reservoir

See the Brakes Page.

Auxiliary Supply

System for providing power for vehicle or train lighting, air conditioning, heating, on-board catering or passenger facilities and emergency battery systems. Generally a train has two power supply systems, one for traction and the other for auxiliaries. Auxiliary systems can be supplied from the main traction power source through a generator or converter, or through an axle driven generator. 

Auxiliary Wayside System

A backup or train control system, capable of providing full or partial automatic train protection for trains not equipped with train borne CBTC equipment, and/or trains with partially or totally inoperative train borne CBTC equipment. The auxiliary wayside system generally includes train borne equipment and may also provide broken rail detection.UoS

Auxiliary Wire

See Compound Catenary.UoS


The circular shaft connecting two wheels to form a 'wheelset' (q.v.). The wheels are an interference fit to ensure the gauge is maintained. Wheels are removed by forcing them off after injecting oil under high pressure into the wheel hub through a specially designed aperture drilled in the hub. 


The housing attaching the axle end to the bogie which contains the bearing allowing the axle to rotate. 

Axle Brush

Axle mounted contact used to provide a return path for power circuits on electric vehicles. Nowadays normally mounted on the axle end as part of the axlebox assembly. 

Axle Load

The weight limit applied to trains passing over a line by the railway civil engineer. It is the limit allowed to be applied to any one axle on the train. Always the bane of the life of a rolling stock designer. Axle load refers to the maximum weight permitted on a single axle. A four-axle vehicle weighing 60 t (metric tonnes) would have an axle load of approximately 15 t depending on how the weight was distributed. In the UK the maximum axle load is 20 t on most main lines. The European maximum is 22.5 t.


Balancing Speed

The economical service speed at which the tractive effort of the train equals the train resistance and no further acceleration takes place. 


The material most commonly used to form the road bed of a railway track. It is laid on the base formation of the track with the track laid on top of it and provides a storm water drainage medium. It usually consists of granite, whinstone or furnace slag. Ash is sometimes used in yards but not where any sort of speed is required as the dust gets into the rolling stock equipment. A properly maintained railway will have regular tamping of ballast to ensure the track itself is maintained to provide an acceptable standard of ride. Other track forms include slab or non-ballasted track which does not require ballast. 

Ballast Train

A generic term often used to refer to any sort of track engineer's train. 


Common UK name for the driver's vacuum brake control handle, arising from its shape. The term is also sometimes used to refer to a disc shaped ground signal. 


A section of railway line on a gradient. In the US known as a grade. 

Banking Locomotive

A UK term meaning a locomotive used to assist trains over an uphill section of line incorporating a long or steep 'bank'. Many banks had permanent allocations of 'banking engines', which were attached to the rear of trains which stopped specially to pick them up. At the end of the section where assistance was required, the banking engine would drop off without stopping the train and later return to the bottom of the bank to assist another train. In US known as 'helpers'. 


Locomotives and carriages are nowadays invariably fitted with large, heavy-duty batteries to provide start up and emergency power. Batteries are usually recharged from a power line running along the train or from the traction power supply through a generator, alternator or converter. 

Battery Locomotive

Some electric railways, particularly those with long underground sections like the London Underground or the Hong Kong Mass Transit Railway, employ battery powered locomotives for use on engineer's trains at night when the main traction power supply is switched off. They are arranged to recharge from the traction power supply during the daytime when they are not required for engineer's trains. Their disadvantage is the time required out of service for recharging and the additional weight of the batteries. 

Bi-Directional Signalling

Used to allow trains to run in either direction over the same section of track subject to the built-in safety systems which prevent collisions. Bi-directional signalling is very useful in releasing for maintenance a single track of a two-track railway but it is more complex and expensive to install than single direction signalling. 

Bi-Mode (U.K.) or Dual-Mode (U.S.)

A railway traction vehicle that can receive energy from wayside electrification or an on-board source or a combination of both. An example is a locomotive that can draw power from overhead electrification or an on-board diesel-generator set, also known as an electro-diesel (e.g., Bombardier ALP-45DP).


The moving part of a point or rail switch which causes a train to change direction at a diverging junction.


In signalling terminology, a physical length of track protected by a fixed signal which indicates to a driver when it is safe to proceed into the section. See Signalling Pages

Blocking Back

A term used to denote a queue of trains detained behind a delayed train or other obstruction.


The wheel notation given to a locomotive mounted on two 4-wheeled bogies where all the axles are powered. See also A1A-A1A and Co-Co

Body Bolster

See Bolster


A 4- or 6-wheeled truck used in pairs under long-bodied railway vehicles. The bogie has a central pivot point which allows it to turn as the track curves and thus guide the vehicle into the curve. In the US it is always referred to as a truck. There are almost as many bogie designs as there are bogies. All-welded box-frame bogies with some steering capability are currently the fashion in Europe. Good design is crucial to good riding, although track condition is also very important in giving a good ride.


The transverse member of a bogie frame or vehicle underframe through which the bogie pivot passes or is connected. Thus a bolster can be a body bolster or a bogie bolster.


The centre part of a wheel through which the axle passes. Also called the hub.


UK railway term for signal box or signal cabin. Known as a Tower in the US.


Railway term for the sideways motion of a bogie which has a damaging effect on rails. Also known as hunting.


For all items dealing with brake systems and how they work, see the Brakes Page.


Term for the accidental breakage of couplings which results in a train becoming divided. The brake system is arranged to ensure that both portions of the train will stop in such an event.

Buckeye Coupler

An automatic coupler invented in 1879 by Eli Janney in the US and now used world-wide. Vehicles are coupled by pushing them together and are released by a lever under the coupling head. The term Buckeye comes from the combination of the nickname of the US state of Ohio 'the Buckeye state' and the Ohio Brass Co. which originally marketed the coupler.


A cushioning device mounted on the extreme ends of vehicles to absorb shocks arising during coupling and motion. The buffer consists of a plate on the end of a spring-loaded plunger which compresses upon contact with another buffer. Buffers are either mounted singly in the centre of the underframe ends or in pairs towards the corners.

Buffer Beam

The transverse member at the extreme ends of a vehicle underframe upon which the buffers are mounted. Also known as the 'headstock'.

Buffer Locking

The result of the entanglement of the buffers of adjacent vehicles traversing sharp curves. As straight track is regained, the buffers force the vehicles off the track and cause a derailment. The cause is usually poor buffer design or the use of vehicles over lines for which they were not designed. The oval buffer was introduced in the 1880s to try to reduce buffer locking.

Buffer Stop

Structure at the end of a track to prevent vehicles proceeding off the end of the line. Sometimes these are cushioned by hydraulic rams or protected by emergency braking devices such as a sand trap. In the US known as a "bump stop”.


Cab Signalling

A system where signal indications are displayed to the driver in his cab, usually from a trackside induction system. Cab signals may either augment existing lineside signals or replace them. Cab signalling is usually used in conjunction with some sort of automatic protection system which prevents a driver allowing his train to enter an occupied section or exceeding a predetermined safe speed. See also Signalling Pages


US term for brake van

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.


Used with ropes for moving vehicles in restricted areas like workshops, where a locomotive or other power unit cannot be accommodated. Most common where ground mounted wheel lathes are used.


The term used to denote the raising of the outer rail on curved track to allow higher speeds than if the two rails were level. Cant compensates for the centrifugal force arising from a train traversing a curve. If a track was canted to the level required for the maximum speed of the fastest train, the level of tilt would be too high for a slower train. A compromise degree of cant is therefore used, known as 'cant deficiency'.

Cant Rail

Longitudinal vehicle body member which forms the boundary between the bodyside and the roof.


US term for a railway carrying vehicle, e.g."freight car" or "passenger car". In the UK the term is used to denote an electric multiple unit vehicle.

Cardan Shaft

A drive shaft with flexible couplings provided between a motor and an axle to allow for the movements of the axle relative to the motor.


Transverse structural member of a vehicle roof which is formed in the shape of the roof profile required. Normally supports the roof covering.


UK term for passenger carrying vehicle. Also known as a coach. In the US is referred to as a car.


Originally the term used to denote an overhead power line support wire derived from the curve a suspended wire naturally assumes under the force of gravity. Now adopted to mean the whole overhead line system. See overhead.

Centre Siding

A track laid between two running lines for the purpose of reversing trains, usually beyond a station. It allows a train to reverse direction without crossing a track carrying through trains. Sometimes referred to as a "reversing siding". In the US it is referred to as a "pocket track" or a "turnback track".

Centering Device

System provided to ensure that a coupler returns to a central position when released and thus make re-coupling easier. Used particularly for Automatic Couplers.


The cast steel fixture on a sleeper which secures the rail in the correct position. Depending on the design, of which there are many, the rail is secured to the chair by a form of clip or key.

Check Rail

Additional rail inserted inside the normal running rail at points or curves to provide guidance for the flange to ensure that the correct route is taken.

Chopper Control

A development in electric traction control which eliminates the need for power resistors by causing the voltage to the traction motors to be switched on and off (chopped) very rapidly during acceleration. It is accomplished by the use of thyristors and will give up to 20% improvement in efficiency. For more information see the Electric Traction Pages Page.


UK term for passenger carrying vehicle. Also known as a carriage. The US term is car and is used by London Underground.


Allowing a train to freewheel to maintain a reasonable speed downhill. Of the 50 non stop electrified miles between London and Brighton, 29 miles can be run with the train coasting.

Coefficient of Friction

The factor used to determine the maximum tractive effort which can be applied by a locomotive under a given rail condition before slip occurs. It is denoted by the Greek letter µ and may vary between 0.1 and 0.4 in UK conditions.

Collector Shoe

See Shoe.

Commonwealth Bogie

Another name for the 'equaliser bar bogie'. Illustration and description here.


An air pump, usually electrically driven, which supplies air under pressure (generally between 90 and 140 psi) for use on trains. Brakes, doors and other items of equipment like suspension and whistles commonly require compressed air. Compressors may be driven directly off a diesel engine or from an electrical supply on the locomotive or train. See the Brakes Page for more details.


US term for train staff member whose duties vary with different administrations but who is primarily responsible for train and passenger safety. Often also involved with ticket inspection. In UK parlance was often referred to as the 'guard' but the same term is now common.

Conductor Rail

An additional rail (or rails) provided on those electric railways where power is transmitted to trains from the track. Often referred to as the 'third rail' or 'current rail' , it is normally at positive potential and is mounted on insulators to the outside of and slightly higher than the running rails. The return of the circuit is via the running rails. The current is collected by the train through 'shoes', attached to the bogies, which slide along or under the rail. Varieties of the system include top, side and bottom contact rails. Top contact rails are susceptible to ice and snow contamination in cold climates and present a certain risk to persons walking on the track. For this reason, bottom contact rails are preferred for modern systems. Illustrations and descriptions here. The continuity of conductor rails must be broken at junctions in the track to allow continuity of the running rails. Such 'gaps' may cause momentary loss of power to the train. There are cases from time to time of trains becoming 'gapped' at complex junctions, i.e. they stall over a gap and have to be rescued by another train. London Underground has a fourth rail (negative) for a completely insulated circuit. It is known as a four rail system.


US term for train formation e.g. 'This vehicle was in the consist'. Now heard in the UK amongst trendy railway people.

Continuous Brake

See Brakes Page


Electronic system for converting alternating current to direct current. Used, for example, where an AC supply has to be converted to DC for battery charging purposes. Also was used for converting AC traction supplies required for DC traction motors. See also inverter. For more information see the Electric Traction Page.

Creep Control

See the Electric Traction Pages Page.


Defective vehicle or train. Known in the US as a Bad Order.


A track providing a connection between two parallel tracks using two sets of points. A scissors crossover provides two connections, one in each direction.

Current Rail

See Conductor Rail.


US term for uncoupling. Was also used in the UK to refer to the sections a train was broken into when passing over a hump in a marshalling yard. Since there isn't any hump shunting in the UK any more I suppose this is obsolete.


Dead Heading

US term for empty train or light engine running.


A safety device, commonly known as 'the deadman's handle', fitted to master controllers to ensure driver attention during driving in single-manned cabs. If the controller handle is released, the power is cut off and the emergency brake applied. More modern versions, referred to as a 'driver's safety device' or a 'vigilance device', often take the form of a foot operated pedal which must be reset within a given time to prevent the train being stopped automatically. Usually, an advance warning is given to allow the driver to reset. It is a matter of some pride amongst drivers that they can time the need to reset within a few seconds without causing an alarm.


In railway signalling, the ability to determine that a track section or block is occupied by a train. Detection is usually by a track circuit or equivalent electrical loop. Also used to verify that a point or signal has operated correctly as part of the interlocking.


Explosive devices carried on locomotives or trains for use in emergency situations where they are placed on the top of the running rail so that they explode to give a warning to the driver if a train runs over them. First appeared in 1841.  Known in the US as "torpedos".

Diamond Crossing

Point where two tracks cross without connection. Named after the shape of the track formation which occurs.

Diesel Locomotive

A locomotive whose principle power source is a diesel engine. This engine drives the wheels either by mechanical transmission or electrical transmission. Electrical transmission is by far the most common. Diesel locomotives with electrical transmission are known as Diesel-Electric locomotives. The diesel engine drives a generator (or an alternator on more modern machines) which produces the current required to power the electric traction motors which drive the axles.


A US term referring to the act of putting a train into service from a station or depot or when they are reversed at a terminus. It was common for a "dispatcher" to allot crews to trains and issue "dispatch orders" to send train out. The function is similar to the UK "controller".

Disc Brake

See Brakes Page


See Brakes Page


Diesel Multiple Unit - the generic term for a diesel powered train where a separate locomotive is not required because the traction system is contained under various cars in the train. Has also been tried in a freight train configuration. See also multiple unit.


UK term for the provision of two locomotives to haul a train. Usually these are coupled "in multiple" to allow control by one crew.

Double-EndingDouble 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.

Down Line

See Up line.

Dragging Detector

A device designed to alert a railway control centre that a train has become derailed or a part of the train is dragging on the right of way. Normally consists of a bar placed across the four-foot (between the rails) which will be broken if struck. Often used on remote heavy haul freight lines where it is difficult for the crew to detect a mishap of this sort.

Drain Cock

Used to discharge compressed air from reservoirs. As air is expelled under high pressure, these cocks are normally provided with baffles to reduce the pressure as the air escapes. Note that brake reservoirs are not usually provided with drain cocks as they are part of a safety system although they have a sealed, screwed plug for maintenance purposes. Drain cocks are also useful for draining water which collects in reservoirs as a result of condensation.

Driver's Safety Device (DSD)

See deadman

Driving Trailer (DT)

An unpowered passenger vehicle with a driver's cab used to remotely control a power car or locomotive. Sometimes referred to as a Driving Van Trailer (DVT) where the vehicle is used for luggage or conductor's accommodation. A driving trailer (DT) is the term usually used in a multiple unit train.

Driving Van Trailer (DVT)

A development of the driving trailer which was introduced in the UK following an accident at Polmadie in Scotland when a diesel multiple unit struck a cow and derailed, causing the deaths of several people. It is now forbidden in the UK to carry passengers in the leading vehicle of a train operating at speeds over 160 km/h, hence the introduction of the DVT.

Dual Voltage Locomotive (Train)

Locomotive or multiple unit train designed to operate over lines having two different electric traction power supply systems. Locomotives have been designed to operate with up to four different voltages covering both AC and DC systems. Some trains can operate on lines with either overhead or third rail current collection as for the Eurostar Trains and UK Class 92 Channel Tunnel locomotives.

Dump Valve

See Brakes Page

Duplex Gauge

See Brakes Page

Dynamic Braking

A train braking system using the traction motors of the power vehicle(s) to act as generators. For more information see the Electric Traction Pages Page.



End of Train Device. An electronic device (also known as the flashing rear-end device, or FRED) mounted on the end vehicle of freight trains. There are two types: passive units that provide a visible indication of the rear of the train with a flashing red tail light and a smart version which can send data to the crew in the locomotive via radio. Originally developed in North America, but are used elsewhere.

Electro-Diesel Locomotive

A locomotive which can operate with either electric or diesel power. The motors are electric but can be supplied from the diesel driven alternator or from the line's external power supply. The preference is usually for collecting electric power. The South African Class 38 is a locomotive of this type which has 3000v DC overhead electric supply as well as a 780 kW diesel engine. The UK Class 73 is another type but it collects electric power at 750v DC from a 3rd Rail to provide about 1500 h.p. or 600 h.p. with the diesel engine. The Swiss RhB railway also had two electro-diesel locomotives.

Electro-Pneumatic Brake

See Brakes Page

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.


Electric Multiple Unit - the generic term for an electrically powered suburban or metro train where a separate locomotive is not required because the traction drive and control system is contained under various cars in the train. See also multiple unit.

Equaliser Bar Bogie

A US design of bogie, dating from the late 19th century and still popular, where the primary suspension is arranged by attaching a longitudinal steel bar to each pair of axle-boxes and depositing the bogie frame onto a pair of coil springs resting on the bar. It gained favour in the UK during the 1950s and 60s where it was known as the "Commonwealth" bogie, a US design originally manufactured by the Commonwealth Steel Co. The UK version made by the English Steel Casting Co was built under license. It is a simple and reliable design but its main disadvantage is its high weight.  Illustration and description here.  

Equalising Reservoir

See Brakes Page


See Brakes Page

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Facing Points

Points where a single track diverges into two, i.e. where the points face the oncoming train. The opposite is trailing points, where two tracks become one.


Part of an automatic fare collection (AFC) system where the device is placed at station entrances and exits to regulate access by reading a ticket inserted by the passenger and restricting access if the ticket is not correct. Various types are in use around the world to prevent passenger fraud and to permit the handling of large numbers of passengers with a minimum of staff.  Modern systems are now adopting non-contact electronic card readers like the Hong Kong "Octopus" and London "Oyster" cards


Larger part of wheel form used as principal means of railway vehicle guidance system. See Wheelset.

Flange Greasing

Synonymous with Flange Lubrication.

Flat (1)

A freight wagon with no sides. Known as a flat car in the US.

Flat (2)

A spot on a wheel, caused by skidding or wheel slide, which causes a tapping sound as the wheel rotates and which can usually only be removed by expensive re-profiling of the wheel on a lathe or wheel turning machine. Drivers are cautioned against too heavy braking in bad weather thus causing "flats". Many attempts have been made over the years to reduce "flats" by wheel slide control systems which automatically reduce a brake application in the event of a slide. Such systems generally encourage a driver to apply emergency braking which eliminates the wheel slide control and puts "flats" on the whole train instead of a few wheelsets. An effective solution to this problem is still awaited.

Floating Slab Track

A track system using a concrete base mounted on rubber pads to reduce vibration transmitted to adjacent property. A number of railways have tried it with some anecdotal evidence suggesting that the maintenance costs are high and that riding quality of trains suffers.

Foot Iron

A bracket mounted on the outside of a vehicle to aid access by the crew when boarding from the ground. Also known as a "step iron".

Four Foot 

Nickname for the gap between the running rails, the gauge. Comes from the standard gauge measurement of 4ft 8 1/2 ins (1435mm).

Four Rail System

A now almost unique current collection system used by London Underground which has separate positive and negative current rails. The same system was used by the LNWR and the Mersey Railway at one time. The usual 3-rail method of connecting return current via the running rails is replaced by a fully insulated system using separate positive and negative rails. Originally used to reduce the risk of stray currents causing damage to nearby utilities and structures through electrolysis. Has the disadvantage of requiring special fault detection as earth faults do not cause current to automatically switch off. See conductor rail.


Flashing Rear End Device - see EDT

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Flexible structure provided at vehicle ends where necessary to provide access from one vehicle to another. The gangway is divided between the two adjacent vehicles and is normally closed off when the vehicles are uncoupled.


A break in the continuity of a conductor rail at a set of points on a line equipped with 3rd rail traction. See conductor rail.


A train stalled over a gap in the conductor rail of an electric railway is said to be "gapped". This occurs when the shoes on the train which collect the current have all lost contact with the current rail due to gaps left for junctions. Particularly prevalent at complex junctions such as the entrances to yards. See also conductor rail. A driver who has "gapped" his train will always be the subject of ridicule from his peers. Knowing where the gaps are is part of road learning.

Gauge Line

A line five eighths of an inch, about 15mm below the running surface of a rail on the side of the head nearest the track centre; the line from which measurements of gauge are made.

Gauge, narrow (see Narrow Gauge.)Gauging (of track) 

Bringing two opposite rails into their correct relative positions as regards to their distance apart. UoS


Generic term for limiting or monitoring device as in "speed governor" or air pressure governor, more often the latter. Pressure governors are used to monitor the rise or fall of air pressure to operate systems or give warnings. Compressor governors are used to automatically control compressors running between predefined air pressure settings to ensure air supplies are maintained. A brake pipe governor may be used to switch off power control automatically if the brake pipe is discharged, initiating an emergency brake application. Speed governors perform the usual functions in a diesel engine control system.


US term for sloping track. UK terms are gradient or "bank". "At grade" means level track.

Grade Crossing

A US term for a level crossing.


See "grade".

Gradient Post

A trackside post with two arms indicating the point where there is a change in track gradient.


Train staff member originally provided to assist with train braking before the introduction of continuous brakes
- the name derives from the days of horse-drawn road coaches when guards were employed to protect the passengers from highwaymen. In more recent times, guards have been used to carry out ticketing duties and have become known by the US name - conductor.

Guard Irons

Steel arms suspended in front of the front wheels of a railway vehicle to prevent small obstructions getting under the wheels and derailing it.

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H Frame Bogie

Bogie design where headstocks are omitted and the bolster is fixed. Usually of welded, box frame construction.


Nowadays synonymous with the term parking brake but originally a vehicle brake applied by hand action to a wheel or lever on the vehicle. See also the Brakes Page.


Term used to denote the orientation of a vehicle which may require identification of the direction it faces, e.g. a locomotive with a cab at one end only. Particularly applies to some types of multiple unit  vehicles which are semi-permanently coupled and which must face the right way round to allow the correct electrical and pneumatic connections to be made. Handing is avoided by duplicating wiring and hoses on both sides at vehicle ends but gives rise to additional costs. Handing is also used to denote the location of different items of equipment on a vehicle or train.


Transverse structural members located at the extreme ends of vehicle underframes. The headstock supports the buffer(s) and is also known as a "buffer beam". Bogies may also have headstocks.

HeadwayHigh Speed Train (HST)Horn (1)

Electrically or pneumatically operated warning device provided for a driver to sound at will.  Replaces the traditional whistle.

Horn (2)

The part of a pantograph which curves down at each end of the collector head and which fractures if struck at speed to give, in the most modern examples, a detection signal to lower the pantograph.

Horn (3)

Part of an axlebox guidance assembly mounted on the exterior of a bogie frame.


A flexible connection provided between vehicles for compressed air, vacuum or steam.   Braking and other systems on the train use compressed air both as a power source and a control medium. Vacuum is used for braking control on some older trains and steam was the traditional source of carriage heating.  The connections between vehicles are through flexible pipes usually referred to as hoses. Hoses are normally equipped with isolating cocks to shut off the supply and bleed the hose when vehicles are uncoupled.


A US term for a small power and brake controller provided for the driver at certain positions on a locomotive or multiple unit train for shunting movements where the expense of a driver's cab is not considered necessary. Also known in the UK as a shunting controller. The term is derived from the US name for a person working in an engine shed under the operating foreman. This is in turn derived from 'Ostler' who looked after the horses for the mail coaches, so it's a survival from English practice.

Hot Box

A term for an axlebox which has become over heated because of a breakdown of lubrication or excessive overloading. Nowadays largely eliminated by the adoption of roller bearing axleboxes which have replaced plain bearing axleboxes. Lineside hot box detectors are used by some railways.


The sideways motion of a bogie at speed caused by irregularities in the track or wheels. Different designs "hunt" in different ways and under different conditions. Suspension design often affects ride as much as anything and the whole science of bogie design can be a bit of a black art. Hunting is also sometimes referred to as "boxing".


A railway traction vehicle that has at least two power sources. There are several types of hybrid railway vehicles: 1) A multi-system electric vehicle, for example, a locomotive that can operate from overhead electrification or third rail electricity supply (e.g., BR Class 92). 2) A Bi-Mode or Dual-Mode vehicle, where power is supplied from wayside infrastructure or an on-board generator or a combination of both (e.g., Bombardier ALP-45DP). 3) A vehicle with at least one primary power supply and a re-chargeable on-board energy storage device, for example, a diesel-generator set as prime mover and a battery-pack as on-board storage device (e.g., JR East KiHaE200). Many of these vehicles, but not all, utilise regenerative braking to re-charge the energy storage device in addition to the prime mover. The primary power supply can also be through wayside electrification and the energy storage device allows operation through short non-electrified sections. The storage device is re-charged when the vehicle operates on the electrified network (e.g., Tramway in Nice). Typical energy storage devices are batteries, supercapacitors, and flywheels. A primary power source can be electricity through wayside electrification, diesel engines, other combustion engines (e.g., Natural Gas), turbines, and fuel cells.


Railway vehicle that uses hydrogen as an energy carrier. The hydrogen might be used in a fuel cell or a combustion engine to provide power to traction motors.

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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.

Inter-car Gangway

See gangway.


A station where passenger may alight from one train and board another on a different route. In the US it is referred to as a "transfer".


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".


Descriptive term for freight traffic involving transfer of containers to and from road and rail vehicles. Sometimes referred to as container traffic.


Electronic power device mounted on trains to provide alternating current from direct current. For more information see the Electric Traction Pages Page.

Island Platform

A single station platform with a track on either side, which is more efficient in facilities provision than two side platforms. It does tend to increase the land take however, because of the need to widen the track centres on the approaches to the station.

Isolating Cock

Used in pneumatic and hydraulic systems to shut off flow or to drain systems. Those required to drain are provided with bleed holes to allow air to escape from the up-stream side of the closed cock. Where reservoirs are required to be drained, they are provided with a direct acting drain cock. See also the Brakes Page.

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The bearing in which an axle turns.


Multi-core cables used to provide electrical connections between railway vehicles. Presumably they allowed the electricity to "jump" between coaches. The term is also used as a slang for persons who jump in front of moving trains to commit suicide.

Jumper Heads

The coupling sockets provided at the ends of a jumper.

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Knife Switch

In US practice, a standard electric power isolating system mounted on the underframe of an electric vehicle to disconnect power and auxiliary systems from the traction current collection system and provide a link to shore supplies. Now also being adopted in the UK.

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Lamp Iron

UK term for bracket on vehicle for mounting removable head or tail light


The act of lowering a vehicle on to its bogies, as in "bogie landing". Not a common term.


Driver's brake valve position of air brake control used to hold the brake pipe pressure at its existing level. Details on train air brake control are also in North American Freight Train Brakes.

Lay Up

US term for putting a train out of service into a siding or depot. The UK term is "stabling".

Lead (1)

US term for a track giving access from a main line to a railway yard.

Lead (2)

Electric cable used in maintenance for shore supplies or wander lights.

Levelling Valve

A levelling valve is used to determine the variations in vehicle weight caused by loading and unloading. It is a pneumatic device mounted on the vehicle underframe and connected to the bogie, which measures the body's vertical displacement relative to the bogie caused by weight changes. The valve sends a pneumatic signal to the traction and braking systems to adjust their rates according to the vehicle weight. It is used in conjunction with air suspension to cause the vehicle height to remain constant regardless of load. The levelling valve is a fairly recent development (in railway terms) over the last 15 years and is used as part of modern traction and braking control systems. Some trains can be heard expelling air from their suspension system levelling valves as passengers alight and the system adjusts.


The act of raising the vehicle body off its bogies. It was originally always done by a crane or cranes. Modern installations often use synchronised electric jacks. A "lifting shop" is a workshop specially reserved for this purpose. The layout of a train maintenance lifting shop has to provide sufficient space for each vehicle to be lifted and the bogies rolled clear to give access to the equipment on the bogie. There must also be sufficient space on either side to allow a fork lift or other small powered lifting vehicle to access the underfloor equipment from the side of the vehicle.

Lifting Shop

A workshop where "lifting" is done.

Lifting Points

Marks shown on the sides of a railway vehicle to denote where it is safe to place a lifting device or jack. Sometimes referred to as jacking points.

Light Rail Vehicle(LRV) 

Modern generic term for tram or streetcar. An electrically powered rail vehicle using rails embedded in the roadway or using dedicated rail tracks, or a combination of the two as in Manchester, Sheffield, and many other European and US cities. Nowadays light rail vehicles (LRVs) are much favoured as an alternative to full blown subway or underground (heavy metro) lines for urban rail systems due to their reduced construction costs. Modern LRV design concentrates on low floor construction to make easier access for passengers and to reduce the height of platforms at stations. Much innovation is appearing in the industry as a result.

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.

Live Rail

Synonymous with conductor rail.

Lineside Signals

Visual signals which are located along the route of a railway (by the side of the line) for observation by the driver. They differ from cab signals which are transmitted from the track to the train to provide visuals on the driver's control desk.

Loading Gauge

Maximum dimensions to which a vehicle can be built or loaded without risk of striking a lineside structure.


See light rail vehicle.


Light Rail Transit, a generic term often used to describe a system employing light rail vehicles as a cheaper alternative to a high capacity urban underground system.

Lubrication, Flange

One of the critical areas of wear on railways occurs at the point of contact between wheel flange and rail at curves. This wear reduces the flange profile and, if allowed to develop, can cause derailment. It also damages the inside edge of the rail head. The wear can be reduced by lubrication of the area. The lubricators may consist of flange-actuated track mounted lubricators at the entrance to curves or trains may be fitted with on-board flange lubrication. The Paris Metro, for example, used a train-mounted lubricator which was actuated by links on the bogie which detected the change in angle as it turned onto a curve and injected a small amount of oil onto the wheel. The risk with flange lubrication is over application. This will leave lubricant on the wheel tread or rail head and result in skidding during braking. One such celebrated occasion occurred on London's Victoria Line some years ago which resulted in 35% of the trains being unserviceable due to flatted wheels damaged by skidding.


Main Reservoir

Pressure vessel mounted in or under a railway vehicle to store compressed air for pneumatic systems such as brakes, power doors and air suspension. See the Brakes Page for more details.

Main Reservoir Pipe

Air pipe connecting all main reservoirs on a train from which supplies for pneumatic systems are drawn. Connections between cars are via flexible hoses. Normally, each vehicle has main reservoir pipe isolating cocks at each end of the pipe to allow uncoupling of hoses without loss of main reservoir pipe pressure. See the Brakes Page for more details.

Marker Lights

A US term for the front end lamps provided on many trains to denote the route or type of train. These lights were often colour coded or arranged in special formats to distinguish between different trains. In the UK they were referred to as headlamp codes. Originally used to assist signalmen in identifying trains, they are not common today, having been replaced by automatic train description systems.

Master Controller

Driver's power control device located in the cab. For more information see the Electric Traction Pages Page.

Match Wagon

A vehicle equipped with different types of couplers at each end and placed between a locomotive and train where the couplers are of different types.


A type of coal train operation (shortened to MGR) introduced in the UK to carry out loading and unloading of coal without stopping the train.


The term used to denote an urban railway, often partly or wholly underground, carrying large numbers of passengers on trains at close headways. In the US synonymous with the term "subway". The word is a diminution of the Metropolitan Railway of London, the first urban underground railway in the world. It has since been adopted by many transport authorities to give a catchy name to their system, even if not strictly correct.

Monobloc Wheel

A railway wheel cast in a single bloom and machined to the required profile. Unlike the traditional spoked wheel, the tyre is integral with the wheel and cannot be separately changed.

Motor Bogie

A powered bogie. The term is usually confined to multiple unit trains so as to distinguish them from trailer (unpowered) bogies. Some railways operate trains with all bogies motored. See also "bogie".

Motor Car

A passenger vehicle in a multiple unit train which is provided with traction power equipment.

Multiple Control

If one locomotive isn't powerful enough to pull the train, others can be coupled to it with the control system of the leading loco connected to the others so that the driver's commands are repeated on the additional loco(s). The locos are connected by multi-core cables called jumpers which are plugged into sockets on the front and rear of the vehicles. See also multiple unit.

Multiple Unit

See Train Operations - Multiple Unit Operation.


Nose Cone

US term for a detachable front-end assembly popular in US rapid transit car design.

Nose Suspended Motor

System for mounting an electric traction motor in bogie. One end of the motor is attached to the axle it drives by two suspension bearings, while the other end is hung off the bogie transom plate at a single point by a bracket.

Notching Relay

Electrical relay provided in vehicle traction power circuits using "resistance control" which monitors the rise and fall in current values and actuates the next step in the acceleration phase by permitting a resistance step to be disconnected from the circuit.



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. 


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.


Distance allowed beyond a normal stopping point in case a train fails to stop in the correct position. The distance is dependent upon speed and braking capacity of the train.


P-Wire Control

An analogue form of electro-pneumatic brake control using a single wire carrying a pulse width modulated signal. The current level on the circuit determines the rate of brake demanded. Zero current initiates an emergency brake demand. This type of control can eliminate the need for a brake pipe, a source of much trouble on trains.

Paid Area

The area of a station which can only be accessed by passengers who have paid a fare or who are in possession of a valid ticket. See also Unpaid Area.


Folding traction current collection device mounted on the roof of a vehicle on a railway employing an overhead supply system. Nowadays, pantographs are sophisticated aero-dynamically designed devices which can operate at high speeds without loss of contact and with built-in safety devices which reduce the risk of damage to wires in the event of a fault. A common problem is when a pantograph catches above the wire and pulls it down for considerable distances before it is noticed by the crew and the train stopped. Modern pantographs are fitted with automatic detection and lowering devices. The horns (curved edges) of the pantograph are equipped with frangible pneumatic sensors which, if broken by a wire support, cause the detector system to lower the pantograph.

Parking Brake

See Brakes Page

Permanent Way

Generic term for railway track, referring to the rails, sleepers (ties in US) and ballast. The term "permanent" arose to distinguish it from the temporary track laid during the construction of the railway.


A person appointed to guide a driver of a train over a line with which he is not familiar or under special circumstances where the movement of trains is restricted.

Platform Screen Doors

Doors placed along a platform edge to separate passengers from the exposed railway. Usually only used on metro systems (e.g. Singapore, Lille France, Leningrad Russia, Kobe Japan) where they are designed to match the train doorways. Their use may be justified for safety reasons or where there are extremes of climate when they can assist with reducing energy wastage. They are however, expensive at over US$1.5 million a platform edge and they add another reliability and maintenance dimension. Also known as Platform Edge Doors (PEDs)


Referred to in the US as a switch. The trackwork mechanism where a track divides into two. The rails are specially shaped to allow a smooth transition from the main track to the diverging track. Also often referred to as a turnout.

Point Locks

Mechanical devices attached to points to ensure that they remain fixed for the passage of a train through them. In many countries, they are a legal requirement where passenger trains are operated. Points are also electrically locked by their control system and by track circuits occupied by a train passing through them (detection).


When a section of track is required for maintenance and trains cannot run, it is handed over by the operators to the engineers, who take "possession". Special protective measures are used to prevent access by unauthorised trains. When the track is returned to the operators, the engineers "give up possession".

Primary Suspension

On a railway bogie, the flexible interface between the vehicle axle and the bogie frame. It can consist of steel leaf or coils springs or rubber blocks.


Longitudinal roof member of vehicle, usually fitted between the transverse members known as carlines.


A method of rescuing a failed train by using the following train or locomotive to push it to a depot or siding. Requires careful management and good training of crews if what is already a long delay is not to be made worse.

Push-Pull Train

See Train Operations - Push Pull.


Quill Drive

Traction motor drive system where the motor drives the wheel through a set of rubber bushed suspension links. The links are fitted to either end of a hollow tube (the quill) surrounding the axle. One set of links is attached to the output drive of the motor, the other to the wheel. The system reduces the unsprung mass on the axle compared with the nose suspended motor.


Radio Control (of locomotives)

Some railways employ radio control of locomotives to reduce the manning required for shunting. This allows a locomotive to be moved from the ground and assists with safety as well as reducing the time required for coupling and uncoupling. Radio control is also employed for long and heavy freight trains where locomotives are provided at the front and rear of trains to assist with power and braking. This allows a single driver in the leading cab to control all other locomotives without the need to provide control wiring throughout the train. In any case, on very long trains the voltage drop for hard wired control signals would make their use impossible. For braking, air brakes are standard. The propagation rate for a long train would be excessive using a brake pipe controlled only from the front. Radio control allows the pipe to be controlled from several points on the train and speed up operation.


Self-powered vehicle capable of operating as a single unit and often passenger carrying. Usually diesel powered and used on lightly trafficked lines.


Term to denote the operation of re-opening powered passenger doors. Depending on the system, doors can be designed to re-open in the event of obstacle detection or failing to reach to fully closed mode within a predetermined time.

Regenerative Braking

Train braking using electric motors. See the Electric Traction Pages Page. Details on train braking can be found in the Brakes Page.

Resistance Control

Method of traction motor control formerly almost universal on DC electric. For more information see the Electric Traction Pages Page.

Reversing siding

See centre siding. Also known in the US a a "pocket track".

Rheostatic braking

See dynamic braking. For more detailed information see the Electric Traction Pages Page. Details on train braking can be found in the Brakes Page.

Road Learning

The process by which train crew become familiar with a route over which they will work. Gradients, layouts of tracks at junctions and positions of stations and signals are the most important features to learn. Oh yes, and places to get refreshments.

Roof Dome

End cap of vehicle roof, where possible manufactured as a single piece.

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.

Running Rails

The two rails of a railway track upon which the wheels of the train rest and which provide the guidance for the train.


Sand Box

Receptacle on locomotive for containing the sand used for assisting adhesion.

Sand Drag

A pile of sand placed at the end of a track to absorb the energy of a train overrunning the end of the track. Sometimes the same function is performed by a hydraulic buffer or other energy absorbing device.


A method for assisting adhesion between driving wheel and rail. The sand is carried on the locomotive in a sandbox and is ejected, normally under air pressure, onto rails immediately in front of the driving wheels to assist adhesion. It is usually operated by a push button in the driving cab.

Scissors Crossover

See crossover.

Secondary Suspension

The flexible interface between the vehicle body and its bogies. Like primary suspension, it can be steel or rubber and is now, in addition, often composed of an air cushion system employing rubber bags or air bags. Originally, steel springs were used. In UK practice, they were mounted on a transverse beam known as a spring plank. Guides and shock absorbers were strategically placed to ensure stability. Such systems can still often be seen today and there are many variations on the theme.

Section Isolators

Used on an electrified railway to divide the current supply system into separate areas or sections. Electrified railways are usually supplied from feeder stations (AC traction) or sub-stations (DC traction) located at intervals along the line. Section Isolators are placed in trackside rooms at the boundaries between the feeds from two adjacent feeder stations. They are often referred to as Track Section Cabins. In addition to the track sectioning cabins, catenary isolators will be provided at strategic locations (crossovers and junctions) to facilitate maintenance and to minimise the operational impact of any catenary incident. These isolators will be either manually operated or motorised depending upon their respective safety and operational importance.

Semi Automatic Signalling

Signalling system using "track circuits" as in automatic signalling, but with the ability of manual intervention to control trains or routes. Nowadays, large areas can be controlled semi-automatically using computers to route and regulate trains as well as record movements and log manual actions. The latest techniques involve satellite location of trains.

Semi Permanent Coupling

Coupling between vehicles provided for normally fixed formation train sets like multiple unit consisting of a bar linked to the adjacent car underframes by pins. This form of coupling is usually only disconnected in a workshop.


See the Electric Traction Pages Page.

Shed Receptacle

A socket provided on an electric railway vehicle where a shore supply lead can be inserted to provide power when the normal traction supply is not available. Usually used in sheds and workshops.


Term used as a shortened version of "collector shoe" to denote a third rail current collection device mounted on the bogie of a direct current electric train. Shoes are normally distributed along the train and connected by a power train line cable to avoid loss of power at gaps in the current rail. See also conductor rail and gapping.

Shore Supply

A power supply provided in a workshop or yard for vehicles which are disconnected from their normal traction or auxiliary supply. Special sockets or receptacles are provided on many railway vehicles for connecting shore supplies. Sometimes referred to as shed supplies. See also knife switch.

Short Circuiting Device

A hand tool for preventing traction current from being switched on to a DC electrified line. Applies only to third rail systems. Generally mounted on trains and stations for use in emergency, they are not supposed to be used for discharging current, only for preventing recharge. A shorting tool is also used to earth overhead line by connecting the contact wire to the track rail in the section where it has been isolated.


To marshal vehicles in a given order to form a train. A rough shunt can cause damage to vehicle couplings or even bodies. The risks of damage are high as often this is carried out without adequate attention being paid to coupling of brake pipes. Thus one locomotive may be moving several vehicles without brakes.


In railway terminology, a shuttle usually means a service operating back and forth between two stations without an intermediate stop. The Channel Tunnel service is called Le Shuttle and many cities operate shuttle services between airports and city centres. The Gatwick Express, which operates in the UK between Gatwick Airport and London (Victoria) is one such. Sometimes also erroneously used to refer to short distance, regular interval services with intermediate stops.

Side Chains

Chains provided at vehicle ends on some railways for emergency coupling purposes in case the standard coupling breaks.

Side Sill

US term, see solebar.


Visual indication passed to a train driver to advise the speed, direction or route of the train. There are almost as many types of signals as there are railways but they fall into the following main categories:

  • handsignals - used mainly where there are no fixed signals or where the fixed signalling has failed. Generally, each railway has its own defined handsignals recognised by its operators. 
  • semaphore signals - a fixed lineside signal where the stop indication is displayed as a horizontally positioned arm and proceed as a 45º or vertical arm. 
  • colour light signal - a fixed lineside signal showing light indications to drivers. 
  • cab signals - where the indications are displayed in the driver's cab. 


UK term for person employed to operate or supervise the control of signals. Traditionally housed in a signal box, more recently a control room, where the signalling levers or controls are located. Politically correct grade now identified as "Signaller" by Network Rail. Not to be confused with the same term used in the US for a signal maintenance person.

Slab Track

A form of railway track comprising a concrete base to which the chairs carrying the rails are secured. It eliminates the need for individual "sleepers" (q.v.).


In the US known as "ties", short for "crossties". The transverse members of trackwork, made of wood, concrete or sometimes steel, which are used to secure the rails at the correct gauge. Cast steel chairs fixed to the sleepers hold the rails in place by means of clips or keys.


Main longitudinal structural member of vehicle underframe which forms the extreme edges of the frame. Also known in the US as a "side sill".

Spring buckle

A retaining clip which wraps round the leaves of a laminated vehicle spring at the centre point.

Spring Hanger

Means by which a laminated vehicle spring is attached to the bogie frame.

Spring Plank

Transverse member in traditional UK bogie design, which was suspended from the bogie side frames and carried the secondary springs supporting the vehicle, body.

Spring Points

Trailing points, which are spring-loaded to force the point blades to the original position after a wheelset, has passed through them.


The act of taking a train out of service and parking it in a siding without a crew.

Static Load Test Bed

A locomotive test facility provided to see if the performance requirements of a design are met. Called a "load tank" in the US.

Step Iron

See foot iron

Stepping Back

See the article on Crews, Stepping Back.


US term for a shore supply lead used to provide power to electric trains inside workshops.

Straight Air Brake

A simple compressed air brake fitted to locomotives for use on the locomotive only. For details, see the article in the Brakes Page.

Swing Links

Parts of the secondary suspension system which attach the spring plank to the bogie side frames and which allow the plank some dynamic movement. 

Synchronous Motor

See the Electric Traction Pages Page.



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. 

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. See conductor rail 


See the Electric Traction Pages Page. 

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. 

Track Gauge

The distance between the inner faces of the rail heads of a railway track, commonly referred to as "the gauge". 

Track Section Cabins

See Section Isolators.

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. See also Master Controller 

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. 

Traction Link

A means of transmitting power from the bogie to the body of a locomotive. The traction link usually consists of a steel bar attached at one end to the bogie frame and at the other end to the underframe of the locomotive. Both ends are fitted with rubber damping to reduce transmission of vibration. The purpose of the bar is to remove the stress of traction forces from the central pivot of the bogie and to reduce weight transfer. Traction links are relatively new on locomotives, having appeared over the last fifteen years or so. Prior to this, power transmission was through a central pivot in the bogie. 

Traction Motor

Electric motor used to provide the final drive to a locomotive or train axle. Used in diesel-electric and electric systems. The traction motor is mounted close to the axle and transmits power through a reduction gearbox. See the Electric Traction Pages Page. 

Tractive Effort

The power that a locomotive is able to exert before the wheels slip out of control. It is calculated by multiplying the weight on the driving axles by the coefficient of adhesion. 

Trailer Car

A passenger vehicle in a multiple unit train which has no traction power equipment. Sometimes referred to as a trailer. 


Description of non-powered axles or vehicles in a train as in trailer car. Also used to describe points at a converging junction. 

Train Line

In UK parlance, a cable running the length of a train for control or power purposes. It is connected between vehicles by a jumper. The term train line is sometimes used in the US to denote the brake pipe - see Brakes Page. 


Transverse bogie frame member fixed between the side frames to give strength. 

Tread Brake

See Brakes Page


The name given to the inward curve of the body profile which often occurs at the lower bodyside level. In this design the bodyside is flat until it begins to curve in towards the floor or solebar level. 

Turnback Track

A US term for a reversing track or centre siding. 


Trackwork where a single track splits to become two tracks and equipped with moving rails to change the route. Also referred to as points in the UK and a switch in the US. See also points.



Union Internationale de Chemin de Fer - International Union of Railways - the French dominated European railway regulating body which sets engineering and operating standards for railways. Equivalent to US AAR. 

Ultrasonic Flaw Detection

A system for examining the condition of rails to determine the integrity of the steel. The data is collected by an electronic instrument run along the track   Also used to detect flaws in railway axles. 


Railway vehicle base which forms the support for the body structure or is an integral part of a body shell. 


UK expression usually meaning an electric or diesel multiple unit train. 

A unit can consist of two or more cars (e.g. a 3-car unit) and a train may consist of one or more units. 

Unpaid area

The area of a station which can be freely accessed by the public and which is separated from the paid area by ticket checks or faregates. 

Up Line

In UK terminology, the track normally used by trains proceeding towards the main terminus. The line used by trains proceeding away from the terminus is normally called the Down Line. The terminology is believed to originate from the early railways in the north east of England which connected mines to coastal ports. Trains ran "down" to the coast or "up" to the mine.


Vacuum Brake

See the Brakes Page. 

Vigilance Device

See deadman


Variable Voltage Variable Frequency traction drive system. Used where 3-phase AC motors are provided on rolling stock. For more information see the Electric Traction Pages Page.


Waist Rail

Longitudinal vehicle body structural member at mid height between floor and cant rail. This is normally the level at which any upper body tapering of the bodyline begins. 

Weight transfer

When a locomotive (or other powered vehicle) begins motoring or braking, the distribution of weight on the axles changes due to the shift in the body weight. This can give rise to wheels slipping or sliding. Modern systems of motor and brake control can reduce the risk but never eliminate it entirely. See also Creep Control and Traction Link. 

Westinghouse Brake

Widely used automatic air brake invented in the 1870s by George Westinghouse and developed worldwide. Was the basis upon which the various Westinghouse corporations and WABCO companies were founded. See the Brakes Page for more details. 

Wheel Truing Machine

Machine for reprofiling rolling stock wheels. The surfaces of wheels become worn over time varying between months and years depending on the usage and design. Reprofiling is required to ensure that the ride of the vehicle continues to be acceptable both from a safety and comfort point of view. If wheel flanges become too sharp, they can force point blades apart and cause a derailment. Some machines are designed to permit reprofiling without removing the wheels from the vehicle. The lathe is mounted in the floor of the workshop and the vehicle positioned over it for work to be carried out. The axle end design has to be arranged to allow the wheelset to be turned by the lathe. Wheels can be re-profiled by cutting or by milling. Cutting seems to be the preferred method for most administrations. 


A fixed formation of an axle with two wheels set at the correct gauge for the track. The wheels are pressed onto the axle and rotate with it as a unit. It is mounted into the bogie (or vehicle) frame with axleboxes.

Wheel Slide

Synonymous with skidding and usually caused by over braking during poor adhesive conditions. It is a common cause of wheel damage, as it produces a flat spot (called a "flat") on the wheel where the skid occurred. Severe flats have been known to derail a train. Modern rolling stock is equipped with various systems to assist with the elimination of wheel slide. These include load control, automatic brake "dumping" if a slide is detected, cosmetic rail applications like Sandite to improve adhesion and attention to maintenance of correct mechanical brake settings. See also the Brakes Page.

Wheel Slip

Phenomenon caused on a locomotive or power vehicle by over application of power to the drive system relative to the available adhesion. It can cause damage to electric motors and is normally automatically detected to immediately eliminate or reduce the power being applied.  A modern system recently developed using microprocessors is known as creep control and permits a certain degree of slip as this has been proven to improve acceleration efficiency. 

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