Rail transport terms are a form of technical terminology applied to railways. Although many terms are uniform across different nations and companies, they are by no means universal, with differences often originating from parallel development of rail transport systems in different parts of the world, and in the national origins of the engineers and managers who built the inaugural rail infrastructure. An example is the term railroad, used (but not exclusively) in North America, and railway, generally used in English-speaking countries outside North America and by the International Union of Railways. In English-speaking countries outside the United Kingdom, a mixture of US and UK terms may exist. Various terms, both global and specific to individual countries, are listed here. The abbreviation "UIC" refers to terminology adopted by the International Union of Railways in its official publications and thesaurus. For more elaborate country-specific guides, see Glossary of United Kingdom railway terms and Glossary of North American railroading.
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A
Acorn. A general term used to finish the ends of rods of various forms.
Adhesion railway The most common type of railway, where power is applied by driving some or all of the wheels of the locomotive.
Adhesive weight The weight on the driving wheels of a locomotive, which determines the frictional grip between wheels and rail, and hence the drawbar pull a locomotive can exert
Adjusting spring A heavy spiral spring or nest of springs used for controlling the side motion of a two-wheel radial trailing truck.
Adjusting spring case Also Centering spring cylinder. A cylindrical cast-iron holder in which an adjusting string is placed.
Adjusting spring seat A casting, or a part of the bolster of a two-wheel trailing truck, forming a bearing for the end of the adjusting spring.
Admission The opening of steam port to admit steam to one end of a cylinder. If the valve has no lead, admission takes place at the moment the piston of its stroke and just as it is to begin the return stroke.
Air brake Also Railway air brake. Any brake operated by air pressure, but usually restricted to systems of continuous brakes operated by compressed air, in distinction from Vacuum Brakes, which are operated by creating a vacuum. The air is compressed by some form of steam pump on the locomotive, or a motor-compressor on electric locomotives, and is conveyed by pipes and flexible hose between the engine, tender and cars to cylinders and pistons under the tender and each car, by which the pressure is transmitted to the brake levers, and thence to the brake shoes. This system is what is now termed the straight-air brake. This brake is now obsolete in steam road practice, having been replaced by the Automatic Air Brake.
Air brake hose Flexible tubes made of alternate layers of rubber and canvas by which the brake pipes under engines, tenders, and cars are connected together, and compressed air, which operates the brakes, conducted through the train. The hose is made with a coupling at each end of the engine and tender so that it can readily be connected or disconnected. Also called air hose and brake hose.
Air cylinder (air pump) A cylinder forming part of the air brake pump and having its piston fastened to the same rod to which the piston of the steam cylinder is fastened. It is furnished with air inlet and discharge valves at each end, communicating respectively with the air inlet and the discharge pipe.
Air cylinder bracket A projecting piece of metal bolted to the frame of a locomotive or tender, to which the brake cylinder is attached. See Truck Brake, Tender Brake.
Air cylinder gasket See Gasket.
Air cylinder oil cup (air pump) A small brass receptacle with a stopcock or faucet, screwed to the air cylinder of an air pump, to hold a supply of lubricant for the air cylinder. See Automatic Air Cylinder Oil Cup.
Air drum Also Main Reservoir and Reservoir. A cylindrical reservoir, made of sheet steel, into which air is pumped and stored for use in the air brake system and train air signal line. Sometimes placed under the cab deck or between the frames in front of the guide yoke; but now two are commonly used, placed under the running board near the cab, one on each side of the engine.
Air drum hanger An iron strap riveted to the lower side of the running board, or to the boiler, to support the air drum.
Air drum head The end of the air drum, to which the cylindrical body is riveted or welded.
Air drum saddle A strip of iron fastened to the locomotive frame for supporting the air drum or drums when the drums are placed between the cylinder saddles and the guide yoke.
Air gauge (air brake) A gauge to register the pressure of air in the reservoirs, brake pipe, or brake cylinders, similar to an ordinary steam pressure gauge. They are made either with a single pointer or with two pointers, to indicate on one dial both the reservoir pressure and the brake pipe pressure. The latter type is called a duplex gauge.
Air gage fitting A pipe connection by means of which an air gauge is connected to an engineer's brake valve in a locomotive cab.
Air gauge stand A bracket or support to hold an air gauge.
Alerter or watchdog Similar to the dead man's switch other than it does not require the operator's constant interaction. Instead, an alarm is sounded at a preset interval in which the operator must respond by pressing a button to reset the alarm and timer if no other controls are operated. If the operator does not respond within a preset time, the prime mover is automatically throttled back to idle and the brakes are automatically applied.
All-weather adhesion The adhesion available during traction mode with 99% reliability in all weather conditions
Alternator An electrical generator that converts mechanical energy to electrical energy in the form of alternating current
American Locomotive Company (Alco) The second largest builder of steam locomotives in the United States
American type A steam locomotive with a 4-4-0 wheel arrangement.
Angle cock A valve affixed to each end of a piece of rolling stock that, when opened, admits compressed air to the brake pipe (or vents it to the atmosphere if air hose is detached)
Annett's key A large key which locks levers or other items of signalling apparatus, thereby serving as a portable form of interlocking
Articulated locomotive A steam locomotive with one or more engine units that can move relative to the main frame
Articulated vehicles (articulation) The sharing of one truck by adjacent ends of two rail vehicles.
Ashpan A feature of a locomotive with the same form and purpose as the domestic variety (i.e. to collect the ashes that fall through the bars of the grate). The only significant difference is the size, measured in feet rather than inches.
Asynchronous motor An alternating current electric motor whose speed varies with load and has no fixed relation to the frequency of the supply.
Atlantic type
A steam locomotive with a 4-4-2 wheel arrangement.
Automatic block signaling (ABS) A system that consists of a series of signals that divide a railway line into a series of blocks and then functions to control the movement of trains between them through automatic signals.
Automatic train control (ATC) A system that applies an emergency brake if the driver does not react to certain signals or speed restrictions
Automatic train operation (ATO) A technology for automation of trains.
Automatic train protection (ATP) A system that enforces obedience to signals and speed restrictions by speed supervision, including automatic stop at signals
GWR Autotrain A branch-line train consisting of a steam locomotive and passenger carriages that can be driven from either end by means of rodding to the regulator and an additional vacuum brake valve. The fireman remains with the locomotive and, when the driver is at the other end, the fireman controls the cut off and vacuum ejectors in addition to his usual duties. See also: Push–pull train.
Axlebox The housing that holds the axle bearings on a rail vehicle The housing that attaches to the end of the axle to the bogie and contains the bearing on which the axle rotates See also journal box below.
B
Backhead The cab-side rear panel of a steam locomotive boiler through which the firebox is accessed.
Bad order A tag or note applied to a defective piece of equipment. Generally, equipment tagged as bad order must not be used until repaired, inspected, and approved for use.
Bail off To release the locomotive brakes while the train brakes are applied, to permit smoother handling and prevent excessive slack, wheel slide and flat wheels.
Balancing The reciprocation and revolving masses of any steam, diesel or electric locomotive need balancing, if it is to work smoothly. Revolving masses can easily be balanced by counterweights, but the balancing of reciprocating parts is a matter of compromise and judgement.
Balise A transponder that is used as an intermittent data point in an automatic train protection (ATP) system or as reference point for train location in radio-based train control
Ballast Aggregate stone, gravel, or cinders forming the track bed on which sleepers (ties) and track are laid to ensure stability and proper drainage
Ballast tamper See Tamping machine.
Balloon A looped length of track, usually at the end of a spur or branch, which trains use to turn around for the return trip without reversing or shunting. Can be used as part of a freight installation to allow the loading or unloading of bulk materials without the need to stop the train (see merry-go-round train (MGR)).
Bay platform A platform and track arrangement where the train pulls into a siding, or dead-end, when serving the platform.
Bellmouth A widening of an underground rail tunnel, in preparation for future connection or expansion of service. Used particularly in subway nomenclature.
Berkshire type A steam locomotive with a 2-8-4 wheel arrangement.
Bilevel rail car A type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.
Blastpipe A part of a steam locomotive that discharges exhaust steam from the cylinders into the smokebox beneath the chimney to increase draught through the fire.
Block section A section of track in a fixed block system that a train may only enter when it is not occupied by other vehicles.
Bo-Bo (Europe) A locomotive with a four-wheel, two wheels per truck configuration, each individually powered, as opposed to a six-wheel "Co-Co" configuration.
Bogie A swivel-mounted wheel assembly; known as a Truck in North America.
Boiler A cylindrical container adjacent to the firebox in which steam is produced to drive a steam locomotive.
Bolster A transverse floating beam member of a truck suspension system supporting the weight of a vehicle body.
Boom barrier
A pivoted road barrier at a level crossing
Booster engine An extra set of cylinders that can be engaged on a steam locomotive to drive a trailing truck or tender truck to give additional tractive effort at starting and low speeds
Brakeman's cabin or brakeman's cab A small hut at one end of a railway wagon to protect the brakeman from the elements.
Brake pipe The main air pipe of a train's air brake system
Branch line A secondary railway line that splits off from a main line
Brick arch A brick or concrete baffle provided at the front of a locomotive firebox below the tubes to extend the flame path. Early locomotives burned coke; provision of a brick arch was necessary before coal could be used without producing excessive smoke.
British Rail Universal Trolley Equipment (BRUTE) A type of platform trolley found on stations all over the UK rail network from the late 1960s to the early 1980s.
Broad gauge Track where the rails are spaced farther apart than standard gauge, or 1,435 mm (4 ft 8+1⁄2 in)
Bubble car A nickname for a British Rail Class 121 railcar
Buckeye coupler A side-operated version of the top- or bottom-operated Janney coupler
Buffer A device that cushions the ends of rail vehicles against each other.
Buffer stop or bumper post The barrier installed at the end of a dead-end track to prevent rail vehicles from proceeding further.
Builder's plate The nameplate fitted by their manufacturer to locomotives and items of rolling stock.
Bulkhead flatcar An open-top flatcar with a wall at each end.
Bungalow The housing for signals and communications computers that control switches, crossings, and other such controls, relaying information to and from the rail traffic control (RTC)
Bustitution A blend of the words "bus" and "substitution", the practice of replacing a train service with one provided by buses, whether as a temporary or a permanent measure.
C
Cab The control room of a locomotive housing the engine crew and the controls
Cab forward A steam locomotive with its cab at the leading end of the boiler, rather than the usual trailing end adjacent to the tender. The best known example is the Southern Pacific Railroad's AC type, built to handle drag freights through the SP's many tunnels and snow sheds without the danger of the exhaust asphyxiating the engine crew.
Cabless A locomotive without a cab. Commonly referred to as a B unit or a Slug, although not all Slugs are cabless.
Caboose
In North America, a railroad car attached usually to the end of a train, in which railroad workers could ride and monitor track and rolling stock conditions. Largely obsolete, having been replaced by the electronic end-of-train device (ETD), or flashing rear-end device (FRED).
Cant The angle of an individual rail relative to vertical (e.g. around curves).
Carbody unit A locomotive that derives structural strength from a bridge-truss design framework in the sides and roof, which cover the full width of the locomotive.
Catenary
The overhead wire system used to send electricity to an electric locomotive or multiple unit, tram or light rail vehicle
Centerbeam A bulkhead flatcar with a braced beam bisecting its length, used to transport lumber products
Challenger type
A steam locomotive with a 4-6-6-4 wheel arrangement.
Chord A section of subsidiary track that interconnects two primary tracks that cross at separated grades, to permit traffic to flow between them.
Co-Co locomotive (EU) A heavier duty locomotive with six wheels, three wheels per truck (all axles being separately driven) configuration as opposed to a four-wheel "Bo-Bo" configuration. The correct classification is Co'Co', but Co-Co is used more often.
Coal pusher A steam-operated device in the tender intended to push coal forward to a point where it can be shovelled directly into the fire.
Colour light signal A signal in which the colour of the light determines the signal meaning.
Colour position signal A signal that uses both colour and light position to indicate meaning.
Combined power handle A handle or lever that controls both the throttle and dynamic braking on the locomotive: on a desktop-type control stand, forward (away from operator) past center operates the dynamic brake, backward (toward operator) past center, is throttle up.
Compound locomotive A steam locomotive passing steam through two sets of cylinders. One set uses high pressure steam, then passes the low pressure exhausted steam to the second.
Configurable System Capability of the system to allow users to select, from pre-programmed functions (modular software units), those functions necessary to accomplish a control strategy or other complex function, without the use of computer language.
Consist Single vehicle or a group of vehicles that are not separated during normal operation.
Consolidation type
A steam locomotive with a 2-8-0 wheel arrangement.
Container on flat car (COFC) The loading of a shipping container onto a simple flat car.
Continuous welded rail (CWR) A form of track made from rails welded together by a thermite reaction or flash butt welding to form one continuous rail that may be several kilometres long.
Control car A passenger coach with a full set of train controls at one end, allowing for the use of push–pull train operation.
Control System The microprocessor based control and fault diagnostic system has been developed for conventional electric locomotives including locos provided with static converter. It performs logical control of the locomotive by continuously monitoring various digital/ analog inputs and checks for any abnormality in the operation.
Coupler pulling faces, length over Effective length of piece of rolling stock
Coupling rods Rods between crank pins on the wheels, transferring power from a driving axle to a driven axle of a locomotive.
Covered goods wagon (UIC) A type of rolling stock with a flat bottom enclosed on all sides and top, which is loaded and unloaded from sliding doors on each side.
Cow–calf or cow and calf A diesel locomotive with a crew cab permanently coupled to and acting as a controller for a similar slave diesel locomotive without a crew cab, primarily used for switching or shunting duties for large groups of rolling stock. Also known as master and slave.
Crank pin A pin protruding from a wheel into a main or coupling rod.
Crosshead In a steam locomotive, the moving member of a sliding guide that absorbs upward and downward forces from the connecting (main) rod, which otherwise would tend to bend the piston rod.
Cut To uncouple one or more cars from a train (i.e. to "make a cut"). Same as "cutting"
Cut lever A manual lever that releases the pin of an automatic coupler when pulled to separate cars or locomotives.
Cut off Also see Reverser handle. A variable device on steam locomotives that closes the steam valve to the steam cylinder before the end of the piston stroke, thus conserving steam while letting steam in the cylinder expand under its own energy.
Cutting A channel dug through a hillside to enable rail track to maintain a shallow gradient. See also embankment.
Cycle braking Making repeated service brake reductions in short succession to maintain a constant speed on short but steep grades. With the brake systems commonly used on North American freight railroads, each reduction must be at least 5 PSI lower than the previous one to keep the brakes applying regularly, but excessive cycle braking can deplete the air supply and require an emergency application. Also referred to as "fanning the brakes" in North America.
Cylinder A cavity in a reciprocating engine in which a piston travels.
Cylinder cock On steam locomotives, crews use this appurtenance to drain water from the steam cylinders when the throttle is open, thus preventing damage to the pistons, running gear, and cylinder heads.
D
Dark signal A block signal that is displaying no discernible aspect, often due to burned out lamps or local power failure. Most railroads require that a dark signal be treated as displaying its most restrictive aspect (e.g. stop and stay for an absolute signal).
Dark territory A section of track without block signals.
Dead-end rail A railway ending in a locality (terminus) with no other rail services. Typically includes buffer stops at the end of the tracks. The opposite of rail crossing
Dead man's handle A safety mechanism on a train controller that automatically applies the brake if the driver releases the handle. It is intended to stop a train if the driver is incapacitated. In some forms, this device may be pedal-actuated. See also Dead-man's vigilance device.
Decapod type
A steam locomotive with a 2-10-0 wheel arrangement.
Defect detector A track side device used to detect various defects such as hotboxes (overheated axle bearings), dragging equipment, leaning cars, overloaded cars, overheight cars, seized (locked) wheels, etc.
Degraded Operation Operation resulting from an unplanned event that prevents the normal delivery of train services.
Demurrage A monetary charge levied by a railroad to a customer for excessive delay in loading or unloading cars.
Derail or derailer A safety device that derails vehicles that pass it, typically to prevent rolling stock from accidentally entering the mainline from a siding.
Detonator
A small explosive charge placed on the running rail, which detonates loudly when run over to warn drivers in following trains of an incident ahead. Known as a torpedo in the United States.
Diamond
Track that lets a rail line cross another at grade
Diesel multiple unit (DMU)
A set of diesel-powered self-propelling passenger rail vehicles able to operate in multiple with other such sets. Such units, especially those consisting of a single vehicle, are sometimes termed railcars.
Direct traffic control (DTC) A system in which train dispatchers communicate directly with train crews via radio to authorize track occupancy in predefined blocks.
Distributed power A practice originally used to move large trains through the mountains. Now commonly used to facilitate longer, heavier trains in all types of terrain. Consists of the locomotives on the head end, a "swing" (mid-train) helper or two, and pusher locomotive(s) on the rear; today, all units are remotely controlled by the engineer in the lead unit. The remote locomotives are referred to as Distributed Power Units (DPUs). The power distribution alleviates stress on the couplers and relieves the lead units of the full weight of the train, making it easier to move on grades.
Ditch lights
A pair of lights, usually found on modern locomotives, located some distance below and outboard of the main headlight. They may also flash alternately when a locomotive sounds its horn.
Division In North America, the trackage area under the jurisdiction of a railway superintendent.
Dog or dogspike (India) A spike with a slightly altered head shape for easier extraction when the spike has become too loose in the sleeper.
Doodlebug A self-powered gasoline–electric passenger car used for small-capacity rural commuter service. Also a British Rail Class 153 DMU.
Double If a train has insufficient power to climb a grade and no helpers are available, the crew splits the train into two sections and runs them separately to the top.
Double heading A configuration in which two locomotives are coupled head-to-tail so they can haul a heavy train up a long or steep hill. Currently, double heading (and occasionally triple heading) are used primarily by large passenger trains or as a show for railfans.
Drag A long, heavy freight train moving at low speed.
Dragging equipment detector See Defect detector.
Drawbar The part of a coupler that attaches to the frame of the car or locomotive; may be equipped with a pneumatic cushion depending on a freight car's design cargo (e.g. an autorack). Alternately, the pinned double bars coupling a steam locomotive to its tender.
Driver or engine driver The operator of a locomotive.
Driver only operation (DO or DOO) Operation of a train by the engineer or driver only. Also known as one person train operation (OPTO)
Driver A wheel in contact with the rail that also propels a locomotive
Dual control stand the practice of having two control stands (a "control stand" is a diesel locomotive subsystem which integrates all engine and brake functional controls within the operational radius of the locomotive engineer's left forearm from his/her customary seating position, facing forward at all times) in the cab of a hood unit locomotive, one on either side facing opposite directions to allow operation either long hood or short hood forward at all times.
Dwarf signal A signal light that is considerably smaller and closer to the ground than a high-mast signal; often absolute, and placed within interlocking limits, its aspects tend to differ from those conveyed by a taller signal for certain indications. Also called 'pot' or 'jack'.
Dwell time The time a train spends at a scheduled stop without moving. Typically, this time is spent boarding or deboarding passengers, but it may also be spent waiting for traffic ahead to clear, or idling time in order to get back on schedule.
Dynamic braking The use of a traction motors' output, working as generators, to retard train speed without relying solely on the air brakes.
E
Ejector A component of vacuum brake system usually fitted in pairs. Steam passing through a cone sucks air from the train pipe to create the vacuum. A small ejector running continuously to overcome leaks and to restore the vacuum after light braking and a large ejector operated when needed to release the brakes quickly after a heavy application or to create the initial vacuum after coupling
Electric multiple unit (EMU) A set of electrically powered self-propelling passenger rail vehicles able to operate in multiple with other such sets.
Electro-Motive Diesel (EMD) The world's second largest builder of railroad locomotives. EMD was previously Electro-Motive Division of General Motors before being sold.
Elevated railway, el, or L A railway built on supports over city streets.
Embankment A bank, usually of earth but sometimes of stone, constructed to form a level or minimally graded trackbed for a line of railway needing to pass over a depression in the terrain or other pre-existing surface feature. See also cutting.
Empty coaching stock (ECS) A train used to bring carriages into (or out of) service. They usually run between sidings and main stations, with the carriages then forming a service train to another destination. They are often worked under freight train rules (e.g. without needing a guard in the UK).
Emergency release A device accessible under certain conditions that permits the operation of an apparatus in case of failure.
End-cab switcher A switching locomotive with no short hood, thus having its cab forming one end of its car body.
Engineer In North America, the operator of a locomotive.
Equalizing reservoir A small air reservoir in a locomotive control stand. When the automatic brake valve is operated, this reservoir responds by reducing or increasing the air pressure in the brake pipe.
Event recorder A device that continuously captures analog and digital train systems information and stores that data for a minimum of 48 hours. This data is used to evaluate incidents and accidents. Typical stored data includes speed, brake pressure, dynamic brake, horn activation, track signal, etc. In the U.S., event recorders are mandated by the Federal Railroad Administration (FRA) for freight, passenger and commuter rail. Regulations for railroads outside the U.S. vary by country. Transit operations are not generally required to have event recorders, but have begun to add them voluntarily.
Express train A train that passes selected stations without stopping.
Extra A train not included in the normal schedule of a railroad. They often run during busy holiday travel periods in order to handle larger crowds and reduce the number of passengers waiting or stranded at a station. In train order territory, extras are required to clear the main line for scheduled trains to pass.
F
Facing A turnout that can select which way to diverge a train—the opposite of trailing.
Fairlie A type of articulated locomotive, typically (but not exclusively) with two boilers and connected fireboxes in a central cab.
Fall plate A heavy, hinged steel plate attached in a horizontal position to the rear of the locomotive footplate or front of a locomotive tender. When the tender is attached to its locomotive the plate is allowed to fall to cover the gap in the "floor" between the two units. The sliding edge is not fixed and has a smooth chamfer so as to avoid a trip hazard.
Fallen flag An abandoned or bankrupt railroad or one absorbed by another company that loses its historic name.
Feedwater heater A device to preheat the water for a steam locomotive to improve efficiency.
Feed valve or regulating valve A valve that controls the amount of air pressure channelled from the locomotive's main reservoir to the brake pipe, in accordance with the set pressure in the equalizing reservoir.
Fiddle yard In railway modelling, a concealed group of sidings used to provide more realistic operation in a limited space.
Firebox In steam locomotives, a chamber in which a fire produces sufficient heat to create steam once the hot gases created there are carried into the adjacent boiler via tubes or flues.
Fireman, stoker, or boilerman A worker whose primary job is to shovel coal into the firebox and ensure that the boiler maintains sufficient steam pressure.
Flat A wheel defect where the tread of a wheel has a flat spot and is no longer round; flats can be heard as regular clicking or banging noises when the wheel passes by. This is caused either by a locked bearing, or a brake that was not fully released before the car was moved, dragging the wheel without turning.
Flying junction or flyover A railway junction that has a track configuration in which merging or crossing railroad lines provide track connections with each other without requiring trains to cross in front of opposing traffic on the same level
Fouling point A point of a switch turnout where a car or locomotive on one track obstructs movements on the adjacent track.
Four-quadrant gate
A type of boom barrier
Free-mo A type of modular layout in model railroading.
Freight wagon (UIC) A rail vehicle designed for the carriage of freight.
Full service reduction The maximum air pressure that can be exerted against brake pistons in a normal brake application. To increase pressure beyond this point, the brakes must be placed in emergency. Fusee A pyrotechnic device similar to an automotive flare that is used in signalling.
Fusible plug A threaded plug, with a soft metal core, that is screwed into the crown plate of a firebox. If the water level gets too low the core melts and the noise of the escaping steam warns the enginemen.
G
Garratt locomotive
A type of steam locomotive that is articulated into three parts
Gauge The width between the inner faces of the rails.
Geep
Any of the GP ("general-purpose") series of Electro-Motive four-axle diesel locomotives; originally applied only to EMD GP7, GP9, and GP18 models
Generator field The control switch of a diesel–electric locomotive that opens or closes the circuit between the main generator and the traction motors.
Get a knuckle To break a train in two, usually by shearing the knuckle pin in a coupler, often caused by the application of excessive head end power at startup.
GEVO A nickname for General Electric's Evolution series of modern diesel locomotives.
Gladhand connector A quick coupling and uncoupling connector at the end of a trainline air hose that resembles a pair of shaking hands when hoses are connected.
Go-devil A hand-powered railroad car (see Handcar and Draisine), or a small gasoline powered railroad car.
Grab bar or Grab iron A handle on the side of a car to allow switching personnel to hold on.
H Harmonic rock or harmonic rock and roll The condition of locomotives and cars swaying in opposite directions when traversing depressions on the roadbed. A potentially dangerous condition that can cause coupler damage, lading damage, or derailments at slower speeds. Head-End Power A scheme whereby the locomotive engine or a separate generator provides hotel power to carriages Headboard A sign attached to a locomotive to identify a named train or charter, or for other special occasions Headstock A transverse structural member located at the extreme end of a rail vehicle's underframe. The headstock supports the coupling at that end of the vehicle, and may also support buffers, in which case it may also be known as a "buffer beam". Heavy haul Heavy freight operations High rail The upper rail in a curve or superelevation, which typically experiences higher lateral loads and greater wear Hole A passing siding. Inferior trains "lay over in the hole" to let superior ones pass. Home signal See absolute signal. Horn blocks Plates lining the axlebox cut-outs in a locomotive frame to allow smooth vertical movement under control of the springs Hostling The action of shuttling a locomotive from the yard to the engine house or vice versa Hotbox An axle bearing that has become excessively hot due to friction Hotbox detector A device attached to the track that monitors passing trains for hot axles, and reports results via radio transmission (typical in the US) or a circuit to the signal box (typical in the UK). See defect detector. Hudson type A steam locomotive with a 4-6-4 wheel arrangement Hump A raised section in a rail sorting yard that allows operators to use gravity to move freight railcars into the proper position within the yard when making up trains of cars. This is faster and requires less effort than moving cars with a switching engine. Hunting Swaying motion of a railway vehicle or bogie caused by the coning action on which the directional stability of an adhesion railway depends. The truck or bogie wanders from side to side between the rails, "hunting" for the optimum location based on the forces at play.
I Independent brake or locomotive brake The braking system that applies or releases the brakes of a locomotive independently from its train Infill station or in-fill station A train station built on an existing passenger line to address demand in a location between existing stations Injector A device to force water into a steam locomotive's boiler by steam pressure Insulated rail joint (IRJ) or insulated block joint (IBJ) Rail joints incorporating insulation to isolate individual track circuits Interchange Any track or yard where rail cars are transferred from one carrier to another Interlocking An arrangement of switches and signals interconnected in a way that each movement follows the other in a proper and safe sequence Intermodal freight transport Moving goods by more than one type of vehicle, often achieved using shipping containers that are transferred among railroad flatcars, ships, airplanes, and tractor-trailer trucks Intermodal passenger transport Moving people by more than one type of vehicle Interoperability Ability of a transport network to operate trains and infrastructures to provide, accept and use services so exchanged without any substantial change in functionality or performance Island platform A railway platform that has tracks along the full lengths of both sides Island railway station A railway station with a station building on an island platform
J
Jacobs Bogie A Bogie, or truck (American), shared between two pieces of rolling stock. Cars joined with Jacobs bogies are semi-permanently joined in an articulated configuration. A weight-saving feature used on lightweight passenger trains. Joint bar or rail joiner A metal plate that joins the ends of rails in jointed track Jointed track Track in which the rails are laid in lengths of around 20 m and bolted to each other end-to-end by means of fishplates or joint bars Journal bearing A bearing without rolling elements; a plain bearing Journal box The housing of a journal bearing. See also Axlebox above. Jubilee type A steam locomotive with a 4-4-4 wheel arrangement Junction A point at which two lines or separate routes diverge from each other
K Keeper A padlock or hook securing the lever of a hand-operated switch, thereby preventing the switch points from moving as rolling stock passes over them Kick To shove a car a short distance and uncouple it in motion, allowing it to roll free under gravity and/or its own inertia onto a track. Commonly practiced in bowl or hump yards to make up or break down trains or classify large numbers of cars in an expedient fashion. Differs from a flying switch in that the locomotive is pushing the car rather than pulling it when the cut is made. Kicker A freight car with a defect in its brake valve that causes the entire train's brake system to go into emergency when any application is made Kinematic envelope (KE) The outline of the space beside and above the track that must be kept clear of obstructions for the train to pass. This can be larger than the static clearance around an unmoving engine or car. See also: loading gauge and structure gauge Knuckle The articulating part of a coupler that locks automatically in its closed position to join rail cars; so named because its movement resembles that of the human finger
L Lead track A non-main track from which several others branch within a short distance, such as within a rail yard or engine terminal Level crossing (LC), railroad crossing, railway crossing, train crossing, or grade crossing A crossing on one level ("at-grade intersection")—without recourse to a bridge or tunnel—generally of a railway line by a road or path. Not to be confused with non-dead-end railways (see Rail crossing) Light engine A locomotive travelling on its own, or perhaps with just a caboose (brake van) attached Light rail A city-based rail system based on tram design standards that operates mostly in private rights-of-way separated from other traffic but sometimes, if necessary, mixed with other traffic in city streets. Light rail vehicles (LRVs) generally have a top speed of around 55 mph (89 km/h) though mostly operating at much lower speeds, more akin to road vehicles. Link and pin An obsolete method of coupling rail cars, consisting of manually dropping the coupling pin into the drawbar as the cars joined. Extremely hazardous to the brakemen of its day, it was outlawed in the United States by the Railroad Safety Appliance Act of 1893. Local train A train that stops at most, if not all, stations along its route Lunar An off-white color of railway signal light, like the Moon, achieved by the use of a clear lens of very light blue, to make it distinct from a light that has a broken lens.
M Maglev A system of high speed train transportation that uses two sets of magnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage of the lack of friction. Main generator The electric generator in a diesel–electric locomotive that is coupled directly to the prime mover and feeds electrical energy to the traction motors Main reservoir The compressed-air tank of a locomotive containing source air for the brakes and other pneumatic appliances Mallet locomotive A type of compound articulated locomotive designed by the Swiss mechanical engineer Anatole Mallet (pronounced "mallay"). See Compound engine. Manifest An express freight train carrying a variety of general merchandise Mars Light A nose-mounted mechanically oscillated light used to warn traffic of an approaching locomotive. Functionally replaced by ditch lights on modern locomotives. Mechanical semaphore signal A signal in which the aspect is conveyed by moving an arm Meet In rail transport operations, a meet occurs when two trains arrive at a location and pass each other on parallel tracks, such as on a siding, usually in opposing directions. This is also sometimes referred to as a crossing of two trains. Mikado type A steam locomotive with a 2-8-2 wheel arrangement Milk train In the U.S., milk trains ran from the countryside to cities making numerous stops at minor depots to pick up cans of fresh milk, making them a colloquial expression for a very slow train. In the U. K., an aggregator for transporting milk from farms to dairies, such as British Railways Milk Trains; as these trains invariably ran very early in the morning, "milk train" became a colloquialism for a particularly early train. Modalohr An inter-modal car Mogul type A steam locomotive with a 2-6-0 wheel arrangement Mothballed A track that is still serviceable but no trains are running on them. Mountain type A steam locomotive with a 4-8-2 wheel arrangement Mud ring The bottom of the water space surrounding a steam locomotive's firebox that collects solids precipitating from