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A railway track (British English and UIC terminology) or railroad track (
American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances i ...
), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the
rails Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail transport) or railway lines, the running surface of a railway Arts and media Film * ''Rails'' (film), a 1929 Italian film by Mario Camerini * ''Rail'' ( ...
,
fasteners A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...
,
railroad ties A railroad tie, crosstie (American English), railway tie (Canadian English) or railway sleeper (Australian English, Australian and British English) is a rectangular support for the Track (rail transport), rails in railroad tracks. Generally la ...
(sleepers, British English) and
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
(or
slab track A ballastless track or slab track is a type of railway track infrastructure in which the traditional elastic combination of ties/sleepers and ballast is replaced by a rigid construction of concrete or asphalt. Characteristics In ballastless ...
), plus the underlying
subgrade In transport engineering, subgrade is the native material underneath a constructed road,http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com'' pavement or railway track (US: railroad ...
. It enables
train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often ...
s to move by providing a dependable surface for their wheels to roll upon. Early tracks were constructed with wooden or cast iron rails, and wooden or stone sleepers; since the 1870s, rails have almost universally been made from steel.


Historical development

The first railway in Britain was the
Wollaton Wagonway The Wollaton Wagonway (or Waggonway), built between October 1603 and 1604 in the East Midlands of England by Huntingdon Beaumont in partnership with Sir Percival Willoughby, has sometimes been credited as the world's first ''overground'' wagon ...
, built in 1603 between Wollaton and Strelley in Nottinghamshire. It used wooden rails and was the first of around 50 wooden-railed tramways built over the next 164 years. These early wooden tramways typically used rails of oak or beech, attached to wooden sleepers with iron or wooden nails. Gravel or small stones were packed around the sleepers to hold them in place and provide a walkway for the people or horses that moved wagons along the track. The rails were usually about long and were not joined - instead, adjacent rails were laid on a common sleeper. The straight rails could be angled at these joints to form primitive curved track. The first iron rails laid in Britain were at the Darby Ironworks in
Coalbrookdale Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. It lies within the civil parish called the Gorge. This is where iron ore was first s ...
in 1767. When steam locomotives were introduced, starting in 1804, the track then in use proved too weak to carry the additional weight.
Richard Trevithick Richard Trevithick (13 April 1771 – 22 April 1833) was a British inventor and mining engineer. The son of a mining captain, and born in the mining heartland of Cornwall, Trevithick was immersed in mining and engineering from an early age. He w ...
's pioneering locomotive at
Pen-y-darren : ''For Trevithick's Pen-y-darren locomotive, see Richard Trevithick.'' Penydarren is a community and electoral ward in Merthyr Tydfil County Borough in Wales. Description The area is most notable for being the site of a 1st-century Roman fort, a ...
broke the
plateway A plateway is an early kind of railway, tramway or wagonway, where the rails are made from cast iron. They were mainly used for about 50 years up to 1830, though some continued later. Plateways consisted of "L"-shaped rails, where the flange ...
track and had to be withdrawn. As locomotives became more widespread in the 1810s and 1820s, engineers built rigid track formations, with iron rails mounted on stone sleepers, and cast-iron chairs holding them in place. This proved to be a mistake, and was soon replaced with flexible track structures that allowed a degree of elastic movement as trains passed over them.


Structure


Traditional track structure

Traditionally, tracks are constructed using flat-bottomed steel rails laid on and spiked or screwed into timber or pre-stressed concrete sleepers (known as ties in North America), with crushed stone
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
placed beneath and around the sleepers. Most modern railroads with heavy traffic use continuously welded rails that are attached to the sleepers with base plates that spread the load. When concrete sleepers are used, a plastic or rubber pad is usually placed between the rail and the tie plate. Rail is usually attached to the sleeper with resilient fastenings, although
cut spike A rail fastening system is a means of fixing rails to railroad ties ( North America) or sleepers (British Isles, Australasia, and Africa). The terms ''rail anchors'', ''tie plates'', ''chairs'' and ''track fasteners'' are used to refer to parts ...
s are widely used in North America. For much of the 20th century, rail track used softwood timber sleepers and jointed rails, and a considerable amount of this track remains on secondary and tertiary routes. In North America and Australia, flat-bottomed rails were typically fastened to the sleepers with dog spikes through a flat tie plate. In Britain and Ireland, bullhead rails were carried in cast-iron chairs which were spiked to the sleepers. In 1936, the London, Midland and Scottish Railway pioneered the conversion to flat-bottomed rail in Britain, though earlier lines had made some use of it. Jointed rails were used at first because contemporary technology did not offer any alternative. However, the intrinsic weakness in resisting vertical loading results in the ballast becoming depressed and a heavy maintenance workload is imposed to prevent unacceptable geometrical defects at the joints. The joints also needed to be lubricated, and wear at the fishplate (joint bar) mating surfaces needed to be rectified by shimming. For this reason jointed track is not financially appropriate for heavily operated railroads. Timber sleepers are of many available timbers, and are often treated with
creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types were ...
, chromated copper arsenate, or other wood preservatives. Pre-stressed concrete sleepers are often used where timber is scarce and where tonnage or speeds are high. Steel is used in some applications. The
track ballast Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down veget ...
is customarily crushed stone, and the purpose of this is to support the sleepers and allow some adjustment of their position, while allowing free drainage. File:Close-up of railway track.jpg, Traditional railway track showing ballast, part of sleeper and fixing mechanisms File:Track of Singapore LRT.jpg, Track of
Singapore LRT The Light Rail Transit (LRT) is a series of localised automated guideway transit systems acting as feeder services to the heavy rail Mass Rapid Transit, which together forms the core of Singapore's rail transport services. The first LRT line ...


Ballastless track

A disadvantage of traditional track structures is the heavy demand for maintenance, particularly surfacing (tamping) and lining to restore the desired
track geometry Track geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad track. The term is also applied to measurements used in design, construction and maintenance of t ...
and smoothness of vehicle running. Weakness of the subgrade and drainage deficiencies also lead to heavy maintenance costs. This can be overcome by using ballastless track. In its simplest form this consists of a continuous slab of concrete (like a highway structure) with the rails supported directly on its upper surface (using a resilient pad). There are a number of proprietary systems; variations include a continuous reinforced concrete slab and the use of pre-cast pre-stressed concrete units laid on a base layer. Many permutations of design have been put forward. However, ballastless track has a high initial cost, and in the case of existing railroads the upgrade to such requires closure of the route for a long period. Its whole-life cost can be lower because of the reduction in maintenance. Ballastless track is usually considered for new very high speed or very high loading routes, in short extensions that require additional strength (e.g. railway stations), or for localised replacement where there are exceptional maintenance difficulties, for example in tunnels. Most
rapid transit Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be ...
lines and rubber-tyred metro systems use ballastless track.


Continuous longitudinally supported track

Early railways (c. 1840s) experimented with ''continuous bearing'' railtrack, in which the rail was supported along its length, with examples including Brunel's
baulk road Baulk road is the name given to a type of railway track or 'rail road' that is formed using rails carried on continuous timber bearings, as opposed to the more familiar 'cross-sleeper' track that uses closely spaced sleepers or ties to give inte ...
on the Great Western Railway, as well as use on the
Newcastle and North Shields Railway The Newcastle & North Shields Railway opened in June 1839 from a temporary terminus in Carliol Square in Newcastle upon Tyne to North Shields. The railway was absorbed by the Newcastle & Berwick Railway in November 1844. The Newcastle & Berwick ...
, on the
Lancashire and Yorkshire Railway The Lancashire and Yorkshire Railway (L&YR) was a major British railway company before the 1923 Grouping. It was incorporated in 1847 from an amalgamation of several existing railways. It was the third-largest railway system based in northern ...
to a design by
John Hawkshaw Sir John Hawkshaw FRS FRSE FRSA MICE (9 April 1811 – 2 June 1891), was an English civil engineer. He served as President of the Institution of Civil Engineers 1862-63. His most noteworthy work is the Severn Tunnel. Early life He was born ...
, and elsewhere. Continuous-bearing designs were also promoted by other engineers. The system was tested on the
Baltimore and Ohio The Baltimore and Ohio Railroad was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. Merchants from Baltimore, which had benefited to some extent from the construction of ...
railway in the 1840s, but was found to be more expensive to maintain than rail with cross sleepers. This type of track still exists on some bridges on Network Rail where the timber baulks are called waybeams or longitudinal timbers. Generally the speed over such structures is low. Later applications of continuously supported track include
Balfour Beatty Balfour Beatty plc () is an international infrastructure group based in the United Kingdom with capabilities in construction services, support services and infrastructure investments. A constituent of the FTSE 250 Index, Balfour Beatty works acr ...
's 'embedded slab track', which uses a rounded rectangular rail profile (BB14072) embedded in a
slipform Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete is poured into a continuously moving form.Nawy, ''Concrete Construction Engineering Handbook,'' 2008, p. 10—33. Slip formi ...
ed (or pre-cast) concrete base (development 2000s). The 'embedded rail structure', used in the Netherlands since 1976, initially used a conventional UIC 54 rail embedded in concrete, and later developed (late 1990s) to use a 'mushroom' shaped SA42 rail profile; a version for light rail using a rail supported in an asphalt concrete–filled steel trough has also been developed (2002). Modern
ladder track Ladder track is a type of railway track in which the track is laid on longitudinal supports with transverse connectors holding the two rails at the correct gauge distance. Modern ladder track can be considered a development of baulk road, which ...
can be considered a development of baulk road. Ladder track utilizes sleepers aligned along the same direction as the rails with rung-like gauge restraining cross members. Both ballasted and ballastless types exist.


Rail

Modern track typically uses hot-rolled steel with a
profile Profile or profiles may refer to: Art, entertainment and media Music * ''Profile'' (Jan Akkerman album), 1973 * ''Profile'' (Githead album), 2005 * ''Profile'' (Pat Donohue album), 2005 * ''Profile'' (Duke Pearson album), 1959 * '' ''Profi ...
of an asymmetrical rounded
I-beam An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an or -shape ...
. Unlike some other uses of
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
and steel, railway rails are subject to very high stresses and have to be made of very high-quality steel alloy. It took many decades to improve the quality of the materials, including the change from iron to steel. The stronger the rails and the rest of the trackwork, the heavier and faster the trains the track can carry. Other profiles of rail include: bullhead rail; grooved rail; flat-bottomed rail (Vignoles rail or flanged T-rail); bridge rail (inverted U–shaped used in
baulk road Baulk road is the name given to a type of railway track or 'rail road' that is formed using rails carried on continuous timber bearings, as opposed to the more familiar 'cross-sleeper' track that uses closely spaced sleepers or ties to give inte ...
); and
Barlow rail Barlow rail was a rolled rail section used on early railways. It has wide flaring feet and was designed to be laid direct on the ballast, without requiring sleepers. It was widely adopted on lightly trafficked railways, but was ultimately unsuccess ...
(inverted V). North American railroads until the mid- to late-20th century used rails long so they could be carried in gondola cars ( open wagons), often long; as gondola sizes increased, so did rail lengths. According to the '' Railway Gazette International'' the planned-but-cancelled 150-kilometre rail line for the Baffinland Iron Mine, on Baffin Island, would have used older carbon steel alloys for its rails, instead of more modern, higher performance alloys, because modern alloy rails can become brittle at very low temperatures.


Iron-topped wooden rails

Early North American railroads used iron on top of wooden rails as an economy measure but gave up this method of construction after the iron came loose, began to curl, and intruded into the floors of the coaches. The iron strap rail coming through the floors of the coaches came to be referred to as "snake heads" by early railroaders. The Deeside Tramway in
North Wales North Wales ( cy, Gogledd Cymru) is a region of Wales, encompassing its northernmost areas. It borders Mid Wales to the south, England to the east, and the Irish Sea to the north and west. The area is highly mountainous and rural, with Snowdonia N ...
used this form of rail. It opened around 1870 and closed in 1947, with long sections still using these rails. It was one of the last uses of iron-topped wooden rails.


Rail classification (weight)

Rail is graded by weight over a standard length. Heavier rail can support greater axle loads and higher train speeds without sustaining damage than lighter rail, but at a greater cost. In North America and the United Kingdom, rail is graded by its
linear density Linear density is the measure of a quantity of any characteristic value per unit of length. Linear mass density (titer in textile engineering, the amount of mass per unit length) and linear charge density (the amount of electric charge per unit ...
in pounds per yard (usually shown as ''pound'' or ''lb''), so ''130-pound rail'' would weigh . The usual range is . In Europe, rail is graded in kilograms per metre and the usual range is . The heaviest rail mass-produced was and was rolled for the Pennsylvania Railroad. The United Kingdom is in the process of transition from the imperial to metric rating of rail.


Rail lengths

The rails used in
rail transport Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a p ...
are produced in sections of fixed length. Rail lengths are made as long as possible, as the joints between rails are a source of weakness. Throughout the history of rail production, lengths have increased as manufacturing processes have improved.


Timeline

The following are lengths of single sections produced by steel mills, without any
thermite welding Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composit ...
. Shorter rails may be welded with flashbutt welding, but the following rail lengths are unwelded. * (1767) Richard Reynolds laid the first iron rails at Coalbrookdale. * (1825) Stockton and Darlington Railway * (1830)
Liverpool and Manchester Railway The Liverpool and Manchester Railway (L&MR) was the first inter-city railway in the world. It opened on 15 September 1830 between the Lancashire towns of Liverpool and Manchester in England. It was also the first railway to rely exclusively ...
. Fish-belly rails at , laid mostly on stone blocks * (1831) long and weighing , reached
Philadelphia Philadelphia, often called Philly, is the List of municipalities in Pennsylvania#Municipalities, largest city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, the List of United States cities by population, sixth-largest city i ...
the first use of the flanged T rail in the United States * (1880) United States to suit gondola waggons * (1928) London, Midland and Scottish RailwayLMS Drawings of Standard Railway Equipment Permanent Way 1928The LMS Society
- Resources)
* (1950) British Rail * (1900) – steel works weighing machine for rails (
steelyard balance A steelyard balance, steelyard, or stilyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the longer arm to counterbalance the load and indicate its weight. A steelyard is also known as ...
) * (1940s) – double 39 ft US * (1953) Australia Welding of rails into longer lengths was first introduced around 1893, making train rides quieter and safer. With the introduction of thermite welding after 1899, the process became less labour-intensive, and ubiquitous. * (1895) Hans Goldschmidt developed
exothermic welding Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composit ...
* (1899) the Essen Tramway became the first railway to use thermite welding; also suited
track circuit A track circuit is an electrical device used to prove the absence of a train on rail tracks to signallers and control relevant signals. An alternative to track circuits are axle counters. Principles and operation The basic principle behind t ...
s * (1904) George Pellissier welded the Holyoke Street Railway, first to use the process in the Americas * (1935)
Charles Cadwell Charles Cadwell, was a professor at the Case School of Applied Science (now Case Western Reserve University Case Western Reserve University (CWRU) is a private research university in Cleveland, Ohio. Case Western Reserve was established in 1967, ...
developed non-ferrous
exothermic welding Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composit ...
* (1950) welded – (4 x ) Modern production techniques allowed the production of longer unwelded segments. * (2011)
Voestalpine Voestalpine AG – stylized as voestalpine – is an Austrian steel-based technology and capital goods group based in Linz, Austria. The company is active in steel, automotive, railway systems, profilform and tool steel industries. As of 201 ...
, * (2011) Jindal * (2013)
Tata Steel Europe Tata Steel Europe Ltd. (formerly Corus Group plc) was a steelmaking company headquartered in London, England, with its main operations in the United Kingdom and the Netherlands. The company was created in 2007, when Tata Group took over the ...


Multiples

Newer longer rails tend to be made as simple multiples of older shorter rails, so that old rails can be replaced without cutting. Some cutting would be needed as slightly longer rails are needed on the outside of sharp curves compared to the rails on the inside.


Boltholes

Rails can be supplied pre-drilled with boltholes for fishplates or without where they will be welded into place. There are usually two or three boltholes at each end.


Joining rails

Rails are produced in fixed lengths and need to be joined end-to-end to make a continuous surface on which trains may run. The traditional method of joining the rails is to bolt them together using metal
fishplate A fishplate joins two lengths of track A fishplate, splice bar or joint bar is a metal connecting plate used to bolt the ends of two rails into a continuous track. The name is derived from ''fish'', a wooden reinforcement of a "built-up" ship's ...
s (jointbars in the US), producing ''jointed track''. For more modern usage, particularly where higher speeds are required, the lengths of rail may be welded together to form ''continuous welded rail'' (CWR).


Jointed track

Jointed track is made using lengths of rail, usually around long (in the UK) and long (in North America), bolted together using perforated steel plates known as ''fishplates'' (UK) or ''joint bars'' (North America). Fishplates are usually long, used in pairs either side of the rail ends and bolted together (usually four, but sometimes six bolts per joint). The bolts have alternating orientations so that in the event of a
derailment In rail transport, a derailment occurs when a rail vehicle such as a train comes off its rails. Although many derailments are minor, all result in temporary disruption of the proper operation of the railway system and they are a potentially ...
and a wheel
flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the f ...
striking the joint, only some of the bolts will be sheared, reducing the likelihood of the rails misaligning with each other and exacerbating the derailment. This technique is not applied universally; European practice being to have all the bolt heads on the same side of the rail. Small gaps which function as
expansion joint An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...
s are deliberately left between the rail ends to allow for expansion of the rails in hot weather. European practice was to have the rail joints on both rails adjacent to each other, while North American practice is to stagger them. Because of these small gaps, when trains pass over jointed tracks they make a "clickety-clack" sound. Unless it is well-maintained, jointed track does not have the ride quality of welded rail and is less desirable for
high speed train High-speed rail (HSR) is a type of rail system that runs significantly faster than traditional rail, using an integrated system of specialised rolling stock and dedicated tracks. While there is no single standard that applies worldwide, lines ...
s. However, jointed track is still used in many countries on lower speed lines and sidings, and is used extensively in poorer countries due to the lower construction cost and the simpler equipment required for its installation and maintenance. A major problem of jointed track is cracking around the bolt holes, which can lead to breaking of the rail head (the running surface). This was the cause of the
Hither Green rail crash On 5 November 1967, a busy Sunday evening train service from to derailed near the Hither Green maintenance depot in London, between and railway stations. Of the twelve coaches, many full of standing passengers, eleven were derailed and four ...
which caused British Railways to begin converting much of its track to continuous welded rail.


Insulated joints

Where
track circuit A track circuit is an electrical device used to prove the absence of a train on rail tracks to signallers and control relevant signals. An alternative to track circuits are axle counters. Principles and operation The basic principle behind t ...
s exist for
signalling In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
purposes, insulated block joints are required. These compound the weaknesses of ordinary joints. Specially-made glued joints, where all the gaps are filled with epoxy resin, increase the strength again. As an alternative to the insulated joint,
audio frequency An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch. The generally accepted ...
track circuits can be employed using a tuned loop formed in approximately of the rail as part of the blocking circuit. Some insulated joints are unavoidable within turnouts. Another alternative is an
axle counter An axle counter is a system used in railway signalling to detect the clear or occupied status of a section of track between two points. The system generally consists of a wheel sensor (one for each end of the section) and an evaluation unit for c ...
, which can reduce the number of track circuits and thus the number of insulated rail joints required.


Continuous welded rail

Most modern railways use ''continuous welded rail'' (CWR), sometimes referred to as ''ribbon rails''. In this form of track, the rails are
welded Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as braz ...
together by utilising flash butt welding to form one continuous rail that may be several kilometres long. Because there are few joints, this form of track is very strong, gives a smooth ride, and needs less maintenance; trains can travel on it at higher speeds and with less friction. Welded rails are more expensive to lay than jointed tracks, but have much lower maintenance costs. The first welded track was used in Germany in 1924. and has become common on main lines since the 1950s. The preferred process of flash butt welding involves an automated track-laying machine running a strong electric current through the touching ends of two unjoined rails. The ends become white hot due to electrical resistance and are then pressed together forming a strong weld.
Thermite welding Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composit ...
is used to repair or splice together existing CWR segments. This is a manual process requiring a reaction crucible and form to contain the molten iron. North American practice is to weld segments of rail at a rail facility and load it on a special train to carry it to the job site. This train is designed to carry many segments of rail which are placed so they can slide off their racks to the rear of the train and be attached to the ties (sleepers) in a continuous operation. If not restrained, rails would lengthen in hot weather and shrink in cold weather. To provide this restraint, the rail is prevented from moving in relation to the sleeper by use of clips or anchors. Attention needs to be paid to compacting the ballast effectively, including under, between, and at the ends of the sleepers, to prevent the sleepers from moving. Anchors are more common for wooden sleepers, whereas most concrete or steel sleepers are fastened to the rail by special clips that resist longitudinal movement of the rail. There is no theoretical limit to how long a welded rail can be. However, if longitudinal and lateral restraint are insufficient, the track could become distorted in hot weather and cause a derailment. Distortion due to heat expansion is known in North America as sun kink, and elsewhere as buckling. In extreme hot weather special inspections are required to monitor sections of track known to be problematic. In North American practice, extreme temperature conditions will trigger slow orders to allow for crews to react to buckling or "sun kinks" if encountered. The German railway company Deutsche Bahn is starting to paint rails white to lower the peak temperatures reached in summer days. After new segments of rail are laid, or defective rails replaced (welded-in), the rails can be artificially stressed if the temperature of the rail during laying is cooler than what is desired. The stressing process involves either heating the rails, causing them to expand, or stretching the rails with
hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched elastic firmly fastened down. In extremely cold weather, rails are heated to prevent "pull aparts". CWR is laid (including fastening) at a temperature roughly midway between the extremes experienced at that location. (This is known as the "rail neutral temperature".) This installation procedure is intended to prevent tracks from buckling in summer heat or pulling apart in the winter cold. In North America, because broken rails are typically detected by interruption of the current in the signaling system, they are seen as less of a potential hazard than undetected heat kinks. Joints are used in the continuous welded rail when necessary, usually for signal circuit gaps. Instead of a joint that passes straight across the rail, the two rail ends are sometimes cut at an angle to give a smoother transition. In extreme cases, such as at the end of long bridges, a breather switch (referred to in North America and Britain as an ''expansion joint'') gives a smooth path for the wheels while allowing the end of one rail to expand relative to the next rail.


Sleepers

A sleeper (tie) is a rectangular object on which the rails are supported and fixed. The sleeper has two main roles: to transfer the loads from the rails to the
track ballast Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down veget ...
and the ground underneath, and to hold the rails to the correct width apart (to maintain the rail gauge). They are generally laid transversely to the rails.


Fixing rails to sleepers

Various methods exist for fixing the rail to the sleeper. Historically spikes gave way to cast iron chairs fixed to the sleeper, more recently springs (such as ''
Pandrol Pandrol is a global rail technology company, founded in 1953 and operating in over 100 countries worldwide, with over 400 railway systems having adopted its products. A member of the Delachaux Group, Pandrol is based in Colombes, France and ...
clips'') are used to fix the rail to the sleeper chair.


Portable track

Sometimes rail tracks are designed to be portable and moved from one place to another as required. During construction of the
Panama Canal The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a condui ...
, tracks were moved around excavation works. These track gauge were and the rolling stock full size. Portable tracks have often been used in open pit mines. In 1880 in
New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...
, sections of heavy portable track (along with much other improvised technology) helped in the epic move of the ancient obelisk in Central Park to its final location from the dock where it was unloaded from the cargo ship '' SS Dessoug''.
Cane Cane or caning may refer to: *Walking stick or walking cane, a device used primarily to aid walking * Assistive cane, a walking stick used as a mobility aid for better balance *White cane, a mobility or safety device used by many people who are ...
railways often had permanent tracks for the main lines, with portable tracks serving the canefields themselves. These tracks were
narrow gauge A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and . Since narrow-gauge railways are usually built with tighter curves, smaller structu ...
(for example, ) and the portable track came in straights, curves, and turnouts, rather like on a model railway.
Decauville Decauville () was a manufacturing company which was founded by Paul Decauville (1846–1922), a French pioneer in industrial railways. Decauville's major innovation was the use of ready-made sections of light, narrow gauge track fastened to stee ...
was a source of many portable light rail tracks, also used for military purposes. The ''permanent way'' is so called because ''temporary way'' tracks were often used in the construction of that permanent way.


Layout

The geometry of the tracks is three-dimensional by nature, but the standards that express the speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface are usually expressed in two separate layouts for horizontal and
vertical Vertical is a geometric term of location which may refer to: * Vertical direction, the direction aligned with the direction of the force of gravity, up or down * Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...
. Horizontal layout is the track layout on the horizontal plane. This involves the layout of three main track types: ''tangent track'' (straight line), ''curved track'', and ''
track transition curve A track transition curve, or spiral easement, is a mathematically-calculated curve on a section of highway, or railroad track, in which a straight section changes into a curve. It is designed to prevent sudden changes in lateral (or centripetal ...
'' (also called ''transition spiral'' or ''spiral'') which connects between a tangent and a curved track. Vertical layout is the track layout on the
vertical plane In astronomy, geography, and related sciences and contexts, a '' direction'' or ''plane'' passing by a given point is said to be vertical if it contains the local gravity direction at that point. Conversely, a direction or plane is said to be hor ...
including the concepts such as crosslevel,
cant Cant, CANT, canting, or canted may refer to: Language * Cant (language), a secret language * Beurla Reagaird, a language of the Scottish Highland Travellers * Scottish Cant, a language of the Scottish Lowland Travellers * Shelta or the Cant, a la ...
and
gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...
. A ''sidetrack'' is a railroad track other than siding that is auxiliary to the main track. The word is also used as a verb (without object) to refer to the movement of trains and railcars from the main track to a siding, and in common parlance to refer to giving in to distractions apart from a main subject. Sidetracks are used by railroads to order and organise the flow of rail traffic.


Gauge

During the early days of rail, there was considerable variation in the gauge used by different systems. , about 60% of the world's railways use a gauge of , known as
standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object th ...
or international gauge Gauges wider than standard gauge are called broad gauge; narrower,
narrow gauge A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and . Since narrow-gauge railways are usually built with tighter curves, smaller structu ...
. Some stretches of track are dual gauge, with three (or sometimes four) parallel rails in place of the usual two, to allow trains of two different gauges to use the same track. Gauge can safely vary over a range. For example, U.S. federal safety standards allow standard gauge to vary from to for operation up to .


Maintenance

Track needs regular maintenance to remain in good order, especially when high-speed trains are involved. Inadequate maintenance may lead to a "slow order" (North American terminology, or temporary speed restriction in the United Kingdom) being imposed to avoid accidents (see
Slow zone In the United States, a slow zone is an area where a train is forced to slow down for either structural, construction, power, signal, or track problems. Slow zones limit a train to about . Notification to train crews is referred to as a "slow ord ...
). Track maintenance was at one time hard
manual labour Manual labour (in Commonwealth English, manual labor in American English) or manual work is physical work done by humans, in contrast to labour by machines and working animals. It is most literally work done with the hands (the word ''manual ...
, requiring teams of labourers, or trackmen (US:
gandy dancer Gandy dancer is a slang term used for early Rail transport, railroad workers in the United States, more formally referred to as "section hands", who laid and maintained Track (rail transport), railroad tracks in the years before the work was don ...
s; UK:
platelayer A platelayer (British English), fettler (British English – UK, Australia, NZ) or trackman (American English) is a railway employee who inspects and maintains the permanent way of a railway, usually under the charge of a foreman called (in UK ...
s; Australia: fettlers), who used lining bars to correct irregularities in horizontal alignment (line) of the track, and tamping and jacks to correct vertical irregularities (surface). Currently, maintenance is facilitated by a variety of specialised machines. The surface of the head of each of the two rails can be maintained by using a
railgrinder A railgrinder (or rail grinder) is a maintenance of way vehicle or train used to restore the profile and remove irregularities from worn tracks to extend its life and to improve the ride of trains using the track. Rail grinders were developed ...
. Common maintenance jobs include changing sleepers, lubricating and adjusting
switches In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
, tightening loose track components, and surfacing and lining track to keep straight sections straight and curves within maintenance limits. The process of sleeper and rail replacement can be automated by using a
track renewal train A track renewal train (also known as a track renewal system or new track construction machine) is a work train that consists of many units of machinery and materials required for track renewal (rail and sleeper replacement) projects. Rail prepa ...
. Spraying ballast with herbicide to prevent weeds growing through and redistributing the ballast is typically done with a special weed killing train. Over time, ballast is crushed or moved by the weight of trains passing over it, periodically requiring relevelling ("tamping") and eventually to be cleaned or replaced. If this is not done, the tracks may become uneven, causing swaying, rough riding and possibly derailments. An alternative to tamping is to lift the rails and sleepers and reinsert the ballast beneath. For this, specialist " stoneblower" trains are used.
Rail inspection Rail inspection is the practice of examining rail tracks for flaws that could lead to catastrophic failures. According to the United States Federal Railroad Administration Office of Safety Analysis, track defects are the second leading cause of ...
s utilize nondestructive testing methods to detect internal flaws in the rails. This is done by using specially equipped HiRail trucks, inspection cars, or in some cases, handheld inspection devices. Rails must be replaced before the railhead profile wears to a degree that may trigger a derailment. Worn mainline rails usually have sufficient life remaining to be used on a
branch line A branch line is a phrase used in railway terminology to denote a secondary railway line which branches off a more important through route, usually a main line. A very short branch line may be called a spur line. Industrial spur An industr ...
, siding or stub afterwards and are "cascaded" to those applications. The environmental conditions along railroad track create a unique railway ecosystem. This is particularly so in the United Kingdom, where steam locomotives are only used on special services and vegetation has not been trimmed back so thoroughly. This creates a fire risk in prolonged dry weather. In the UK, the
cess Cess is a tax that is generally levied for promoting services like health and education. Governments often charge cess for the purpose of development in social sectors. The word is a shortened form of "assess". The spelling is due to a mistaken ...
is used by track repair crews to walk to a work site, and as a safe place to stand when a train is passing. This helps when doing minor work, while needing to keep trains running, by not needing a Hi-railer or transport vehicle blocking the line to transport crew to get to the site. File:Risanatrice.jpg, Maintenance of way equipment in Italy File:Maintenance of way.jpg, A
track renewal train A track renewal train (also known as a track renewal system or new track construction machine) is a work train that consists of many units of machinery and materials required for track renewal (rail and sleeper replacement) projects. Rail prepa ...
in
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
File:Plasser & Theurer 09-32 CSM CFR.jpg,
Plasser & Theurer Plasser & Theurer is an Austrian manufacturer of rail track maintenance and track laying machines. It accounts for 6% of Austrian exports of the machinery and iron and steel construction industry. History The company was established in 1953 by ...
09-32 CSM continuous action levelling, lining and tamping machine of the
Romanian Railways Romanian may refer to: *anything of, from, or related to the country and nation of Romania **Romanians, an ethnic group **Romanian language, a Romance language ***Romanian dialects, variants of the Romanian language **Romanian cuisine, traditional ...


Bed and foundation

Railway tracks are generally laid on a bed of stone
track ballast Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down veget ...
or
track bed The track bed or trackbed is the groundwork onto which a railway track is laid. Trackbeds of disused railways are sometimes used for recreational paths or new light rail links. According to Network Rail, the trackbed is the layers of ballast a ...
, which in turn is supported by prepared earthworks known as the track formation. The formation comprises the
subgrade In transport engineering, subgrade is the native material underneath a constructed road,http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com'' pavement or railway track (US: railroad ...
and a layer of sand or stone dust (often sandwiched in impervious plastic), known as the blanket, which restricts the upward migration of wet clay or silt. There may also be layers of waterproof fabric to prevent water penetrating to the subgrade. The track and ballast form the permanent way. The foundation may refer to the ballast and formation, i.e. all man-made structures below the tracks. Some railroads are using asphalt pavement below the ballast in order to keep dirt and moisture from moving into the ballast and spoiling it. The fresh asphalt also serves to stabilize the ballast so it does not move around so easily. Additional measures are required where the track is laid over permafrost, such as on the Qingzang Railway in
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa, Taman ...
. For example, transverse pipes through the subgrade allow cold air to penetrate the formation and prevent that subgrade from melting.


Geosynthetic reinforcement

Geosynthetics Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosyntheti ...
are used to reduce or replace traditional layers in trackbed construction and rehabilitation worldwide to improve track support and reduce track maintenance costs. Reinforcement geosynthetics, such as geocells (which rely on 3D soil confinement mechanisms) have demonstrated efficacy in stabilizing soft subgrade soils and reinforcing substructural layers to limit progressive track degradation. Reinforcement geosynthetics increase soil bearing capacity, limit ballast movement and degradation and reduce differential settlement that affects track geometry. They also reduce construction time and cost, while reducing environmental impact and carbon footprint. The increased use of geosynthetic reinforcement solutions is supported by new high-performance geocell materials (e.g., NPA -
Novel Polymeric Alloy Novel polymeric alloy (NPA) is a polymeric alloy composed of polyolefin and Thermoplastic polymer, thermoplastic engineering polymer with enhanced engineering properties. NPA was developed for use in geosynthetics. One of the first commercial NPA ...
), published research, case studies projects and international standards (ISO, ASTM, CROW/SBRCURnet) The hybrid use of high-performance geogrids at the subgrade and high-performance geocell in the upper subbase/subballast layer has been shown to increase the reinforcement factor greater than their separate sums, and is particularly effective in attenuating heaving of expansive subgrade clay soils. A field test project on
Amtrak The National Railroad Passenger Corporation, doing business as Amtrak () , is the national passenger railroad company of the United States. It operates inter-city rail service in 46 of the 48 contiguous U.S. States and nine cities in Canada ...
's NE Corridor suffering clay mud-pumping demonstrated how the hybrid solution improved track quality index (TQI) significantly reduced track geometry degradation and lowered track surface maintenance by factor of 6.7x utilizing high-performance NPA geocell. Geosynthetic reinforcement is also used to stabilize railway embankments, which must be robust enough to withstand repeated cyclical loading. Geocells can utilize recycled marginal or poorly graded granular material to create stable embankments, make railway construction more economical and sustainable.


Buses

Some buses can use tracks. This concept came out of Germany and was called . The first such track, the
O-Bahn Busway The O-Bahn Busway is a guided busway that is part of the bus rapid transit system servicing the northeastern suburbs of Adelaide, South Australia. The O-Bahn system was conceived by Daimler-Benz to enable buses to avoid traffic congestion by s ...
, was built in Adelaide, Australia.


See also

*
Degree of curvature Degree of curve or degree of curvature is a measure of curvature of a circular arc used in civil engineering for its easy use in layout surveying. Definition The degree of curvature is defined as the central angle to the ends of an agreed lengt ...
* Difference between train and tram rails *
Exothermic welding Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composit ...
*
Gauntlet track Gauntlet track or interlaced track (also gantlet track) is an arrangement in which railway tracks run parallel on a single track bed and are interlaced (i.e., overlapped) in such a way that only one pair of rails can be used at any time. Since th ...
* Glossary of rail terminology
(including US/UK and other
regional/national differences) *
Maglev Maglev (derived from '' magnetic levitation''), is a system of train transportation that uses two sets of electromagnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage ...
* Minimum railway curve radius *
Monorail A monorail (from "mono", meaning "one", and " rail") is a railway in which the track consists of a single rail or a beam. Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurat ...
*
Permanent way (history) The railway track or permanent way is the elements of railway lines: generally the pairs of rails typically laid on the sleepers or ties embedded in ballast, intended to carry the ordinary trains of a railway. It is described as permanent way ...
*
Rack railway A rack railway (also rack-and-pinion railway, cog railway, or cogwheel railway) is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with th ...
* Rail profile *
Roll way A roll way or running pad is the pad placed on a concrete slab or on the ties on the outside of the conventional track along both running rails of a rubber-tyred metro or along the unconventional track of a tram. The rubber-tyred wheels roll d ...
, part of the track of a rubber-tyred metro * Rubber-tyred metro * Street running *
Subgrade In transport engineering, subgrade is the native material underneath a constructed road,http://www.highwaysmaintenance.com/drainage.htm The Idiots' Guide to Highways Maintenance ''highwaysmaintenence.com'' pavement or railway track (US: railroad ...
*
Tie plate A rail fastening system is a means of fixing rails to railroad ties (North America) or sleepers (British Isles, Australasia, and Africa). The terms ''rail anchors'', ''tie plates'', ''chairs'' and ''track fasteners'' are used to refer to parts ...
*
TGV track construction High-speed railway track construction is the process by which (LGV, litt. "''high-speed railway line''"), the land on which TGV trains are to run, is prepared for their use, involving carving the track bed and laying the track. This constructio ...
*
Tramway (industrial) Tramways are lightly laid railways, sometimes with the wagons or carriages moved without locomotives. Because individual tramway infrastructure is not intended to carry the weight of typical standard-gauge railway equipment, the tramways over ...
*
Tramway track Tramway track is used on tramways or light rail operations. Grooved rails (or girder rails) are often used to provide a protective flangeway in the trackwork in city streets. Like standard rail tracks, tram tracks consist of two parallel s ...


References


Bibliography

* Pike, J., (2001), ''Track'', Sutton Publishing, * Firuziaan, M. and Estorff, O., (2002), ''Simulation of the Dynamic Behavior of Bedding-Foundation-Soil in the Time Domain'', Springer Verlag. * *


External links


Table of North American tee rail (flat bottom) sections







"Drawing of England Track Laying in Sections at 200 yards an hour" ''Popular Mechanics'', December 1930
* illustrated description of the construction and maintenance of the railway
Railway technical
{{Authority control Railway track layouts Structural steel Rail infrastructure