Rail tracks

Rail tracks

Overview

The track on a railway or railroad
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast (or slab track), plus the underlying subgrade
Subgrade
In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track. It is also called formation level.The term can also refer to imported material that has been used to build an embankment....

. For clarity it is often referred to as railway track (British English and UIC terminology
International Union of Railways
The UIC , or International Union of Railways, is an international rail transport industry body.- Brief history :The railways of Europe originated as separate concerns. There were many border changes after World War I and the Treaty of Versailles. Colonial railways were the responsibility of the...

) or railroad track (predominantly in the United States).

The term permanent way also refers to the track in addition to lineside structures such as fences etc.


Notwithstanding modern technical developments, the overwhelmingly dominant track form worldwide consists of flat-bottom steel rails supported on timber or pre-stressed concrete sleepers (railroad ties in the US), which are themselves laid on crushed stone ballast
Track ballast
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

.

Most railroads with heavy traffic use continuously welded rails supported by sleepers (ties) attached via baseplates which spread the load.
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Encyclopedia

The track on a railway or railroad
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast (or slab track), plus the underlying subgrade
Subgrade
In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track. It is also called formation level.The term can also refer to imported material that has been used to build an embankment....

. For clarity it is often referred to as railway track (British English and UIC terminology
International Union of Railways
The UIC , or International Union of Railways, is an international rail transport industry body.- Brief history :The railways of Europe originated as separate concerns. There were many border changes after World War I and the Treaty of Versailles. Colonial railways were the responsibility of the...

) or railroad track (predominantly in the United States).

The term permanent way also refers to the track in addition to lineside structures such as fences etc.

Traditional track structure



Notwithstanding modern technical developments, the overwhelmingly dominant track form worldwide consists of flat-bottom steel rails supported on timber or pre-stressed concrete sleepers (railroad ties in the US), which are themselves laid on crushed stone ballast
Track ballast
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

.

Most railroads with heavy traffic use continuously welded rails supported by sleepers (ties) attached via baseplates which spread the load. A plastic or rubber pad is usually placed between the rail and the tieplate where concrete sleepers (ties) are used. The rail is usually held down to the sleeper (tie) with resilient fastenings, although cut spikes are widely used in North American practice.

Timber sleepers (ties) are of many available timbers, and are often treated with creosote
Creosote
Creosote is the portion of chemical products obtained by the distillation of a tar that remains heavier than water, notably useful for its anti-septic and preservative properties...

, copper-chrome-arsenic, or other wood preservative. Pre-stressed concrete sleepers (ties) 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
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

 is customarily crushed stone, and the purpose of this is to support the ties and allow some adjustment of their position, while allowing free drainage.

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 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, and variations include continuous in situ placing of a reinforced concrete slab, or alternatively 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 is very expensive in first cost, and in the case of existing railroads requires closure of the route for a somewhat long period. Its whole life cost can be lower because of the great reduction in maintenance requirement. Ballastless track is usually considered for new very high speed or very high loading routes, in short extensions that require additional strength (i.e. rail station), or for localised replacement in the case of exceptional maintenance difficulties.

Ladder track



Ladder track utilizes longitudinal sleepers with gauge restraining cross members, it can be considered a development of Baulk road
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 intermittent support to taller rails...

. Both ballasted and ballastless types exist.

Obsolete track types


For much of the 20th century, rail track used softwood timber ties and jointed rails, and considerable extents of this track type remains on secondary and tertiary routes. The rails were typically of flat bottom section fastened to the ties with dogspikes through a flat tieplate in North America and Australia, and typically of bullhead section carried in cast iron chairs in British and Irish practice.

Jointed rails were used, at first because the technology did not offer any alternative. However the intrinsic weakness in resisting vertical loading results in the ballast support becoming depressed and a heavy maintenance workload is imposed to prevent unacceptable geometrical defects at the joints. The joints also required 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.

Historical development



The technology of rail tracks developed over a long period, starting with primitive timber rails in mines in the 17th century. This is fully discussed in the article Permanent way.

Rail




Hot rolled steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 in the profile
Profile (engineering)
In standardization, a profile consists of an agreed-upon subset and interpretation of a specification. Many complex technical specifications have many optional features, such that two conforming implementations may not inter-operate due to choosing different sets of optional features to support...

 (cross section
Cross section (geometry)
In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...

) of an asymmetrical I-beam
I-beam
-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...

 is usually used as the surface on which railway wheels run. Unlike some other uses of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, 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 heavier the rails and the rest of the trackwork, the heavier and faster the trains the track can carry.

Profiles of rail include:
  • Bullhead rail
  • Grooved rail
  • Vignoles rail (flat-bottomed rail)
  • Flanged T rail
  • Bridge rail
    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 intermittent support to taller rails...

     (inverted U)
  • Barlow rail
    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...

     (inverted V)


North American railroads until the mid- to late-20th century used rails 39 ft (11.89 m) long so they could be carried to and from a worksite in gondola cars
Gondola (rail)
In railroad terminology, a gondola is an open-top type of rolling stock that is used for carrying loose bulk materials. Because of its low side walls, gondolas are used to carry either very dense material, such as steel plates or coils, or bulky items such as prefabricated pieces of rail...

 (open wagons), often 40 ft (12.2 m) long; as gondola sizes increased, so did rail lengths.

The world's longest rail sections are 120m long and are made by various companies.,,

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 UK, rail is graded in pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

 per yard
Yard
A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches...

 (usually shown as pound or lb), so 130-pound rail would weigh 130 lb/yd. The usual range is 115 lb/yd. In Europe, rail is graded in kg/m and the usual range is 40 kg/m. The heaviest rail mass-produced was 155 lb/yd and was rolled for the Pennsylvania Railroad
Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....

. The UK is in the process of transition from the imperial to metric rating of rail.

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 fishplates, 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 20 m (66 ft) long (in the UK) and 39 or long (in North America), bolted together using perforated steel plates known as fishplates (UK) or joint bars (North America).

Fishplate
Fishplate
In rail terminology, a fishplate, splice bar or joint bar is a metal bar that is bolted to the ends of two rails to join them together in a track. The name is derived from fish, a wooden bar with a curved profile used to strengthen a ship's mast...

s are usually 600 mm (1.97 ft) long, used in pairs either side of the rail ends and bolted together (usually four, but sometimes six bolts per joint). The bolts may be oppositely-oriented so that in the event of a derailment
Derailment
A derailment is an accident on a railway or tramway in which a rail vehicle, or part or all of a train, leaves the tracks on which it is travelling, with consequent damage and in many cases injury and/or death....

 and a wheel flange
Flange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...

 striking the joint, only some of the bolts will be sheared, reducing the likelihood of the rails misaligning with each other and exacerbating the seriousness of the derailment. (This technique is not applied universally, British practice being to have all the bolt heads on the same side of the rail.) Small gaps known as expansion joint
Expansion joint
An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, to hold certain parts together, or to allow movement due to ground settlement or earthquakes...

s are deliberately left between the rail ends to allow for expansion of the rails in hot weather. The holes through which the fishplate bolts pass are oval to allow for movement with expansion.

British practice was to have the rail joints on both rails adjacent to each other, while North American practice is to stagger them.

Because of the small gaps left between the rails, 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 trains
High-speed rail
High-speed rail is a type of passenger rail transport that operates significantly faster than the normal speed of rail traffic. Specific definitions by the European Union include for upgraded track and or faster for new track, whilst in the United States, the U.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 the rail head (the running surface) breaking. This was the cause of the Hither Green rail crash
Hither Green rail crash
The Hither Green rail crash was an accident on the British railway system that occurred on 5 November 1967 near Hither Green maintenance depot, between Hither Green and Grove Park railway stations, in south-east London....

 which caused British Rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...

ways to begin converting much of its track to Continuous Welded Rail.

Insulated joints


Where track circuit
Track circuit
A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...

s exist for signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...

 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
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....

, increase the strength again.

As an alternative to the insulated joint, audio frequency
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...

 track circuits can be employed using a tuned loop
LC circuit
An LC circuit, also called a resonant circuit or tuned circuit, consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C...

 formed in approximately 20 m of the rail as part of the blocking circuit. Another alternative is the axle counter
Axle counter
An axle counter is a device on a railway that detects the passing of a train in lieu of the more common track circuit. A counting head is installed at each end of the section, and as each axle passes the head at the start of the section, a counter increments...

, 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
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 together by utilising flash butt welding
Flash welding
Flash welding is a type of resistance welding that involves pressing two ends together, while simultaneously running a current between them. This has the effect of forming a joint between the two metals that is free of oxides as the surfaces of the two joining parts is forced out the sides of the...

 to form one continuous rail that may be several kilometres long, or thermite welding to repair or splice together existing CWR segments. 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 the US in 1930 and has become common on main lines since the 1950s.

Flash butt welding is the preferred process which involves an automated track-laying machine running a strong electrical current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 through the touching ends of two unjoined pieces of rail. The ends become white hot due to electrical resistance and are then pressed together forming a strong weld. Thermite welding is a manual process requiring a reaction crucible and form to contain the molten iron. Thermite-bonded joints are also seen as less reliable and more prone to fracture or break.

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. Anchors are more common for wooden sleepers, whereas most concrete or steel sleepers are fastened to the rail by special clips which 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
Sun kink
Sun kink refers to a condition that can occur on hot days in rail tracks. The phenomenon is caused by what is properly termed as buckling.The buckling force in the track due to warming up is a function of the rise in temperature only and is independent of the track length: F = E A \alpha_L \Delta...

, and elsewhere as buckling
Buckling
In science, buckling is a mathematical instability, leading to a failure mode.Theoretically, buckling is caused by a bifurcation in the solution to the equations of static equilibrium...

. In North America a rail broken due to cold-related contraction is known as a pull-apart. 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. In extreme hot weather special inspections are required to monitor sections of track known to be problematic.

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 different than what is desired. The stressing process
Rail stressing
Stressing is a technique developed in the 1960s to avert rail track problems that can occur when installing Continuous welded rail . When installing new rail the rail must be returned to its former temperature or length.- Technique :...

 involves either heating the rails causing them to expand, or stretching the rails with hydraulic
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...

 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
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

 firmly fastened down.

CWR rail 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, along with normal track structure strength, is intended to prevent tracks from buckling in summer heat or pulling apart in winter cold. In North America, because broken rails are typically detected by the signaling system; they are seen as less of a problem than heat kinks which are not detected.
Joints are used in 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
Breather switch
A breather switch, expansion joint or adjustment switch is an intentional gap in lengths of railway tracks created to allow for expansion in long sections of otherwise unbroken rail...

 (referred to in North America and Britain as an expansion joint) gives a smooth path for the wheel while allowing the end of one rail to expand in relation to the next rail.

Rail support (sleeper/tie)


A railroad tie (also called a cross-tie in North American usage, or a railway sleeper outside North America) is a rectangular object on which the rails are supported and fixed. The tie has two main roles: to transfer the loads from the rails to the track ballast
Track ballast
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

 and the ground underneath, and to hold the rails to the correct width apart (to maintain the rail gauge
Rail gauge
Track gauge or rail gauge is the distance between the inner sides of the heads of the two load bearing rails that make up a single railway line. Sixty percent of the world's railways use a standard gauge of . Wider gauges are called broad gauge; smaller gauges, narrow gauge. Break-of-gauge refers...

). They are generally laid transverse (perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

) to the rails.

Fixing rails to railroad ties


Various methods exist for fixing the rail to the sleeper (railroad tie). Historically spikes gave way to cast iron chairs fixed to the sleeper, more recently springs (such as Pandrol 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.

On the Panama Canal
Panama Canal
The Panama Canal is a ship canal in Panama that joins the Atlantic Ocean and the Pacific Ocean and is a key conduit for international maritime trade. Built from 1904 to 1914, the canal has seen annual traffic rise from about 1,000 ships early on to 14,702 vessels measuring a total of 309.6...

, tracks were so lifted around as is seen in moving pictures taken of the excavation works. These tracks were standard gauge
Standard gauge
The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

, and the rolling stock full size.

Cane railways often had permanent tracks for the main lines, with portable tracks serving the canefields themselves. These tracks were narrow gauge
Narrow gauge
A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...

 (for example) and the portable track came in straights, curves and turnouts rather like on a model railway.

Decauville
Decauville
The Decauville manufacturing company was founded by Paul Decauville , a French pioneer in industrial railways. Decauville's major innovation was the use of ready-made sections of light, narrow gauge track fastened to steel sleepers; this track was portable and could be disassembled and transported...

 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.

Gauge



During the early days of rail, there was considerable variation in the gauge used by different systems. Today, 60% of the world's railways use a gauge of , known as standard
Standard gauge
The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

 or international gauge
Standard gauge
The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

. Gauges wider than standard gauge are called broad gauge
Broad gauge
Broad-gauge railways use a track gauge greater than the standard gauge of .- List :For list see: List of broad gauges, by gauge and country- History :...

; narrower, narrow gauge. Some stretches of track are dual gauge
Dual gauge
A dual-gauge or mixed-gauge railway has railway track that allows trains of different gauges to use the same track. Generally, a dual-gauge railway consists of three rails, rather than the standard two rails. The two outer rails give the wider gauge, while one of the outer rails and the inner rail...

, 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 60 mph (96.6 km/h).

Track 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, a "slack" or speed restriction in the United Kingdom) being imposed to avoid accidents (see Slow zone
Slow Zone
A slow zone, in America, 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 10-35 MPH...

). Track maintenance was at one time hard manual labour
Manual labour
Manual labour , manual or manual work is physical work done by people, most especially in contrast to that done by machines, and also to that done by working animals...

, requiring teams of labourers (US: gandy dancer
Gandy dancer
Gandy dancer is a slang term used for early railroad workers who laid and maintained railroad tracks in the years before the work was done by machines....

s, UK: platelayers or trackmen, 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
Railgrinder
A railgrinder is a maintenance of way vehicle or train used to restore the profile and remove irregularities from worn rail track to extend its life and to improve the ride of trains using the track....

.

Common maintenance jobs include changing crossties (sleepers), lubricating and adjusting switches, tightening loose track components, and surfacing and lining track to keep straight sections straight and curves within maintenance limits.

Spraying ballast with herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...

 to prevent weeds growing through and disrupting 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 "stone blower" trains are used.

Rail inspection
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 accidents on railways in the United States. The...

s utilize nondestructive testing
Nondestructive testing
Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....

 methods to detect internal flaws in the rails. This is done by using specially equipped HiRail truck
Road-rail vehicle
A road–rail vehicle is a self-propelled vehicle that can be legally used on both roads and rails. Combining the words "highway" and "rail", one is often referred to as a hi-rail truck or just hi-rail, sometimes spelled high-rail, HiRail or Hy-rail. They are normally converted rubber-tired road...

s, 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 to be used on a branch line
Branch line
A branch line is 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...

, siding or stub afterwards and are "cascaded" to those applications.

The environmental conditions along railroad track create a unique railway ecosystem
Railroad ecology
Railroad ecology is a term used to refer to the study of the ecological community growing along railroad tracks. Such ecosystems have been studied primarily in Europe...

. This is particularly so in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 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
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, the cess 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.

Track bed and foundation


Railway tracks are generally laid on a bed of stone track ballast
Track ballast
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

 or track bed
Track bed
A track bed or trackbed is the term used to describe the groundwork onto which a railway track is laid. Trackbeds of disused railways are sometimes used for recreational paths or new light rail links....

, in turn is supported by prepared earthworks known as the track formation. The formation comprises the subgrade
Land grading
Grading in civil engineering and construction is the work of ensuring a level base, or one with a specified slope, for a construction work such as a foundation, the base course for a road or a railway, or landscape and garden improvements, or surface drainage...

 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. The may also be layers of waterproof fabric to prevent water penetrating to the subgrade. The track and ballast form the permanent way. The term foundation may be used to refer to the ballast and formation, i.e. all man-made structures below the tracks.
Additional measures are required where the track is laid over permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

, such as on the Qingzang Railway
Qingzang railway
The Qinghai–Xizang railway, Qingzang railway, or Qinghai–Tibet railway , is a high-elevation railway that connects Xining, Qinghai Province, to Lhasa, Tibet Autonomous Region, in People's Republic of China....

 in Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...

. For example, transverse pipes through the subgrade allow cold air to penetrate the formation and prevent that subgrade from melting.

The sub-grade layers are slightly sloped to one side to help drainage of water. Rubber sheets may be inserted to help drainage and also protect iron bridgework from being affected by rust.

See also


  • Degree of curvature
    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....

  • Difference between train and tram rails
    Difference between train and tram rails
    A railroad or railway is a track where the vehicle travels over two parallel steel bars, called rails. The rails support and guide the wheels of the vehicles, which are traditionally either trains and trams. Modern light rail is a relatively new innovation which combines aspects of those two...

  • Double track
    Double track
    A double track railway usually involves running one track in each direction, compared to a single track railway where trains in both directions share the same track.- Overview :...

  • Flanged T rail
  • Gandy dancer
    Gandy dancer
    Gandy dancer is a slang term used for early railroad workers who laid and maintained railroad tracks in the years before the work was done by machines....

  • Glossary of rail terminology
    (including US/UK and other
    regional/national differences)
  • Grade (slope)
  • Grand union
    Grand union
    A grand union is a rail track junction where two double-track railway lines cross at grade, often in a street intersection or crossroads. A total of sixteen railroad switches allow streetcars coming from any direction to take any of the three other directions...

  • Grooved rail
  • Main line (railway)
    Main line (railway)
    The Mainline or Main line of a railway is a track that is used for through trains or is the principal artery of the system from which branch lines, yards, sidings and spurs are connected....

  • Minimum railway curve radius
    Minimum railway curve radius
    The minimum railway curve radius, the shortest design radius, has an important bearing on constructions costs and operating costs and, in combination with superelevation in the case of train tracks, determines the maximum safe speed of a curve. Superelevation is not a factor on tramway tracks...

  • Monorail
    Monorail
    A monorail is a rail-based transportation system based on a single rail, which acts as its sole support and its guideway. The term is also used variously to describe the beam of the system, or the vehicles traveling on such a beam or track...

  • Passing loop
    Passing loop
    A passing loop is a place on a single line railway or tramway, often located at a station, where trains or trams in opposing directions can pass each other. Trains/trams in the same direction can also overtake, providing that the signalling arrangement allows it...

  • Permanent way: historical development
  • Plateway
    Plateway
    A plateway is an early kind of railway or tramway or wagonway, with a cast iron rail. They were mainly used for about 50 years up to 1830, though some continued later....

  • Rack railway
    Rack railway
    A rack-and-pinion railway is a 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 this rack rail...

  • Radius of curvature (applications)
  • Rail lengths
    Rail lengths
    Rail lengths are made as long as possible, as joints between rails are a source of weakness. Over the decades, lengths increased as manufacturing processes improved.The following are lengths from the steel mill, without any thermite welding.- Examples :...

  • Railroad ecology
    Railroad ecology
    Railroad ecology is a term used to refer to the study of the ecological community growing along railroad tracks. Such ecosystems have been studied primarily in Europe...

  • Railroad switch
    Railroad switch
    A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another at a railway junction....

     (points)
  • Rail transport
    Rail transport
    Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

  • Railway station layout
    Railway station layout
    A railway station is a place where trains make scheduled stops. Stations usually have one or more platforms constructed alongside a line of railway. However, railway stations come in many different configurations - influenced by such factors as the geographical nature of the site, or the need to...

  • Siding (rail)
  • Single track
    Single track (rail)
    A single track railway is where trains in both directions share the same track. Single track is normally used on lesser used rail lines, often branch lines, where the traffic density is not high enough to justify the cost of building double tracks....

  • Speed limits in the United States (rail)
    Speed limits in the United States (rail)
    Rail speed limits in the United States are regulated by the Federal Railroad Administration. Railroads also implement their own limits and enforce speed limits. Speed restrictions are based on a number of factors including curvature, signaling, track condition, the physical condition of a train,...

  • Street running
    Street running
    On-street running or street running is when a railroad track or tramway track runs directly along city streets, without any separation. The rails are embedded in the road....

  • TGV track construction
    TGV track construction
    LGV construction is the process by which the land on which TGV trains are to run is prepared for their use, involving carving the trackbed and laying the track. It is similar to the building of standard railway lines, but there are differences. In particular, construction process is more precise in...

  • TGV tracks
  • Third rail
    Third rail
    A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...

  • Track transition curve
    Track transition curve
    A track transition curve, or spiral easement, is a mathematically calculated curve on a section of highway, or railroad track, where a straight section changes into a curve. It is designed to prevent sudden changes in centripetal force...

  • Tramway (industrial)
  • Tramway track
    Tramway track
    Tramway track is used on tramways or light rail operations. Grooved rails are often used in order to make street running feasible...

  • Vignoles rail
  • Wagonway
    Wagonway
    Wagonways consisted of the horses, equipment and tracks used for hauling wagons, which preceded steam powered railways. The terms "plateway", "tramway" and in someplaces, "dramway" are also found.- Early developments :...

  • Wye

  • Further reading

    • Pike, J., (2001), Track, Sutton Publishing, ISBN 0-7509-2692-9
    • Firuziaan, M. and Estorff, O., (2002), Simulation of the Dynamic Behavior of Bedding-Foundation-Soil in the Time Domain, Springer Verlag.

    External links