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Rail tracks

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track
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track

Rail tracks are used on railways (or railroads), which, together with railroad switches (or points), guide trains without the need for steering. Tracks consist of two parallel steel rails, which are laid upon sleepers (or cross ties) that are embedded in ballast to form the railroad track. The rail is fastened to the ties with rail spikes or with lag screws and baseplates (or fishplates) for wooden sleepers or Pandrol clips, [link] and [link] for cement or concrete ties. For illustrations see [link] and [link]

Rails, being made of steel, can carry heavier loads than any other material. Railroad ties spread the load from the rails over the ground, and also serve to hold the rails a fixed distance apart (called the gauge.)

Rail tracks are normally laid on a bed of coarse stone chippings known as a ballast, which combines resilience, some amount of flexibility, and good drainage; however, track can also be laid on or into concrete (a slab track). Across bridges, track is often laid on ties across longitudinal timbers or longitudinal steel girders.

Additional detail on tracks used for tram and light rail operations, as opposed to heavy rail, is available at tramway track.

Contents

Railway rail

Rail from 1896
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Rail from 1896

Unlike some other uses of iron and steel, railway rails are subject to very high stresses and have to be made of very high quality steel. It took many decades to improve the quality of the materials, including the change from iron to steel. Minor flaws in the steel that pose no problems with, say, reinforcing rods for buildings, can lead to broken rails and dangerous derailments when used on railway tracks.

By and large, the heavier the rails and the rest of the track, the heavier and faster the trains on those tracks can be.

The rails represent a substantial fraction of the cost of a railway line. Only a small number of rail sizes are made by the steelworks at the one time, so a railway must choose the nearest suitable size. Worn, heavy rail from a mainline is often cascaded down to branchline, siding, or yard use.

Jointed track

Track joint.
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Track joint.

There are different ways of joining rails together to form tracks. The traditional way of doing this was to bolt rails together in what is known as jointed track. In this form of track, lengths of rail, usually around 20 metres (60 feet) long, are laid and fixed to sleepers (U.K.) (crossties, or simply ties in North American parlance), and are joined to other lengths of rail with steel plates known as fishplates (U.K.) or joint bars (N.A.).

Historically, North American railroads until the mid to late 20th century used sections of rail that measured 39 feet (11.9 m) long so they could be carried to and from a worksite in conventional gondolas, which often measured 40 feet (12.2 m) long; as car sizes increased, so did rail lengths.

Alternative view of track joints
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Alternative view of track joints

Fishplates or joint bars are usually 60 centimetres (2 feet) long, and are bolted through each side of the rail ends with bolts (usually four, but sometimes up to six.) Small gaps known as "expansion joints" are deliberately left between the rails to allow for expansion of the rails in hot weather. The holes through which the fishplate bolts pass are oval to allow for expansion.

British practice was always to have the rail joints on both rails at the same place on each rail, 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, clickety clack" noise. Unless it is very well maintained, jointed track gives a fairly bumpy and uncomfortable ride, and is unsuitable for high speed trains because it is too weak. However, it is still used in many countries on lower speed lines, unimportant lines, and sidings. Most railroad track in the United States is still of this type, however, and laid on timber ties; the lower speeds of American railroads make the disadvantages less apparent, and the abundant supply of timber in the United States makes its use for railroad ties much cheaper than in Europe.

Jointed track is still extensively used in poorer countries, due to the cheaper construction costs and lack of modernisation of their railway systems.

Insulated Joints

Where there are track circuits for signalling purposes, insulated block joints are required. These compound the weakness of ordinary block joints. Specially made glued joints, where all the gaps filled with epoxy resin increases the strength again. Audio frequency track circuits such as those made by CSEE replace the conventional block joint with a tuned loop which uses say 20m of the rail as part of the blocking circuit. Axle counters can also reduce the number of track circuits and thus the number of insulated rail jounts.

Continuous Welded Rail

welded rail joint
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welded rail joint

Most modern railways use continuous welded rail (CWR); in this form of track, the rails are welded together by utilising the thermite reaction 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. Welded track has become common on main lines since the 1950s.

Because of its strength, trains travelling on welded track can travel at higher speeds and with less friction. Welded rails are more expensive to lay than jointed tracks, but are significantly cheaper to maintain.

As mentioned earlier, rails expand in hot weather and shrink in cold weather. Because welded track has very few expansion joints, if no special measures are taken, it could become distorted in hot weather and cause a derailment.

To avoid this, welded rails are very often laid on concrete or steel sleepers, which are so heavy they hold the rails firmly in place, and with plenty of ballast to stop the sleepers moving. After new segments of rail are laid, or defective rails replaced (welded in), the rails are artificially stressed.

The stressing process, involves either heating the rails causing them to expand, or stretching the rails with hydraulic 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.

Engineers try to heat the rail to a temperature roughly midway between the average extremes of hot and cold (this is known as the 'rail neutral temperature'). If temperatures reach outside normal ranges however, welded rail can buckle in a hotter than usual summer or can actually break in a colder than anticipated winter.

Joints are used in continuously welded rail when necessary; instead of a joint that passes straight across the rail, producing a loud noise and shock when the wheels pass over it, two sections of rail are cut at a steep angle and put together with a gap between them (a breather switch). This gives a much smoother transition yet still provides some expansion room.

Methods of Fixing Rail to Sleepers/Ties

Cross-sections of flat-bottomed which can rest directly on the sleepers, and bullhead rails which sit in chairs (not shown).
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Cross-sections of flat-bottomed which can rest directly on the sleepers, and bullhead rails which sit in chairs (not shown).

Screwless rail attachement
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Screwless rail attachement

There are several methods used to fasten rail to wooden sleepers / ties. The worldwide standard type of rail used today is flat-bottomed rail (Vignoles rail), which, as the name suggests, has a flat base and can stand upright without support. A flat-bottomed rail has a cross-section like that of an upside-down 'T' and is usually held to the sleeper with a baseplate, a metal plate attached to the sleeper; although for cheap construction FB rails can be laid directly onto the sleepers.

Modern sleepers can be made of reinforced concrete and pressed steel, with rubber pads inserted between the sleeper and rail. This is done for two reasons: to give a smoother ride and to prevent the sleeper from shorting the track circuit, a low voltage passed through the rails for signalling purposes. This is different from a "traction current," which powers electric trains. See also [link]

A rail clip
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A rail clip

A variety of different types of heavy-duty clips are used to fasten the rails to the underlying baseplate, one common one being the Pandrol fastener (Pandrol clip), named after its maker, which is shaped like a sturdy, stubby paperclip.[link], [link] and [link]

North American practice normally uses rail spikes, which are fundamentally very large nails with bent-over heads to clasp the flat-bottomed rail. These are cheaper and simpler to install but can loosen if the tie rots, much more easily than the British chair (a type of baseplate) does. This is mitigated by using very large and solid creosoted ties or using another rot-proofing preservative. See also timber treatment.

In traditional British practice, cast metal chairs were screwed to the sleepers, which took a style of rail known as bullhead that was somewhat figure-8 in cross-section — wider at top and bottom (known as the head and foot respectively) and smaller in the middle (the web). Keys (wedges of wood or sprung steel) were then driven in between chair and rail to hold it in place. This was common practice on British railways until the 1950s, but is now largely obsolete.

The idea behind bullhead rails was that because both the top and bottom of the rails were the same shape, when one side of the rail became worn, the rail could be turned over to the unused side, thus extending the rail's lifespan. However the bottom head turned out to get dented, rendering the original idea useless. Since the turnover requirement was no longer needed, bullhead rails came to have a flat base (narrower than flat-bottomed rail), and the top part has curved edges that fit the profile of the train wheels.

In recent years, methods have been developed to put tracks on concrete without using conventional sleepers or track ballast. While this method's construction cost is high, this system is expected to have significantly lower maintenance cost than conventional tracks. It is mainly used on high-speed lines and in tunnels, where maintenance access is difficult.
Image:Stanthorpe Rail Bridge DSC03186.jpg|Wooden Sleepers Image:Adelaide Darwin Railway Line between Adelaide River and Pine Creek DSC03643.jpg|Concrete Sleepers Image:Pine Creek Rail Steel Sleepers DSC03637.jpg|Steel Sleepers Image:Trevethick rail DSC00322.JPG|Iron & Brick Sleepers

See also

Track maintenance

A damaged railroad trestle in Alaska
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A damaged railroad trestle in Alaska

Track needs frequent maintenance to remain in good order; the frequency increases with higher-speed or heavier trains. This was formerly hard manual labour, requiring teams of gandy dancers who used levers to force rails back into place on steep turns, correcting the gradual shifting caused by the centripetal force of passing trains. Currently, maintenance is facilitated by a variety of specialised machines.

The profile of the track is maintained by using a railgrinder.

Common maintenance jobs include spraying ballast with weedkiller to prevent weeds growing through and disrupting the ballast. This is typically done with a special weedkilling train.

Over time, ballast is crushed by the weight of trains passing over it, and periodically it needs to be replaced. If this is not done, the tracks become uneven.

Broken or worn-out rails also need replacing periodically. Mainline rails that get worn out usually have life left in branch line or rail siding use and are "cascaded" to those branch lines.

See also Maintenance of way

History

Rail Bender
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Rail Bender

Some early rails were made by William Jessop in the 1790s.

Early rails were used on horse drawn wagonways. In the early days the rails were flanged (i.e 'L' shaped) with the wagon wheels being flat. Over time it was realised that flanged wheels with flat rails worked better.

Early rails were sometimes strap-iron rails, which consisted of thin strips of iron strapped onto wooden rails . These rails were too fragile to carry heavy loads, but because the initial construction cost was less, this method was sometimes used to quickly build an inexpensive rail line. Strap rails sometimes separated from the wooden base and speared into the floor of the carriages above! However, the long-term expense involved in frequent maintenance outweighed any savings.

Early metal rails were made mostly from cast iron which was a brittle material which could break easilly. The first steel rails were made in 1857 by Robert Forester Mushet, who layed them at Derby station in England. Steel was a much stronger material, which steadily replaced iron for use on railway rail.

The use of welded rather than jointed track began in around the 1940s and had become widespread by the 1960s.

It took many decades for weak and fragile iron rails to evolve into the strong and robust steel rails of today. But problems can still occur, such as happened with the Hatfield train derailment in Great Britain on October 17, 2000. The accident involved gauge corner cracking, which is now referred to as rolling contact fatigue, as the defect doesn't only occur on corners.

Rail sizes

Europe

Rails are made in a large number of different sizes. Some common European rail sizes include:

North America

Some common North American rail sizes include: Some common North American crane rail sizes include:

Australia

Some common Australian rail sizes include: Rails in Canada, the United Kingdom, and United States are still described using imperial units. However, in Australia they are now described in metric units and always have been on mainland Europe.

U.S. Track Classes

In the United States, the Federal Railroad Administration has developed a system of classification for track quality. The class a track is placed in determines speed limits and the ability to run passenger trains.

See also

Wikimedia Commons has media related to:
[Special]

Rail gauge
Broad gauge
Standard gauge
Narrow gauge
Dual gauge
Break-of-gauge
Breitspurbahn
Rail tracks
Tramway track
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