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Rail tracks

Railroad or railway tracks are used on railways to guide trains. They consist of two parallel steel rails, which are laid and fastened upon sleepers (or cross ties) which are embedded in ballast to form the railroad track. Rail tracks are normally laid on a bed of coarse stone chippings known as ballast, which combines resilience, some amount of flexibility, and good drainage; however, track can also be laid on or into concrete (across bridges, for example).

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 (UK) (crossties, or simply ties in US practice), and are joined to other lengths of rail with steel plates known as fishplates (UK) or splices (US).

Fishplates or splices are usually 60 centimetres (2 feet) long, and are bolted through each side of the rail ends with four bolts. Small gaps are deliberately left between the rails, which are known as "expansion joints" 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, while 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 and unimportant lines. 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 much cheaper supply of timber in the US makes its use for railroad ties much cheaper than in Europe.

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

There are several methods used to fasten rail to wooden sleepers / ties. In traditional British practice, cast metal chairs were bolted to the sleepers, which took a style of rail known as bullhead which was somewhat figure-8 in cross-section - wider at top and bottom and smaller in the middle. Wedges of wood or sprung steel were then driven in between chair and rail to hold it in place.

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 unnused side, thus extending the rail's lifespan.

Like most of the world, Britain now uses flat bottomed rail which has become the worldwide standard type of 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 held to the sleeper with a baseplate, a metal plate which is attached to the sleeper.

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, named after its maker, which is shaped like a sturdy, stubby paperclip.

American practice normally uses 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 does. This is mitigated by using very large and solid ties and using rot-proofing preservative.

Most modern railways use continuous welded rail (CWR) in this form of track the rails are welded together for several kilometres, to form one long continuous rail. Because there are few joints, this form of track is very strong and gives a smooth ride, and also needs less maintenance.

Because of its strength, trains traveling 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 no expansion joints, if special measures are not taken, it could become distorted in hot weather and cause a derailment.

To avoid this happening welded rails are nearly always laid on concrete sleepers, which are so heavy they hold the rails firmly in place. Soon after the segments of rail are laid, the rails are artificially heated to normal summertime temperatures so that they expand, they are then quickly fastened tightly to the sleepers in their expanded form and then welded to the next segment of rail, this ensures that the rail will not expand any further in subsequent hot weather. And because they are firmly fastened to the sleepers, they cannot shrink in cold weather either. However if temperatures reach outside normal ranges (i.e a hotter than usual summer), it can cause problems with welded rails.

Joints are used in continuously welded rail when necessary, though; 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. This gives a much smoother transition yet still provides some expansion room.

Track needs frequent maintenance to remain in good order, the frequency increasing with higher-speed or heavier trains. This was formerly hard manual labor, but these days is handled by a variety of specialised machines.

See also