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Railroad or railway tracks are used on railways, which, together with railroad switches (points), guide trains without the need for steering. Tracks 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.
Rails, being made of steel, can carry heavier loads than any other material.
Sleepers spread the load on the rails, 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 ballast, which combines resilience, some amount of flexibility, and good drainage; however, track can also be laid on or into concrete (this is called slab track).
Across bridges track is often laid on sleepers across longitudinal timbers.
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 bolts (usually four, but sometimes up to six). 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, 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 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. Early railroads sometimes used 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. However, the long term expense involved in frequent maintenance outweighed any savings.
Unlike 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.
The rails represent a substantial fraction of the cost of a railway line.
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 very few 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, 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 stretched so they expand (this is called stressing), they are then fastened (clipped) to the sleepers in their expanded form. This ensures that the rail will not expand much further in subsequent hot weather. 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; 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.