RAIL TRACKS

Rail tracks (also railway tracks, railroad tracks (US) or tracks) are used on railways (or railroads), which, together with points (UK) (or switches, US), guide trains without the need for steering. Tracks consist of two parallel steel rails, generally laid on sleepers (cross ties) that are embedded in ballast, to form the railroad track. The rail is fastened to the ties with spikes, lag screws, bolts, or clips such as Pandrol clips.The type of fastener depends partly on the type of sleeper, with spikes being used on wooden sleepers, bolts on steel sleepers, and clips being used more on concrete sleepers.

Usually, a baseplate (tie plate) is used between the rail and wood sleepers, to spread the load of the rail over a larger area of the sleeper. Sometimes spikes are driven through a hole in the baseplate to hold the rail, while at other times the baseplates are spiked or screwed to the sleeper and the rails clipped to the baseplate.Steel rails can carry heavier loads than any other material. Railroad ties spread the load from the rails over the ground and also hold the rails a fixed distance apart (the gauge.)

Rail tracks are normally laid on a bed of coarse, crushed stone known as ballast, which combines resilience, some amount of flexibility, and good drainage. Steel rails can also be laid onto a concrete slab (slab track). Across bridges, track is often laid on ties across longitudinal timbers ("wheeltimbers" or "waybeams") or longitudinal steel girders. 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 per yard (usually shown as 'pound' or 'lb'), so "130-pound rail" would weigh 130 lb per linear yard (64 kg/m). The usual range is 115 to 141 lb/yd (about 57 to about 70 kg/m). In Europe, rail is graded in kg/m and the usual range is 40 to 60 kg/m (81 to 121 lb/yd). The heaviest rail mass-produced was 155 pounds per yard (about 77 kg/m) and was rolled for the Pennsylvania Railroad. The UK is in the process of transition from the imperial to metric rating of rail.

Fishplates are usually 600 mm (2 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 and a wheel flange 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 joints 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.