Railway track

Gravel or small stones were packed around the sleepers to hold them in place and provide a walkway for the people or horses that moved wagons along the track.

As locomotives became more widespread in the 1810s and 1820s, engineers built rigid track formations, with iron rails mounted on stone sleepers, and cast-iron chairs holding them in place.

This proved to be a mistake, and was soon replaced with flexible track structures that allowed a degree of elastic movement as trains passed over them.

[5][6] Most modern railroads with heavy traffic use continuously welded rails that are attached to the sleepers with base plates that spread the load.

Rail is usually attached to the sleeper with resilient fastenings, although cut spikes are widely used in North America.

In North America and Australia, flat-bottomed rails were typically fastened to the sleepers with dog spikes through a flat tie plate.

In 1936, the London, Midland and Scottish Railway pioneered the conversion to flat-bottomed rail in Britain, though earlier lines had made some use of it.

However, the intrinsic weakness in resisting vertical loading results in the ballast becoming depressed and a heavy maintenance workload is imposed to prevent unacceptable geometrical defects at the joints.

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).

However, ballastless track has a high initial cost, and in the case of existing railroads the upgrade to such requires closure of the route for a long period.

[10] The system was tested on the Baltimore and Ohio railway in the 1840s, but was found to be more expensive to maintain than rail with cross sleepers.

Ladder track utilizes sleepers aligned along the same direction as the rails with rung-like gauge restraining cross members.

The traditional method of joining the rails is to bolt them together using metal fishplates (jointbars in the US), producing jointed track.

Because of these small gaps, when trains pass over jointed tracks they make a "clickety-clack" sound, and in time the rail ends are deflected downwards.

Unless it is well-maintained, jointed track does not have the ride quality of welded rail and is not suitable for high speed trains.

A major problem of jointed track is cracking around the bolt holes, which can lead to breaking of the rail head (the running surface).

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.

The preferred process of flash butt welding involves an automated track-laying machine running a strong electric current through the touching ends of two unjoined rails.

In North American practice, extreme temperature conditions will trigger slow orders to allow for crews to react to buckling or "sun kinks" if encountered.

[34] The German railway company Deutsche Bahn is starting to paint rails white to lower the peak temperatures reached in summer days.

This installation procedure is intended to prevent tracks from buckling in summer heat or pulling apart in the winter cold.

In North America, because broken rails are typically detected by interruption of the current in the signaling system, they are seen as less of a potential hazard than undetected heat kinks.

In 1880 in New York City, sections of heavy portable track (along with much other improvised technology) helped in the move of the ancient obelisk in Central Park to its final location from the dock where it was unloaded from the cargo ship SS Dessoug.

Track maintenance was at one time hard manual labour, requiring teams of labourers, or trackmen (US: gandy dancers; UK: platelayers; Australia: fettlers or packers) under the supervision of a skilled ganger, who used lining bars to correct irregularities in horizontal alignment (line) of the track, and tamping and jacks to correct vertical irregularities (surface).

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.

Worn mainline rails usually have sufficient life remaining to be used on a branch line, siding or stub afterwards and are "cascaded" to those applications.

In the UK, 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.

The formation comprises the subgrade 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.

Reinforcement geosynthetics increase soil bearing capacity, limit ballast movement and degradation and reduce differential settlement that affects track geometry.

Geocells can utilize recycled marginal or poorly graded granular material to create stable embankments, make railway construction more economical and sustainable.