History of the railway track
The railway track or permanent way is the elements of railway lines: generally the pairs of rails typically laid on the sleepers or ties embedded in ballast, intended to carry the ordinary trains of a railway. It is described as a permanent way because, in the earlier days of railway construction, contractors often laid a temporary track to transport spoil and materials about the site; when this work was substantially completed, the temporary track was taken up and the permanent way installed.
The earliest tracks consisted of wooden rails on transverse wooden sleepers, which helped maintain the spacing of the rails. Various developments followed, with cast iron plates laid on top of the wooden rails and later wrought iron plates or wrought iron angle plates. Rails were also individually fixed to rows of stone blocks, without any cross ties to maintain correct separation. This system also led to problems, as the blocks could individually move. The first version of Isambard Kingdom Brunel's broad gauge system used rails laid on longitudinal sleepers whose rail gauge and elevation were pinned down by being tied to piles, but this arrangement was expensive and Brunel soon replaced it with what became the classic broad gauge track, in which the piles were forgone and transoms, similar to sleepers, maintained the rail gauge. Today, most rail track uses the standard system of rail and sleepers; ladder track is used in a few applications.
Developments in manufacturing technologies has led to changes to the design, manufacture and installation of rails, sleepers and the means of attachments. Cast iron rails, long, began to be used in the 1790s and by 1820, wrought iron rails were in use. The first steel rails were made in 1857 and standard rail lengths increased over time from. Rails were typically specified by units of weight per linear length and these also increased. Railway sleepers were traditionally made of Creosote-treated hardwoods and this continued through to modern times. Continuous welded rail was introduced into Britain in the mid 1960s and this was followed by the introduction of concrete sleepers.
Wooden tracked systems
Plank ways
The earliest use of a railway track seems to have been in connection with mining in Germany in the 12th century. Mine passageways were usually wet and muddy, and moving barrows of ore along them was extremely difficult. Improvements were made by laying timber planks so that wheeled containers could be dragged along by manpower. By the 16th century, the difficulty of keeping the wagon running straight had been solved by having a pin going into a gap between the planks. Georg Agricola describes box-shaped carts, called "dogs", about half as large again as a wheelbarrow, fitted with a blunt vertical pin and wooden rollers running on iron axles. An Elizabethan era example of this has been discovered at Silvergill in Cumbria, England, and they were probably also in use in the nearby Mines Royal of Grasmere, Newlands and Caldbeck. Where space permitted round-section wooden tracks to take trucks with flanged wheels were installed: a painting from 1544 by the Flemish artist Lucas Gassel shows a coppermine with rails of this type emerging from an adit.Edged rails
A different system was developed in England, probably in the late 16th century, near Broseley for conveying coal from mines, sometimes drift mines down the side of the Severn Gorge to the River Severn. This, probably a rope-hauled incline plane, had existed 'long before' 1605. This probably preceded the Wollaton Wagonway of 1604, which has hitherto been regarded as the first.In Shropshire, the gauge was usually narrow, to enable the wagons to be taken underground in drift mines. However, by far the greatest number of wagonways were near Newcastle upon Tyne, where a single wagon was hauled by a horse on a wagonway of about the modern standard gauge. These took coal from the pithead down to a staithe, where the coal was loaded into river boats called keels.
Wear of the timber rails was a problem. They could be renewed by turning them over, but had to be regularly replaced. Sometimes, the rail was made in two parts, so that the top portion could easily be replaced when worn out. The rails were held together by wooden sleepers, covered with ballast to provide a surface for the horse to walk on.
Early iron rails
Cast iron strips could be laid on top of timber rails, and the use of such materials probably occurred in 1738, but there are claims that this technology went back to 1716. In 1767, Ketley ironworks began producing cast iron plates, which were fixed to the top of wooden rails with nails, to provide a more durable running surface. This construct was known as strap-iron rail and was widely used on pre-steam railways in the United States. Although relatively cheap and quick to build, they were unsuited to heavy loads and required 'excessive maintenance'. Train wheels rolling over the spikes loosened them, allowing the rail to break free and curve upwards sufficiently that a car wheel could get beneath it and force the end of the rail up through the floor of the car, writhing and twisting, endangering passengers. These broken rails became known as "snake heads".When wrought iron became available, wrought iron plates provided an even more durable surface. The rails had projecting lugs with a hole to enable them to be fixed to the underlying wooden rail.
Iron plateways
An alternative was developed by John Curr of Sheffield, the manager of the Duke of Norfolk's colliery there. This had a L-shaped rail, so that the flange was on the rail rather than on the wheel. This was also used by Benjamin Outram of Butterley Ironworks and William Jessop. These were used to transport goods for relatively short distances down to canals, though Curr's ran between the manor colliery and Sheffield town. These rails are referred to as plates, and the railway is sometimes called a plateway. The term "platelayer" also derives from this origin. In theory, the unflanged wheels could have been used on ordinary highways, but in practice this was probably rarely done, because the wagon wheels were so narrow that they would have dug into the road surface.The system found wide adoption in Britain. Often, the plates were mounted on stone blocks, and sometimes without sleepers, but that was liable to cause the rails to spread apart, increasing the gauge. Railways of this kind were widely used in south Wales, particularly to transport limestone down to the ironworks, and then to take the iron to a canal, sometimes several miles away, which took the products to market. The rails were at first made of cast iron, typically in lengths of, spanning between stone blocks.
The stone blocks had been assumed to be permanent, but experience quickly showed that they settled and gradually moved under traffic, creating chaotic track geometry and causing derailments. Another problem was that the running surface was liable to become obstructed by stones, displaced from the ballast. An alternative was to use an iron tie bar to keep the rails to the proper gauge, incorporating a shoe in which the rail was fixed.
An example of this was the Penydarren or Merthyr tramway. This was used by Richard Trevithick to demonstrate a pioneer locomotive in 1804, using one of his high pressure steam engines, but the engine was so heavy that it broke many of the rails.
Early edge rails
Cast iron edge rails were used by Thomas Dadford Jr. when building the Beaufort and Blaenavon lines to the Monmouthshire canal in 1793. These were rectangular, in width with a depth of and in length, and required flanges on the wagon wheels. The same year, Benjamin Outram used edge rails on the Cromford Canal. T-shaped beams were used by William Jessop on the Loughborough-Nanpantan line in 1794, and his sons used I-shaped beams in 1813–15 on a railway from Grantham to Belvoir Castle. Samples of these rails are held in the Science Museum, London.A short-lived alternative was the fish-bellied profile, first used by Thomas Barnes at Walker Colliery, near Newcastle in 1798, which enabled rails to have a longer span between blocks. These were T-section edge rails, three feet long and laid on transverse stone sleepers. These were still made of cast iron.
Butt and lap joints
The earliest rails had square butt joints, which were weak and difficult to keep in alignment. George Stephenson introduced lapped joints, which maintained their alignment quite well.Modern edge rails
The breakthrough came when John Birkinshaw of Bedlington Ironworks in Northumberland developed rolled wrought iron rails in 1820 in lengths, as used for the Stockton and Darlington Railway. This was strong enough to bear the weight of a locomotive and of a train of wagons pulled by it. This marks the beginning of the modern rail era. This system was instantly successful, although some false starts took place. Some early rails were made in a T cross section, but the lack of metal at the foot limited the bending strength of the rail, which has to act as a beam between supports.As metal technologies improved, these wrought iron rails were made progressively somewhat longer, and with a heavier, and therefore stronger, cross-section. By providing more metal in the foot of the rail, a stronger beam was created, achieving much better strength and stiffness, and a section was created similar to the bullhead rail section still visible today. This was expensive, however, and the promoters of early railways struggled with decisions about the appropriate weight of their rails.
At first, the rail section was almost symmetrical top-to-bottom, and was described as a double-headed rail. The intention was to invert the rail after the top surface had become worn, but rails tend to develop chair gall, an attrition of the rail where it is supported in the chairs, and this would have made running on the former bottom surface impossibly noisy and irregular. It was better to provide the extra metal on the top surface and gain extra wear there without the need to invert the rail at its half life.
Many railways preferred a flat bottom rail section, where the rails could be laid directly on the sleepers, representing a marked cost saving. Indenting of the sleeper was the problem; where the traffic was heavy, it became necessary to provide a sole plate under the rails to spread the load on the tie, partly vitiating the cost saving. However, in main line situations, this form found almost universal adoption in North America and Australia, and in much of continental Europe. The United Kingdom persisted with bullhead rail in main line use, with widespread introduction of flat-bottom rail only starting in about 1947.