The usual track form consists of the two steel rails, secured on sleepers (or crossties, shortened to ties, in the US) so as to keep the rails at the correct distance apart (the gauge) and capable of supporting the weight of trains. There are various types of sleepers and methods of securing the rails to them. Sleepers are normally spaced at 650 mm (25 ins) to 760 mm (30 ins) intervals, depending on the particular railway's standard requirements.
The gauge of track is the distance between the inner edges of the rails at points 1.59 cm (0.626 in) below the top of the heads. In the United States, Canada, the United Kingdom, Mexico, Norway, Sweden, and much of continental Europe, the standard gauge is 143.51 cm (56.5 in). Why this measurement became the standard is a matter of speculation. Probably the tradition is inherited from early tramroads built to accommodate wagons with axles 1.5 m (5 ft) long; some of the early edge rails were 4.45 cm (1.75 in) wide at the top, and the installation of such rails on plateways of the traditional width would have resulted in the 143.51-cm gauge.
Traditionally, sleepers (known as ties in the US) are wooden. They can be softwood or hardwood. Most in the UK are softwood, although London Underground uses a hardwood called Jarrah wood. Sleepers are normally impregnated with preservative and, under good conditions, will last up to 25 years. They are easy to cut and drill and used to be cheap and plentiful. Nowadays, they are becoming more expensive and other types of materials have appeared, notably concrete and steel.
Concrete is the most popular of the new types (left). Concrete sleepers are much heavier than wooden ones, so they resist movement better.
They work well under most conditions but there are some railways which have found that they do not perform well under the loads of heavy haul freight trains. They offer less flexibility and are alleged to crack more easily under heavy loads with stiff ballast. They also have the disadvantage that they cannot be cut to size for turnouts and special trackwork. A concrete sleeper can weighs up to 320 kg (700 lbs) compared with a wooden sleeper which weighs about 100 kg or 225 lbs. The spacing of concrete sleepers is about 25% greater than wooden sleepers.
Throughout most of the 19th century many railroad companies each built track with a different gauge; some gauges were wider than 143.51 cm and some narrower. About 1870 many railroads began to adopt a narrower gauge, usually 0.9 m (3 ft). The arguments in favor of this gauge were that narrower fills and clearances were needed, lighter rails could be used, and a sharper curvature of the tracks was permissible. In 1871, 1,476 km (917 mi) of narrow-gauge track was under construction in the United States.
After the so-called railroad panic of 1873, in which the price of railroad stocks fell sharply, railroad construction of all sorts slowed down. Some authorities maintain that the panic accelerated the use of narrow-gauge tracks in the construction that did take place because it was more economical. Freight shipped over long distances, however, had to be transferred from one freight car to another whenever it reached a junction where the rail gauge changed. The excessive cost of handling at junctions between different roads led to the adoption of the standard gauge by almost all U.S. railroads by about 1886. In the years immediately following, mutual agreements to handle one another's rolling stock at fixed rates were worked out by numerous U.S. railroads.
There was little standardization in the early days of railroad construction. As a result, many railroads in different parts of the world use different gauges. Several countries use standard gauge for their railroads, but many use wider or narrower gauges. The lack of standardized rail widths creates problems for international passengers wishing to travel through several countries. If the tracks of neighboring countries are incompatible, passengers have to change trains at border crossings before continuing on their journey.