Track gauge in the context of "Loading gauge"

A train (from Old French trahiner, from Latin trahere, "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often known simply as "engines"), though some are self-propelled, such as multiple units or railcars. Passengers and cargo are carried in railroad cars, also known as wagons or carriages. Trains are designed to a certain gauge, or distance between rails. Most trains operate on steel tracks with steel wheels, the low friction of which makes them more efficient than other forms of transport. Many countries use rail transport.

Trains have their roots in wagonways, which used railway tracks and were powered by horses or pulled by cables. Following the invention of the steam locomotive in the United Kingdom in 1802, trains rapidly spread around the world, allowing freight and passengers to move over land faster and cheaper than ever possible before. Rapid transit and trams were first built in the late 1800s to transport large numbers of people in and around cities. Beginning in the 1920s, and accelerating following World War II, diesel and electric locomotives replaced steam as the means of motive power. Following the development of cars, trucks, and extensive networks of highways which offered greater mobility, as well as faster airplanes, trains declined in importance and market share, and many rail lines were abandoned. The spread of buses led to the closure of many rapid transit and tram systems during this time as well.

The Hejaz railway (also spelled Hedjaz or Hijaz; Arabic: سِكَّة حَدِيد الحِجَاز sikkat ḥadīd al-ḥijāz or Arabic: الخَط الحَدِيدِي الحِجَازِي, Ottoman Turkish: حجاز دمیریولی, Turkish: Hicaz Demiryolu) was a narrow-gauge railway (1,050 mm / 3 ft 5+11⁄32 in track gauge) that ran from Damascus to Medina, through the Hejaz region of modern-day Saudi Arabia, with a branch line to Haifa on the Mediterranean Sea. The project was ordered by Sultan Abdul Hamid II in March 1900.

It was a part of the Ottoman railway network and the original goal was to extend the line from the Haydarpaşa Terminal in Kadıköy, Istanbul beyond Damascus to the Islamic holy city of Mecca. However, construction was interrupted due to the outbreak of World War I, and it reached only to Medina, 400 kilometres (250 mi) short of Mecca. The completed Damascus to Medina section was 1,300 kilometres (810 mi). It was the only railway completely built and operated by the Ottoman Empire.

A standard-gauge railway is a railway with a track gauge of 1,435 mm (4 ft 8+1⁄2 in). The standard gauge is also called Stephenson gauge (after George Stephenson), international gauge, UIC gauge, uniform gauge, normal gauge in Europe, and SGR in East Africa. It is the most widely used track gauge around the world, with about 55% of the lines in the world using it.

All high-speed rail lines use standard gauge except those in Russia, Finland, Uzbekistan, and some line sections in Spain. The distance between the inside edges of the heads of the rails is defined to be 1,435 mm except in the United States, Canada, and on some heritage British lines, where it is defined in U.S. customary/British Imperial units as exactly "four feet eight and one half inches", which is equivalent to 1,435.1 mm.

Track geometry is concerned with the properties and relations of points, lines, curves, and surfaces in the three-dimensional positioning of railroad track. The term is also applied to measurements used in design, construction and maintenance of track. Track geometry involves standards, speed limits and other regulations in the areas of track gauge, alignment, elevation, curvature and track surface. Standards are usually separately expressed for horizontal and vertical layouts although track geometry is three-dimensional. Modern maintenance regimes increasingly use 3D laser scanning (LiDAR) to capture these geometric parameters and assess structure gauge compliance without physical contact.

A dual gauge railroad track has three or four rails, allowing vehicles of two track gauges to run on it.

Signalling and sidings are more expensive to install on dual gauge tracks than on two single gauge tracks. Dual gauge is used when there is not enough room for two single tracks or when tracks of two different gauges meet in marshalling yards or train stations.

Tramway track is used on tramways or light rail operations. As with standard rail tracks, tram tracks have two parallel steel rails, the distance between the heads of the rails being the track gauge. When there is no need for pedestrians or road vehicles to traverse the track, conventional flat-bottom rail is used. However, when such traffic exists, such as in urban streets, grooved rails are used.

Tram rails can be placed on several surfaces, such as on ground over which track ballast topped by sleepers (US: ties) and flat-bottom rails are laid – as with railway tracks – or, for street running, with grooved rails usually embedded into a concrete pavement. In some places, tracks are laid into grass turf surfaces; they are known as green track, grassed track or track in lawn.

Gauntlet track, also called interlaced track or gantlet track (AE) is an arrangement in which railway tracks run parallel on a single track bed and are interlaced (i.e., overlapped) in such a way that only one pair of rails can be used at any time. Since this requires only slightly more width than a single track, all rails can be carried on the same crossties/sleepers. Trains run on the pair of rails appropriate to their direction, track gauge or loading gauge.

The term gauntlet refers to the expression running the gauntlet, which means running between two confining rows of adversaries.

Metre-gauge railways (US: meter-gauge railways) are narrow-gauge railways with track gauge of 1,000 mm (3 ft 3+3⁄8 in) or 1 metre.

Metre gauge is used in around 95,000 kilometres (59,000 mi) of tracks around the world. It was used by several European colonial powers including France, Britain and Germany in their colonies. In Europe, large metre-gauge networks remain in use in Switzerland, Spain and many European towns with urban trams, but most metre-gauge local railways in France, Germany and Belgium closed down in the mid-20th century, although some still remain. With the revival of urban rail transport, metre-gauge light metros were built in some cities. The slightly-wider 1,009 mm (3 ft 3+23⁄32 in) gauge is used in Sofia, Bulgaria. Another similar gauge is 3 ft 6 in (1,067 mm).