Third rail

Some high third rail voltages (1000 volts and more) include:


In Nazi Germany, a railway system with a 3,000 mm (9 ft 10+1⁄8 in) gauge width was planned. For this Breitspurbahn railway system, electrification with a voltage of 100 kV taken from a third rail was considered, in order to avoid damage to overhead wires from oversize rail-mounted anti-aircraft guns. However, such a power system would not have worked as it is not possible to insulate a third rail for such high voltages in close proximity to the rails. The whole project did not progress any further owing to the onset of World War II.

Third-rail electrification systems are, apart from on-board batteries, the oldest means of supplying electric power to trains on railways using their own corridors, particularly in cities. Overhead power supply was initially almost exclusively used on tramway-like railways, though it also appeared slowly on mainline systems.


An experimental electric train using this method of power supply was developed by the German firm of Siemens & Halske and shown at the Berlin Industrial Exposition of 1879, with its third rail between the running rails. Some early electric railways used the running rails as the current conductor, as with the 1883-opened Volk's Electric Railway in Brighton. It was given an additional power rail in 1886, and is still operating. The Giant's Causeway Tramway followed, equipped with an elevated outside third rail in 1883, later converted to overhead wire. The first railway to use the central third rail was the Bessbrook and Newry Tramway in Ireland, opened in 1885 but now, like the Giant's Causeway line, closed.


Also in the 1880s, third-rail systems began to be used in public urban transport. Trams were first to benefit from it: they used conductors in conduit below the road surface (see Conduit current collection), usually on selected parts of the networks. This was first tried in Cleveland (1884) and in Denver (1885) and later spread to many big tram networks (e.g. New York; Chicago; Washington, DC; London; Paris, all of which are closed) and Berlin (the third-rail system in the city was abandoned in the early 20th century after heavy snowfall.) The system was tried in the beachside resort of Blackpool, UK, but was soon abandoned as sand and saltwater were found to enter the conduit and cause breakdowns, and there was a problem with voltage drop. Some sections of tramway track still have the slot rails visible.


A third rail supplied power to the world's first electric underground railway, the City & South London Railway, which opened in 1890 (now part of the Northern line of the London Underground). In 1893, the world's second third-rail powered city railway opened in Britain, the Liverpool Overhead Railway (closed 1956 and dismantled). The first US third-rail powered city railway in revenue use was the 1895 Metropolitan West Side Elevated, which soon became part of the Chicago 'L'. In 1901, Granville Woods, a prominent African-American inventor, was granted a U.S. patent 687,098, covering various proposed improvements to third-rail systems. This has been cited to claim that he invented the third-rail system of current distribution. However, by that time there had been numerous other patents for electrified third-rail systems, including Thomas Edison's U.S. patent 263,132 of 1882, and third rails had been in successful use for over a decade, in installations including the rest of Chicago 'elevateds', as well as those used in Brooklyn Rapid Transit Company, not to mention the development outside the US.


In Paris, a third rail appeared in 1900 in the main-line tunnel connecting the Gare d'Orsay to the rest of the CF Paris-Orléans network. Main-line third-rail electrification was later expanded to some suburban services.


The Woodford haulage system was used on industrial tramways, specifically in quarries and strip mines in the early decades of the 20th century. This used a 250-volt center third rail to power remotely-controlled self-propelled side dump cars.^[19][20] The remote control system was operated like a model railroad, with the third rail divided into multiple blocks that could be set to power, coast, or brake by switches in the control center.


Top contact or gravity type third rail seems to be the oldest form of power collection. Railways pioneering in using less hazardous types of third rail were the New York Central Railroad on the approach to New York's Grand Central Terminal (1907 – another case of a third-rail mainline electrification), Philadelphia's Market–Frankford Line (1907), and the Hochbahn in Hamburg (1912) each had bottom contact rail, also known as the Wilgus-Sprague system.^[21] However, the Manchester-Bury Line of the Lancashire & Yorkshire Railway tried side contact rail in 1917. These technologies appeared in wider use only at the turn of the 1920s and in the 1930s on, e.g., large-profile lines of the Berlin U-Bahn, the Berlin S-Bahn and the Moscow Metro. The Hamburg S-Bahn has used a side contact third rail at 1200 V DC since 1939.


In 1956, the world's first rubber-tyred railway line, Line 11 of Paris Metro, opened. The conductor rail evolved into a pair of guiding rails required to keep the bogie in proper position on the new type of track. This solution was modified on the 1971 Namboku Line of Sapporo Subway, where a centrally placed guiding/return rail was used plus one power rail placed laterally as on conventional railways.


In 2004, the third-rail technology at street tram lines was in the new system of Bordeaux (2004). This is a completely new technology (see below).


Third-rail systems are not considered obsolete. There are, however, countries (particularly Japan, South Korea, Spain) more eager to adopt overhead wiring for their urban railways. But at the same time, there were (and still are) many new third-rail systems built elsewhere, including technologically advanced countries (e.g. Copenhagen Metro, Taipei Metro, Wuhan Metro). Bottom-powered railways (it may be too specific to use the term third-rail) are also usually used with systems having rubber-tyred trains, whether it is a heavy metro (except two other lines of Sapporo Subway) or a small capacity people mover (PM). New electrified railway systems tend to use overhead for regional and long-distance systems. Third-rail systems using lower voltages than overhead systems still require many more supply points.