Third rail
Overview
 
A third rail is a method of providing electric power
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 to a railway
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

 train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit
Rapid transit
A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 system, which has alignments in its own corridors, fully or almost fully segregated from the outside environment. In most cases, third rail systems supply direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 electricity.

The third-rail system of electrification is unrelated to the third rail used in dual-gauge railways.
Third rail systems are a means of providing electric traction power to railway trains, and they use an additional rail (called a "conductor rail") for the purpose.
Encyclopedia
A third rail is a method of providing electric power
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 to a railway
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

 train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit
Rapid transit
A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 system, which has alignments in its own corridors, fully or almost fully segregated from the outside environment. In most cases, third rail systems supply direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 electricity.

The third-rail system of electrification is unrelated to the third rail used in dual-gauge railways.

Description

Third rail systems are a means of providing electric traction power to railway trains, and they use an additional rail (called a "conductor rail") for the purpose. On most systems, the conductor rail is placed on the sleeper ends outside the running rails, but in some cases a central conductor rail is used. The conductor rail is supported on ceramic insulators or insulated brackets, typically at intervals of 10 feet (3 m) or so.

The trains have metal contact blocks called "shoes" which make contact with the conductor rail. The traction current is returned to the generating station through the running rails. The conductor rail is usually made of high conductivity steel, and the running rails have to be electrically connected using wire bonds or other devices, to minimize resistance in the electric circuit.

The conductor rails have to be interrupted at level crossings and at crossovers, and ramps are provided at the ends of the sections to give a smooth transition to the train shoes.

There is considerable diversity about the contact position between the train and the rail; some of the earliest systems used top contact, but developments used side or bottom contact, which enabled the conductor rail to be covered, protecting track workers from accidental contact and protecting the conductor rail from snow and leaf fall.

Benefits and disadvantages of third-rail systems

Electric traction systems (where electric power is generated at a remote power station and transmitted to the trains) are considerably more cost-effective than diesel or steam units, where the power unit is carried on the train. This advantage is especially marked in urban and rapid transit systems with a high traffic density.

So far as initial cost is concerned, third-rail systems are cheaper to install, compared to overhead wire
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 contact systems, as no structures for carrying the overhead contact wires are required, and there is no need to reconstruct overbridges to provide clearances. There is also much less visual intrusion on the environment.

However as third rail systems present the hazard of electric shock, higher system voltages (above 1500 V) are not considered safe. Very high currents are therefore used, resulting in considerable power loss in the system, and requiring relatively closely spaced feed points (sub-stations).

The presence of an electrified rail also makes it extremely dangerous for a person to fall into the tracks. This, however, can be avoided using platform screen doors
Platform screen doors
Platform screen doors and platform edge doors at train or subway stations screen the platform from the train. They are a relatively new addition to many metro systems around the world, with some platform doors retrofitted rather than installed with the metro system itself. They are widely used in...

 or the risk minimized by ensuring that the conductor rail is on the side of the track away from the platform.

Furthermore, third rail systems must either be fully grade-separated, or, if they operate at-grade, they must implement some kind of mechanism to effectively stop pedestrians from walking onto the tracks at grade crossings
Level crossing
A level crossing occurs where a railway line is intersected by a road or path onone level, without recourse to a bridge or tunnel. It is a type of at-grade intersection. The term also applies when a light rail line with separate right-of-way or reserved track crosses a road in the same fashion...

. A famous 1992 Supreme Court of Illinois
Supreme Court of Illinois
The Supreme Court of Illinois is the state supreme court of Illinois. The court's authority is granted in Article VI of the current Illinois Constitution, which provides for seven justices elected from the five appellate judicial districts of the state: Three justices from the First District and...

 decision affirmed a $1.5 million verdict against the Chicago Transit Authority
Chicago Transit Authority
Chicago Transit Authority, also known as CTA, is the operator of mass transit within the City of Chicago, Illinois and some of its surrounding suburbs....

 for failing to stop an intoxicated person from walking onto the tracks at a grade crossing and attempting to urinate on the third rail.

The end ramps of conductor rails (where they are interrupted, or change sides) present a practical limitation on speed due to the mechanical impact of the shoe, and 160 km/h (99.4 mph) is considered the upper limit of practical third-rail operation, however no testing over 100 mph (44.7 m/s) has been attempted. The world speed record for a third rail train is 174 km/h (108.1 mph) attained on 11 April 1988 by a British Class 442
British Rail Class 442
The British Rail Class 442 Wessex Electric electrical multiple units were introduced in 1988 on the South Western Main Line from London Waterloo to Southampton Central, Bournemouth, Poole and Weymouth. Twenty-four of these 5-car units were built in 1988/89 by BREL at its Derby works...

 EMU.

Third rail systems using top contact are prone to accumulations of snow, and ice formed from refrozen snow, and this can interrupt operations. Some systems operate dedicated de-icing trains to deposit an oily fluid on the conductor rail to prevent the build-up.

Because of the gaps in the conductor rail (at level crossings and crossovers) it is possible for a train to stop in a position where all of its shoes are in gaps, so that no traction power is available. The train is said to be "gapped". In these circumstances a following train is brought up behind the stranded train to push it on to the conductor rail or a jumper cable is used to supply enough power to the train to get one of its contact shoes back on the third rail. On some systems this prevents the running of very short trains (which have fewer shoes).

History

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
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

 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
Volk's Electric Railway
Volk's Electric Railway is the oldest operating electric railway in the world. It is a narrow gauge railway that runs along a length of the seafront of the English seaside resort of Brighton...

 in Brighton. It was given an additional power rail in 1886, and is still operating. The Giant's Causeway Tramway
Giant's Causeway Tramway
The Giant's Causeway Tramway, operated by the Giant's Causeway, Portrush and Bush Valley Railway & Tramway Company Ltd, was a pioneering gauge electric narrow gauge railway operating between Portrush and the Giant's Causeway on the coast of County Antrim, Northern Ireland...

 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
Public transport
Public transport is a shared passenger transportation service which is available for use by the general public, as distinct from modes such as taxicab, car pooling or hired buses which are not shared by strangers without private arrangement.Public transport modes include buses, trolleybuses, trams...

. Trams were first to benefit from it: they used conductors in conduit below the road surface (see Conduit current collection
Conduit current collection
Conduit current collection is a system of electric current collection used by electric trams, where the power supply is carried in a channel under the roadway, rather than located overhead.-Description:...

), 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. Manhattan, Chicago, Washington DC, London, Paris, all closed) and Berlin (the third rail system in the city was abandoned in the first years of the 20th century after heavy snowfall.) The system was tried in the beachside resort of Blackpool
Blackpool
Blackpool is a borough, seaside town, and unitary authority area of Lancashire, in North West England. It is situated along England's west coast by the Irish Sea, between the Ribble and Wyre estuaries, northwest of Preston, north of Liverpool, and northwest of Manchester...

, UK but was soon abandoned as sand and saltwater was 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
City & South London Railway
The City and South London Railway was the first deep-level underground "tube" railway in the world, and the first major railway to use electric traction...

, which opened in 1890 (now part of the Northern Line
Northern Line
The Northern line is a London Underground line. It is coloured black on the Tube map.For most of its length it is a deep-level tube line. The line carries 206,734,000 passengers per year. This is the highest number of any line on the London Underground system, but the Northern line is unique in...

 of the London Underground). In 1893, the world's second third-rail powered city railway opened in Britain, the Liverpool Overhead Railway
Liverpool Overhead Railway
The Liverpool Overhead Railway was the world's first electrically operated overhead railway. The railway was carried mainly on iron viaducts, with a corrugated iron decking, onto which the tracks were laid. It ran close to the River Mersey in Liverpool, England, following the line of Liverpool Docks...

 (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'
Chicago 'L'
The L is the rapid transit system serving the city of Chicago and some of its surrounding suburbs. It is operated by the Chicago Transit Authority...

. In 1901, Granville Woods
Granville Woods
Granville T. Woods , was an African-American inventor who held more than 60 patents. Most of his work was on trains and street cars. Woods also invented the Multiplex Telegraph, a device that sent messages between train stations and moving trains. Born in Columbus, Ohio, on April 23, 1856,...

, a prominent African-American inventor, was granted a , 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
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...

's 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 these in Brooklyn
Brooklyn
Brooklyn is the most populous of New York City's five boroughs, with nearly 2.6 million residents, and the second-largest in area. Since 1896, Brooklyn has had the same boundaries as Kings County, which is now the most populous county in New York State and the second-most densely populated...

, New York (if not to mention the development outside the US). To what extent Woods' ideas were adopted is thus a matter of controversy.

In Paris, third rail appeared in 1900 in the main-line tunnel connecting the Gare d'Orsay
Gare d'Orsay
Gare d'Orsay is a former Paris railway station and hotel, built in 1900 to designs by Victor Laloux, Lucien Magne and Émile Bénard; it served as a terminus for the Chemin de Fer de Paris à Orléans . It was the first electrified urban rail terminal in the world, opened 28 May 1900, in time for the...

 to the rest of the CF Paris-Orléans network. Main-line third rail electrification was later expanded to some suburban services.

Top contact third rail (see below) 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
New York Central Railroad
The New York Central Railroad , known simply as the New York Central in its publicity, was a railroad operating in the Northeastern United States...

 on the approach to its NYC's Grand Central Terminal
Grand Central Terminal
Grand Central Terminal —often incorrectly called Grand Central Station, or shortened to simply Grand Central—is a terminal station at 42nd Street and Park Avenue in Midtown Manhattan in New York City, United States...

 (1907 — another case of a third-rail mainline electrification), Philadelphia's Market Street Subway-Elevated
Market-Frankford Line
The Market–Frankford Line is a rapid transit line in Philadelphia, Pennsylvania, United States, operated by the Southeastern Pennsylvania Transportation Authority .-Route:The Market–Frankford Line begins at 69th Street Transportation Center, in Upper Darby...

 (1907), and the Hochbahn in Hamburg
Hamburg U-Bahn
The Hamburg U-Bahn is a rapid transit system serving the cities of Hamburg, Norderstedt and Ahrensburg in Germany. Although technically an underground, most of the system's track length is above ground. The network is interconnected with the city's S-Bahn system, which also has underground...

 (1912) — all had bottom contact rail, also known as the Wilgus-Sprague system. 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
Berlin U-Bahn
The Berlin is a rapid transit railway in Berlin, the capital city of Germany, and is a major part of the public transport system of that city. Opened in 1902, the serves 173 stations spread across ten lines, with a total track length of , about 80% of which is underground...

, the Berlin S-Bahn
Berlin S-Bahn
The Berlin S-Bahn is a rapid transit system in and around Berlin, the capital city of Germany. It consists of 15 lines and is integrated with the mostly underground U-Bahn to form the backbone of Berlin's rapid transport system...

 and the Moscow Metro
Moscow Metro
The Moscow Metro is a rapid transit system serving Moscow and the neighbouring town of Krasnogorsk. Opened in 1935 with one line and 13 stations, it was the first underground railway system in the Soviet Union. As of 2011, the Moscow Metro has 182 stations and its route length is . The system is...

. 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
Paris Métro
The Paris Métro or Métropolitain is the rapid transit metro system in Paris, France. It has become a symbol of the city, noted for its density within the city limits and its uniform architecture influenced by Art Nouveau. The network's sixteen lines are mostly underground and run to 214 km ...

, 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.
The third rail technology at street tram lines has recently been revived in the new system of Bordeaux
Tramway de Bordeaux
The Bordeaux tramway network consists of three lines serving the city of Bordeaux in southwestern France. The first line was opened on 21 December 2003; further extensions have increased the route length to . The system is notable for using a ground-level power supply of the Alimentation par Sol...

 (2004). This is a completely new technology (see below).

Third rail is not obsolete. There are, however, countries (particularly Japan, South Korea, India, Spain) more eager to adopt overhead wiring
Pantograph (rail)
A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...

 to 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
Copenhagen Metro
Copenhagen Metro is a rapid transit system serving Copenhagen, Frederiksberg and Tårnby in Denmark. The system opened between 2002 and 2007, and has two lines, M1 and M2. The driverless light metro supplements the larger S-train rapid transit system, and is integrated with DSB local trains and...

, Taipei Metro, Wuhan Metro
Wuhan Metro
The Wuhan Metro is an elevated and underground metro system in the city of Wuhan, Hubei, China. The system opened on 28 July 2004, making Wuhan the fifth city in mainland China to have a metro system after Beijing, Tianjin, Shanghai, Guangzhou...

). Bottom powered railways (it may be too specific to use the term 'third rail') are also usually those having rubber-tyred trains, whether it is a heavy metro (except two other lines of Sapporo Subway) or a small capacity people mover
People mover
A people mover or automated people mover is a fully automated, grade-separated mass transit system.The term is generally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes applied to considerably more complex automated...

 (PM). New electrified railway systems tend to use overhead for regional and long distance systems. Third rail systems using lower voltage than overhead required many more supply points.

Running rails for power supply

The first idea for feeding electricity to a train from an external source was by using both rails on which a train runs, whereby each rail is a conductor for each pole insulated by the sleepers.
This method is used by most model trains, however it does not work so well for large trains as the sleepers are not good insulators, furthermore the use of insulated wheels or insulated axles is required. As most insulation materials have worse static properties compared with metals used for this purpose, this results in a less stable train vehicle.
Nevertheless, it was sometimes used at the beginning of the development of electric trains. The following systems used it:
  • Gross-Lichterfelde Tramway
    Gross-Lichterfelde Tramway
    The Gross Lichterfelde Tramway was the world's first electric tramway. It was built by the Siemens & Halske company in Lichterfelde, a suburb of Berlin, and went in service on 16 May 1881....

  • Ungerer Tramway
    Ungerer Tramway
    The Ungerer Tramway was the first electrical tramway in Munich. It was built by engineer and owner of the Ungerer Bath, August Ungerer to connect the bath with the 750m distant stop of the horse powered tramway. The 1.2 km long Ungerer Tramway existed from 1 July 1886 to June 1895, when it was...



Some trains used for rides for children at beer festivals also use this method for power supply.

Technical aspects

The third rail is usually located outside the two running rails, but occasionally between them. The electricity is transmitted to the train by means of a sliding shoe, which is held in contact with the rail. On many systems an insulating cover is provided above the third rail to protect employees working near the track; sometimes the shoe is designed to contact the side (called side running) or bottom (called bottom running) of the third rail, allowing the protective cover to be mounted directly to its top surface. When the shoe slides on top, it is referred to as top running. When the shoe slides on the bottom it is not affected by the build-up of snow, ice, or leaves.

As with overhead wires, the return current usually flows through one or both running rails, and leakage to ground is not considered serious. Where trains run on rubber tyres, as on parts of the Paris Métro
Paris Métro
The Paris Métro or Métropolitain is the rapid transit metro system in Paris, France. It has become a symbol of the city, noted for its density within the city limits and its uniform architecture influenced by Art Nouveau. The network's sixteen lines are mostly underground and run to 214 km ...

, Mexico City metro
Mexico City Metro
The Mexico City Metro , officially called Sistema de Transporte Colectivo, is a metro system that serves the metropolitan area of Mexico City...

 and Santiago Metro
Santiago Metro
Metro de Santiago is South America's most extensive metro system with 5 lines, 108 stations and 103 kilometres of track making it the second longest in Latin America after that of Mexico City. The metro system serves the city of Santiago, Chile. Three of the lines are rubber-tyred...

, and on all of the Montreal Metro
Montreal Metro
The Montreal Metro is a rubber-tired metro system, and the main form of public transportation underground in the city of Montreal, Quebec, Canada....

, live guide bars must be provided to feed the current. The return is effected through the rails of the conventional track between these guide bars (see rubber-tyred metro
Rubber-tyred metro
A rubber-tyred metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tyres which run on rolling pads inside guide bars for traction, as well as traditional railway steel wheels with deep flanges on steel tracks for guidance through...

). Another design, with a third rail (current feed, outside the running rails) and fourth rail (current return, half way between the running rails), is used by a few steel-wheel systems, see fourth rail. The London Underground
London Underground
The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...

 is the largest of these, see railway electrification in Great Britain.

On line M1 of the Milan Metro
Milan Metro
The Milan Metro is the rapid transit system serving Milan, Italy, operated by Azienda Trasporti Milanesi. Milan metro is the longest metro system in Italy, and is the core of the Milan Transportation System...

 the third rail is used as the return electrical line (with potential near the ground) and the live electrical connection is made with a sliding block on the side of the car contacting an electrical bar parallel to the track approximately 1 m (3') above rail level. In this manner there are four rails. In the northern part of the line the more common overhead line system is used.

The third rail is an alternative to overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 that transmit power to trains by means of pantograph
Pantograph (rail)
A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...

s attached to the trains. Whereas overhead-wire systems can operate at 25 kV
25 kV AC
The 25 kV Alternating current railway electrification system is commonly used in railways worldwide, especially for high-speed rail.-Overview:This electrification system is ideal for railways that cover long distances and/or carry heavy traffic...

 or more, using alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 (AC), the smaller clearance around a live rail imposes a maximum of about 1500 V (Line 4, Guangzhou Metro
Line 4, Guangzhou Metro
Line 4 of the Guangzhou Metro or Nansha Line is a north-south line on the system that runs between Huangcun and Jinzhou stations, spanning a total of 43.7 km with 16 stations. It will eventually run from the Guangzhou Science Town to Nansha. The section of the line from Huangcun to Xinzao is...

, Line 5, Guangzhou Metro
Line 5, Guangzhou Metro
Line 5 of the Guangzhou Metro or Huanshilu Line runs from Liwan District to Huangpu District. It starts at Jiaokou and ends at Wenchong. The total length is 31.9 km. Line 5's color is red. Huangpu Line began operation on December 28, 2009 from Jiaokou to Wenchong.-Huanshi Line...

, Longgang Line, Shenzhen Metro
Longgang Line, Shenzhen Metro
Longgang Line of Shenzhen Metro in first phrase it runs northeastward from Yitian to Shuanglong. Longgang Line opened December 28, 2010. It also has an unofficial name Universide Line because it connected the playground about Universide and the center of Shenzhen.-Current Stations:-References:...

), and direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 (DC) is used. Trains on some lines or networks use both power supply modes (cf. below, "Compromise systems").

One method for reducing current losses (and thus increase the spacing of feeder/sub stations, a major cost in third rail electrification) is to use a composite conductor rail of a hybrid aluminium/steel design. The aluminium is a better conductor of electricity, and a running face of stainless steel gives better wear.

There are several ways of attaching the stainless steel to the aluminium. The oldest is a co-extruded method, where the stainless steel is extruded with the aluminium. This method has suffered, in isolated cases, from de-lamination (where the stainless steel separates from the aluminium); this is said to have been eliminated in the latest co-extruded rails. A second method is an aluminium core, upon which two stainless steel sections are fitted as a cap and linear welded along the centre line of the rail. Because aluminium has a higher coefficient of thermal expansion than steel, the aluminium and steel must be positively locked to provide a good current collection interface. A third method rivets aluminum bus strips to the web of the steel rail. The photo below-right depicts such a rail.

Compromise systems

Several systems use third rail for part of the system, and other systems such as overhead catenary
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 or diesel power for the remainder. These may exist because of the connection of separately-owned railways using the different systems, local ordinances, or other historical reasons.

On the southern region of British Rail, freight yards were wire with overhead wiring to avoid the hazards of third rail. The locomotives were fitted with a pantograph as well as pick up shoes.

USA

In New York City, electric trains that must use the third rail leaving Grand Central Terminal
Grand Central Terminal
Grand Central Terminal —often incorrectly called Grand Central Station, or shortened to simply Grand Central—is a terminal station at 42nd Street and Park Avenue in Midtown Manhattan in New York City, United States...

 on the former New York Central Railroad
New York Central Railroad
The New York Central Railroad , known simply as the New York Central in its publicity, was a railroad operating in the Northeastern United States...

 (now Metro-North Railroad
Metro-North Railroad
The Metro-North Commuter Railroad , trading as MTA Metro-North Railroad, or, more commonly, Metro-North, is a suburban commuter rail service that is run and managed by the Metropolitan Transportation Authority , an authority of New York State. It is the busiest commuter railroad in the United...

) switch to overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

 at Pelham when they need to operate out onto the former New York, New Haven and Hartford Railroad
New York, New Haven and Hartford Railroad
The New York, New Haven and Hartford Railroad , was a railroad that operated in the northeast United States from 1872 to 1968 which served the states of Connecticut, New York, Rhode Island, and Massachusetts...

 (now Metro North's New Haven Line) line to Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...

. The switch is made "on the fly" controlled from the engineer's position.

Also in New York City where diesel exhaust would pose a health hazard in underground station areas, Metro-North, Long Island Rail Road
Long Island Rail Road
The Long Island Rail Road or LIRR is a commuter rail system serving the length of Long Island, New York. It is the busiest commuter railroad in North America, serving about 81.5 million passengers each year. Established in 1834 and having operated continuously since then, it is the oldest US...

 and Amtrak
Amtrak
The National Railroad Passenger Corporation, doing business as Amtrak , is a government-owned corporation that was organized on May 1, 1971, to provide intercity passenger train service in the United States. "Amtrak" is a portmanteau of the words "America" and "track". It is headquartered at Union...

 use diesel locomotives that can also be electrically powered by third-rail. This kind of locomotive (for example the P32AC-DM or the EMD/Siemens built DM30AC of LIRR), can transition between the two modes while underway. The third-rail auxiliary system is not as powerful as the diesel engine, so on open-air (non-tunnel) trackage the engines typically run in diesel mode, even where third rail power is available.

In Manhattan
Manhattan
Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...

, New York City, and in Washington, D.C.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

, local ordinances required electrified street railways to draw current from a third rail and return the current to a fourth rail, both installed in a continuous vault underneath the street and accessed by means of a collector that passed through a slot between the running rails. When streetcars on such systems entered territory where overhead lines were allowed, they stopped over a pit where a man detached the collector (plow) and the motorman
Motorman
A motorman is the person who operates an electrified trolley car, tram, light rail, or rapid transit train.The term refers to the person who is in charge of the motor in the same sense as a railroad engineer is in charge of the engine. The term was gender-neutral...

 placed a trolley pole
Trolley pole
A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a tram or trolley bus. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J....

 on the overhead. Some sections of the former London tram system also used the conduit current collection
Conduit current collection
Conduit current collection is a system of electric current collection used by electric trams, where the power supply is carried in a channel under the roadway, rather than located overhead.-Description:...

 system, also with some tramcars that could collect power from both overhead and under-road sources.

The Blue Line
Blue Line (MBTA)
The Blue Line is one of four subway lines of the Massachusetts Bay Transportation Authority serving Downtown, East Boston and the North Shore. It runs from northeast to southwest, extending from Wonderland station in Revere, Massachusetts to Bowdoin station near Beacon Hill in Boston...

 of Boston's MBTA
Massachusetts Bay Transportation Authority
The Massachusetts Bay Transportation Authority, often referred to as the MBTA or simply The T, is the public operator of most bus, subway, commuter rail and ferry systems in the greater Boston, Massachusetts, area. Officially a "body politic and corporate, and a political subdivision" of the...

 uses third rail electrification from the start of the line downtown to Airport
Airport (MBTA station)
Airport Station is a subway station on the Massachusetts Bay Transportation Authority's Blue Line. It serves as a mass transit connection to the nearby Logan International Airport...

, where it switches to overhead catenary for the remainder of the line to Wonderland
Wonderland (MBTA station)
Wonderland is the northern terminus of the Blue Line in the Massachusetts Bay Transportation Authority mass transit system serving greater Boston. The station is located near the site of the now-closed Wonderland Greyhound Park in Revere, Massachusetts, and is handicapped accessible. See MBTA...

. The Orange Line's
Orange Line (MBTA)
The Orange Line is one of the four subway lines of the Massachusetts Bay Transportation Authority. It extends from Forest Hills in Jamaica Plain, Boston in the south to Oak Grove in Malden, Massachusetts in the north. It meets the Red Line at Downtown Crossing, the Blue Line at State, and the Green...

 Hawker Siddeley 01200 series rapid transit cars (essentially a longer version of the Blue Line's 0600's) recently had their pantograph mounting points removed during a maintenance program; these mounts would have been used for pantographs which would have been installed had the Orange Line been extended.

Dual power supply method was also used on some US interurban
Interurban
An interurban, also called a radial railway in parts of Canada, is a type of electric passenger railroad; in short a hybrid between tram and train. Interurbans enjoyed widespread popularity in the first three decades of the twentieth century in North America. Until the early 1920s, most roads were...

 railways that made use of newer third rail in suburban areas, and existing overhead streetcar (trolley) infrastructure to reach downtown, for example the Skokie Swift in Chicago.

United Kingdom


Several types of British trains have been able to operate on both overhead and third rail systems, including class British Rail Class 313
British Rail Class 313
British Rail Class 313 electric multiple units were built by BREL at York Works between February 1976 and April 1977 and were the first second-generation EMUs to be constructed for British Rail...

, 319
British Rail Class 319
The British Rail Class 319 dual-voltage electric multiple units were built by BREL York in two batches in 1987–88 and 1990. The trains were introduced for new north-south cross-London services from Bedford to Brighton, and since privatisation these services have been operated by Thameslink and...

, 325
British Rail Class 325
The British Rail Class 325 is a 4 car dual-voltage 25 kV alternating current or 750 V direct current electric multiple unit train used for postal train services. They are based on the Class 319. The Class 325 was British Rail's newest unit to take over parcels working on electrified...

, 365
British Rail Class 365
The British Rail Class 365 "Networker Express" are dual-voltage 25 kV AC and 750 V DC) electric multiple units built by ABB at York from 1994 to 1995. These were the last units to be built at the York factory before it closed...

, 375/6
British Rail Class 375
The British Rail Class 375 Electrostar electric multiple unit train was built by Bombardier Transportation at their Derby Works, from 1999 to 2005...

, 377/2
British Rail Class 377
The Class 377 Electrostar is an electric multiple unit type built by Bombardier Transportation at their Derby Works, from 2001 to present. The Electrostar family, which also includes Classes 357, 375, 376, 378, and 379, is the most numerous type of EMU built in the post-privatisation period of...

, 377/5
British Rail Class 377
The Class 377 Electrostar is an electric multiple unit type built by Bombardier Transportation at their Derby Works, from 2001 to present. The Electrostar family, which also includes Classes 357, 375, 376, 378, and 379, is the most numerous type of EMU built in the post-privatisation period of...

, 378
British Rail Class 378
The Class 378 Capitalstar is a type of electric multiple-unit train, part of Bombardier Transportation's Electrostar family. These trains are operating on the new London Overground network...

, 373
British Rail Class 373
The British Rail Class 373 or TGV-TMST train is an electric multiple unit that operates Eurostar's high-speed rail service between Britain, France and Belgium via the Channel Tunnel...

 and 395
British Rail Class 395
British Rail Class 395 is a dual-voltage electric multiple unit used by train operating company Southeastern for its services along High Speed 1 and onwards to the Kent coast. The trains were built in Japan by Hitachi and shipped to the United Kingdom to operate new high speed domestic services...

 EMUs, plus Class 92
British Rail Class 92
The British Rail Class 92 is a dual-voltage electric locomotive which can run on 25 kV AC from overhead wires or 750 V DC from a third rail. It was designed specifically to operate services through the Channel Tunnel between Britain and France...

 locomotives.

Eurostar / High Speed 1

The Class 373
British Rail Class 373
The British Rail Class 373 or TGV-TMST train is an electric multiple unit that operates Eurostar's high-speed rail service between Britain, France and Belgium via the Channel Tunnel...

 used for international services operated by Eurostar
Eurostar
Eurostar is a high-speed railway service connecting London with Paris and Brussels. All its trains traverse the Channel Tunnel between England and France, owned and operated separately by Eurotunnel....

 via the Channel Tunnel
Channel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

 uses overhead collection at 25 kV AC for most of its journey, with sections of 3 kV DC or 1.5 kV DC on the Continent. As originally delivered, the Class 373 units were additionally fitted with 750 V DC collection shoes, designed for the journey in London via the suburban commuter lines to Waterloo. A switch between third-rail and overhead collection was performed while running at speed, initially at Continental Junction near Folkestone, and later on at Fawkham Junction
Fawkham Junction
Fawkham Junction is a railway junction that currently connects High Speed 1 with the Kent Rail Network.Originally the Junction was part of the London, Chatham and Dover Railway's line to Gravesend West . The intermediate stations were: Longfield Halt, Southfleet, Rosherville Halt and Gravesend West...

 after the opening of the first section of the Channel Tunnel Rail Link
Channel Tunnel Rail Link
High Speed 1 , officially known as the Channel Tunnel Rail Link and originally as the Continental Main Line , is a high-speed railway line running from London through Kent to the British end of the Channel Tunnel.The line was built to carry international passenger traffic from the United Kingdom...

. Between Kensington Olympia railway station and North Pole depot
North Pole depot
North Pole depot was the London depot for Eurostar from 1994 until 2007. It was used for maintaining and stabling the fleet of British Rail Class 373 trains...

 further switchovers were necessary.

The dual system caused some problems when drivers forgot to switch between modes. Failure to retract the shoes when entering France caused severe damage to trackside equipment, leading to SNCF installing a concrete block at the Calais end of the Channel Tunnel to break off the 3rd rail shoe if it had not been retracted. On the other hand, an accident occurred in the UK when a Eurostar driver failed to retract the pantograph before entering the 3rd rail system, damaging a signal gantry and the pantograph.

On 14 November 2007, Eurostar's passenger operations were transferred to St Pancras railway station
St Pancras railway station
St Pancras railway station, also known as London St Pancras and since 2007 as St Pancras International, is a central London railway terminus celebrated for its Victorian architecture. The Grade I listed building stands on Euston Road in St Pancras, London Borough of Camden, between the...

 and maintenance operations to Temple Mills depot making the requirement for the 750DC third rail collection equipment redundant and leading to its removal from the fleet.

In 2009, Southeastern
Southeastern (train operating company)
London & South Eastern Railway Limited, trading as Southeastern is a train operating company in south-east England. On 1 April 2006 it became the franchisee for the new Integrated Kent Franchise , replacing the publicly owned South Eastern Trains on the former South East Franchise...

 began operating domestic services over High Speed 1 from St Pancras using its new Class 395
British Rail Class 395
British Rail Class 395 is a dual-voltage electric multiple unit used by train operating company Southeastern for its services along High Speed 1 and onwards to the Kent coast. The trains were built in Japan by Hitachi and shipped to the United Kingdom to operate new high speed domestic services...

 EMUs. These services operate on the high speed line as far as or , before transferring to the classic lines to serve north and mid Kent. As a consequence, these trains are dual voltage enabled, as the majority of the routes over which they operate are third rail electrified.

North London Line

In London, the North London Line
North London Line
The North London Line is a railway line which passes through the inner suburbs of north London, England. Its route is a rough semicircle from the south west to the north east, avoiding central London. The line is owned and maintained by Network Rail...

 changes its power supply several times between Richmond
Richmond station (London)
Richmond station is a National Rail and London Underground station in the London Borough of Richmond upon Thames in south west London which is managed by South West Trains....

 and Stratford
Stratford station
Stratford station is a large multilevel railway station in Stratford, east London. The station is served by the National Rail services National Express East Anglia, London Overground and c2c, by London Underground's Central and Jubilee lines, and by the Docklands Light Railway . Stratford is in...

 stations. The route was originally third rail throughout but a number of technical electrical earthing problems, plus part of the route also being covered already by overhead electric wires provided for electrical-hauled freight and Regional Eurostar
Regional Eurostar
Regional Eurostar was the name given to plans to operate Eurostar train services from Paris and Brussels to locations in the United Kingdom beyond London...

 services led to the change.

Thameslink

The cross-city Thameslink
Thameslink
Thameslink is a fifty-station main-line route in the British railway system running north to south through London from Bedford to Brighton, serving both London Gatwick Airport and London Luton Airport. It opened as a through service in 1988 and by 1998 was severely overcrowded, carrying more than...

 service runs on the Southern Region third rail network from Farringdon station
Farringdon station
Farringdon station is a London Underground and National Rail station in Clerkenwell, just north of the City of London in the London Borough of Islington...

 southwards and on overhead line northwards from Farringdon to Bedford
Bedford
Bedford is the county town of Bedfordshire, in the East of England. It is a large town and the administrative centre for the wider Borough of Bedford. According to the former Bedfordshire County Council's estimates, the town had a population of 79,190 in mid 2005, with 19,720 in the adjacent town...

. The changeover is made whilst stationary at Farringdon.

Northern City

On the Moorgate to Hertford and Welwyn suburban service routes, the East Coast Main Line
East Coast Main Line
The East Coast Main Line is a long electrified high-speed railway link between London, Peterborough, Doncaster, Wakefield, Leeds, York, Darlington, Newcastle and Edinburgh...

 sections are 25 kV AC, with a changeover to third-rail made at Drayton Park railway station
Drayton Park railway station
Drayton Park railway station is on the Network Rail Northern City Line which carries First Capital Connect services between Moorgate and Welwyn Garden City or Hertford via Finsbury Park...

. Third-rail is still used in the tunnel-section of the route, because the size
Structure gauge
The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse...

 of the tunnels leading to Moorgate station
Moorgate station
Moorgate station is a central London railway terminus and London Underground station on Moorgate in the City of London; it provides National Rail services by First Capital Connect for Hertford, Welwyn Garden City and Letchworth and also serves the Circle, Hammersmith & City, Metropolitan Lines and...

 were too small to allow overhead electrification.

Continental Europe

The older lines in the west of the Oslo T-bane
Oslo T-bane
The Oslo Metro is the rapid transit system of Oslo, Norway, operated by Oslo T-banedrift on contract from the transit authority Ruter. The network consists of six lines that all run through the city centre, with a total length of . It has a daily ridership of 268,000 with 105 stations of which 16...

 system were built with overhead lines while the eastern lines were built with third rail, although the entire system has since been converted to third rail. Prior to the conversion, the now-retired OS T1300 and OS T2000 trains could operate on both systems. To mitigate investment costs, the Rotterdam Metro
Rotterdam Metro
The Rotterdam Metro is a rapid transit system operated in Rotterdam and surrounding municipalities by RET. The first line, called Noord - Zuidlijn opened in 1968 and ran from Centraal Station to Zuidplein, crossing the river Nieuwe Maas in a tunnel. It was the first metro system to open in the...

, basically a third-rail powered system, has been given some outlying branches built on surface as light rail
Light rail
Light rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...

 (called 'Sneltram' in Dutch), with numerous level crossings protected with barriers and traffic lights. These branches have overhead wires. Similarly, in Amsterdam one 'Sneltram' route goes on Metro
Amsterdam Metro
The Amsterdam Metro is a mixed rapid transit and light rail system in Amsterdam, and its surrounding municipalities Amstelveen, Diemen, and Ouder-Amstel in the Netherlands. The network is owned by the city of Amsterdam and operated by the Gemeentelijk Vervoerbedrijf, the company that also operates...

 tracks and passes to surface alignment in the suburbs, which it shares with standard trams. In most recent developments, the RandstadRail
RandstadRail
RandstadRail network in the southern part of the Randstad conurbation in the west of the Netherlands, connecting The Hague, Zoetermeer and Rotterdam, consists of a metro-like line between The Hague and Rotterdam and two light rail lines between The Hague and Zoetermeer...

 project also requires Rotterdam Metro trains to run under wires on their way along the former mainline railway to The Hague.

The new tramway in Bordeaux
Bordeaux
Bordeaux is a port city on the Garonne River in the Gironde department in southwestern France.The Bordeaux-Arcachon-Libourne metropolitan area, has a population of 1,010,000 and constitutes the sixth-largest urban area in France. It is the capital of the Aquitaine region, as well as the prefecture...

 (France) uses a novel system with a third rail in the center of the track. The third rail is separated into 8 metre long conducting and 3 metre long isolation segments. Each conducting segment is attached to an electronic circuit which will make the segment live once it lies fully beneath the tram (activated by a coded signal sent by the train) and switch it off before it becomes exposed again. This system (called "Alimentation par Sol" (APS), meaning "current supply via ground") is used in various locations around the city but especially in the historic centre: elsewhere the trams use the conventional overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...

, see also ground-level power supply
Ground-level power supply
Ground-level power supply, also known as surface current collection and Alimentation par Sol is a modern method of third-rail electrical pick-up for street trams. It was invented for the Bordeaux tramway, which was constructed from 2000 and opened in 2003. Until 2011, this is the only place it is...

. In summer 2006 it was announced that two new French tram systems would be using APS over part of their networks. These will be Angers
Angers
Angers is the main city in the Maine-et-Loire department in western France about south-west of Paris. Angers is located in the French region known by its pre-revolutionary, provincial name, Anjou, and its inhabitants are called Angevins....

 and Reims
Reims
Reims , a city in the Champagne-Ardenne region of France, lies east-northeast of Paris. Founded by the Gauls, it became a major city during the period of the Roman Empire....

, with both systems expected to open around 2009–2010.

The French Culoz–Modane railway was electrified with 1,500 V DC third rail, later converted to overhead wires at the same voltage. Stations had overhead wires from the beginning.

Conversions

Despite various technical possibilities of operating stock with dual power collecting modes, the desire to achieve full compatibility of entire networks seems to have been the decisive cause of conversions from third rail to overhead supply (or vice versa).

Suburban corridors in Paris from Gare Saint-Lazare
Gare Saint-Lazare
Paris Saint-Lazare is one of the six large terminus train stations of Paris. It is the second busiest in Paris, behind the Gare du Nord, handling 274,000 passengers each day.-History:...

, Gare des Invalides (both CF Ouest) and Gare d'Orsay
Gare d'Orsay
Gare d'Orsay is a former Paris railway station and hotel, built in 1900 to designs by Victor Laloux, Lucien Magne and Émile Bénard; it served as a terminus for the Chemin de Fer de Paris à Orléans . It was the first electrified urban rail terminal in the world, opened 28 May 1900, in time for the...

 (CF PO), were electrified from 1924, 1901, 1900 respectively. They all changed to overhead wires by stages after they became part of a wide scale electrification project of the SNCF
SNCF
The SNCF , is France's national state-owned railway company. SNCF operates the country's national rail services, including the TGV, France's high-speed rail network...

 network in the 1960s–70s.

In Manchester area, the L&YR
Lancashire and Yorkshire Railway
The Lancashire and Yorkshire Railway was a major British railway company before the 1923 Grouping. It was incorporated in 1847 from an amalgamation of several existing railways...

 Bury line was first electrified with overhead wires (1913), then changed to third rail (1917, cf. Railway electrification in Great Britain
Railway electrification in Great Britain
Railway electrification in Great Britain started towards of the 19th century. A great range of voltages have been used in the intervening period using both overhead lines and third rails, however the most common standard for mainline services is now 25 kV AC using overhead lines and the...

) and again in 1992 to overhead wires in the course of its adaptation for the Manchester Metrolink
Manchester Metrolink
Metrolink is a light rail system in Greater Manchester, England. It consists of four lines which converge in Manchester city centre and terminate in Bury, Altrincham, Eccles and Chorlton-cum-Hardy. The system is owned by Transport for Greater Manchester and operated under contract by RATP Group...

. Trams in city centre streets, carrying collector shoes projecting from their bogies, were considered too dangerous for pedestrians and motor traffic to attempt dual-mode technology (in Amsterdam and Rotterdam Sneltram vehicles go out to surface in suburbs, not in busy central areas). The same thing happened to the West Croydon — Wimbledon Line in Greater London (originally electrified by the Southern Railway) when Tramlink
Tramlink
Tramlink is a tramway system in south London in the United Kingdom which began operation in May 2000...

 was opened in 2000.

Three lines of five making up the core of Barcelona Metro
Barcelona Metro
The Barcelona Metro , part of the public transportation system of Barcelona, Catalonia, is an extensive network of electrified railways that run underground in central Barcelona and above ground into the city's suburbs. Since July 31, 2010, Barcelona Metro system consists of 11 lines with 165...

 network changed to overhead power supply from third rail. This operation was also done by stages and completed in 2003.

The opposite took place in south London. The South London Line of the LBSCR
London, Brighton and South Coast Railway
The London, Brighton and South Coast Railway was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey...

 network between Victoria and London Bridge was electrified with catenary in 1909. The system was later extended to Crystal Palace, Coulsdon North
Coulsdon North railway station
Coulsdon North is a closed railway station on the Brighton Main Line.- Opening :The station was opened as "Stoats Nest and Cane Hill" on 5 November 1899 by the London, Brighton and South Coast Railway . It took its name partly from the nearby Cane Hill asylum and partly from the nearby Stoats Nest...

 and Sutton. In the course of main-line third rail electrification in south-east England, the lines were converted by 1929.

The first overhead electric trains appeared on the Hamburg-Altonaer Stadt- und Vorortbahn in 1907. Thirty years later, the main-line railway operator, Deutsche Reichsbahn
Deutsche Reichsbahn
Deutsche Reichsbahn was the name of the following two companies:* Deutsche Reichsbahn, the German Imperial Railways during the Weimar Republic, the Third Reich and the immediate aftermath...

, influenced by the success of the third-rail Berlin S-Bahn
Berlin S-Bahn
The Berlin S-Bahn is a rapid transit system in and around Berlin, the capital city of Germany. It consists of 15 lines and is integrated with the mostly underground U-Bahn to form the backbone of Berlin's rapid transport system...

, decided to switch what was now called Hamburg S-Bahn
Hamburg S-Bahn
The Hamburg S-Bahn is a railway network for public rapid mass transit in the Hamburg Metropolitan Region. Together the S-Bahn, the Hamburg U-Bahn, the AKN railway and the regional railway form the backbone of railway public transport in the city and the surrounding area...

 to third rail. The process began in 1940 and was not finished until 1955.

In 1976–1981, the third-rail Vienna U-Bahn
Vienna U-Bahn
The Vienna U-Bahn is a rapid transit system consisting of five lines. It is the backbone of one of the best performing public transport systems worldwide according to UITP in June 2009. More than 1.3 million passengers use the Vienna U-Bahn every day...

 U4 Line substituted the Donaukanallinie and Wientallinie of the Stadtbahn
Wiener Stadtbahn
The Wiener Stadtbahn was a public transportation system operated under this name from 1898 to 1989. Today, the Vienna U-Bahn lines U4 and U6 and the Vienna S-Bahn run on its former lines....

, built c1900 and first electrified with overhead wires in 1924. This was part of a big project of consolidated U-Bahn network construction. The other electric Stadtbahn line, whose conversion into heavy rail stock was rejected, still operates under wires with light rail cars (as U6), though it has been thoroughly modernised and significantly extended. As the platforms on the Gürtellinie were not suitable for raising without much intervention into historic Otto Wagner
Otto Wagner
Otto Koloman Wagner was an Austrian architect and urban planner, known for his lasting impact on the appearance of his home town Vienna, to which he contributed many landmarks.-Life:...

's station architecture, the line would anyway remain incompatible with the rest of the U-Bahn network. Therefore an attempt of conversion to third rail would have been pointless. In Vienna, paradoxically, the wires were retained for aesthetic (and economic) reasons.

The western portion of the Skokie Swift
Yellow Line (Chicago Transit Authority)
The Yellow Line, formerly known as the Skokie Swift, is part of the Chicago Transit Authority's Chicago 'L' heavy rail rapid transit system in Chicago, Illinois...

 of the Chicago 'L'
Chicago 'L'
The L is the rapid transit system serving the city of Chicago and some of its surrounding suburbs. It is operated by the Chicago Transit Authority...

 changed from catenary wire to third rail in 2004, making it fully compatible with the rest of the system.

The reasons for building the overhead powered Tyne & Wear Metro network roughly on lines of the long-gone third-rail Tyneside Electrics
Tyneside Electrics
The Tyneside Electrics refers to the suburban railways on Tyneside that were electrified by the North Eastern Railway and the London and North Eastern Railway. The North Tyneside loop was electrified from 1904 onwards and formed one of the earliest suburban electric networks, the South Tyneside...

 system in Newcastle area are likely to have roots in economy and psychology rather than in the pursuit of compatibility. At the time of the Metro opening (1980), the third rail system had already been removed from the existing lines, there were no third-rail light rail vehicles on the market and the latter technology was confined to much more costly heavy rail stock. Also the far-going change of image was desired: the memories of the last stage of operation of the Tyneside Electrics were far from being favourable. This was the construction of the system from scratch after 11 years of ineffective diesel service.

Highest voltages

  • Hamburg S-Bahn
    Hamburg S-Bahn
    The Hamburg S-Bahn is a railway network for public rapid mass transit in the Hamburg Metropolitan Region. Together the S-Bahn, the Hamburg U-Bahn, the AKN railway and the regional railway form the backbone of railway public transport in the city and the surrounding area...

    : 1,200 V, since 1940
  • Manchester - Bury, England: 1,200V (side Contact)
  • Culoz–Modane railway, France: 1,500 V, 1925–1976
  • Guangzhou Metro
    Guangzhou Metro
    Guangzhou Metro is the metro system of the city of Guangzhou in Guangdong Province of China. It is operated by the state-owned Guangzhou Metro Corporation and was the fourth metro system to be built in mainland China, after those of Beijing, Tianjin and Shanghai.The earliest effort of preparation...

    , Line 4
    Line 4, Guangzhou Metro
    Line 4 of the Guangzhou Metro or Nansha Line is a north-south line on the system that runs between Huangcun and Jinzhou stations, spanning a total of 43.7 km with 16 stations. It will eventually run from the Guangzhou Science Town to Nansha. The section of the line from Huangcun to Xinzao is...

    &Line 5
    Line 5, Guangzhou Metro
    Line 5 of the Guangzhou Metro or Huanshilu Line runs from Liwan District to Huangpu District. It starts at Jiaokou and ends at Wenchong. The total length is 31.9 km. Line 5's color is red. Huangpu Line began operation on December 28, 2009 from Jiaokou to Wenchong.-Huanshi Line...

    : 1,500 V


In Germany during the Third Reich, a railway system with three-metre gauge width was planned. For this Breitspurbahn
Breitspurbahn
The Breitspurbahn was a planned broad-gauge railway, a personal pet project of Adolf Hitler during the Third Reich of Germany, supposed to run on 3 metre gauge track with double-deck coaches between major cities of Grossdeutschland, Hitler's expanded Germany.-History:Since reparations due after...

 railway system, electrification with a voltage of 100 kV taken from a third rail was considered, in order to avoid destruction of overhead wires by 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 the proximity of the rails. The whole project did not progress any further owing to the onset of World War II.

Simultaneous use with overhead wire

A railway can be electrified with an overhead wire and a third rail at the same time. This was the case, for example, on the Hamburg S-Bahn between 1940 and 1955. A modern example is Birkenwerder Railway Station near Berlin, which has third rail on both sides and overhead wire. The whole Penn Station
Pennsylvania Station (New York City)
Pennsylvania Station—commonly known as Penn Station—is the major intercity train station and a major commuter rail hub in New York City. It is one of the busiest rail stations in the world, and a hub for inbound and outbound railroad traffic in New York City. The New York City Subway system also...

 complex in New York City is also electrified with both systems. However, such systems have problems with the influence of the different supplies. If one supply is DC and the other AC, an undesired premagnetization of the AC transformers can occur. For this reason, double electrification
Double electrification
Double electrification is a system whereby a railway line is supplied power both via overhead catenary and a third rail. This is done to enable trains that use either system of power to share the same railway line, for example in the case of mainline and suburban trains...

 is usually avoided.

The border station of Modane on the French-Italian Fréjus railway was electrified at both 1,500 V DC third rail for French trains and with overhead wires (initially three-phase, later 3,000 V DC) for Italian trains. When the French part of the line was converted to overhead wires, the voltage of the wires was dropped to 1,500 V DC. Now Italian trains run in Modane feed with 1,500 V DC instead of 3000, with half of their power.

Technical advances

The introduction of supercapacitor
Supercapacitor
An electric double-layer capacitor , also known as supercapacitor, supercondenser, electrochemical double layer capacitor, or ultracapacitor, is an electrochemical capacitor with relatively high energy density. Their energy density is typically hundreds of times greater than conventional...

s has the potential to lower the cost for trains running on third rail and overhead wires. Kinetic energy generated while braking is stored in supercapacitors on board the vehicle. This energy is then used when accelerating. This allows the supercapacitors to reduce current draw through the electrical pickup during acceleration, putting less stress on the electrical grid. Claimed peak energy reduction is around 30%.

The technology can be used equally well for diesel electric locomotives, where 25% to 40% reduction in energy consumption is claimed.

Since 2003, Mannheim Stadtbahn in Mannheim, Germany has operated a light-rail vehicle using electric double-layer supercapacitors to store braking energy.

A number of companies are developing electric double-layer supercapacitor technology. Siemens AG
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

 is developing mobile energy storage based on double-layer supercapacitors called Sibac Energy Storage Sitras SES, are developing stationary trackside version. The company Cegelec is also developing an electric double-layer capacitor-based energy storage system.

In model trains

In 1906, the Lionel
Lionel Corp.
Lionel Corporation was an American toy manufacturer and retailer that did business from 1900 to 1993. Founded as an electrical novelties company, Lionel specialized in various products throughout its existence, but toy trains and model railroads were its main claim to fame...

 electric trains became the first model trains to use a third rail
Third rail (model railroading)
The use of a third rail in model railroading is a technique that is sometimes applied in order to facilitate easier wiring.-Two-rail versus three-rail system:Early toy trains used two metal rail tracks like most real trains...

 to power the locomotive. Lionel track uses a third rail in the center, while the two outer rails are electrically connected together. This solved the problem two-rail model trains have when the track is arranged to loop back on itself, as ordinarily this causes a short-circuit. (Even if the loop was gapped, the locomotive would create a short and stop as it crossed the gaps.) Lionel electric trains also operate on alternating current. The use of alternating current means that a Lionel locomotive cannot be reversed by changing polarity; instead, the locomotive sequences among several states (forward, neutral, backward, for example) each time it is started. Märklin three-rail trains use a short spike of DC voltage to reverse a relay within the locomotive while it is stopped. Märklin's track does not have an actual third rail; instead, a series of short pins provide the current, taken up by a long "shoe" under the engine. This shoe is long enough to always be in contact with several pins. This is known as the stud contact system
Stud contact system
The Stud Contact System is a once-obsolete ground-level power supply system for electric trams. Power supply studs were set in the road at intervals and connected to a buried electric cable by switches operated by magnets on the tramcars. Current was collected from the studs by a "skate" or "ski...

 and has certain advantages when used on outdoor model railway systems. The ski collector rubs over the studs and thus inherently self cleans. When both track rails are used for the return in parallel there is much less chance of current interruption due to dirt on the line.

Modern model train sets today use only two rails. Many supply locomotives with direct current (DC) where the voltage and polarity of the current controls the speed and direction of the DC motor in the train. A growing exception is Digital Command Control
Digital Command Control
Digital Command Control is a standard for a system to operate model railways digitally. When equipped with Digital Command Control, locomotives on the same electrical section of track can be independently controlled....

 (DCC), where bi-polar DC is delivered to the rails at a constant voltage, along with digital signals that are decoded within the locomotive. The bi-polar DC carries digital information to indicate the instruction and the locomotive that is being commanded when multiple locomotives are present on the same track.

Some model railroads realistically mimic the third rail configurations of their full-sized counterparts; such models may or may not actually draw power from the third rail (most do not).

In politics

The "Third Rail" of politics refers to extremely controversial issues in which it is observed that when acting unilaterally, "touch it, and you die." The concept was that touching anything that powerful required the neutral application of members of competing and opposed political parties.

The expression was coined in 1982 by Kirk O'Donnell an aide to former House Speaker Tip O'Neill
Tip O'Neill
Thomas Phillip "Tip" O'Neill, Jr. was an American politician. O'Neill was an outspoken liberal Democrat and influential member of the U.S. Congress, serving in the House of Representatives for 34 years and representing two congressional districts in Massachusetts...

 in reference to a budget issue involving the US Social Security
Social Security (United States)
In the United States, Social Security refers to the federal Old-Age, Survivors, and Disability Insurance program.The original Social Security Act and the current version of the Act, as amended encompass several social welfare and social insurance programs...

 program, an issue that at the time was itself settled by bi-partisan compromise. In Canadian usage the "Third Rail" of politics may traditionally refer to health care
Health care
Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...

.

See also

  • Conduit current collection
    Conduit current collection
    Conduit current collection is a system of electric current collection used by electric trams, where the power supply is carried in a channel under the roadway, rather than located overhead.-Description:...

  • Contact shoe
    Current collector
    Electric current collectors are used for trolleybuses, trams, electric locomotives or EMUsto lead electrical power from overhead lines or electrical third rails to the electrical equipment of the vehicles....

  • Fourth rail
  • Ground-level power supply
    Ground-level power supply
    Ground-level power supply, also known as surface current collection and Alimentation par Sol is a modern method of third-rail electrical pick-up for street trams. It was invented for the Bordeaux tramway, which was constructed from 2000 and opened in 2003. Until 2011, this is the only place it is...

  • Linear motor
    Linear motor
    A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque it produces a linear force along its length...

  • List of rail transport systems using third rail
  • List of suburban and commuter rail systems
  • Railway electrification in Great Britain
    Railway electrification in Great Britain
    Railway electrification in Great Britain started towards of the 19th century. A great range of voltages have been used in the intervening period using both overhead lines and third rails, however the most common standard for mainline services is now 25 kV AC using overhead lines and the...

  • Rubber-tyred metro
    Rubber-tyred metro
    A rubber-tyred metro is a form of rapid transit system that uses a mix of road and rail technology. The vehicles have wheels with rubber tyres which run on rolling pads inside guide bars for traction, as well as traditional railway steel wheels with deep flanges on steel tracks for guidance through...

  • Stud contact system
    Stud contact system
    The Stud Contact System is a once-obsolete ground-level power supply system for electric trams. Power supply studs were set in the road at intervals and connected to a buried electric cable by switches operated by magnets on the tramcars. Current was collected from the studs by a "skate" or "ski...

  • Third rail (model railroading)
    Third rail (model railroading)
    The use of a third rail in model railroading is a technique that is sometimes applied in order to facilitate easier wiring.-Two-rail versus three-rail system:Early toy trains used two metal rail tracks like most real trains...

  • Third-rail power for trams

  • External links

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