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The term Multiple Unit or MU is used to describe a self propelling train unit capable of coupling with other like units and being controlled from one cab. The term is most often used on passenger trainsets that consists of more than one Coach (rail), but single self propelling carriages, or railcars, can be referred to as multiple units if capable of operating with other units.

Multiple units are of two main types:

• Electric Multiple Unit (EMU)
• Diesel Multiple Unit (DMU)

History and description Multiple unit operation was made possible by the development of multiple-unit train control by the United States inventor (Frank J. Sprague). This allowed electricity-powered rapid transit trains to be operated from a single driving position.

Most MUs are powered either by a diesel engine driving the wheels through a gearbox or hydraulic transmission (diesel multiple unit), or by electric motors, receiving their power through a Third rail electric system or overhead lines (EMU). DEMU (DEMUs) have a diesel engine that drives a generator producing electricity to drive electric motors in a similar fashion to a Diesel locomotive#Diesel-electric.

Trainset Virtually all rapid transit rolling stock, such as ones used in subway systems, are multiple unit trainsets, usually EMUs. Many high-speed rail rolling stocks are also multiple unit trainsets, such as the Japanese Shinkansen and the Germany Siemens Velaro High-speed rail.

A multiple unit trainset has the same power and traction components as a locomotive, but instead of the components concentrating in one carbody, they are spread out on each car that makes up the set. Therefore these cars can only propel themselves when they are part of the complete trainset, thus making them semi-permanently coupled. For example, a DMU might have one car carry the prime mover and traction motors, and another the engine for head end power generation; an EMU might have one car carry the Pantograph (rail) and transformer, and another car carry the traction motors.

Multiple Units vs. Locomotives Advantages EMUs waiting for service in Poznań

Multiple units have several advantages over locomotive-hauled trains:

• Energy Efficiency - MUs are more energy efficient than locomotive-hauled trains. They are more nimble, especially on grades, as much more of the train's weight (sometimes all of it) is carried on power-driven wheels, rather than suffer the dead weight of unpowered hauled coaches;

• No need to turn locomotive - Most MUs have cabs at both ends, resulting in quicker turnaround times, reduced crewing costs, and enhanced safety. The faster turnaround time and the reduced size (due to higher frequencies) as compared to large locomotive-hauled trains, has made the MU a major part of commuter rail commuter rail services in many countries. MUs are also used by most rapid transit systems.

• Consist can be changed mid journey - MUs may usually be quickly made up or separated into sets of varying lengths. Several multiple units may run as a single train, then be broken at a junction point into smaller trains for different destinations.

• Reliability – Due to having multiple engines the failure of one engine does not prevent the train from continuing its journey. A locomotive drawn train typically only has one power unit whose failure will disable the train. Some locomotive hauled trains may contain more than one power unit and thus be able to continue at reduced speed after the failure of one.

EMU in Zürich HB railway station

• Safety – Multiple units normally have completely independent braking systems on all cars meaning the failure of the brakes on one car does not prevent the brakes from operating on the other cars

• Axle load - Multiple units have lighter axle loads, allowing operation on lighter tracks, where locomotives are banned, such as the Whitby line in the UK. Another side effect of this is reduced track wear, as traction forces can be provided through many axles, rather than just four or six.

Disadvantages Multiple Units do have some disadvantages as compared to locomotive hauled trains:

• Maintenance - It may be easier to maintain one locomotive than many self-propelled cars.

• Safety - In the past it was often safer to locate the train's power systems away from passengers. This was particularly the case for steam locomotives, but still has some relevance for other power sources. A head on collision involving a multiple-unit (with passengers potentially right at the front of the train) is likely to result in more casualties than one with a locomotive (where the locomotive would act as a 'crumple zone').

• Easy replacement of motive power - Should a locomotive fail, it is easily replaced. Failure of a multiple unit train-set will often require a whole new train or time-consuming switching.

• Efficiency - Idle trains do not waste expensive motive power resources. Separate locomotives mean that the costly motive power assets can be moved around as needed.

• Flexibility - Large locomotives can be substituted for small locomotives where the gradients of the route become steeper and more power is needed.

• Noise - The passenger environment of a multiple unit is often noticeably noisier than in a locomotive-hauled train, due to the presence of underfloor machinery. This is a particular problem with Diesel multiple units.

• Obsolescence cycles - Separating the motive power from the payload-hauling cars means that either can be replaced when obsolete without affecting the other.

• It is difficult to have gangways between coupled sets, and retain an aerodynamic leading front end.

Features 3 on the Cologne-Frankfurt high-speed rail line near Montabaur

It is not necessary for every single car in a MU to be motorized. Therefore EMU cars can be motor units, or can be trailing units. Instead of motors, trailing units can contain some supplemental equipment such as air compressors, batteries, etc.

In some EMU trains, every car is equipped with a driving console, and other controls necessary to operate the train. Therefore every car can be used as a cab car whether it is motorised or not, if on the end of the train. This is the case with NJ Transit Arrows, Metro-North Railroad (New York) EMUs, etc. However, other EMUs can be driven/controlled only from dedicated Cab cars. Among such EMUs are Ex-USSR-made ER2, ER9 electric trainset, German classes 423-426, etc.

Well-known examples of MUs are the Japanese Shinkansen and the last generation German InterCityExpress. Most trains in Netherlands and Japan are MUs, making them suitable for use in areas of high population density. Even some freight trains are MUs: the M250, whose four front and end carriages are EMUs, has been operating in Japan since March 2004.

EMUs are also extensively used in all local train networks in India that provide commuter transport in all the major cities.

Ireland , 2006. EMU train passing through Bray.

Córas Iompair Éireann (CIE), which controlled the Republic's railways between 1945-86, mainly used locomotives and hauled stock for its passenger trains. Since 1987, Iarnród Éireann (IE) have been increasing the use of this type of train, in order to replace older locomotives and carriages. The only electrified railway network in Ireland is the Dublin Area Rapid Transit (DART) system.

A wide variety of diesel and electric multiple units have been used on Ireland's railways.

In Northern Ireland the majority of passenger services have been operated by diesel multiple units since the mid-1950s under the tenure of both the Ulster Transport Authority (1948-1966) and Northern Ireland Railways (since 1967).

In the Republic of Ireland the railway operator Iarnród Éireann has purchased a number of new multiple units since 1987 to replace older locomotives and carriages.

North America Most long-distance trains in North America are locomotive-hauled. However, commuters, Rapid transit, and light rail operations make extensive use of MUs. Most electrically powered trains are MUs. The Southeastern Pennsylvania Transportation Authority (SEPTA) Regional Rail Division uses EMUs almost exclusively - the exception being some of its peak express service. New Jersey Transit service on the Northeast Corridor is split between electric locomotives and EMUs.

M2, M4, M6 and future M8 EMUs which operate on the New Haven Line (Metro-North) of Metro-North Railroad, are “dual mode” meaning they can draw power from either the third rail or from overhead lines. This allows operation under the wires between Pelham (Metro-North station) and Union Station (New Haven), a section of track owned by Metro North but shared with Amtrak's Northeast Corridor service, and on third rail between Pelham and Grand Central Terminal. EMUs are used on Agence métropolitaine de transport's Deux-Montagnes Line (AMT).

DMUs are less common, partly because new light rail operations are almost entirely electric, with many commuter routes already electrified, and also because of the difficulties posed by Federal Railway Administration rules limiting their use on shared passenger/freight corridors. When the Budd RDC was developed following World War II, it was adopted for many secondary passenger routes in the U.S. (especially on the Boston and Maine Railroad) and Canada. These operations generally survived longer in Canada, but several were abandoned in the VIA Rail cutbacks of the early 1990s. One that survives is Malahat, British Columbia on Vancouver Island.

DMUs are used on the River Line (New Jersey Transit) in New Jersey. Currently Colorado Railcar is demonstrating an FRA Crash Compliant DMU in the United States. NJ Transit has experimented with this DMU on the Princeton Branch (a.k.a. Princeton "Dinky") line. In August 2006 it was announced that Amtrak wants the State of Vermont to experiment with DMUs on the state-subsidized Vermonter line from New Haven (Amtrak station) north to St. Albans, Vermont to replace the less efficient diesel locomotive trainsets currently used.

Russia , Moscow

Elektrichka (, ) is an informal word for elektropoezd (), a Soviet Union or post-Soviet regional (mostly suburban) electrical multiple unit passenger train. Elektrichkas are widespread in Russia, Ukraine and some other countries of former Soviet Union. The first elektrichka ride occurred in August 1929 along the line Moscow-Mytishchi.

See also

• Rail terminology
• Pacer (train) units.
• Railcar
• Hybrid Locomotive

The term Multiple Unit or MU is used to describe a self propelling train unit capable of coupling with other like units and being controlled from one cab. The term is most often used on passenger trainsets that consists of more than one Coach (rail), but single self propelling carriages, or railcars, can be referred to as multiple units if capable of operating with other units.

Multiple units are of two main types:

• Electric Multiple Unit (EMU)
• Diesel Multiple Unit (DMU)

History and description Multiple unit operation was made possible by the development of multiple-unit train control by the United States inventor (Frank J. Sprague). This allowed electricity-powered rapid transit trains to be operated from a single driving position.

Most MUs are powered either by a diesel engine driving the wheels through a gearbox or hydraulic transmission (diesel multiple unit), or by electric motors, receiving their power through a Third rail electric system or overhead lines (EMU). DEMU (DEMUs) have a diesel engine that drives a generator producing electricity to drive electric motors in a similar fashion to a Diesel locomotive#Diesel-electric.

Trainset Virtually all rapid transit rolling stock, such as ones used in subway systems, are multiple unit trainsets, usually EMUs. Many high-speed rail rolling stocks are also multiple unit trainsets, such as the Japanese Shinkansen and the Germany Siemens Velaro High-speed rail.

A multiple unit trainset has the same power and traction components as a locomotive, but instead of the components concentrating in one carbody, they are spread out on each car that makes up the set. Therefore these cars can only propel themselves when they are part of the complete trainset, thus making them semi-permanently coupled. For example, a DMU might have one car carry the prime mover and traction motors, and another the engine for head end power generation; an EMU might have one car carry the Pantograph (rail) and transformer, and another car carry the traction motors.

Multiple Units vs. Locomotives Advantages EMUs waiting for service in Poznań

Multiple units have several advantages over locomotive-hauled trains:

• Energy Efficiency - MUs are more energy efficient than locomotive-hauled trains. They are more nimble, especially on grades, as much more of the train's weight (sometimes all of it) is carried on power-driven wheels, rather than suffer the dead weight of unpowered hauled coaches;

• No need to turn locomotive - Most MUs have cabs at both ends, resulting in quicker turnaround times, reduced crewing costs, and enhanced safety. The faster turnaround time and the reduced size (due to higher frequencies) as compared to large locomotive-hauled trains, has made the MU a major part of commuter rail commuter rail services in many countries. MUs are also used by most rapid transit systems.

• Consist can be changed mid journey - MUs may usually be quickly made up or separated into sets of varying lengths. Several multiple units may run as a single train, then be broken at a junction point into smaller trains for different destinations.

• Reliability – Due to having multiple engines the failure of one engine does not prevent the train from continuing its journey. A locomotive drawn train typically only has one power unit whose failure will disable the train. Some locomotive hauled trains may contain more than one power unit and thus be able to continue at reduced speed after the failure of one.

EMU in Zürich HB railway station

• Safety – Multiple units normally have completely independent braking systems on all cars meaning the failure of the brakes on one car does not prevent the brakes from operating on the other cars

• Axle load - Multiple units have lighter axle loads, allowing operation on lighter tracks, where locomotives are banned, such as the Whitby line in the UK. Another side effect of this is reduced track wear, as traction forces can be provided through many axles, rather than just four or six.

Disadvantages Multiple Units do have some disadvantages as compared to locomotive hauled trains:

• Maintenance - It may be easier to maintain one locomotive than many self-propelled cars.

• Safety - In the past it was often safer to locate the train's power systems away from passengers. This was particularly the case for steam locomotives, but still has some relevance for other power sources. A head on collision involving a multiple-unit (with passengers potentially right at the front of the train) is likely to result in more casualties than one with a locomotive (where the locomotive would act as a 'crumple zone').

• Easy replacement of motive power - Should a locomotive fail, it is easily replaced. Failure of a multiple unit train-set will often require a whole new train or time-consuming switching.

• Efficiency - Idle trains do not waste expensive motive power resources. Separate locomotives mean that the costly motive power assets can be moved around as needed.

• Flexibility - Large locomotives can be substituted for small locomotives where the gradients of the route become steeper and more power is needed.

• Noise - The passenger environment of a multiple unit is often noticeably noisier than in a locomotive-hauled train, due to the presence of underfloor machinery. This is a particular problem with Diesel multiple units.

• Obsolescence cycles - Separating the motive power from the payload-hauling cars means that either can be replaced when obsolete without affecting the other.

• It is difficult to have gangways between coupled sets, and retain an aerodynamic leading front end.

Features 3 on the Cologne-Frankfurt high-speed rail line near Montabaur

It is not necessary for every single car in a MU to be motorized. Therefore EMU cars can be motor units, or can be trailing units. Instead of motors, trailing units can contain some supplemental equipment such as air compressors, batteries, etc.

In some EMU trains, every car is equipped with a driving console, and other controls necessary to operate the train. Therefore every car can be used as a cab car whether it is motorised or not, if on the end of the train. This is the case with NJ Transit Arrows, Metro-North Railroad (New York) EMUs, etc. However, other EMUs can be driven/controlled only from dedicated Cab cars. Among such EMUs are Ex-USSR-made ER2, ER9 electric trainset, German classes 423-426, etc.

Well-known examples of MUs are the Japanese Shinkansen and the last generation German InterCityExpress. Most trains in Netherlands and Japan are MUs, making them suitable for use in areas of high population density. Even some freight trains are MUs: the M250, whose four front and end carriages are EMUs, has been operating in Japan since March 2004.

EMUs are also extensively used in all local train networks in India that provide commuter transport in all the major cities.

Ireland , 2006. EMU train passing through Bray.

Córas Iompair Éireann (CIE), which controlled the Republic's railways between 1945-86, mainly used locomotives and hauled stock for its passenger trains. Since 1987, Iarnród Éireann (IE) have been increasing the use of this type of train, in order to replace older locomotives and carriages. The only electrified railway network in Ireland is the Dublin Area Rapid Transit (DART) system.

A wide variety of diesel and electric multiple units have been used on Ireland's railways.

In Northern Ireland the majority of passenger services have been operated by diesel multiple units since the mid-1950s under the tenure of both the Ulster Transport Authority (1948-1966) and Northern Ireland Railways (since 1967).

In the Republic of Ireland the railway operator Iarnród Éireann has purchased a number of new multiple units since 1987 to replace older locomotives and carriages.

North America Most long-distance trains in North America are locomotive-hauled. However, commuters, Rapid transit, and light rail operations make extensive use of MUs. Most electrically powered trains are MUs. The Southeastern Pennsylvania Transportation Authority (SEPTA) Regional Rail Division uses EMUs almost exclusively - the exception being some of its peak express service. New Jersey Transit service on the Northeast Corridor is split between electric locomotives and EMUs.

M2, M4, M6 and future M8 EMUs which operate on the New Haven Line (Metro-North) of Metro-North Railroad, are “dual mode” meaning they can draw power from either the third rail or from overhead lines. This allows operation under the wires between Pelham (Metro-North station) and Union Station (New Haven), a section of track owned by Metro North but shared with Amtrak's Northeast Corridor service, and on third rail between Pelham and Grand Central Terminal. EMUs are used on Agence métropolitaine de transport's Deux-Montagnes Line (AMT).

DMUs are less common, partly because new light rail operations are almost entirely electric, with many commuter routes already electrified, and also because of the difficulties posed by Federal Railway Administration rules limiting their use on shared passenger/freight corridors. When the Budd RDC was developed following World War II, it was adopted for many secondary passenger routes in the U.S. (especially on the Boston and Maine Railroad) and Canada. These operations generally survived longer in Canada, but several were abandoned in the VIA Rail cutbacks of the early 1990s. One that survives is Malahat, British Columbia on Vancouver Island.

DMUs are used on the River Line (New Jersey Transit) in New Jersey. Currently Colorado Railcar is demonstrating an FRA Crash Compliant DMU in the United States. NJ Transit has experimented with this DMU on the Princeton Branch (a.k.a. Princeton "Dinky") line. In August 2006 it was announced that Amtrak wants the State of Vermont to experiment with DMUs on the state-subsidized Vermonter line from New Haven (Amtrak station) north to St. Albans, Vermont to replace the less efficient diesel locomotive trainsets currently used.

Russia , Moscow

Elektrichka (, ) is an informal word for elektropoezd (), a Soviet Union or post-Soviet regional (mostly suburban) electrical multiple unit passenger train. Elektrichkas are widespread in Russia, Ukraine and some other countries of former Soviet Union. The first elektrichka ride occurred in August 1929 along the line Moscow-Mytishchi.

See also

• Rail terminology
• Pacer (train) units.
• Railcar
• Hybrid Locomotive

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