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Amultiple-unit train (ormultiple unit (MU)) is a self-propelledtrain composed of one or morecarriages joined, and where one or more of the carriages have the means of propulsion built in. By contrast, a locomotive-hauled train has all of the carriages unpowered.
An implication of this is that all the powered carriages needs to be controllable by a single engineer or driver, which is a case of the broader concept ofmultiple-unit train control. In other words, all "multiple units" employ some variation of multiple-unit train control. In the broader context "unit" means any powered rail vehicle, including locomotives (that does not carry cargo) and powered cargo-carrying carriages. In the context of this article, "unit" refers specifically to the latter only (whether the cargo is passengers or some other cargo).
What follows is that if coupled to another multiple unit, all MUs can still be controlled by the single driver,[1] withmultiple-unit train control.
Although multiple units consist of several carriages, single self-propelled carriages – also calledrailcars,rail motor coaches orrailbuses – are in fact multiple units when two or more of them are working connected through multiple-unit train control (regardless of whether passengers can walk between the units or not).
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Multiple-unit train control was first used inelectric multiple units in the 1890s.
TheLiverpool Overhead Railway opened in 1893 with two-car electric multiple units,[2] controllers in cabs at both ends directly controlling the traction current to motors on both cars.[3]
The multiple-unit traction control system was developed byFrank Sprague and first applied and tested on theSouth Side Elevated Railroad (now part of theChicago 'L') in 1897. In 1895, derived from his company's invention and production of direct-current elevator control systems, Frank Sprague invented a multiple-unit controller for electric train operation. This accelerated the construction of electric-traction railways and trolley systems worldwide. Each car of the train has its own traction motors: by means of motor control relays in each car energized by train-line wires from the front car, all the traction motors in the train are controlled in unison.
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Most MUs are powered either bytraction motors, receiving their power through athird rail oroverhead wire (EMU), or by adiesel engine (DMU) driving a generator producing electricity to drive traction motors.
A MU has the same power and traction components as alocomotive, but instead of the components being concentrated in one car, they are spread throughout the cars that make up the unit. In many cases these cars can only propel themselves when they are part of the unit, so they are semi-permanently coupled. For example, in a DMU one car might carry theprime mover andtraction motors, and another the engine forhead-end power generation; an EMU might have one car carry thepantograph andtransformer, and another car carry the traction motors.
MU cars can be a motor or trailer car, it is not necessary for every one to be motorized. Trailer cars can contain supplementary equipment such as air compressors, batteries, etc.; they may also be fitted with a driving cab.
In most cases, MU trains can only be driven/controlled from dedicated cab cars. However, in some MU 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. An example of this arrangement is theNJ Transit Arrows.
An advantage of multiple unit trains is that they can be engineered to be lighter thanlocomotive-hauled trains with separate carriages, usinglightweighting techniques to reduce energy use, track wear, and operating costs.[4][5] The term "light-weight train" was first used in the 1930s,[6] with early designs such as the 1934M-10000 andPioneer Zephyr in the United States, and Germany's 1932Flying Hamburger.[7]
Modern light-weight multiple units typically use fewerbogies and distributetraction equipment across the train, improvingefficiency and axle loading.[8] However, they require particular design attention forbridge loading andcrosswind safety,[9][10] and often includenoise and vibration mitigation systems.[11]
Examples from the 21st century include the lightweightTalgo sets used inSpain and exported toGermany andDenmark,[12] India's modernVande Bharat Express units,[13] and the upcomingTELLi fleet forSNCF regional lines inFrance.[14]
Virtually all rapid-transit rolling stock, such as on theNew York City Subway, theLondon Underground, theParis Metro and other subway systems, are multiple-units, usually EMUs.[citation needed] Most trains in the Netherlands and Japan are MUs, being suitable for use in areas of high population density.[citation needed]
Manyhigh-speed rail trains are also multiple-units, such as the JapaneseShinkansen and the GermanIntercity-ExpressICE 3high-speed trains. A new high-speed MU, theAGV, was unveiled by France'sAlstom on 5 February 2008. It has a claimed service speed of 360 km/h (220 mph). India's ICF announced the country's first high-speed engine-less train named 'train 18', which would run at 250 km/h (160 mph) maximum speed.[15]
Passenger multiple units can be divided into articulated trains and non-articulated trains. The first type can be divided again into theTGV/AGV subtype (which usesJacobs bogies) and theTalgo subtype.[16]
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This section is specifically about multiple units for freight traffic. For freight traffic powered through multiple locomotive "units", seeMultiple-unit train control andDistributed power.
Multiple units have been occasionally used for freight traffic, such as carrying containers or for trains used for maintenance. The JapaneseM250 series train has four front and end carriages that are EMUs, and has been operating since March 2004. The GermanCargoSprinter have been used in three countries since 2003.
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They are more energy-efficient than locomotive-hauled trains.[citation needed]
They have betteradhesion, as more of the train's weight is carried on driven wheels, rather than the locomotive having to haul the dead weight of unpowered coaches.
They have a higher power-to-weight-ratio than a locomotive-hauled train since they don't have a heavy locomotive that does not itself carry passengers, but contributes to the total weight of the train. This is particularly important where train services make frequent stops, since the energy consumed for accelerating the train increases significantly with an increase in weight. Because of theenergy efficiency and higher adhesive-weight-to-total-weight ratio values, they generally have higher acceleration ability than locomotive-type trains and are favored in urban trains and metro systems for frequent start/stop routines.
Most of them 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 largelocomotive-hauled trains, has made the MU a major part ofsuburban commuter rail services in many countries. MUs are also used by most rapid transit systems. However, the need to turn a locomotive is no longer a problem for locomotive-hauled trains due to the increasing use ofpush pull trains.
Multiple units 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 shorter trains for different destinations. As there are multiple engines/motors, the failure of one engine does not prevent the train from continuing its journey. A locomotive-drawn train typically has only one power unit, whose failure will disable the train. However, 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.
They have lighter axle loads, allowing operation on lighter tracks, where locomotives may be banned. Another side effect of this is reduced track wear, as traction forces can be provided through many axles, rather than just the four or six of a locomotive. They generally have rigid couplers instead of the flexible ones often used on locomotive-hauled trains. That means brakes/throttle can be more quickly applied without an excessive amount of jerk experienced in passenger coaches. In a locomotive-hauled train, if the number of cars is changed to meet the demand, acceleration and braking performance will also change. This calls for performance calculations to be done taking the heaviest train composition into account. This may sometimes cause some trains in off-peak periods to be overpowered with respect to the required performance. When 2 or more multiple units are coupled, train performance remains almost unchanged. However, in locomotive-hauled train compositions, using more powerful locomotives when a train is longer can solve this problem.
It may be easier to maintain one locomotive than many self-propelled cars. 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 casualties than one with a locomotive[clarification needed] (where the heavy locomotive would act as a "crumple zone").
If a locomotive fails, it can be easily replaced with minimal shunting movements. There would be no need for passengers to evacuate the train. Failure of a multiple unit will often require a whole new train and time-consuming switching activities; also passengers would be asked to evacuate the failed train and board another one. However, if the train consists of more than one multiple unit they are often designed such that in the event of the failure of one unit others in the train can tow it in neutral if brakes and other safety systems are operational.
Idle trains do not waste expensive motive power resources. Separate locomotives mean that the costly motive power assets can be moved around as needed and also used for hauling freight trains. A multiple unit arrangement would limit these costly motive power resources to use in passenger transportation.
It is difficult to havegangway connections between coupled units and still retain an aerodynamic leading front end. Because of this, there is usually no passage between high-speed coupled units, though lower-speed coupled units frequently have connections between coupled units.[citation needed] This may require more crew members, so that ticket inspectors, for example, can be present in all of them. This leads to higher operating costs and lower use of crew resources. In a locomotive-hauled train, one crew can serve the train regardless of the number of cars in the train provided limits of individual workload are not exceeded. Likewise, in such instances, buffet cars and other shared passenger facilities may need to be duplicated in each unit, reducing efficiency.
Large locomotives can be used instead of small locomotives where more power is needed. Also, different types of passenger cars (such as reclining-seats, compartment cars, couchettes, sleepers, restaurant cars, buffet cars, etc.) can be easily added to or removed from a locomotive-drawn train. This is not so easy for a multiple unit, since individual cars can be attached or detached only in a maintenance facility. This also allows a loco-hauled train to be flexible in terms of number of cars. Cars can be removed or added one by one, but on multiple units two or more units have to be coupled. This is not so flexible.
The passenger environment of a multiple unit is often noticeably noisier than that of a locomotive-hauled train, due to the presence of underfloor machinery. The same applies to vibration. This is a particular problem withDMUs.
Separating the motive power from the payload-carrying cars means that either can be replaced when obsolete without affecting the other.
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Algeria possesses 17 units of the Coradia El Djazaïr, a multiple unit train produced by Alstom. These units are similar to the French version of Régiolis, which belongs to the Coradia family.[17]
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Metrorail, which provides commuter rail service in major urban areas of South Africa, operates most services using electric multiple unit train sets of the type5M2A. These trains are being gradually refurbished and subsequently designated as 10M3 (Cape Town), 10M4 (Gauteng) or 10M5 (Durban). Metrorail services are split into four regions;Gauteng,KwaZulu-Natal,Eastern Cape andWestern Cape.
Gautrain, a commuter rail system inJohannesburg, operates withBombardier Electrostar electric multiple units.
The concept of multiple unit has entered the horizon of the Chinese since the 6th Speed-up Campaign ofChina Railway in 2007. With the upgrade ofJinghu Railway, NorthJingguang Railway,Jingha Railway andHukun Railway, and the construction of new Passenger Dedicated Lines (or Passenger Railways) completed,CRH (China Railway High-speed) trains have been put into service, mainly in North and Northeast China, and East China. All these CRH trains are electric multiple units. This was the beginning of the general service of multiple unit trains in China's national railway system.
Far earlier than the introduction of CRH brand, multiple unit trains have been running on all major cities' metro lines in China.
In Japan almost all passenger trains, including the high-speedShinkansen, are of the multiple-unit (MU) type, with most locomotives now used solely in freight operations. Of the locomotive-hauled passenger services still in operation, the majority are tourist-oriented, such as the numerous steam-hauled trains operated seasonally on scenic lines throughout the country, as well as some of the luxury cruise trains.
Japan is a country of high population density with a large number of railway passengers in relatively small urban areas, and frequent operation of short-distance trains has been required. Therefore, the high acceleration ability and quick turnaround times of MUs have advantages, encouraging their development in this country. Additionally, the mountainous terrain gives the MUs an advantage on grades steeper than those found in most countries, particularly on small private lines many of which run from coastal cities to small towns in the mountains.
Most long-distance trains in Japan were operated by locomotives until the 1950s, but by utilizing and enhancing the technology of short-distance urban MU trains, long-distance express MU-type vehicles were developed and widely introduced starting in the mid-1950s. This work resulted in the originalShinkansen development which optimized all of the EMU's efficiencies to maximize speed. It was introduced upon completion of theTokaido Shinkansen (literally "new trunk line") in 1964. By the 1970s, locomotive traction was regarded as slow and inefficient, and its use is now mostly limited to freight trains.
From 1999, there have been development efforts infreight EMU technology, but it is currently used only for an express freight service on theTokaido Main Line between Tokyo and Osaka. The government has been pushing for the adoption of freight EMU technology on energy efficiency grounds in the hope that widespread adoption could assist in meeting CO2 emissions targets. The effort has been principally targeted at express package shipping that would otherwise travel by road.
In South Korea, theKTX-I andKTX-Sancheon, which are still centralized power trains, are the main trains, but theKTX-Eum, which opened in 2021, and theKTX-Cheongryong, which opened in 2024, are the multiple unit.[18][19]
Thefirst EMUs have been introduced in Belgium in the 1930s. Several models have followed since then, such as theAM75.
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CIÉ introduced its firstDMUs, the 2600-class, in 1951.
Elektrichka (Russian:электри́чка,Ukrainian:електри́чка,romanized: elektrychka) is an informal word forelektropoezd (Russian:электропо́езд), aSoviet or post-Soviet regional (mostlysuburban)electrical multiple unit passengertrain. Elektrichkas are widespread in Russia,Ukraine and some other countries of the former Soviet Union. The firstelektrichka ride occurred in August 1929 between Moscow andMytishchi.
Swedish railroads have been privatized in steps for about 25 years, and today many different companies operate different types of multiple units. A majority of passenger trains today consists of multiple unit trains of which regional traffic exclusively use them.
TheSwiss Federal Railways use many multiple units, mainly on regional lines (S-Bahn).
In the UK, both electric and diesel multiple units are commonplace on suburban and intercity lines, having been introduced from the early 1900s.
Early electric multiple units include theSouthern Railway3Subs,London and North Western 'Oerlikons' andLondon Underground1903 Stock. More extensive adoption of multiple units, especially diesel multiple units (DMUs), came about in the 1950s, asBritish Rail sought toreplace steam-hauled services. This would result in several classes offirst generation DMUs being built, all similar in design. The vast majority of this design were withdrawn in the 1980s and 1990s, although theClass 121 was used in service withChiltern Railways from 2003 to 2017.
Examples of modern multiple units include theSprinter andElectrostar families, as well as the newerAventra family.
TheLondon Underground passenger system is operated exclusively by EMUs. Work trains on the Underground employ separate locomotives, some of which are dual battery/live rail powered.
In Northern Ireland the majority of passenger services have been operated by diesel multiple units since the mid-1950s under the tenure of both theUlster Transport Authority (1948–1966) andNorthern Ireland Railways (since 1967).
The first multiple unis in Australia were theTait trains, wooden bodiedElectric Multiple Unit train that operated inMelbourne,Victoria. They were originally introduced as steam locomotive hauled carriages but were converted to electric traction from 1919 during Melbourne's electrification project.[21]
Indian Railways has recently introduced a semi-high-speed EMU namedVande Bharat Express, capable of running at 183 km/h (114 mph). And it continues to use diesel and electrical multiple units on its national network. All suburban and rapid transit lines are served by EMUs.
Indonesia uses diesel since 1976 and electric MUs since 1925. Most of these MUs were built in Japan.
The Manila Railroad Company (MRR) acquired its first multiple units in the 1930s. The locally-built MC class was initially powered by gasoline and was changed to diesel duringWorld War II. Both the MRR and its successor, thePhilippine National Railways (PNR), has since acquired various classes of diesel multiple units. All multiple units owned by MRR and all of the older MUs of the PNR were built by Japanese firms. On the other hand, its newer rolling stock were built inSouth Korea andIndonesia. There will also be DMUs that will be built inChina.[22]
The first electric multiple units were acquired in 1984 for theLRT Line 1 built byLa Brugeoise et Nivelles inBelgium.[23] The first EMUs to be used outside ofrapid transit will enter service between 2021 and 2022.[24]
Most trains in North America are locomotive-hauled and use Multiple Unit (MU) control to control multiple locomotives. The control system of the leading locomotive connects to the other locomotives so that the engineer's control is repeated on all the additional locomotives. The locomotives are connected by multi-core cables.The Railway Technical Website, vol. US Locomotive MU Control. This does not make these locomotives MUs[dubious –discuss]for the purposes of this article. Seelocomotive consist.
However, commuters,rapid transit, andlight rail operations make extensive use of MUs. Most[citation needed] 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 theNortheast Corridor Line is split between electric locomotives and EMUs.
M2,M4,M6 andM8 EMUs which operate on theNew Haven Line ofMetro-North Railroad, are “multi-system” meaning they can draw power from either the third rail or fromoverhead lines. This allows operation under the wires betweenPelham, NY andNew Haven, CT, a section of track owned by Metro North but shared with Amtrak's Northeast Corridor service, and on third rail between Pelham andGrand Central Terminal. EMUs are used onAMT'sMontreal/Deux-Montagnes line.
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 byFederal Railway Administration rules limiting their use on shared passenger/freight corridors. When theBudd RDC was developed following World War II, it was adopted for many secondary passenger routes in the United States (especially on theBoston and Maine Railroad) and Canada. These operations generally survived longer in Canada, but several were abandoned in theVia Rail cutbacks of the early 1990s. One that survives isVictoria - Courtenay train on Vancouver Island. DMU use in Canada has been resurrected in recent years, beginning with the opening ofUnion Pearson Express in 2015.
While most DMUs need to comply with strictFRA crash requirements for simultaneous operation with freight railways, European-style DMUs are used withtimesharing arrangements on several rail lines, including theRiverLINE in New Jersey. Only a handful of manufacturers in the United States produce or have produced FRA-compliant DMUs, includingColorado Railcar (nowUS Railcar) andNippon Sharyo/Sumitomo Corporation.NJ Transit has experimented with this DMU on thePrinceton Branch line. In August 2006 it was announced that Amtrak wants the State of Vermont to experiment with DMUs on the state-subsidized Vermonter line fromNew Haven north toSt. Albans to replace the less efficient diesel locomotive trainsets currently used.
MU streetcars were used in Toronto by theToronto Transportation Commission (laterToronto Transit Commission) from 1949 to 1966 using 100PCC A-7 built bySt. Louis Car Company andCanadian Car and Foundry.[25] These two car units ran along theBloor Street route only beginning in 1950 and ceased operations after the opening of the Bloor–Danforth subway line in 1966. The A-7 units were later converted to single use.
This is one of the original motor coaches which has electric motors mounted beneath the floor, a driving cab at one end and third-class accommodation with wooden seats.
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