Diesel multiple unit

Diesel multiple unit
Multiple unit trains

Electric multiple unit
Diesel multiple unit
Push–pull train


Multiple-unit train control

By Country

Britain (DMU)
Britain (EMU)

The Transwa Prospector DEMU capable of up to 200 km/h (124 mph) provides a passenger service between Perth, Western Australia and the mining town of Kalgoorlie

A diesel multiple unit or DMU is a multiple unit train consisting of multiple carriages powered by one or more on-board diesel engines. They may also be referred to as a railcar or railmotor, depending on country.



The diesel engine may be located above the frame in an engine bay or under the floor. Driving controls can be at both ends, on one end, or none.


DMUs are usually classified by the method of transmitting motive power to their wheels.[citation needed]


In a diesel-mechanical multiple unit (DMMU) the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, such like a car. The transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs, but in most applications gears are changed automatically.


In a diesel-hydraulic multiple unit, a hydraulic torque converter, a type of fluid coupling, acts as the transmission medium for the motive power of the diesel engine to turn the wheels. Some units feature a hybrid mix of hydraulic and mechanical transmissions, usually reverting to the latter at higher operating speeds as this decreases engine RPM and noise.


In a diesel-electric multiple unit (DEMU) a diesel engine drives an electrical generator which produces electrical energy. The generated current is then fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel electric locomotive.[1]

In modern DEMUs, such as the Bombardier Voyager family, each car is entirely self-contained and has its own engine, generator and electric motors.[1] In older designs, such as the British Rail Class 207, some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electrical current from other cars in the consist which have a generator and engine.


A train composed of DMU cars scales well as it allows extra passenger capacity to be added at the same time as motive power. It also permits passenger capacity to be matched to demand, and for trains to be split and joined en-route. It is not necessary to match the power available to the size and weight of the train - each unit is capable of moving itself, so as units are added, the power available to move the train increases by the necessary amount.

Distribution of the propulsion among the cars also results in a system that is less vulnerable to single-point-of-failure outages. Many classes of DMU are capable of operating with faulty units still in the consist. Because of the self contained nature of diesel engines, there is no need to run overhead electric lines or electrified track, which can result in lower system construction costs.

These advantages often outweigh the underfloor noise and vibration that may be a problem with this type of train.

Around the World



TransAdelaide's 3100-class diesel-electric railcars operating in Adelaide, South Australia

DMUs were first introduced to Australia in the early 20th century for use on quiet branchlines that could not justify a locomotive hauled service.


Idonesian DMU Sri Lelawangsa, Medan

Japan manufactured DMU introduced in Indonesia in 1970s, First line which served by DMU is Surakarta - Jogja line or also called Kudaputih (white Horse) line. Indonesian manufactured DMU (KDRI) introduced in 2000s, manufactured by Indonesian Train Industry (PT Industri Kereta Api) now its served Surakarta - Yogyakarta line, or Prambanan Express, Sri Lelewangsa (Medan - Binjai) line, Joglosemar (Semarang - Yogyakarta) line, and Surabaya - Sidoarjo line.


JR Hokkaido KiHa 283 tilting DMU on Hakodate Main Line

The development of DMUs in Japan started in 1950s following the improvement of fuel supply that was critical during World War II. In 1953, the Japanese National Railways put the hydraulic torque converter into practical use. This invention facilitated the development of DMUs, which spread all over the nation, not only on local services but also on long distance express services. In 1960, 9-car KiHa 80 series DMUs debuted on Hatsukari limited express services connecting Tokyo and Aomori (about 750 km). In the early 1970s, Japanese National Railways operated more than 5,000 DMU vehicles at its peak.[citation needed]

On the JR lines not yet electrified, locomotive-hauled trains were abandoned apart from a small number of sleeper trains. There is also a number of independent railway lines that operate DMUs.[citation needed]

New Zealand

A refurbished ADL class DMU at Britomart Transport Centre in Auckland

Only two classes of DMUs, the NZR ADL class and the NZR ADK class are operated in New Zealand.[citation needed]

The NZR ADL class consists of 10 DMU trains owned by the Auckland Regional Council and operated on the suburban train network by Veolia Transport Auckland. They were originally built by Goninan for the Western Australian Government Railways in the early 1980s, but were purchased by New Zealand Rail Limited in 1993. The entire class underwent a NZ$8.5 million upgrade beginning in April 2002 with all 10 trains being finished by November 2003. Since then the units are typically operated as two car sets with one ADC trailer unit but sets can be coupled together for additional capacity.[citation needed]

The NZR ADK class consists of nine DMU trains (eight operational at any one time) which are also owned by the Auckland Regional Council and operated by Veolia. They were built by Commonwealth Engineering for the Western Australian Government Railways in 1967-1968 and purchased alongside the ADL class by NZR in 1993. The operational units underwent refurbishment following the ADL class in 2004 and are since run as permanent 4-car sets (with two ADB trailer units) on the Auckland regional train network. Due to their older age however the ADKs have problems such as a lack of air conditioning, ineffective suspension, and underpowered engines. These issues do not exist with the newer ADL trains.[citation needed]


The Southrail or the South Main Line of the Philippine National Railways which travels South of the Luzon island being one of the oldest rail lines in Asia and in the world which started back in 1875 under the Spanish Colonial Rule of the country used several different types of trains from steam engined trains to DMU's some of which are different models of General Electric locomotives, Former JR Trains and the newly accuired Hyundai Rotem trains.

Also, before the Northrail or North Main Line which travels North of the Luzon island of the Philippines shared the same locomotives except for the Hyundai Rotems due to the line's conversion to an elevated right-of-way Electrical multiple unit or EMU configuration similar to the country's LRT-1, MRT-2 and MRT-3 which operates on electricity or overhead electric wires via a pantograph as part of the Priority Projects under the Arroyo Administration to provide a faster link from Diosdado Macapagal International Airport to the country's National Capital Region.

South Korea

Korail DHC-PP with new CI colour

Korail operates many DMUs. The DHC (Diesel Hydraulic Car), which made its debut for the 1988 Seoul Olympics, can reach speeds up to 150 km/h (93 mph) and serves Saemaul-ho trains. The NDC (New Diesel Car) serves Mugunghwa-ho trains and the CDC (Commute Diesel Car) serves Tonggeun trains. The NDC and CDC can reach speeds up to 100 km/h (62 mph) and are not used for mountainous lines such as the Taebaek Line.


A DMU in India

Indian Railways operates DMUs in India. However, most major services such as the Rajdhani Express and Shatabdi Express are locomotive hauled. Some local feeder services are operated by DMUs but since many large cities such as Mumbai are electrified they use EMU services. A few DMUs are used on the Mumbai Suburban Railway for lines with limited service (such as Diva-Vasai).[citation needed] DMU is used recently in Jammu and Kashmir, where Indian Railways connected the remote areas of the state by railways. These DMUs run daily across whole Punjab (India) and are known as life line of Punjab[citation needed]


SNCF's turbotrain in Houlgate on the Deauville-Dives line. Turbotraines in Iran were converted to DMU

Iranian Railways operates many type of DMUs in Iran. The first MU with turbine was introduced in 1974 by ANF of France that in 2009 was converted to DMU. In 2006 the Paradise DMU[clarification needed] from Seiemens with 4 cars started working (locally manufactured in Wagon Pars Co.) and in 2009 the railbuses DMU from ROTEM of Korea (locally manufactured by IRICO) .

Sri Lanka

A Sri Lankan DMU - Class S10

DMU's were first introduced to Sri Lanka in 1940. Aim of this was connecting minor railway stations and stops on the main line where most of express trains are not stopping. Currently there are about 120 Diesel Multiple Units operated by Sri Lanka Railways. DMUs are classified as Class S in Sri Lanka. First Diesel Multiple Unit Class S1 manufactured by English Electric was imported in 1940 and latest Indian manufacture one Class S11 was imported in 2011. Currently operating DMUs are

  • Class S3 - Operating Between Galle & Mathara (MAN Germany) - 1 Train
  • Class S5 - Tourist Train (Hitachi Japan) - 4 Trains
  • Class S6 - Operating On Broad gauge Kalani Valley Line Between Colombo & Awissawella - 10 Trains
  • Class S7 - Operating On Broad gauge Kalani Valley Line Between Colombo & Awissawella - 10 Trains
  • Class S8 - Running On Main Line, connecting Colombo and Sub Urbs. This DMU has a remarkably high acceleration rate from zero to 60mph - 20 Trains Available
  • Class S9 - Running On Main Line, capable of running with a overhead Pantograph connected to a Catenary. 15 Trains are available
  • Class S10 - Chinese MTU Diesel Electric Train
  • Class S11 - Manufactured By Indian Railworks

Out of these Class S1, S2, S4 are not in operation. These trains are very popular among sri lankan passengers and known as Colombo Commuter in SL coaster.



German ICE TD DMU near Rostock

The Flying Hamburger of Germany, introduced in 1933, was the fastest regular railway connection in the world. Its top speed was 160 km/h (99 mph), the average speed being 124 km/h (77 mph) on the tracks between Berlin and Hamburg.

The Trans Europ Express travelled international traffic between countries like Germany, France, Italy, Netherlands in the 1950s and 1960s. The most famous German train was the DB Class VT 11.5, a diesel multiple unit since the electrical systems varied a lot.[citation needed]

Also from Germany is the CargoSprinter concept. With two motorized units and three flatbed wagons between them, this DMU container train tried to compete with container road trucks by profiting from existing railway access to factories and businesses, but eliminating the need for inflexible locomotive-pulled cargo trains. The payload was 160 tons. Suffering from technical problems and failing political support for short-haul cargo railway connections, the prototypes were sold to Austria.

Currently DMUs are used in large numbers for local traffic (for example, DB Class 642) and fast, tilting regional traffic (for example, DB Class 612). The introduction of DB Class 605 as a diesel variant of the tilting EMU DB Class 411/415 in 2001 was not successful at first, several adaptations were needed.


DMU 2751 in Colbert Station, 2006

In the Republic of Ireland the Córas Iompair Éireann (CIE), which controlled the republic's railways between 1945–86, introduced DMUs in the mid-1950s and they were the first diesel trains on many main lines. The Great Northern Railway, merged into CIE at this time, also brought some DMUs of its own of a similar style. They were not well suited to the long-distance tasks and were replaced in a few years by traditional trains with new diesel locomotives, being then mostly restricted to Dublin commuter lines. The power systems were worn out by the 1970s so they were converted to normal carriages pulled by diesel locomotives on these suburban routes, and DMUs disappeared from CIE. But since 1987, Iarnród Éireann (IE) have been increasing the use of this type of train, to replace older locomotives and carriages, using new types of train manufactured in a number of overseas countries.[citation needed]

United Kingdom

The first significant use of DMUs in the United Kingdom was by the Great Western Railway, which introduced its small but successful series of diesel-mechanical GWR railcars in 1934. The London, Midland and Scottish Railway also experimented with DMUs in the 1930s, both on its own system, and on that of its Northern Irish subsidiary, but development was curtailed by World War II.

After nationalisation, British Railways revived the concept in the early 1950s. At that time there was an urgent need to move away from expensive steam traction which led to many experimental designs using diesel propulsion and multiple units. The early DMUs proved successful, and under BR's 1955 Modernisation Plan the building of a large fleet was authorised. These BR "First Generation" DMUs were built between 1956 and 1963, and some are still in service as of 2008. Most were diesel-mechanical, but a few designs had hydraulic transmissions (these were generally less successful and were withdrawn earlier than the main diesel-mechanical types).

BR's owners, the British Government, required that contracts for the design and manufacture of new locomotives and rolling stock be split between numerous private firms as well as BR's own workshops, while different BR Regions laid down different specifications. The result was a multitude of different types, some of which were built only in small numbers, but in general the First Generation units fell into five distinct groups:[citation needed]

  • "Low Density" units (such as Class 101), designed for use on rural lines and provincial commuter services. These had 3+2 seating in standard class, and had doors located in vestibules separated from the seats. They were initially allocated to all BR regions except the Western and Southern Regions;
  • "High Density" units (such as Class 121), designed for the busy commuter services into London, and also for local services in Birmingham, Liverpool and throughout the BR Western Region. These were built with doors at each seating bay, and bench seats across the full width of the carriage for maximum seating capacity. Many were later rebuilt with 3+2 seating and gangways between carriages;
  • "Cross Country" units, which were essentially more luxurious Low Density units, with 2+2 seating in standard class. They were designed for longer distance rural services, and were originally allocated to the Western and Scottish Regions;
  • 'Intercity' units, which were more substantially constructed, and shared many features with contemporary hauled coaching stock. They were built for express services on important secondary routes on the Scottish, North Eastern and Western Regions.
  • Parcels cars. Those built as such were invariably single cars with a cab at each end, and were built for the Western and London Midland Regions. Later some passenger DMUs were also rebuilt as parcels units.

There were also a small number of four-wheeled railbuses built for the most lightly used branch lines, but these failed to prevent the closure of such lines, and all of the railbuses had gone by the end of the 1960s.

Diesel Electric Multiple Units (DEMUs) were also developed during the 1950s and 1960s, for use on the Southern Region. The Southern was largely electrified, but required diesel units for the remaining lines, in some cases as stop-gaps pending planned electrification. Diesel-mechanical and diesel-hydraulic units were judged to have inadequate acceleration, which would have caused delays to other traffic when operated over electrified lines. Examples of Southern DEMUs included Classes 205 and 207, which were nicknamed "Thumpers" because of their characteristic sound.[citation needed]

In 1960, British Railways introduced its Blue Pullman high speed DEMUs.[2] These were few in number and relatively short-lived,[2] but they paved the way for the very successful British Rail "InterCity 125" or High Speed Train (HST) units, which were built between 1975 and 1982 to take over most principal express services on non-electrified routes.[3][4] These 125 mph (201 km/h) trains run with a streamlined power car at each end and (typically) 7 to 9 intermediate trailer cars.[5][6] Although originally classified as DEMUs, the trailer cars are very similar to loco-hauled stock, and the power cars were later reclassified as locomotives under Class 43.[5][6] They remain in widespread use.[5][6]

The popular Class 170 was the best selling DMU of the last 10 years in the UK.

By the early 1980s, many of the surviving First Generation units were becoming life-expired, which lead to spiralling maintenance costs, poor reliability and a poor public image for the railway. A stopgap solution was to convert some services back to locomotive haulage, as spare locomotives and hauled coaching stock were available, but this also increased operating costs. Commencing in the mid '80s, British Rail embarked upon its so called "Sprinterisation" programme, to replace most of the first generation DMUs and many locomotive-hauled trains with three new families of DMU:

  • Class 140-144 Pacer railbuses, ultra-low-cost diesel-mechanical units utilising 4-wheeled chassis and lightweight bus bodywork, designed for provincial branch line and stopping services. The earliest examples have now been withdrawn from service;
  • Sprinter a family of diesel-hydraulic DMUs. These fall into three sub-groups; Class 150 Sprinters (for branch line/commuter service), Class 153 / 155 / 156 Super Sprinters (for longer cross country services), and Class 158 / 159 Express units (for secondary express services);
  • Networker diesel-hydraulic units, of Class 165 Network Turbo (standard commuter version) and Class 166 Network Express (for longer distance commuter services). These took over the remaining non-electric commuter services into London.

Following the privatisation of British Rail in the late 1990s, several other diesel-hydraulic DMU families have been introduced:

As modern diesel-hydraulic units have sufficient performance to match the acceleration of Electric Multiple Units, they have replaced DEMUs on the former Southern Region local/commuter services. However the vast majority of British non-electric InterCity services are currently operated by Diesel Electric Multiple Units, the HSTs having been joined since privatisation by high speed Bombardier Class 220 Voyager, Class 221 Super-Voyager and Class 222 Meridian/Pioneer express units.

North America

Budd Rail Diesel Car RDC-1 #407 of the Cape May Seashore Lines, New Jersey.

The most popular Diesel Multiple Units in North America was the Budd Rail Diesel Car (RDC). The RDC was a single passenger car with two diesel engines and two sets of controls. Up to 12 cars could be connected together and all the propulsion systems controlled from a single operator's station or cab. Introduced in 1949, the cars were used in many ways: on rural railway lines that did not warrant full passenger trains, on commuter services, in medium distance intercity service, and even in long-haul local services in Western North America.


Two Bombardier Talent low-floor DMUs on the O-Train prototype line in Ottawa Canada.

Canada generally follows similar buffer strength requirements to the USA,[7] but new services are evaluated on a case-by-case basis. As a result several types of lightweight DMUs have been used:

  • Calgary, Alberta has also used European Sprinter DMUs in demonstration service on conventional railway tracks.
  • Canadian National operates the small custom-built Koaham Shuttle between Lillooet, and D'Arcy via Seton Portage, 213 northeast of Vancouver. While on CN Rails, the train is still decorated with BC Rail logos.

United States of America

In the United States only FRA compliant DMU systems are permitted on freight rail corridors. This is due to the Federal Railway Administration setting higher coupling strength requirements than European regulators, effectively prohibiting the use of lighter weight European-style inter-city rail DMUs on U.S. main line railways. This has greatly restricted the development of DMUs within the U.S. as no other country requires the heavier and less efficient FRA compliant vehicles and no export market for them exists.

Several rail operators in the United States use DMUs meeting FRA requirements:

Operations using non FRA compliant vehicles:

  • New Jersey Transit operates the River LINE from Camden, NJ to Trenton, NJ, every 15 minutes during peak hours and every 30 minutes at other times. Trains are one or two cars. The line is classified as light rail because it utilizes imported European DMUs that do not meet FRA crash guidelines. The cars may not operate with the freight rail service that shares the line so evening operating hours are restricted to Saturday nights. This line currently carries over 7,500 passengers on a typical weekday, exceeding expectations.
  • NCTD operates the Sprinter line using DMUs built by Siemens AG. Opened March, 2008, The line operates every half-hour everyday except limitations in the morning and at night on Saturday, Sunday and on holidays. The line runs from Oceanside, CA, where transfer is possible with Coaster commuter rail service to San Diego, to Escondido, CA. Like the New Jersey Transit River LINE, it is classified Light Rail due to European DMUs, but does not run at a more typical light rail frequency.

Proposed operations:

  • BART The eBART expansion plan calls for diesel multiple unit train service to be implemented from the existing Pittsburg/Bay Point station. The first phase of the expansion will proceed east along the Highway 4 corridor to the town of Antioch. The plan includes an option for a station at Railroad Avenue in Pittsburg. Future expansions in this direction could connect the eBART service to Oakley, Brentwood, Byron, and beyond to Tracy and Stockton. The DMU system was chosen as a less-expensive alternative to the existing third-rail BART design. Funding for this expansion was approved in April 2009.[8]
  • Chicago's commuter rail line, Metra, is studying the use of DMUs on its newly proposed lines (STAR line, SES). They claim these DMUs will have better acceleration, be more fuel efficient, and seat more customers than the current diesel locomotive and double decker rail cars that are currently in use.[9]
  • Seattle Area - The Central Puget Sound's regional transit agency Sound Transit, along with the Puget Sound Regional Council evaluated the feasibility of both DMU and diesel locomotive technology for operation in the Eastside BNSF Corridor in response to a state legislative request. The Eastside BNSF corridor runs from the City of Snohomish in the north to Renton in the south of the metro area. Sound Transit has no plans to operate passenger rail service in the eastside BNSF corridor, but has committed limited funds to provide capital improvements in the event another public or private operator proposes to operate the service. Link Light Rail.[10]
  • Anchorage Mat-Su Area- As part of a joint U.S. Forest Service (USFS) and ARRC Chugach Forest Whistle Stop project, a self-propelled rail car was purchased and delivered spring 2009. The diesel multiple unit (DMU) maybe available for flexible demonstration service during winter months.[11]


DMU manufacturers include:

See also


  1. ^ a b "Cutting noise and smoothing the ride". Railway Gazette. 2000-08-01. http://www.railwaygazette.com/news/single-view/view//cutting-noise-and-smoothing-the-ride.html. Retrieved 2011-01-20. "In the Voyager application, every car has a Cummins underfloor engine and alternator supplying power to a pair of body-mounted traction motors. Each drives one inner axle through a cardan shaft and axle-mounted final drive gearbox." 
  2. ^ a b Heaps, Chris (1988). "End of the Blue Pullmans". BR Diary: 1968-1977. London: Ian Allan. pp. 66–67. ISBN 0-7110-1611-9. 
  3. ^ "1976: New train speeds into service". BBC News Online (London). 4 October 1976. http://news.bbc.co.uk/onthisday/hi/dates/stories/october/4/newsid_2486000/2486817.stm. Retrieved 15 February 2011. 
  4. ^ "New opportunities for the railways: the privatisation of British Rail". Railway Archive. p. 8. http://www.railwaysarchive.co.uk/documents/DoT_WP001.pdf. Retrieved 15 February 2011. 
  5. ^ a b c "Class 253 High Speed Train". Railblue.co.uk. http://www.railblue.com/Class%20Headers%20v2.0/class_253V.2.htm. Retrieved 15 February 2011. 
  6. ^ a b c "Class 254 High Speed Train". Railblue.co.uk. http://www.railblue.com/Class%20Headers%20v2.0/class_254V.2.htm. Retrieved 15 February 2011. 
  7. ^ Such as the Railroad Safety Appliance Act of 1893.
  8. ^ [1]
  9. ^ [2]
  10. ^ [3]
  11. ^ [4]

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