| Multiple unit trains |
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| Subtypes |
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Electric multiple unit |
| Technology |
| By country |
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.
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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.
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.
DMUs were first introduced to Australia in the early 20th century for use on quiet branchlines that could not justify a locomotive hauled service.
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 (KRDI / Kereta Rel Diesel Indonesia) 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.
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.
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.
Only two classes of DMUs, the NZR ADL class and the NZR ADK class are operated in New Zealand.
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.
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.
The Southrail or the South Main Line of the Philippine National Railways which travels South of the Luzon island is one of the oldest rail lines in Asia and in the world. The railway was built in 1875 during the Spanish Colonial Rule of the country, and has since 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.
Previously the Northrail or North Main Line which travels North of the Luzon island of the Philippines shared the same locomotives as the South Main Line, with the exception for the Hyundai Rotems. Currently there are plans to rehabilitate and expand this line. convert the line 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.
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.
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). 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
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 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) .
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
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.
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.
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.
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.
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:
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.
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]
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:
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.
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.
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:
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:
Proposed operations:
DMU manufacturers include: