British diesel and electric multiple units

'Multiple Unit' is a term used to describe a train which does not have a separate locomotive. Typically these are passenger trains with accommodation in every vehicle and motors or engines distributed under the floor along the length of the train. The term is further classified by the method of propulsion: Diesel (DMU), Electric (EMU) or Diesel-Electric (DEMU).

The term is also used, more loosely, to describe a train such as the Advanced Passenger Train which was a permanent formation with 'power cars' in the train rather than a locomotive at one end.

This article describes the history, development and current use of diesel and electric multiple units in Great Britain.

Pre-Nationalisation

Prior to the Nationalisation that formed British Railways in 1948, all of the Big Four railway companies (GWR, LMS, LNER, SR) had experimented with using multiple units to some extent.

The Southern Railway went much further, implementing an extensive programme of electrification on its commuter routes, and consequently was a large user of EMUs.

Multiple unit operation on suburban routes was also (by Nationalisation) in use in London, the extensive operations of the LSWR (later part of the Southern) being the most visible example. Multiple unit operation was also in use on some suburban routes of the LMS in London, Manchester and on Merseyside (Mersey Railway). The LNER was also using electric units on Tyneside.

Alongside the mainline railways, urban transit systems in Liverpool (1893), Glasgow (1896) and London were early adopters of multiple unit operation.

The Liverpool system utilised electrically powered units from opening, and it has been suggested that these units were the first electrical multiple units (EMU) globally. The Glasgow Subway began operations with single 'car' units on cable traction, additional trailer cars being provided from 1898 onwards, these were converted to electric traction in 1935.

Great Western Railway

One of the earlier, more-streamlined GWR diesel railcars, still in British Railways service in May 1956.

The GWR network included many minor routes and branch lines, and there was a need for more economical trains for lesser-used routes. Having borrowed an LSWR steam railmotor in 1903, the GWR developed their own range of steam rail-motors. These were single carriages, with a boiler and steam engine unit at one end, and a driving cab at both ends. As the railmotors could not haul additional vehicles, in the 1920s the GWR developed the auto-train for routes where the railmotor was insufficient. An autotrain comprised a suitably equipped steam locomotive that could be controlled from the driving cab of a special 'autocoach'. This arrangement avoided the need for the locomotive to run round the train at the terminus. Up to four autocoaches could be used in a train, with the locomotive in the middle, driven from either end like a multiple unit. Autotrains remained in use right through to the end of steam operation on British Railways in the 1960s.

As the last steam railmotors were being withdrawn in the mid-1930s, the GWR introduced a series of diesel railcars. Although most were single units, there were two sets of 'power twins' (pairs of single-cabbed railcars that operated together), a form of multiple unit that could be expanded to take additional centre coaches. The railcars were also successful and most survived into British Railways ownership, eventually being displaced in the late 1950s by the closure of unprofitable routes and the introduction of the 'first-generation' BR diesel multiple units.

London Midland and Scottish Railway

Main article: LMS railcars

The LMS also used a number of single diesel railcars and built a prototype streamlined multiple unit, prior to nationalisation.

In Northern Ireland, the Northern Counties Committee railcars were also used.

London and North Eastern Railway

Southern Railway

Development of electric multiple units on the Southern Railway, pre-nationalisation, was extensive.

Prior to the Grouping, both the London and South Western Railway (using third rail) and the London, Brighton and South Coast Railway (using overhead wires) where both utilising electric multiple units on commuter routes in their respective territories.

Post-grouping, third-rail electrification (based on the LSWR's experience) became standardised on the Southern Railway and expansion of the system on the mainlines (as opposed to suburban routes) continued at a rapid pace. EMU development saw considerable variation to meet operational requirements. For non-electrified routes, steam locomotive haulage persisted, with no diesel multiple units being designed. A large number of the EMU designs survived long past nationalisation.

London Underground

See also: London Underground rolling stock#Electric multiple units

In London, it was not the first 'under ground' line (the Metropolitan Railway, or 'Metropolitan') that began unit operation on London's tube, but the deep-level Central London Railway, in 1901. Unit operation on the 'surface' lines was again not by the Metropolitan but its rival, the Metropolitan District Railway ('District'). Operation of unit stock by the District began in 1906, and was electric in nature. Prior to the electrification the Metropolitan and District railways had previously been using locomotive-hauled rolling stock (and specialised steam locomotives). Design and technology on these early District units was inspired by developments in the US, and imported a number of characteristics of contemporary American examples.^{[citation needed]}. The Yerkes tubes (Hampstead, Bakerloo and Picadilly) were unit-operated from the opening, with the City and South London Railway (C&SLR) converting from loco haulage in the mid 1920s when it was combined with the "Hampstead tube" to form the core of the present day Northern line. Thus by the late 1920s, all of the deep-level lines of the London Underground were running electrical multiple units.

By the mid-1930s on the Metropolitan Railway, unit stock was in use on the inner suburban portions of the line, and on the Inner Circle (whose operation was shared with the District). However loco-hauled operation continued on the Metropolitan main line well into the 1960s (despite ongoing electrification).

'First Generation' EMUs

A mark 1 (Mk1) 750 volt, 3rd rail electric multiple unit at Victoria station.

A first Generation AC EMU in Scotland

The Southern Region of British Railways continued the legacy and experience the Southern had created. Southern electric multiple units since the late 1920s had mainly consisted of two electrically powered carriages, each with a cab unit at one end, often pulling two non-powered carriages coupled between them. These trains were fairly reliable, based more on evolution rather than innovation.

Although a number of pre-war designs were gradually withdrawn, over the years, the use of others and post-war designs outlived British Rail, although designs evolved to meet changing demands. Even when these 1st generation designs were finally phased out rapidly in 2005 (some after up to 40 years' or more service), it was not for any reasons related to performance or technical reliability. Reasons for the rapid phase out included stricter crash-worthiness standards^{[citation needed]} and a desire to eliminate manually operated 'slam doors'.^{[citation needed]}

Outside of the Southern Region, 1st generation units were varied. Classes AM1-AM11 (later Classes 302-311) were developed from the mid-1950s to support AC electrification schemes across British Railways. Of these Class AM1 was the prototype unit, initially working at 6.6 kV 50 Hz, and later at 25 kV 50 Hz (both AC) and in bodywork terms did not differ considerably from pre-nationalisation DC units already in use by the LMS (from which some of the class were converted), despite the change to AC supply. Class 306 initially a 1500 V DC design was also based on pre war designs (in this case LNER) and shared characteristics with the later British Rail Class 506 units developed for suburban use on the electrified Woodhead route out of Manchester. The initial choice of 6.6 kV for some units was due to clearance concerns, which later technological advances overcame allowing 25 kV to be used exclusively.

Design of other AC units was subject to considerable variation, although the Class 304 is regarded as having influence on a number of related units. This influence included the Class 504 DC units which utilised an unusual (for British Railways) 1200 V DC side contact system and were thus unique to a particular line in the Manchester area. Although developed at a much later date Class 312 Clacton unit stock shares many traits with 1st generation AC EMU.

Non Southern DC unit designs (as they existed) were based on:

• pre-nationalisations designs (Class 502, Class 503, Class 505)
• localised variants on equivalent AC designs , Class 504,(Class 506) (based Class 306 which had began operation as a 1500 V DC unit anyway)
• Contemporary Southern Region DC designs (Class 501)

Some degree of inter-running of these units with earlier pre-nationalisation designs may have taken place^{[citation needed]}. Non Southern 1st generation DC units began to be phased out from the mid-1970s, as line closures and technical advances made newer designs a more viable prospect.

First Generation DMUs

A 1st Generation (Heritage) Diesel Unit

As part of the 1955 Modernisation Plan of British Railways, provision was made for a number of railcars or DMUs. The earliest of these were the "Derby Lightweights", built by BR's own Derby works, and they quickly became popular with crews (for the increased comfort compared to a steam loco), operating authorities (they were, and still are, cheaper to operate than a loco hauled train, and are much more flexible, requiring no run around) and passengers (they were much cleaner than the old steam hauled stock and if you were lucky enough you could get a view of the line ahead).

Over the next few years a number of different designs came about, though nearly all were able to operate together thanks to BR standardising on the 'Blue Square' coupling code for multiple working. Although there were a few design differences, the units could basically be classified as suburban (Doors for each seating bay, 3+2 seating in second class- an example is Class 118), Medium Density (2 doors per vehicle side, 3+2 bus style seating in second class- an example is Class 114), Cross Country (externally similar to Medium Density, 2+2 bus style seating in second class- an example is Class 120) and finally Intercity (Interiors to same standard as loco hauled stock- an example is Class 124).

Today around 300 vehicles survive in preservation, various vehicles (mainly 101s and 121/122s) survive in departmental use, and Chiltern Railways use a Class 121 on its Aylesbury-Princes Risborough Line.

Anyone with an interest in these trains is highly recommended to visit The Railcar Association's website

The Southern Region of British Rail preferred Diesel Electric Multiple units for use on non electrified routes. Routes they were used on included London to Hastings (now electrified), London to Uckfield, Portsmouth to Southampton (now electrified) and Southampton to Salisbury. Each Unit consisted of a motor coach and a number of trailers in formations of between two and six coaches depending on the type.

Second Generation EMUs

A 1980s third rail EMU - these units were built using the electrical equipment from the units they replaced

A early 1990s overhead powerline driven class 321 E.M.U. with air assisted sliding doors.

Later models of EMU had air-assisted sliding-doors added to them. In the late 1970s, new prototype 4Pep trains were issued with air-assisted sliding-doors. These followed by a temporary batch of Class 508 before the production batch of Class 455 units was delivered (The 508's being transferred to Liverpool). These trains were nicknamed 'push-button' units since they were the first in the region to have passenger-operated push-button sliding doors. London Underground, on the other hand, let the drivers open them from the cab controls instead.

In the 1980s the third rail was extended to Weymouth, around the same time the decision was taken replace to the powerful (3200 hp!) 4REP tractor units and 4TC trailers, which were built from redundant loco-hauled stock. However the budget did not permit the construction of completely new units. The decision was taken to salvage the relatively modern electrical equipment from the elderly bodywork and combine it with an improved version of the Mark 3 HST carriage. The central motor coach was based on an Irish generator van with the required floor strength for the traction equipment. The result was the Class 442 Wessex Electric, with a high speed officially of 109 mph (during testing, though it has been known to achieve higher). These have proved popular with both enthusiasts and passengers.

PEP family

Classes 445, 313, 314, 315, 507 and 508.

Mark 3 based designs

Classes 455, 456, 317, 318, 319, 320, 321, 322, 325 and 442.

Networker family

Classes 365, 465 and 466.

Second Generation DMUs

By the early 1980s it had become apparent that the Modernisation Plan DMUs were showing their age, and needed replacement or refurbishment. As several were insulated with blue asbestos, which BR was obliged to eradicate from its stock, the problem was compounded. Many of the designs produced were of non-standard design meaning that the procurement of parts to keep the units running became increasingly hard. For the second generation, British Rail pursued two basic designs - the Class 14x Pacer series, which were based on Leyland bus parts and were intended to be low cost trains to be used on regional branch lines, and the Class 15x Sprinter series - based largely on the Mark 3 bodyshell design, and intended for more demanding commuter routes, and also medium distance inter-city work.

Pacer units

• See Main Article Pacer (train)

Much derided, the Pacers were designed as "railbuses" - and were effectively a Leyland road bus (the Leyland National was used as the prototype) mounted onto a freight bogie. The lack of bogie articulation and two-axle design meant that the Pacers were only suited to low speed operation and also gave rise to the infamous "nodding donkey" ride quality.

They were meant as a cheap replacement for the worn out Mk1 D.M.U.s, but were largely proven to be inferior to the trains they were replacing-not least the hard seats and loud engine noises. Later models were significantly improved. Later Pacer rail-buses have proven successful and are still in use in South Wales, Manchester, Liverpool and Yorkshire.

Sprinter units

A 1980s Sprinter unit in Centro livery at Kidderminster. These also have sliding doors.

Sprinters were intended for longer distance routes and were designed from the outset as rail vehicles - unlike the Pacers. Most were based on the Mark 3 bodyshell design with the exception of the single-car Class 153 and the later 158/159 units. Using technology proven on the continent in the form of Cummins engines and a Voith hydraulic transmission^{[disambiguation needed ]} gave the extremely high reliability required. There are 6 types of Sprinter (plus a prototype for a seventh type that did not make it into production). The first type to enter service was the BREL British Rail Class 150 with a high density layout suitable for short suburban services, quickly followed by the 150/2 with gangway between units and improved interior. For longer distance journeys there were the Leyland Class 155 and Metro-Cammell Class 156. These were fully carpeted with end doors, luxury unheard of at the time on the routes they operated. Some class 155 units were later split into two single car units with a new and very compact cab being grafted onto the inner ends forming Class 153. The conversion was undertaken by Hunslet. The class 153's are used on rural branchlines and for strengthening other services. For regional services the Class 158 was built. This offered near intercity levels of comfort with full air conditioning and a quiet interior. The last of the Sprinters to be built was the Class 159 for Network South East for use of the West of England Main Line between Exeter and London Waterloo. These were three car versions of the Class 158 with an upgraded interior.

Class 210

The British Rail Class 210 was a prototype DEMU. It was based on the then standard design of EMU (Classes 317 and 455) with a diesel engine mounted at the end of one of the driving cars. It was not a success due to weight and cost and the decision was made to order diesel hydraulic Sprinters.

Network Turbo

The Turbo family was originally a standardised model for diesel suburban services around London. There were two types, the first Class 165 was a two or three coach unit used on the Chiltern and Thames routes. This was followed by the Class 166 which featured air conditioning and seating more suited to longer distance services.

Non- mainline developments

London Underground

See also: London Underground rolling stock#Electric multiple units

Deep-level lines

London Underground's unit operations continued post-war, with new units for the deep-level lines (known as 'tube stock') being developed to meet changing needs.

The 1959 tube stock was initially developed to replace pre-war designs, and entered service on the Picadilly Line and later on the Central (1962). An experimental unit (which became known as 1960 stock) did not enter into production.

As new lines were developed by London Transport, the rolling stock developed too. The 1967 tube stock for the Victoria line included (for the time) cutting-edge technology in the form of automatic operation. For the Fleet (later 'Jubilee') line the 1972 tube stock (in two variants) was developed. The 72 stock was, however, eventually cascaded to the Bakerloo, and Northern Lines, with the Jubilee line getting a new design (83 tube stock) to itself. Extension of the Picadilly to Heathrow Airport, saw the introduction of 73 tube stock, which incorporated improved luggage space within the tight constraints of the tube loading gauge.

In the 1980s, prototype designs were trialled in order to generate feedback about future developments. These led directly to the 1992 tube stock which was to replace the ageing 59/62 stock. In the 1990s 95 tube stock also supplanted the 59 and 72 stocks which had (by this date) ended up on the Northern line. The extension of the Jubilee line also saw the development of the externally similar 96 tube stock, but with vastly different internal technology. Although inter-operation of 83 and 95 tube stocks had been considered, the operation of a consistent fleet proved to have better economics and hence the 83 tube stock was withdrawn earlier than had been expected. The PPP of the early 2000s saw commitments to replacement of much of the existing tube stock with modern designs, these upgrades are likely to continue despite the seeming failure of some PPP arrangements.

Surface lines

Post-war development on the 'surface' lines was initially just pre-war designs, suitably updated (London Underground R Stock), for the District line, replacing older units. The District line also continued to operate with the pre-war (CO/CP) and post-war (R) designs, until the late 1970s when the more square-shaped D (District) stock was introduced between 1978 and 1983.

Extension of electrification of the Metropolitan line as far as Amersham (where the original Metropolitan route was truncated) saw the introduction of A60 or A62 surface stock. This extension also effectively saw the end of locomotive-hauled operation, with the former Aylesbury service being operated by Class 115 DMU units operating from Marylebone. (These units would themselves be replaced by Class 165 Networker units when the Chiltern Line route was modernised in the mid 1990s). By comparison to the almost suburban design of the 'A', the 'C' (Circle) stock of 1967 incorporated a number of features for its role in Central London: a greater number of doors, and vastly greater standing/seated passenger ratio were two features to cope with the higher passenger densities and more frequent station stops found on the Circle line.

In the first decade of the new millennium (2000s), it was announced that the A, C and D stock would be phased-out in favour of a common 'S' stock for all the surface lines. The first of these 'S' stocks (designed and built by Bombadier) began entry into service in 2010 on the Metropolitan.

Glasgow

Main article: Glasgow Subway

Tyneside

Main article: Tyne and Wear Metro rolling stock

Post privatisation

Bombardier Electrostar and Turbostar families

During the privatisation process, there was a gap of more than two years during which no new rolling stock orders were placed. The first new order placed was in May 1996 for a fleet of Class 168 Clubman DMUs for Chiltern Railways. These were a development of the Network Turbo design already in use by Chiltern and other operators, and themselves became the basis for the Class 170/171 Turbostar fleet which operate local and regional services throughout the country.

The electric equivalent of the Turbostar is the Electrostar. The first units built were the Class 357 for c2c. These were followed by the Class 375 and Class 376 for Connex South Eastern (now Southeastern) and the Class 377 for Connex South Central (now Southern). A batch of Class 378 units is currently under construction for London Overground.

These units are built by ABB, which became Adtranz and is now part of Bombardier. All units are built in Derby, and it is now the last major rolling stock manufacturer in the UK.

Alstom Coradia family

A modern high speed DMU (Class 180)

Coradia 1000

The Coradia is a family of multiple units produced by Alstom. The British diesel versions are the 100 mph Class 175 for First North Western's North Wales Services (later moving to Arriva Trains Wales) and the 125 mph Class 180 Adelante for First Great Western's semi-fast services. Both types have had a protracted entry into service in common with other Alstom trains.

Coradia Juniper

A modern third rail EMU operates the Gatwick Express

The Juniper family includes the Gatwick Express Class 460 and South West Trains Class 458 third-rail EMUs, plus the Class 334 AC EMUs built for use in Glasgow.

Siemens Desiro family

While the Siemens Desiro has quickly established itself as an Electric train, the diesel version for Transpennine Express (Class 185 Pennine) is in service. The first train was unveiled in Germany in November 2005 and arrived in the UK a month later. The first train went into public service in March 2006 with deliveries of the 51 strong fleet continuing into 2006, and being complete in December 2006, now all 51 units are in operation

Siemens Class 332 and 333

Bombardier Voyager, Meridian and Pioneer

The Voyager family is a series of high speed DEMUs. Virgin Trains were looking to replace the Cross Country fleet as part of their franchise obligations. The new train had to replace a mixture of life expired loco-hauled trains and mid-life HSTs and have tilt for use on the West Coast Mainline. The result was the non-tilt Class 220 Voyager and tilting Class 221 Super Voyager.

Midland Mainline and Hull Trains since ordered a non-tilt version. The Class 222 Meridian and Pioneer units replaced slower Turbostars on semi-fast mainline services. The Class 222 does average much higher reliability than the Virgin units, this is possibly due to the later build taking account of problems encountered in the earlier units with cross feeding power and the omission of tilt capability.

Alstom/Fiat Pendolino

a high speed tilting EMU

Introduced from 2002 onwards by Virgin Trains, the Class 390 units are tilting EMUs built for the West Coast Main Line (WCML) modernisation of the early 2000s. The units are based on Alstom-Fiat Ferroviaria’s Pendolino design, modified for the British loading gauge. The original order of 53 9-car sets were assembled at the former Metro-Cammell works in Washwood Heath, Birmingham. The units are employed almost exclusively on long distance express services between London Euston and Birmingham, Liverpool, Manchester and Glasgow.

The units replaced most of the former WCML long distance fleet made up primarily of Mark 2 and Mark 3 coaches hauled by Class 86, 87 and 90 locomotives. The Class 390 tilting technology has its design roots in British Rail’s ill-fated Advanced Passenger Train, and they were designed with a maximum speed of 140 mph (225 km/h). The units are currently restricted to 125 mph (201 km/h) in operational service, as the proposed installation of moving block signalling systems on the WCML was abandoned.

A further four 11-car sets were procured in 2010, and 31 of the original batch will be lengthened to 11 cars. They are expected to enter service in 2012 under the new InterCity West Coast franchise.

Sources

Platform 5 books

• Locomotives and coaching stock of 1986.
• Locomotives and coaching stock of 1998.

• A.B.C. book- Diesel multiple units- 1979.