An electro-diesel locomotive (also referred to as dual-mode locomotive) is powered either from an electricity supply (like an electric locomotive) or by using the onboard diesel engine (like a diesel-electric locomotive). For the most part, these locomotives are built to serve regional, niche markets with a very specific purpose.
Electro-diesel locomotives and electro-diesel multiple units are used to provide continuous journeys along routes that are only partly electrified without a change of locomotive, extensive running of diesel under the wires or where diesel engines are banned. They may be designed or adapted mainly for electric use, mainly for diesel use or to work well as either electric or diesel.
This is effectively an electric locomotive with a relatively small auxiliary diesel prime mover intended only for low-speed or short-distance operation (e.g. British Rail Class 73). Some of these, such as the British Rail Class 74, were converted from electric locomotives. The Southern Region of British Railways used these locomotives to cross non-electrified gaps and to haul boat trains that used tramways at the ports of Southampton and Weymouth. For economy, the diesel engine and its generator are considerably smaller than the electric capacity. The Southern types were of 1,600 hp or 'Type 3' rating as electrics, but only 600 hp as diesels. Later classes had as much as 2,500 hp on electric power, but still the same diesel engines. Despite this large difference, their comparable tractive efforts were much closer (around three-quarters as diesels) and so they could start and work equally heavy trains as diesels, but not to the same speeds.
This is effectively a diesel locomotive with auxiliary electric motors (or connections to the existing traction motors), usually operating from 750 V DC third rail where non-electric traction is banned (e.g. EMD FL9). The primary function for these models is to provide a one-seat ride between diesel territory and the New York City terminals of Grand Central Terminal and Penn Station, where diesel exhaust is prohibited due to the confined tunnel space. Once out of the tunnels, the third-rail shoes are retracted and operation is as a normal diesel locomotive.
With modern electronics, it is much easier to construct (or adapt) an electro-diesel locomotive or multiple-unit which is equally at home running at high speeds both under the wires and under diesel power (e.g. SNCF Class B 82500). These will normally operate under pure electric traction where possible, and use the diesel engines to extend the journeys along non-electrified sections which would not be cost effective to electrify. They may also be used on long cross-country routes to take advantage of shorter sections of electrified main lines.
- B 81500 – multiple unit trains using 1.5 kV DC catenary, in service since 2005
- B 82500 – multiple unit trains using both 1.5 kV DC and 25 kV AC catenary, currently still being built
- Gmeinder class 478.6 diesel and 750 V DC third-rail (bottom contact).
- Voith Futura, a concept locomotive rebuilt from DB 240 002.
- Bombardier TRAXX "Last Mile Diesel", mainly electric. Orders signed 2010, to be delivered probably 2012.
- PESA 111Ed Gama Marathon – prototype, mainly electric, with auxiliary diesel engine enabling last-mile operation on non-electrified tracks. Gama Marathon was first presented in 2012 at InnoTrans Berlin. Until mid-2013 the locomotive will undergo a series of tests with rail operators Lotos Kolej (in goods traffic) and PKP Intercity (in passenger traffic), after successful conclusion of which first orders are expected.
In Russia, a number of electro-diesels were built which had both pantographs and diesel motors; these locomotives were actually multiple units, with distinct electric, diesel, and motor sections. These included:
- ED16 (ЭД16), ED18 (ЭД18), and TEU1 (ТЭУ1) narrow gauge models
- OPE1 (ОПЭ1), OPE2 (ОПЭ2), NP1 (НП1), PE2(M) (РЭ2(М)), and EL20 standard-gauge locomotives used mostly in quarries
- FEVE 1.900 Series, 1500 V DC overhead wires. This series is a rebuild of FEVE 1.000 Series locomotive.
- CAF Bitrac 3600, 3000 V DC overhead wires. October 2007 order for 9 freight Co-Co locomotives. Available in Bo-Bo and Co-Co wheel configuration, 1,435 or 1,668 mm (56.5 or 65.7 in) gauge, and as freight or passenger versions of 120 and 180 km/h (75 and 110 mph) maximum speeds respectively.
- Rhaetian Railway Gem 4/4, 1000 V DC overhead wires (Bernina Railway)
- Swiss Federal Railways Tem 346 shunters (see image).
- Swiss Federal Railways Eem 923 shunters using both 15 kV 16.7 Hz and 25 kV 50 Hz overhead wires and a 360 kW auxiliary diesel engine are on order from Stadler Rail's Winterthur plant.
An experimental electro-diesel locomotive, DEL120, was built by London Underground in 1940 but was not a success. Only two other types have been built. In both cases, their electricity source was a 750 V DC third rail.
- British Rail Class 73, dating from 1962 – the more successful design, with some still in regular use. They have lower power output in the diesel mode.
- British Rail Class 74 – rebuilt from British Rail Class 71 electric locomotives in 1967 and withdrawn by 1977.
The Hitachi Super Express trains proposed for the electrification of the Great Western Main Line have a variant able to operate in bi-mode as an electro-diesel trainset. This would enable intercity services from Paddington Station to continue beyond Swansea railway station, currently the western limit of the proposed electrification scheme.
Bombardier has plans, apparently known as Operation Thor or Project Thor, to convert 500 existing diesel multiple units (DMUs) into electro-diesel multiple units (EDMUs). Whilst exact details are unclear, one source specifies that these would involve their Voyager family DEMUs, and entail the construction of additional intermediate cars with a pantograph and a transformer which would feed power into the traction motors of the existing diesel-electric cars when running off overhead lines.
- GE three-power boxcab a switcher locomotive model built in 1930, also capable of operating as a battery locomotive retired from service.
- Baldwin RP-210 – primarily diesel-hydraulic, third-rail electric mode for short-term use only; these have been retired from passenger service.
- Roger Williams streamlined, six car, lightweight, DMU passenger train, built by the Budd Company in 1956 for the New York, New Haven and Hartford Railroad – primarily diesel-hydraulic, third-rail electric mode for short-term use only; this has been retired from passenger service.
- Fairbanks Morse P-12-42 – primarily diesel-electric, third-rail electric mode for short-term use only; these have been retired from passenger service.
- EMD FL9 – primarily diesel-electric, third-rail electric mode for short-term use only; these have been retired from passenger service.
- P32AC-DM – dual-mode version of the GE Genesis, electric mode is only used for a few miles of travel.
- EMD DM30AC – specific to the Long Island Rail Road.
- Bombardier ALP-45DP - 35 locomotives are on order by New Jersey Transit, to bridge gaps between non-electrified and electrified sections of track into New York Penn Station.
- Bombardier ALP-45DP - 20 locomotives are on order for the Repentigny-Mascouche Line (AMT). It is a joint order with the New Jersey Transit order above. They will provide a through journey on this mostly un-electrified new line, which joins an existing electrified commuter line to access Montreal's Central Station through the poorly ventilated, 25 kV AC electric only Mount Royal Tunnel.
The South African Class 38-000 is a 3kV DC electro-diesel locomotive designed by Consortium under the leadership of Siemens and built by Union Carriage and Wagon (UCW) in Nigel, Gauteng, South Africa. Between November 1992 and 1993 fifty of these locomotives were placed in service by Spoornet, formerly the South African Railways (SAR) and later renamed Transnet Freight Rail (TFR). The diesel engine enables the locomotive to shunt on unelectrified sidings.
A specialized type of electro-diesel locomotive is the hybrid locomotive. Here, the electricity comes from a battery (charged by the diesel engine) rather than an external supply. An example is the Green Goat switcher.
- Allen, G. Freeman (1962). British Railways Today and Tomorrow (3rd ed.). Ian Allan. pp. 88–89.
- "Bombardier launches Traxx electro-diesel". Railway Gazette International. 10 May 2011. Archived from the original on 10 May 2011. Retrieved 11 May 2011.
- "GAMA On Test". Railvolution. 5 December 2012. Retrieved 20 January 2013.
- "GAMA Marathon Passenger Debut". Railvolution. 02 March 2013. Retrieved 12 March 2013.
- "Maraton – a step closer to the perfect locomotive". PESA Bydgoszcz SA. Retrieved 20 January 2013.
- "Electro-diesel loco offers flexible traction". Railway Gazette International. 2008-01-03. Retrieved 2010-12-02.
- "Electro-diesel shunter order". Railway Gazette International. 2010-07-08. Retrieved 2010-12-02.
- "Colin Walton: Railway man trying to keep Bombardier on track". The Independent. 2010-06-17. Retrieved 2011-03-04.
- "Transport and the economy: Memorandum from Bombardier Transportation UK Limited (TE 89)". Parliament of the United Kingdom. 10 November 2010. Retrieved 2011-03-04. "Project Thor, being developed with a number of UK private sector partners, would see 500 existing diesel multiple unit vehicles converted to bi-mode diesel / electric capability, allowing them to operate as electric trains where there is already electrification infrastructure in place, while continuing their journey in diesel mode where the wires end."
- "Bombardier’s electrification plan presented to ministers". Rail-News.com. 2010-10-06. Retrieved 2011-03-04. "Train builder Bombardier has presented ministers with an offer to construct 123 pantograph vehicles and convert 21 existing vehicles in the 22x fleet into EDMUs."
- "ALP-45DP electro-diesel locomotive debut". Railway Gazette International. 2010-09-23. Retrieved 2010-12-02.
- "Bombardier to supply electro-diesel locos". Railway Gazette International. 2008-08-19. Retrieved 2010-12-02.
- "NJ Transit approves FY2011 spending". Railway Gazette International. 2010-07-19. Retrieved 2010-12-02.
- Pictures of the Russian OPE-1 locomotives
- Pictures of the Russian electro-diesels
- (Russian) Novocherkasskiy electric locomotive factory – Model OPE1