A push–pull train has a locomotive at one end of the train, connected via some form of remote control, such as multiple-unit train control, to a vehicle equipped with a control cab at the other end of the train. This second vehicle may be another locomotive, or an unpowered control car.
In the UK and some other parts of Europe, the control car is referred to as a driving trailer (or Driving Van Trailer/DVT where there is no passenger accommodation); in the USA and Canada, they are called cab cars.
Locomotive at one end
|Multiple unit trains|
Historically, push–pull trains with steam power provided the driver with basic controls at the cab end along with a bell or other signalling code system to communicate with the fireman located in the engine itself in order to pass commands to adjust controls not available in the cab.
At low speeds, some push–pull trains are run entirely from the engine with the guard operating bell codes and brakes from the leading cab when the locomotive is pushing the train.
Many mountain railways also operate on similar principles in order to keep the locomotive lower down than the carriage to prevent any opportunity for a carriage to run away from a train down the gradient and also so that even if the locomotive ever ran away, it would not take the carriage with it.
Modern train control systems use sophisticated electronics to allow full remote control of locomotives. Nevertheless, push–pull operation still requires considerable design care to ensure that control system failure does not endanger passengers and also to ensure that in the event of a derailment, the pushing locomotive does not push a derailed train into an obstacle, worsening the accident. The 1984 Polmont rail accident, in Scotland, occurred when a push–pull train struck a cow on the track.
When operating push–pull, the train can be driven from either the locomotive or the alternative cab. If the train is heading in the direction in which the locomotive end of the train is facing, this is considered 'pulling'. If the train is heading in the opposite direction, this is considered 'pushing' and the motorman or engine driver is located in the alternative cab. This configuration means that the locomotive never needs to be uncoupled from the train and ensures fast turnaround times at a railway station terminus.
Alternatively, a push–pull train, especially a long one, may have a locomotive on both ends so that there is always one locomotive pushing and one locomotive pulling. In this case, caution must be used to make sure that the two locomotives do not put too much stress on the cars from uneven locomotives. It is usual to arrange matters so that the trailing locomotive supplies less power and that the locomotive at the front does more pulling than the locomotive at the rear does pushing. Having an independent locomotive, as opposed to a power car at each end, is also known in the railway world as a top and tail. When this configuration is used in the US, only one locomotive (usually the front locomotive) is allowed to provide head end power (HEP: electricity supply for heating, air conditioning and lighting) to the train. The two-locomotive formation is used by the InterCity 125; its Australian equivalent, the XPT; Virgin Trains USA; Amtrak's Acela; SNCF's TGV; Taiwan Railways Administration 's E1000 series; and New Jersey Transit's longest Northeast Corridor Line multilevel trains.
This form of operation has not necessarily been a function of train length; sometimes it was the most convenient way to set up push–pull operation in pre-HEP days without converting coaches to cab control operation. A prime example of this was the Reading Company which converted its small fleet of streamstyled heavyweight medium-distance coaches for its non-electric commuter operation, with a pair of EMD FP7 diesels bracketing a single five-car train, to supplant the Reading's fleet of RDCs. This train normally operated a weekday peak-hour round trip between Reading Terminal, Philadelphia and Reading, Pennsylvania, from the late 1960s until 1981, with operation in the last five years by Conrail under contract to SEPTA.
Locomotive in the middle
A rare but possible configuration has a locomotive in the middle of the train with control cars at both ends, as was, for instance, used for a time on the Brussels-Amsterdam Benelux train when there were control cars but no three-voltage (3 kV DC, 1.5 kV DC, 25 kV 50 Hz) locomotives supporting the ERTMS train control system in use on the Belgian HSL 4 and the Dutch HSL-Zuid. The "Class 28" TRAXX locomotives were later upgraded, and the service went back to "normal" push-pull operation.
In this configuration, locomotives hauling a train are located other than at the front or the back. It may include remote control locomotives in the middle of a train. If operational considerations or economics require, trains can be made longer if intermediate locomotives are inserted in the train and are remotely controlled from the leading locomotive.
In India, push pull passenger trains (EMU, MEMU: Mainline Electric Multiple Units) have been in use since several decades. In such a type of a train, the driving unit (power cab) is usually every third coach of the train, while driving cabs are available at both the ends. An example of such a type of a train is the Tambaram - Chennai Beach EMU service, equipped with 9 coaches. An example of an Electric Multiple Unit (EMU) in South India leveraging Push Pull Technology In this train service, the 3rd, 6th and 8th coaches have the power unit, while the driving cabs are available at each end. Recently, the Central Railways Division (of Indian Railways) have introduced a WAP - 7 powered electric locomotive at each end of the Rajadhani Express, both these WAP - 7 High Horse Power 3 Phase Electric Locomotives, from Kalyan Electric Loco Shed, power the Rajadhani Express train, and prevent an engine reversal, thereby leading to reduced travel time. The guard sits inside the rear locomotive along with two additional drivers. This leads to an additional usage of electric current, however, as these locomotives use Head-On Generation technique, it leads to an overall economy of usage and a much more eco friendly operation. Example: Mumbai - New Delhi Rajadhani Express trains use the WAP - 7 High Horse Power Locomotive of Kalyan Locomotive Shed (Central Railways) to leverage Push Pull Technology in Western India In this configuration, the Front Pantograph of the locomotive needs to be raised instead of the normal conventional usage of rear pantograph.
- Great Western Railway
The first company to use the system was the Great Western Railway which, in 1904, equipped carriages and 0-6-0 locomotives as an autotrain to run on the Brentford Branch Line (between Southall and Brentford) as an experimental substitute for steam railcars. Control was by rodding and the mechanism allowed the driving compartment to be either one or two carriages-distant from the engine. With the engine in the middle of a formation, up to four carriages could be used. To reduce the surprise of a locomotive at the "wrong" end of its train, some were initially fitted with panelling painted in carriage livery. The experiment was successful and the company's remaining railcars were gradually converted for autotrain use and purpose-built units constructed.
- Other railways
Other companies followed the lead in 1905: the North Eastern and LBSCR using a compressed-air method of control and the Midland, using a cable-and-pulley mechanism. The Great Central deployed the trains in 1906, using cable controls similar to that of the Midland. By the 1920s most companies had them and they remained in use until replaced by diesel multiple units (DMUs) in the 1950s.
Electric and diesel
In 1967, the Southern Region, already familiar with operating electric multiple units, applied the technique to its services from London Waterloo to Bournemouth, which were operated by electro-diesel locomotives.
In the early 1970s, the Scottish Region used a system with a Class 27 locomotive at each end of a rake of coaches that had been retrofitted with the necessary 'Blue Star' multiple working cables to control the remote unit; but some problems of delay in actuation were experienced. They were replaced in 1979 by a system in which a Driving Brake Standard Open (DBSO), converted from a Mark 2, could control the Class 47/7 locomotive via computerised time-division multiplex (TDM) signalling through the train lighting circuits. This had the added benefit that intermediate carriages needed no special equipment, and was found more satisfactory. Such trains became widely used on the intensive passenger service between Edinburgh Waverley and Glasgow Queen Street. When the push–pull sets were replaced by multiple units, the DBSOs were transferred to the Liverpool Street to Norwich service, where they were modified to work with Class 86 electric locomotives.
The original system of using the Blue Star multiple working was later revived after privatisation as a way of allowing locomotive-hauled stock to replace multiple units on certain routes, thus increasing capacity without the complications of having to run around or drag a dead locomotive at the rear. It was used by First North Western and Wessex Trains with Class 31s, and by Abellio Greater Anglia, Arriva Trains Northern, Northern Rail and Northern with Class 37s all with Mark 2 carriages. The same system was also adopted by Network Rail for its track observation trains, although on many trains one locomotive has recently been replaced by a DBSO modified to work with Blue Star.
Driving van trailers (DVTs)
In 1988, 52 Mark 3 Driving Van Trailers were built by British Rail Engineering Limited to allow it to replace life expired electric locomotives on the West Coast Main Line. These operated with Mark 2 and Mark 3 sets.
As part of the electrification of the East Coast Main Line, 31 Mark 4 Driving Van Trailers were built in by Metro-Cammell to operate with Mark 4s as part InterCity 225 sets. Some of these will pass to Grand Central and Transport for Wales Rail in 2020.
Córas Iompair Éireann's first push–pull trains were conversions of their 2600 Class DMUs (Park Royal body, AEC motors) running with the long withdrawn 201 Class Metropolitan-Vickers Bo-Bo diesels re-engined with EMD 567 prime movers; the cars were subsequently renumbered in the 6100 series (Driving van trailers), 6200 series (trailer with "blind" cab end) and 6300 series (double-gangway intermediate car). In push–pull formation, they operated Dublin Suburban Rail services from 1971 until the inauguration of the DART EMU service in July 1984. The remaining push–pull trains operated on Dublin-Maynooth commuter services until they were supplanted by Cravens, and later by the modern 2600 Class DMUs.
Iarnród Éireann employs push–pull trains of two different kinds. The first of these were built in 1996. These are De Dietrich Ferroviaire -built Enterprise push–pull sets, jointly owned with Northern Ireland Railways for operation on the Dublin to Belfast route. These are powered by 201 Class locomotives.
The other type of push–pull train used in Ireland is the Mark 4 type (not to be confused with the British Rail Mark 4 type). These sets, delivered in 2005–2006, are used exclusively on the Dublin to Cork route, again operated by 201 Class locomotives.
Between 1980 and 2009, Iarnród Éireann operated push-pull sets based on the British Rail Mark 3 design, with a non-gangwayed driving cab fitted. These were operated with 201 Class locomotives, although in the past 121 Class locomotives were also used. It remains unknown whether these sets were ever hauled as normal coaching stock by non–push–pull fitted locomotives. The sets originally operated in the Dublin outer-suburban area and on the Limerick to Limerick Junction shuttle, but were gradually moved to mainline InterCity routes out of Dublin Heuston after the introduction of railcar sets elsewhere. The entire Mark 3 fleet was withdrawn in September 2009 and scrapped in 2014.
The first major application of push–pull operation using the modern single diesel configuration was on the Chicago and Northwestern Railroad. In 1959, the C&NW received its first Control Cab equipped Bilevel rail cars for commuter use. The extreme efficiency and success of these trains is why almost all of the commuter rail services in the United States and Canada utilize 100% push–pull operation on their locomotive-hauled trains. Examples include: Chicago (Metra); New York City (Metro-North, the Long Island Rail Road and New Jersey Transit); Philadelphia (SEPTA); the Washington, D.C. and Baltimore area (MARC and VRE); Boston (MBTA); Dallas–Fort Worth Metroplex (Trinity Railway Express); the Greater Miami area (Tri-Rail); the San Francisco Bay Area (Caltrain and ACE); Southern California (Metrolink and Coaster); Toronto (GO Transit); and Montreal (AMT). Most of these systems (except for SEPTA and Metro-North) continue to utilize some type of bi-level passenger cars for push–pull service, either partially or exclusively.
Amtrak has a number of converted Metroliner EMUs in service as cab cars on the Keystone Corridor, where they operate in conjunction with ACS-64 electric locomotives. In addition, many regional services, such as the Michigan Services and Cascades, are operated with Non-Powered Control Units - EMD F40PH locomotives converted to use as a cab control and baggage car, earning itself the nickname 'cabbage cars'. Similarly, the Capitol Corridor, San Joaquin, and Pacific Surfliner services in California are operated in push–pull configuration using purpose-built cab cars and diesel locomotives.
The Muskingum Electric Railroad was a private, coal-hauling railway in central Ohio that ran for more than 20 years with two driverless General Electric E50C electric locomotives that ran backwards from the coal-fired powerplant they served to the mine where their trains were loaded by affixing bogie trucks, a headlight, and a horn to the last freight car on each train.
In 1996, Israel Railways began running GEC Alstom push-pull coaches. Since then, it has also acquired push-pull coaches from Bombardier and Siemens. As of 2016, the bulk of Israel Railways' passenger operations use push-pull coaches.
Until 2015, the Auckland suburban network run by Transdev used rebuilt British Rail Mark 2 carriages in either four, five or six car configurations. Three to five SA class carriages and an SD class driving carriage, fitted with a cab, were coupled to a DC class (4- and 5-car) or DFT/DFB class (6-car) locomotive, leased from KiwiRail.
Following electrification of most of the Auckland suburban railway network, these diesel units have been replaced by a modern electrical fleet that consist of one or two sets of 3 car units (each of which have one carriage that can service passengers with disabilities).
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