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Push–pull is a configuration for locomotive-hauled , allowing them to be driven from either end of the train, whether having a locomotive at each end or not.
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. This formation meant that the locomotive would not have to run-around at the end of a journey before returning.
The trains were also historically knows as "motor trains" or "railmotors", but the term "railmotor" is now used to refer to trains where the locomotive was integrated into a coach. 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 US and Canada, they are called cab cars and in Australia, they are called driving trailers.
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 Train station terminal station.
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.
Historically, the Great Western Railway ran Autotrains with two driving coaches sandwiching a steam locomotive.
In the early 1970s, the Scottish Region used a system with a 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 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 and . When the push–pull sets were replaced by multiple units, the DBSOs were transferred to operate on the Great Eastern Main Line between and , where they were modified to work with 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 , and by Abellio Greater Anglia, Arriva Trains Northern, Northern Rail and Arriva Rail North with 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.
As part of the electrification of the East Coast Main Line, 31 Mark 4 Driving Van Trailers were built in the late 1980s by Metro-Cammell to operate with Mark 4s coaches at the south end of the InterCity 225 sets. Some of these passed to Transport for Wales Rail in 2021 to work on their Holyhead to Cardiff Premier Service.
In the 2000s, some Mark 3s have been modified to operate with locomotives with Arriva Trains Wales, Chiltern Railways and Wrexham & Shropshire.
In 2019, new Mark 5 carriages, one of which has a cab, entered service with locomotives for TransPennine Express, in a push–pull configuration.
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. The sets originally operated in the Dublin outer-suburban area and on the to shuttle, but were gradually moved to mainline InterCity routes out of after the introduction of railcar sets elsewhere. The entire Mark 3 fleet was withdrawn in September 2009 and scrapped in 2014.
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, Downeaster, 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.
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.
All SA and SD class cars were rebuilt by Hillside Workshops. Auckland also operated former Queensland Rail SX carriages in push–pull mode with two DBR class locomotives.
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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