Push–pull train
Push–pull is a mode of operation for locomotive-hauled trains allowing them to be driven from either end.
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.
Train formation
Locomotive at one end
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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 so that there is no opportunity for a carriage to run away from a train down the gradient and also so that, if the locomotive ever did run 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 crash (in Scotland) occurred when a push–pull train struck a cow on the track. Push–pull operation has also been blamed for worsening a number of derailments by trains of the Metrolink commuter rail service in greater Los Angeles.
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.
Locomotive in the middle
In certain situations, the locomotive is placed in the middle of the train rather than at one end but driven from cabs at the train ends. The Great Western Railway sometimes did this when multiple autocoaches were linked up in an autotrain, as the mechanical linkages used to control the steam locomotive were not capable of reliable operation through more than two interconnections.
The Swiss Federal Railways sometimes run trains with the locomotive in the middle during peak times, when additional carriages, generally including one with a cab, are added to a train where the locomotive was previously at the end (more commonly these carriages will however be added onto the cab end). When the locomotive is placed mid-train, both directions are considered 'push'.
Two locomotives
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 is allowed to provide head end power (HEP: electricity supply for heating, air conditioning and lighting) to the train. This two-locomotive formation is used by the InterCity 125; its Australian equivalent, the XPT; Amtrak's Acela; SNCF's TGV; 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 "pull-pull" steam-heated consist, with a control cable between cars, 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.[1]
Distributed power
In this configuration locomotives hauling a train are located other than at the front or back. It may include remote control locomotives in the middle of a train. Where operational considerations or economics require it, trains can be made longer if intermediate locomotives are inserted in the train and remotely controlled from the leading locomotive.
History
Britain
Steam
- 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.[2] 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.[2]
Electric and diesel
In 1967, the Southern Region, already familiar with operating electric multiple units, applied the technique to its services from London Waterloo station to Bournemouth, which were operated by electro-diesel locomotives.[2]
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) 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.[2][3] When the push–pull sets were replaced by multiple units, the DBSOs were transferred to the Liverpool St-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 Wessex Trains with Class 31s, and by Arriva Trains Northern with Class 37s. The same system was also adopted by Network Rail for its engineering 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, Mark 3 driving van trailers (DVT) were built for the extended electrification of the West Coast Main Line and the Mark 4 DVT was built as part of the Electra project for the East Coast Main Line. The Mark 4 DVT can be retro-fitted to tilt.
More recently, some of these DVTs have been modified to operate with Class 67 locomotives for the Wrexham, Shropshire, Marylebone Railway Company.
Ireland
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.[4] 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–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.
Israel
In 1996, Israel Railways began running GEC Alstom Push-pull Coaches.
Australia
The New South Wales XPT long distance passenger trains used by NSW Trains operate in a push-pull operation.
New Zealand
Until recently, 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 ex-Queensland 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). The diesel units continue to operate between a couple of remote stations on the southern line where the tracks haven't been electrified.
North America
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); 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 AEM7 and ACS-64 electrics. In addition, many regional services, such as the Michigan Services and Cascades, are operated with ex-F40s converted to Non-Powered Control cars, also commonly called cabbage cars and a diesel locomotive. 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.
See also
Notes
- ↑ Pawson, John R. (1978). Delaware Valley Rails. Willow Grove, PA: John R. Pawson. pp. 62–63. ISBN 0-9602080-0-3.
- 1 2 3 4 Simmons, Jack; Biddle, Gordon (editors) 1997. Oxford Companion to British Railway History p 407. Oxford University Press. ISBN 0-19-211697-5
- ↑ Glover, John (1999). Railway Operations p 58. Ian Allen, Shepperton, England. ISBN 0-7110-2689-0
- ↑ Grainger, R. P. (1990). "Push–pull trains for Iarnród Éireann – Irish Rail". Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit (Prof Eng Publishing) 204 (16): 21–30. ISSN 0954-4097.
Further reading
- King, Mike (2006). An Illustrated History of Southern Push–Pull Stock. Ian Allan Publishing (OPC). p. 160 pages. ISBN 0-86093-596-5.
- Lewis, John (1991). Great Western Railway Auto Trailers: Pre-grouping Vehicles (Part 1). Wild Swan. p. 208 pages. ISBN 0-906867-99-1.
- Lewis, John (1995). Great Western Railway Auto Trailers: Post-Grouping and Absorbed Vehicles (Part 2). Wild Swan Publications Ltd. p. 184 pages. ISBN 1-874103-25-9.
- Lewis, John (2004). Great Western Steam Railmotors: and their services. Wild Swan Publications Ltd. ISBN 1-874103-96-8.
External links
- The Development of Push–Pull Operation (at Railway Technical Web Pages) – history, mainly UK
- Amtrak cab-baggage (cabbage) cars