More Information

An article on train formations and coupling systems by “The Contact Patch” in the chapter, “Train Formation”. 

Electric Locomotives

Diesel Locomotives

Rolling Stock

The Rubber Tyred Train - the development of the French system on Marc Dufour’s website.

The AVE pages - the Spanish version of the TGV by Julio Castillo Jr in English or Spanish.

The ICE/ICT pages - descriptions of German high speed trains and their development by Tobias Köhler. 

The TGVWeb - the French High Speed System described in French and English by Clem Tillier and Yann Nottara. 

“A train’s a train” you might think but there are different types of train and some trains are quite different from others, which means they require different approaches to operation, control, handling and maintenance. This article describes types of trains seen on railways around the world based on modern practice and showing some examples where suitable. 


A train is defined here as one or more railway vehicles capable of being moved. It may consist of a locomotive (sometimes more than one) to provide power, with various unpowered vehicles attached to it. It may consist of a multiple unit, i.e. several vehicles formed into a fixed formation or set, which carry their own power and do not require a locomotive. A train may be only a locomotive running light (deadheading) to a point elsewhere on the railway. A train may be passenger carrying, freight or, rarely nowadays, mixed.

A train may be manually driven (by a driver, operator or engineer) and may have other crew members (assistant driver, fireman, conductor and/or catering staff) to assist the driver and/or the passengers. Trains may also be operated under a degree of automation, where the traction and braking are controlled by computers and wayside to train transmission systems. 

Fixed Guidance

First, it is important to understand the nature of the railway. A railway is a fixed guidance system. The guideway - the track - decides where the train will run by guiding the wheels, so there is no separate steering mechanism. The route the train follows is guided by the track. The train’s wheels are designed to fit the rails and compensate for curves and to allow them to be negotiated at a reasonable speed. There are other types of guidance systems such as specialist rail designs for street railways and for rubber tyred metro trains but the track form shown in Figure 1 is the normal arrangement.

Figure 1: The rail way. The track is the fixed guidance system used by conventional railways around the world. There are two tracks here, one for each direction. The standard design of track has sleepers (or ties) laid at usually 600mm intervals upon which the rails are fixed to maintain the gauge between them. Ballast is packed around the sleepers to maintain stability and to facilitate drainage. This is the Old Dalby test track in Leicestershire, UK. To allow testing of different types of trains, the line is equipped for overhead electrical supply and the left hand track is equipped with traction current rails for London Underground train testing. Photo: Author.

The Wheel-Rail Interface

Railway wheels and rails are made of steel. The contact between them is sit on the rails without guidance except for the shape of the tyre in relation to the rail head. Contrary to popular belief, the flanges should not touch the rails. Flanges are only a last resort to prevent the wheels becoming derailed - they're a safety feature. The wheel tyre is coned and the rail head slightly curved as shown in Figures 2 and 3.  The rails are also set at an inward angle.

Ideally, the wheel profile should be determined by agreement between the railway infrastructure owner and the rolling stock owner. Of course, it varies from place to place but it is rarely a simple angle. It's usually a carefully calculated compound form.  With respect to the rail angle, in the UK for example, it is set at 1 in 20 (1/20 or 0.05). In the US and France it's usually at 1/40. Light rail systems operating over roadways will have special profiles.

An excellent series of articles on the wheel rail interface is available in the online magazine The Interface Journal and a useful slide show is provided by Dr Stephen Marich of Marich Consulting Services on Wheel rail dynamics.

Figure 2:  A railway wheel on a rail showing the coned wheel profile and how it sits on the rail. Note that the wheel should normally provide guidance without the flange touching it. The flange is, in effect, a safety device. The effect of the coned profile is to maintain a degree of stability and to compensate on curves. Photo: Jim Blaze.

Figure 3:  The location of the wheels in relation to the rails on curved track. On curved track, the outer wheel has a greater distance to travel than the inner wheel. To compensate for this, the wheelset moves sideways in relation to the track so that the larger tyre radius on the inner edge of the wheel is used on the outer rail of the curve, as shown here. The inner wheel uses the outer edge of its tyre to reduce the travelled distance during the passage round the curve.  The flange of the outer wheel will only touch the movement of the train round the curved rail is not in exact symmetry with the geometry of the track.  This can occur due to incorrect speed or poor mechanical condition of the track or train.   It often causes a squealing noise.  It naturally causes wear. Photo: Jim Blaze.

Many operators use flange or rail greasing to ease the passage of wheels on curves. Devices can be mounted on the track or the train. It is important to ensure that the amount of lubricant applied is exactly right. Too much will cause the tyre to become contaminated and will lead to skidding and flatted wheels.

There will always be some slippage between the wheel and rail on curves but this will be minimised if the track and wheel are both constructed and maintained to the correct standards.

Locomotive Hauled Trains

The traditional train comprises a collection of coaches (or freight wagons) with suitable motive power attached in the form of a locomotive (Figure 4). The train is made up of sufficient vehicles to carry the traffic offering and provided with enough power for the job. For passenger operations, one locomotive is usually sufficient.  In heavy freight operations, this number might go up to four locomotives on the front and at some other places along the train.

Figure 4: An example of the traditional locomotive-hauled train with British Class 47 diesel-electric locomotive No. 47853 hauling Manchester to Holyhead train in 2004. Photo:

A good deal of flexibility is possible with locomotive haulage. As long as the train weight remains within the capacity of the locomotive(s), any number of vehicles can be attached, although limits will be imposed by platform or siding lengths. Locomotives themselves can also be flexible, many being designed to cover a range of duties.

The advantages for locomotive hauled trains mean they are the best option for many railway operators around the world, particularly freight but, where traffic is dense, i.e. where a large number of trains are required, a more rational approach is necessary, particularly at terminals.  In addition, in very predictable operations like commuter services or metro lines, fixed formation trains will be the most efficient.

Terminal Operations

One disadvantage of traditional locomotive haulage shows up at the end of the line (Figure 5).  When a train arrives at a dead end terminal, the locomotive is trapped between the train and the buffer stops.  The only way to release the locomotive is to remove the train and for that, a second locomotive is required.  This second loco is attached to the other end of the train and will be used to provide power for the return trip.  When the train has been removed, the first locomotive is released, moved away from the platform to a "loco siding" near the terminus and stored until used for the return trip of another train.  This problem can be solved, if space is available.  The train stops a distance from the buffer stops and a crossover to a run-around track is provided.  This is sometime referred to as a "locomotive escape" and is used as shown in Figure 5.

Figure 5: Schematic of terminal station showing the method for reversing a train with locomotive haulage. Diagram: Author.

Often, the adjacent platform track is used but it must be kept free of other trains.  Sometimes a scissors crossover is used.  Of course, the arrangement would not nowadays be suitable for a major city terminus where space is at a premium and land is very expensive, so efforts are made to use tracks to the optimum.  So, although locomotive changing operations at terminals were, and still are commonplace, where there is intense traffic, additional movements for loco changing can restrict the terminal capacity.  Also additional locomotives are required to cover these terminal operations.  To overcome all these limitations, the "Multiple Unit" was introduced.

Multiple Unit Operation

Locomotive operation of intensive services was rapidly phased out when electric traction, using "multiple unit" operation, was introduced in the late 19th century for US urban railway lines. Within ten years the idea had spread to Europe. The facility for the electric traction system to be spread out along the train, compared with cramming it all together into a bulky locomotive, allowed a number of small power units to be distributed underneath the floors of several vehicles in the train.  They were all simultaneously controlled by the driver in the leading car through wires running the length of the train.  Thus was born the electric multiple unit or EMU. In later years, DMUs (diesel multiple units) were developed using the same principles.

Figure 6: A multiple unit train at work on the Vienna metro (U Bahn). These trains consist of three 2-car units coupled together. Each unit can operate on its own but passenger numbers require the use of three units. Photo: Author.

A modern passenger multiple unit train is now made up of a number of inter-dependent vehicles which cannot operate unless all the vehicles are of the right type and are coupled in the correct position in the train.  Power and auxiliary equipment is usually distributed under more than one vehicle and is all controlled from the driving position.  Vehicles in multiple units are usually referred to as "cars" and are known as "motor cars" if powered and "trailer cars" if not.

Figure 7: Schematics showing typical types of electric multiple units (EMUs). Example 1 shows a 3-car unit with 66% axles motored. Example 2 shows a 4-car unit with 25% axles motored. Example 3 has a 4-car unit with 37.5% axles motored. Diagram: Author.

Multiple unit trains are formed into "units" or "sets"of two or more cars.  They are often semi-permanently coupled together, only being uncoupled inside a workshop for heavy maintenance. Units can operate singly - providing driver's cabs are provided at both ends - or coupled to form longer trains.  Some operations require two (or more) multiple units to be coupled together to provide sufficient capacity for a particular service.  This also allows trains to be lengthened or shortened whilst in service by adding or cutting units.

Some multiple unit trains are designed so that a unit has a full driver's cab at one end only.  At least two units, coupled back to back, are required to make up a train for service.  In the US, a development of this type of formation, known as "married pairs", has been popular since the 1960s. Two cars, coupled together and electrically dependent on each other, form a unit and a number of these are coupled to form trains of four, six, eight etc. cars.  Similar formations have since appeared elsewhere, e.g. London Underground's Central Line.

Multiple unit trains are mainly used for high density suburban operations where traffic levels are easily predicted and form constant patterns which allows fixed train formations.  In recent years, long distance traffics have shown the same tendency and many railways are now adopting the multiple unit formation for these routes - e.g. the French TGV, the UK HST, the Japanese Shinkansen.

Other advantages of the EMU are that it doesn't have to carry its own fuel, it takes it from overhead wires or an additional (third) rail and it is quick and simple to reverse at terminals.  All you have to do was provide drivers controls at both ends of the train, connect them to the train wires and give the driver a key to switch in the controls at the end he wants to use.  Locomotive changing is instantly eliminated, terminal space is released and trains can be turned round more quickly.  All the driver has to do now is change ends. 

Another form of multiple unit operation was adopted in the early 1960s when a new concept appeared called "push-pull".

Push-Pull Operation

Push-pull operation was really only a modification of the multiple unit principle but applied to a locomotive powered train. Assuming a regular level of traffic and an even interval service was required, trains could be formed with a locomotive at one end and a driving cab on the coach at the other end.  If you could find a way of doing it cheaply by converting existing coaches, it could represent a big step forward.  See Development of Push Pull Operation in the UK by Chris Grace.

Figure 8: This is a Youtube video of a New Jersey Transit double desk push pull set at Mount Tabor station on August 10, 2015. The train is seen arriving with the cab car at the front and the locomotive at the rear. As the train departs, the electric locomotive (Bombardier ALP-45DP No. 4521) can be seen at the rear. The train has 8 cars plus the locomotive. Not all the cars have access to the platform. The bell ringing is compulsory for US train entering passenger stations and the horn is for the level crossing. Note the very high reach pantograph on the locomotive. This is because the overhead wires must be high enough to clear double-stack container trains. Video: Fan Railer.

The push pull has now been adopted world-wide in two forms.  One, as described above, uses a locomotive at one end and a coach equipped with a driver's cab at the other end.  In the US, this is called a “cab car”. The number of vehicles in between may be varied seasonally if required but the formation is not normally varied on a train by train basis. In the UK, the driving coach has become designated a Driving Van Trailer (DVT).  It is used to carry luggage and passengers are not permitted to ride in it at speeds over 160 km/h.

The second push-pull form uses two locomotives, one at each end of the train. This was applied to the Channel Tunnel "Le Shuttle" trains and has also appeared elsewhere, notably in Taiwan. The two locomotives are necessary in these cases to provide sufficient power. In many other cases, the second locomotive is used to provide a driving position at the other end of the train and to duplicate systems in case of failure

Figure 9: In Britain, a form of high speed diesel train with a 1200 hp locomotive at each end was introduced from the mid-1970s known as the Inter-City HST.  The design was so successful that it is still in main line use. This video shows Class 43 HST No. 43002 Sir Kenneth Grange at Norton Fitzwarren on 14th May 2016. Video: Classic Traction.

High Speed Multiple Units

The HST name was first used for diesel multiple unit passenger train developed in the UK for 125m/hr running. They were so successful that they are still in service today some 40 years after their intorduction. A “high speed train" is now generally accepted as the definition for any passenger train scheduled to run at over 200 km/h.  

The modern two-locomotive concept for push-pull operation first appeared in 1959 with the UK's Blue Pullman series of trains. A diesel power car was provided at each end of a six- or eight-coach set.  The concept was further developed in the 1970s with the UK High Speed Train (known as the HST) and in France with the TGV (Train à Grande Vitesse).  The former is diesel powered, the latter electric but the concept is the same.  Both these trains employ a power unit at each end with a set of passenger carrying coaches in-between.  The Germans have joined the club with their ICE train.  The only real difference between these trains and the original push-pull concept is that the newer trains were purpose built. 

Electric traction is used for the majority of high speed trains since diesel powered trains cannot offer speeds of more than 200 km/h.

The pioneer system was the Japanese high speed train concept; they were the first to introduce over 200 km/h running on a regular basis and have kept at the forefront of high speed train technology with their German and French counterparts. However, the Japanese HSTs have always been multiple units in the original sense, having many power cars distributed along the train. There are now a number of variations of the design. The video below shows a number of Japanese high speed train types.

Figure 10: Youtube video of various examples of the Japanese Shinkansen high speed train system. Some routes use the standard 1435mm track gauge and some the narrower 1067mm gauge used on older routes in Japan. Note the variety of train designs and the ability to couple different types of unit in the same train. Video: Dotaku.


In the history and development of railways, freight traffic was originally more important financially than passenger traffic. Railways are ideal for the movement of bulk traffic over long distances and many rail routes were built solely for freight traffic or for moving mined ore from mine to port. The long distances of the larger countries like Canada, the United States, South Africa and Australia make the effectiveness of the rail mode come into its own and some railways operate very long heavy trains with a number of locomotives to provide power.

Wagonload freight was also an important part of railway operations until motor vehicles gradually took over the local traffic and goods facilities that were provided at most passenger stations were closed down. 

There is an article on intermodal freight traffic on this site.

Figure 11: The Union Pacific marshalling yard at Fort Worth Tx, USA showing trains formed with three or four locomotives allocated to the front. Handling such trains requires a high level of skill by the engineer (driver) to control up to 10,000 tons of train with pneumatically controlled brakes. Photo: Steve Schmollinger 

© The Railway Technical Website 2017