How Intercity Railways Learned from Metros: Part 5

Push-Pull Operation

The use of multiple unit operations on mainline railways was, for many years, limited to a few suburban routes around major cities. One exception in Britain was the Southern Railway, which installed electric traction on their lines south of London to the towns of Portsmouth, Brighton, Eastbourne and Worthing along the Channel coast in the 1930s. But generally, as far as intercity operations were concerned, locomotive haulage ruled. However, a pointer towards a different form of multiple unit operation appeared in the late 1950s. This was the concept of 'push-pull'.

Push-pull operation was really only an adaption of the multiple unit principle but applied to a locomotive powered train. The train was formed with a locomotive at one end and a driving cab on an unpowered vehicle at the other end. You could do it cheaply by using existing coaches and providing them with a through control cable to connect the controller on the unpowered vehicle at one end with the power system on the locomotive at the other end. With the locomotive at the front, the train was being pulled, with the locomotive at the rear it was being pushed. See more in Development of Push Pull Operation in the UK by Chris Grace.

Figure 8: A push-pull train on the UK's East Coast main line with a non-powered driving car,  known as a Driving Van Trailer (DVT) leading the train. The locomotive is at the rear, pushing the train, thus power is at the rear but controlled from the front. The photo was taken at Finsbury Park by Andy's UK Train Page.

Push-pull operation using multiple unit principles first appeared in France in 1958 and then in the US in the following year. The idea was then gradually adopted in various countries in two forms. In its original form, as described above, uses a locomotive at one end and a coach equipped with a driver's cab at the other end. The number of vehicles in between them 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 is 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 (Figures 8 and 9).

Figure 9: A diagram of the layout of a push-pull train in a terminal. The train arrives with the DVT at the rear and it departs with the DVT at the front. 

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. 

High Speed Multiple Units

The modern two-locomotive concept for push-pull operation first appeared in 1959 with the UK's Blue Pullman series of trains (Figure 10). 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 not to be confused with the new line being built between London and Birmingham) 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 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.

Figure 10: The concept of a power car at each end of a train first appeared in Britain with the Blue Pullman. A diesel Power car was provided at each end of the train. This photo shows one at Paddington in London in 1962.  Source: David Christie Flickr.

While the Blue Pullman concept struggled commercially, partly because all the coaches were to a luxury standard and priced accordingly and partly because of falling traffic, the HST was a standard long-distance train that reduced journey times. It was a huge success. Also, we should not forget 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 largely ahead of 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.

Figure 11: In the early 1970s, the high-speed train (HST) appeared in Britain. This was  designed to run at 125 mi/h and was made up with a diesel locomotive at each end of a set of coaches. Here, one is seen at Cardiff Central. Photo: Wallhere.com

The HST name was first used for diesel multiple unit passenger train developed in the UK for 125m/hr running. It is now generally accepted as the definition for any passenger train scheduled to run at over 200 km/h.  For more information on the different types, see the Railway-Technical Website High Speed Train Page.

The next part of this series, Part 6, looks at the concept of fixed formations, length variations and uncoupling.