How Intercity Railways Learned from Metros: Part 6

Train Formations

For many years, electric urban railways or metros as they are now known, set up the train formations in much the same way as the main line railways. As long as you had suitable coaches you would make up trains with a sufficient number of cars to meet the traffic expected on each particular trip. On an electric railway, this usually meant a combination of powered cars (motor cars with space for passengers) and trailer cars. Motor car were provided with drivers cabs and invariably ended up at the end of the train. Trailer cars were stuck in between them. As long as there was sufficient power available in the motor cars you could add any number of trailers. A 50% ratio was common.

Figure 12: A 3-car District Railway train of 1920 Stock working a  trip between South Harrow and South Acton. The two end cars are powered (motor cars) while the middle car is a trailer car, without power equipment. The train could be lengthened to an 8-car formation by adding a 5-car unit for peak hour operation. 

Some metro operators varied the lengths of trains throughout the day, trying to match each train trip with the number of passengers expected to travel on it. This led to some complicated timetable. A classic example was the District Railway in London where trains could be anything from 10 cars to 2 cars in length. Trains were split (uncoupled) in mid trip or at the terminals. This uncoupling took place various locations along the main roots. It was complex and required a large number of spare vehicles. Some vehicles had driving positions at one end onlywhile others had driving positions at both ends. Some trailer cars were also provided with driving controls. They were referred to as driving trailers or control trailers.

Fixed Formations

Eventually, in the 1930s, train formations began to become consolidated. Units were formed in fixed formations of anything from 2 to 5 cars. They were semi permanently coupled, i.e., a coupler bar was fixed between two vehicles, together with jumper cables and hoses and they could only be disconnected in a depot. Some units were designed with a driver's cab at one end only to save money and increase passenger accommodation. Such units would be operated in back to back pairs. 

Figure 13: By the beginning of the 21st century, main line railways were finally adopting the multiple unit formation for long distance trains. Here we see a 5-car Class 220 "Voyager", a class of diesel-electric high-speed multiple-unit trains built in Belgium by Bombardier Transportation and introduced in Britain in 2001. Photo: Pinterest.

The main line intercity railways were slow to adopt the new idea but with the first generation of diesel locomotives originally introduced in the 1950s and 60s needing replacement and the pointers appearing with high speed train operations in Japan and France, new trains began to appear in fixed, multiple unit formation (Figure 13). 

Coupling Units

The problem with the fixed formation was train length. Capacity requirements on railways vary from day-to-day and even from our to our. If you are ordering a new fixed formation train, the decision has to be on how long should it be. Orders for fix formation trains in the UK have varied between 2-car and 12-car lengths. For mainline long distance formations, the consensus has settled on a 5-car set. However, at busy times. some services require two of these to be coupled together to make a 10-car train. 

Figure 14: Two 5-car Class 801 units on the LNER main line at Grantham, Lincolnshire, coupled demonstrating the total separation of the two halves of the train and the need for two train managers and catering staff.

Coupling two trains together is not ideal. Whilst it doubles the accommodation, it creates a dead portion in the centre of the train where the two middle cab ends meet. This prevents any communication between the two units and it requires double the number of on-board staff. An analysis might reveal that it would be better to buy longer trains. In this way, you avoid the dead centre of the train, you can reduce staffing, you can eliminate the expensive coupling system and you have better flexibility with a standard train in use all along the route all day. For all these reasons, I would only buy an 8-car intercity train. The fallacy of buying anything shorter is evident from the persistent overcrowding seen on 5-car trains.

Uncoupling

Some railways still practice uncoupling in service, It is used in two ways; first, to reduce full length peak hour trains to half or less for off-peak service and second, to divide a train en route so two halves of a train can serve two separate branches. The reduction in train length for off-peak periods obviously saves energy and maintenance costs while the splitting of a train to serve two branches saves a train path over the densely occupied section of line and it saves the cost of two crews for part of the trains' journey. Uncoupling in service is widely practiced in southern England.

It is a high risk strategy. If there is any sort of delay to the service, trains that are supposed to be recoupled later in their duty cycle (say for the evening peak period) may not arrive at the coupling point at the right time. This can mean that a short train gets sent into the evening peak and this creates problems in loading and subsequent timekeeping. 

More lessons being learned by intercity railways are discussed in Part 7.

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.

How Intercity Railways Learned from Metros: Part 4

It Started with a Dream

In America, on 26 July 1897, for one 10 year-old boy a dream came true. He got a brand new train set to play with. This was unusual in those days, since toy trains were rare and expensive but this was no toy. This was a full size train. He was given the controls of the first 6-car multiple-unit electric train to be put together at the General Electric Company’s works in Schenectady, New York and he was allowed to drive the train along the test track in front of the assembled officers and engineers of the Chicago South Side Elevated Railway. 

The boy’s name was Desmond Sprague and he was the son of Frank Sprague, who we saw in Part 3 introduced the first successful electric streetcar system in Richmond, Virginia in 1888. Desmond was showing off his electrical engineer father’s new system of multiple unit control, which Dad was trying to sell to the Chicago South Side Elevated. Well, sell it he did. The demonstration was a resounding success (“Hey, it’s so simple, even a kid can drive the  train”) and, within twelve months of this demonstration, the whole of the Chicago South Side Elevated system had been converted from steam to electric traction with 120 multiple unit cars (Figure 6). Oh that we could do things like this in such a short time today.

Figure 6: one of the Chicago South Side Elevated Railroad electric cars on test in 1898. This was a multiple unit car operating singly. Other cars were attached as required to make up trains.  Sprague himself can be seen second from the left standing behind the motorman. As was standard for many years, American driving positions were in a little cubicle in one corner of the end platform. The rest of the riders were company officials and other assorted hangers on.

Multiple Units

The principle of the multiple unit train was simple. A train could be made up of any number of cars. Each car was equipped with two or more motors mounted on the axles and, like a street car, a controller was provided on each vehicle for the 'motorman'. Additionally, a multi-core cable was was strung along the train and connected to these controllers so that they would all operate under the control of the motorman on the front of the leading vehicle. With this arrangement the train was operating "in multiple".

The arrangement allowed trains of varying lengths to have equal power and turnrounds at terminals were simple. The crew just had to change ends. Trains could be lengthened or shortened during the day by cutting or adding cars as necessary. The idea was an immediate success and quickly spread to other systems, first arriving in London in 1901 on the Central London Railway, now the Central Line of the Underground system.

In later versions of this system, not all trains were made up of motor cars (Figure 7). Some unpowered trailers were sandwiched between motor cars and various combinations were made up but the principal of the remote control of cars from one position remained the same. 

Figure 7: A diagram of a terminal on an urban metro syste (Central London Railway) showing the arrangement of multiple unit traction. It shows a six car train with a motor car at each end containing the traction equipment and driving cab. Because of the small size of the London tube blinds, the early trains built for the system had some of their equipment above the floor. Normally, multiple unit trains built to the original Sprague concept had all the equipment below the floor or under the seats.

Sprague’s conversion of the Chicago South Side Elevated Railroad to electric traction was not without its troubles. During the early months of 1898, while the newly converted trains were being delivered and tested, one of the cars caught fire. It was quickly found that the cause was electrical and that a large batch of the resistor grids were defective. Seventeen of the 20 cars by then delivered had to be taken out of service that day. Suffice to say, teething troubles with new rolling stock are not unique to modern times.

Main Line Reaction

Although urban railway systems quickly adopted multiple unit electric trains, mainline railways were slow to react. This was understandable. Electrification was (and still is) expensive and mainline railways would have to do it over long distances and they would have to convert large fleets of trains. They were already invested deeply in steam locomotive technology and conversion didn't make commercial sense unless the railway was very densely used. Even the improved terminal operations of electric railways weren't enough to convince most mainline railways to get into wholesale electrification.

In Part 5, we look at how it took until the late 20th century for main line railways to fully realise the benefits of metro operational techniques.