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.