Why “Just put another coach on the end” is Not a Good Way to Run a Railway

Dear reader, you have almost certainly heard this phrase uttered on a crowded train somewhere in the country, or, in an unthinking moment, uttered it yourself. In this article, with hopefully a little less waffling than usual, I hope to explain to you why this is very difficult and is rarely done, and hopefully in the process you will learn a little about how the railway works.

To explain, we have to go back in time to, oh, I don’t know, about 1955. In 1955, Britain’s railways were largely steam powered, and the vast majority of trains were formed by a steam locomotive at the front and a set of coaches behind. When summer came, miles of extra (usually very old) coaches that had been stored in sidings all winter were used to cover holiday trains, and thus people standing on such trains was a relatively rare occurrence. Idyllic as it sounds, there were two principle problems with this system.

Firstly it was completely uneconomic. Coaches sat in sidings do not earning money, and all the while they were taking up space on track which cost money to maintain, and land which British Railways (as it then was) frequently had no other use for. During summer, these coaches would then have to be shunted onto other trains, and, while they were being moved around, they were: 1) taking up even more space on the network and 2) still not earning any money. This is all without mentioning the extra guards, shunters and locomotives needed for the whole affair.

Secondly, the standards of maintenance were wildly different between coaches. Frequently, the difference in age between the extra coaches and the newer ones they were coupled to was many decades, and it really showed. Granted, many holidaymakers were glad to have a seat, but as time wore on, old, dirty, and late trains became less and less acceptable.

As time went on, coaches began to be organised into fixed “rakes” or “sets”. This meant that each coach in the set would cover the same number of miles as the others in the set, and would have the same maintenance and cleaning applied to it. It also meant that one could plan exactly which coaches would be where with much greater ease, and timings could be made more consistent, since the locomotive (now diesel or electric) would always be pulling the same load. One problem remained, however – the locomotive would somehow have to be put on the other end of the train at the end of the line. Again, there were two ways of doing this.

One could, using another running line and 2 sets of points, “run around”, that is, run the locomotive alongside the coaches and put it on the other end. Needless to say, this meant that you now could not use the other line for anything else, significantly reducing the number of trains you could have at a station at any one time.

The other way was to leave the locomotive on one end, uncouple it from the train, and put another locomotive on the other end. This was very common at terminus stations where space was limited, but had the severe disadvantage that the incoming locomotive would spend a long time not doing anything on the other end of the train, having to wait for the train to clear the platform before moving off. It also meant the outgoing locomotive would have to run with no train (called a “light engine” move) to attach to the other end, not earning any money, and wasting network capacity, in the process.

Clearly, neither solution was ideal, and the problem of having locomotives on the wrong end was (generally) solved in two ways. Firstly, one could use some form of driving cab on the coach at the other end of the train, sending electronic signals that the locomotive would interpret to push the train along while the driver could still see where he was going. Often (but by no means always) these cabs were put the end of empty guard’s vans, creating the familiar Driving Van Trailer or DVT. You can still see this kind of train today, and (despite early teething problems) it is an effective solution.

The second, and much more radical, solution, is to dispense with the locomotive entirely. Instead, you put all the equipment powering the train under the floor of the train, and just put a cab on either end of your set of coaches. This kind of train is known as a “multiple unit” (often shortened to “unit”) and they are by far the most common kind on the network today, due to their efficiency and usefulness. (Though actually they’ve been around in one form or another for decades).

Each unit is put on a “diagram” – that is, a set of services and empty moves throughout the day. This is handy since you know exactly how many miles the unit has done and thus how much maintenance is required. For a diesel unit, this means that you vastly reduce the risk of running out of fuel, since you can make the diagram shorter than the number of miles it can cover. This system also makes the best use of available trains, since each diagram is several hundred, or a few thousand miles per day (the most hardworking train fleets cover about 2000 miles per train per day).

Units may be coupled together to form longer trains, without any loss of performance, though this is not always ideal. Say you have 2 units. Sure, you can couple them together, so one service has twice the capacity, but you have simultaneously halved the number of services you can run. This also creates complications as much depends on which end of the train each unit is at, as it may then not be in the right place to form the next service on its diagram. In fact, trains straying from their diagrams create many headaches for train control teams, maintenance crews and so on, so generally this is to be avoided, even if it would ease overcrowding.

Crowding in itself is frequently unavoidable at peak times. To seat everybody on a commuter train into London would require a farcically long train, formed of many units and certainly a train that would take a very long time to get people onto and off of. What can be done is to have units with enough room for people to stand comfortably, and try to have many units together for the peak service, without prejudicing more lightly used lines. Suffice to say, there are many teams of people, from planners to controllers to maintenance crews to platform staff, who are trying to make this all happen, but on a system as complicated as Britain’s railway things do go wrong. I would urge you all to be a bit more forgiving to this hard working lot.

In any case, I am afraid this article terminates here. Thank you for reading with Peculiarly Pete, please take all personal belongings, unruly children, lost umbrellas, sunglasses, copies of the Metro and any other detritus with you. Please also mind the gap between the theory and reality. Here at the end of the article, onward connections include:

  • This video, or at least the first 6 minutes, explains diagrams a bit better and is highly recommended. A bit old but well worth the watch
  • This article of mine, which although not directly on the topic, explains some of the complexities of our railway system
  • And finally, if you’re really interested, go to a busy station like Birmingham New Street or any of the London Termini (Euston, King’s Cross etc.), and just observe for a while. The complexity of the system, and the reasons for having units, become apparent after a while












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