Wednesday 10 August 2022


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rail unveiled

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the capacity crunch

Some critics of the railway say the answer to peak hour overcrowding is for the operators to run more trains.

But even if more trains are available, is there always room for them on the railway?

Is there room for more trains?

The short answer is sometimes.

There are several ways to add capacity. One is running more trains.

The second is strengthening existing trains, either by adding another unit (so that, for example, the 07.20 to Waterloo is made up of three four-car units rather than two) or else more individual vehicles (often called carriages).

Whether adding vehicles to existing sets is possible depends on technical factors. It has been done on the West Coast Main Line tilting Pendolinos run by Virgin, which were built as eight-car sets but soon gained a ninth car. Some of them have been strengthened again to 11 cars. Similarly, the Class 378 trains which run on most London Overground lines were built as three-car sets. They have been strengthened twice: first to four cars and more recently to five.

The third way is to change the signalling, so that trains can run more closely together.

A fourth way (usually the most expensive) is to provide more trains and also more tracks for them to use. For example, the West Coast Main Line through the Trent Valley, north of Rugby, used to be two tracks. As part of the lines upgrade around the turn of the present century, it was increased to four. This helped Virgin to increase the frequency of its Pendolino services between London and Manchester from 2008.

Unfortunately, there are often side-effects when capacity is increased. More trains put further demands on the signalling and perhaps the track, which may also need to be upgraded (as in the Trent Valley).

Longer trains sound simpler (since they are not more frequent but do offer more seats), but there are definite limits here too. Longer trains need longer platforms at the stations they use, and above a certain level they start to overflow the space available at junctions, so when a very long train arrives it might block another line needed by other trains. In this case, increasing capacity on one flow can reduce capacity on another.

In short, increasing capacity is far from straightforward. It may, indeed, involve a strategic combination of increasing the rolling stock, upgrading the signalling, lengthening platforms and perhaps improving the track as well.

There is another possible solution as far as signalling is concerned: new technology often described as the Digital Railway should allow trains to run more closely together, which makes better use of the existing infrastructure without building more lines.

how much do new trains cost?
the problem of the peaks
why dont operators buy more trains?


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