Perhaps because they represent a mysterious unseen underworld, disused Underground stations seem to fascinate a lot of people – including those who aren’t generally interested in trains. You could be forgiven for thinking that Underground sidings would carry the same cachet, but they seem to be a subject that is often overlooked.

The majority of London’s underground sidings today have a curious property – almost none of them seem to be used for the purpose for which they were originally intended. We have seen the exceptional case of Smithfield sidings primarily used for freight, but most subterranean sidings were primarily constructed to enable trains to terminate well short of the end of an underground line in order to reduce the number of lightly-loaded trains running all the way to the terminus station. A siding was a relatively cheap option compared with the alternative of a very expensive extra platform – especially on the deep-level tubes.

Deep-level sidings were regularly used on London Underground until the latter part of the 20th century. If you travelled on the underground in the 1960’s you would find destinations such as Liverpool Street, Marble Arch, Archway or Tooting Broadway quite commonplace. Even in the early 1970’s the newly-finished Victoria line regularly had timetabled trains terminating at both Victoria and King’s Cross.

Today, with a more intensive service, the operational philosophy has changed. There are often enough passengers to justify a service from one end of the line to the other which has the benefit of offering a “turn-up and go” service. More critically, with today’s frequent service it is often just not possible to terminate a train in the central area or inner suburbs and check that there are no passengers still on board without delaying the train behind. This is even more true now that it is mandatory to check that no passengers remain on the train. Indeed when the Victoria line was extended to Brixton it was quickly realised that by the time the train was emptied at Victoria, had gone into the sidings, the driver walked down through the eight car train and he had returned northbound in his allocated slot he might just as well have gone to Brixton in revenue-earning service. If you ever wonder why quiet semi-rural places like Cockfosters have such a good service it is simply because there are very few places suitable to terminate trains previously without causing disruption.

The consequence of all this is that expensive underground sidings could not be justified on the basis of their original purpose. Given that they are quite costly to maintain does that mean that they are practically redundant? Not a bit of it!

Any Port in A Storm

The first justification for a siding today is as a “cripple siding”. Basically if a train cannot move at normal speed under its own power, the controller will be desperate to get it off the running lines as soon as possible so that the service can continue. In effect, this is the railway operational equivalent of “any port in a storm”.

This might not be a frequent use of a siding but when used it can mean the difference between “good service” and “service suspended”. On its own this is almost sufficient justification for a siding such as Down Street on the Piccadilly line to be maintained, despite it being extremely inconvenient in many ways – not least the fact that the only permitted way to exit is to walk along the main tracks to Hyde Park Corner. Similarly another siding which is of limited use, but which is still retained, is that at the former British Museum station on the Central line.

British Museum on the Central Line. By Version3point1

Use as a cripple siding is not just limited to passenger trains. If there is a problem with an engineering train at night, or simply the fact that it cannot return to base without impacting on the first trains in service, then the sensible thing is to get it off the “main line” using the nearest available stabling point and worry about it after the end of the day’s service.

Start the Day As You Mean To Go On

The second use of sidings is to be able to provide a decent service from the first train of the day right up to the last train of the day. Obviously this is more important if part of the line is distant from the main depot or depots. For this reason the underground terminus stations of Walthamstow Central, Brixton and Elephant and Castle have sidings beyond the platforms, as did Charing Cross (Jubilee line) when it was open and they are presumably still available for use now. In the case of Elephant & Castle the nearest depot is actually extremely close, but it is awkward to get from there to Elephant & Castle station as it involves a reversal on the running tracks.

Sidings at such locations may seem unnecessary, as the trains could potentially stable in the platforms. This is certainly possible but the sidings also conveniently double as an overrun, allowing the trains to approach the platform at speed as there is no need for “train protection at terminal stations” (colloquially known as “Moorgate control”). Having a train in a siding also means that if it fails at the start of the day, it doesn’t block a platform. It also means that maintenance can be carried out on the track within the platform area itself at night. Generally once a week, however, (usually on a Friday or Saturday night) the train is stabled in the platform. This obviously allows regular inspections and maintenance carried out on the siding itself.

The view towards Walthamstow Sidings. By Chris Pittock

Recovering the Service

The third main benefit of a siding is that it is somewhere to get rid of a train when the service falls to pieces. If a controller experiences a problem on the line (such as a ten minute delay because a door won’t close) then one of the biggest problem this creates is that it causes the trains to bunch. This potentially leaves a number of trains stuck in tunnels for long periods of time. The best and quickest way to get rid of this problem is to thin out the service until it is running smoothly again, and then to reintroduce the trains removed from service in a gradual and orderly manner.

One problem in this situation is that it is almost always worst where the stations are closest – the central section. This is, of course, precisely the section where sidings and other places to temporarily store trains are scarcest. Here the Central line is very fortunate as it has 16 sidings located underneath the Westfield shopping centre at White City which used to be 15 open-air sidings before the over-development. The Victoria line is probably the line that suffers the most, with it possessing no non-intensively used section and being entirely underground. South of Seven Sisters it also only has intermediate sidings at Victoria (2) and King’s Cross (1). Also, as London Underground delight in telling us, the line currently has 37 trains but only 33 platforms, so evacuating people in the event of a train failure becomes quite problematic – and that is before they introduce even more trains at the final stage of the upgrade.

The Central Line Sidings at White City. By Pete

Terminating Early

Another use of sidings is to terminate a train short of destination in order to regulate the service (fill a gap going the other way) but nowadays this can easily become problematic. The driver has a limit to the hours he is allowed to drive and he may be sent away from his signing-on point. Furthermore, the train must return to its home depot at least every 48 hours for a mandatory check and messing around with train diagrams may cause this to be missed. It is a situation not helped by the fact that a controller will not instantly know where the train and the driver are based, which nowadays need not be the same place. Slightly different (but certainly related) is the train held in a siding specifically for the finish of a big event but with the current frequencies run this becomes less of either an option or a necessity.

Doubling Up

At some places other than termini there are actually two sidings. Liverpool Street (Central line) and Victoria (Victoria line) both have two. Victoria actually used to have four but two were used to extend the line to Brixton. More unusually, Down Street (between Green Park and Hyde Park Corner on the Piccadilly line) and Kennington have a double-length siding. In the case of Kennington there is even a second exit half way down, so that one train is not trapped behind another. Due to a fatal accident at Tooting Broadway, however, where it was suspected that the driver mistook his location for the longer siding at Kennington, it has since been the policy to only provide signalling for one-berth at these locations.

This is no great loss. A second berth at Down Street isn’t really needed and Kennington also has a loop although this can only be accessed from the Charing Cross branch. One way around this for the future though would be to arrange for the trains to enter into the sidings unmanned. This would also overcome the problem of leaving the driver trapped with his train for long periods, as well as making it easier for trains to enter and exit sidings by a shunt manoeuvre so that sidings could be used “from the wrong direction”. Of course the problem of the trapped driver would have been less of an issue in true “tube” sidings if a pedestrian exit had been provided, but this is almost never the case. It is said, however, that the siding at Kennington has an exit to Oval station and this does seem plausible given how long it is and how close the end of it is to that station.

The Northbound Trailing Junction at Kennington. The loop is to the right. By Owen D.Smithers.

It is probably a sign of how useful sidings continue to be that there is only one case of a deep-level siding not still being in use. That is at Queensway, but it is located east of the station and must be approached from the west which limits it value. It is also close to the siding at Marble Arch and the far better facilities at White City which are only four stops further down the line. It may be the case that the siding simply was not long enough for the current length of trains which brings us to the issue of sidings being too short.

Length Matters

One of the often forgotten problems of extending train length is that the sidings (and depots) may not be able to accommodate the longer trains. Although it may not be too difficult to extend sidings underground, it would normally be expensive and involve legal procedures before work could start. There is a case of a surface siding at Golders Green that needed extending from six to seven cars but the hillside was in the way. The siding was extended by creating a third tunnel mouth (the Northern line surfaces at Golders Green) that only extends into the hillside by one carriage length.

The sidings at Golders Green – with a 38ts in the middle! By Brapps

Luckily, it appears that short sidings have so far not been a problem for the deep level tubes. The situation is, however, quite different for the sub-surface lines – especially with the introduction of the longer S7 stock. After all, there is no equivalent of simply introducing selective door operation if the siding is too short.

With the main depots on the sub-surface lines being a long way out (Hammersmith, Neasden, Upminster) it is important to have stabling sidings located nearer the centre. The situation is made worse because the current ones (Farringdon, Parsons Green and “Triangle Sidings” near Gloucester Road) cannot be extended easily. In particular Triangle Sidings, more conveniently located than Parsons Green, is a very tight fit even for C6 stock and, due to it both being built over and also abutting the running lines, it is almost impossible to extend. So the hunt is on for alternative options and as mentioned in our article about the Widened lines it seems that the likely solution is to convert these to a long linear siding with the advantage of trains being able to depart in either direction. It is fortunate that these lines have been returned to London Underground, the owners, as a result of the Thameslink Programme. These would of course for the most part be located underground.

It must not be forgotten that there are also subterranean sidings on the National Rail network. Smithfield carriage sidings are located to the west of the running lines between City Thameslink and Farringdon, with the buffer stops almost by Farringdon station. As such the name is slightly misleading and also easily confused with the former Smithfield goods sidings. Unfortunately the two sidings cannot be extended from the current eight carriages and so will be only useable by a proportion of the proposed Thameslink stock. The overhead wires have been extended southwards from Farringdon to City Thameslink and the eventual intention is that in the northbound direction the changeover from AC to DC would takes place at City Thameslink. In the event of a pantograph or similar failure the train could simply continue to Smithfield sidings where it would stable until a convenient opportunity was available to send it to the depot at Three Bridges for the fault to be rectified.

It must not be forgotten that the Waterloo & City line manages in this as in many other cases to be completely different and uniquely has a complete underground depot where the trains are serviced. One suspects that space is extremely cramped. Whilst it is unlikely that the train length will ever be extended due to the difficulty of extending the platforms at Bank it is not known if an extra train could be accommodated if required. Currently there are five trains based there and all five are in service in the morning peak. At present there are no extra trains available, but when the stock is replaced it will presumably be desirable to have a spare – provided there is somewhere to put it.

The Waterloo & City Depot, by jodastephen

Looking to the Future

It would seem then that underground sidings are important to running a reliable service on a deep-level underground line, even though the intention may not be for them to be used on a regular basis. It comes as a bit of a surprise therefore that Crossrail appear to have to have absolutely nowhere (sidings or otherwise) planned as a potential emergency stabling point anywhere between Old Oak Common and Stratford/Abbey Wood. The proposed sidings at Westbourne Park for Paddington terminators may be built, but this is by no means certain. There is also probably land available to build or improve a surface siding at Plumstead, but this is almost at the end of the line anyway. There will be a crossover in the central area, which may help in some circumstances but not others. One presumes that the decision not to have any underground sidings on Crossrail was made on the basis that they are very expensive and should not be necessary on a modern reliable railway. It may well be the right decision, but if not it will be almost impossible to correct…