When signals were introduced - continued

From here on I will sometimes be going out of my specialist area to refer to railways on which I have only a working knowledge. I can give an outline of what happened and can sometimes say when it occurred, and I can express an opinion on the overall developments, but I will have to leave it to others to answer any detailed questions that may arise regarding the operation of signalling on specific railways/lines.


There was an early proposal to install automatic signalling on the Central London Railway using coloured lights controlled by relays. This was not adopted and the railway opened in 1900 using a system similar to the C&SLR.

In my opinion, the CLR's choice of a signalling system was based on what it had seen working on the C&SLR, and this also influenced the type of tunnel signals that it used. We must remember that the control of coloured light signals had not been perfected at that time, whereas the mechanically operated moving spectacle principle that the CLR settled on was well established.

Having chosen a fixed light with moving lenses, the CLR could have used either the C&SLR-type external spectacle frames or the neater and more modern looking W&CR internal variation. I think that they made the right decision in selecting the external frames from the point of practicality.

On those occasions when a signal requires the attention of an engineer, the external frame system appears to be easier to maintain simply because the mechanical components are larger and can be dealt with without wasting time opening the signal housing. In the event, the CLR installed Evans O'Donnell signals that were almost identical to those used on the C&SLR.

Automatic coloured light signalling was tried experimentally on the CLR between Tottenham Court Road and Bond Street within a couple of years of opening, but the trial was abandoned after a dangerous 'false clear' occurred due to a defect that had developed in the wiring. The GN&CR therefore became the first tube railway to properly introduce twin aspect coloured light signalling between Moorgate Street and Finsbury Park on 13 Feb 1904. This was controlled through a system of electric relays and treadles to provide automatic signalling along the line, with semi-automatic signalling at the termini.

The initial GN&CR arrangements did not meet the requirements of the railway inspectorate who identified situations where a signal could display a false clear. The inspectorate allowed the line to open, but demanded that changes be made to the circuitry. The company undertook this work only to discover that it had created a situation where signals could become unnecessarily locked at danger by the additional relays that it had installed. Although the company realised that this would cause operational difficulties, working with the occasional false danger signal could just be tolerated, whereas the possibility of allowing a false clear to be displayed was not acceptable under any circumstances. The GN&CR therefore developed a work-round to deal with an automatic signal that was stuck at danger and it continued to operate its service with this less than perfect system.

I believe that the failure of the automatic signal system on the CLR and the difficulties experienced on the GN&CR are understandable. These both occurred at a time when the use of electricity was in its infancy and when components - particularly relays - were unreliable and/or still being developed. There is little doubt in my mind that all of these factors influenced what happened next...

...and what happened next was Mr Yerkes, an American who set himself the task of trying to electrify the Metropolitan District Railway as well as drawing together a group of uncompleted tube railways that would become the CCE&H, BS&W and GNP&B. His schemes involved cost reduction which was partly achieved by consolidation and standardisation.

On the signalling side, he needed technology that would be reliable and provide value for money. It would also have to be as future-proof as possible and allow the operation of the intensive service that was planned. In order to achieve this latter requirement it was essential that a way was found to improve the interface with the signalling system

No matter how you look at it, this involved (and still does) some sort of mechanical input to switch the signals, to lock the points and ideally to stop the trains. Everything comes down to mechanics - remember, even a relay is nothing more than a mechanical device.

It was also obvious at the start of the 20th century that any successful tube railway would have to shorten the block sections to allow it to increase traffic. This would require more signals and, as each block section was shortened and each new signal was added to protect it, any improvement to the service would be partly offset by the added delay that would inevitably occur if manually operated signals were retained.

Traditional signalling using wires, rods, bell codes and levers for every task, was not up to the job and all electric signalling had not proved itself. And it was not just these issues that had to be resolved in the search for some type of automated system. There was also the complex problem of DC current leakage that could alter the potential in the running rails and upset any electrical circuits that were trying to be used for signalling purposes. (This of course did not apply on non-electrified lines, which is why signalling developments on the surface steam railways could not always be carried across onto electric tube railways.)

Charles Tyson Yerkes burst onto the scene with American money, American ideas and a team of American consultants that included signalling specialists. The word 'American' is rather an important one in this story, which is why I am emphasising it. It influenced the whole structure and character of London's underground from the moment that Charlie made his appearance, right through to the present day.

This even worked its way through into the signalling, with the relevant American consultants selecting a system based on one that had been successfully adopted by the electrically operated Boston Elevated Railway. This employed automatic signals, track circuits, train stops and, equally importantly, a mechanical interface that used pneumatic power to overcome the requirement for many of the relays.

Another vital factor in the adaptation of this system was the fourth rail. Having first appeared underground in a different configuration on the GN&CR, this became standard on the Yerkes lines and eventually spread to the other companies. It was partly introduced to provide an insulated return for the DC traction current that had to operate separately from the DC track circuits.

One difference between the Boston Elevated Railway and London's tube lines was that the former used semaphore signals that were obviously unsuitable within the confines of a tunnel. There was however little need to look very far for a substitute. The signals on the C&SLR and CLR were virtually identical to each other and had operated satisfactory, so the same basic design was adopted on the new lines - vertically moving spectacles in front of a fixed light. There was however one difference; the Yerkes tubes initially used oil lighting instead of electric bulbs, despite the fact that this form of illumination had proved problematic on the C&SLR.

I do not know why these railways reverted to oil, but it has been suggested by others that it was to ensure that there would still be a signal light in event of a current or circuit failure. My conversations with former signalling employees on the C&SLR also highlighted the fact that the electric bulbs were prone to a high failure rate, probably made worse by current fluctuations and vibration.

To summarise;
Twin aspect coloured lights were first used on the GN&CR from 1904, together with an automatic signalling system that was not quite perfect.
Automatic signalling with single light signals was used on the BS&WR from its opening in 1906.
Automatic signalling with twin aspect coloured light signals was installed on the CLR from 1912.
I do not know when the BS&WR, CXE&HR and GNP&BR were converted to twin aspect, but it is documented. Perhaps someone with a better knowledge of these companies could fill in that detail?

That is as far I plan to go with this story, although I propose to round things off in the next couple of days by adding a few comments on why I think that things subsequently developed the way they did . . . if that is all right with everyone?

I do realise that this thread is starting to look like a history lesson and I think that it is probably a little out of place on this forum, which is one of the reasons why I eased up on my posts over the past few years.

Not at all. It has all been very interesting and I think a lot of forum members value the contributions about historical aspects, just as much as the contemporary.

I'd like to add my thanks for the entire series as well. I would love to see more posts of this type, either directly here or perhaps they could be posted on the main site and advertised on the forum. That latter option may be better for the long term preservation of the knowledge actually.

Personally, I am loving this "history lesson"; I have learnt so much from these posts - please continue!

Like you say, if it ain't broke, don't fix it! Where did the Westinghouse Brake & signal Company and others come into the equation? What sort of block instrument were used? Bell code between signal boxes?

A series of memoirs such as this will be a source of historic record for future generation. there can't be many people around now who have spoken with CSLR staff!

As Tom said, Westinghouse came into the story on the Yerkes lines.



Spagnoletti block instruments were used on the C&SLR, but of a different type to the Metropolitan Railway. Bell codes were used between boxes; however, the company began installing outer home signals within 14 months of opening and these used a treadle (instead of a signalman) to accept the train and to send a message back to the block instrument at the cabin in the rear.

The CLR used the same type of Spagnoletti block instruments as the C&SLR.



I was luck to have spoken to quite a few over many years. It was a magic experience to get so close to the story. It was even more remarkable to realise that these people had known and worked with some of the original staff and officials of the company.

The last person from the C&SLR that I ever met had worked in Stockwell depot and was trained by an engineer who had been involved in the first trial running of the experimental locomotives and carriages in 1889 - and you cannot get much earlier than that!

Sadly that gentleman and all of the operational staff that I knew are no longer with us. Their memories remain in folders of notes, sound recordings and some video.

SPOILER: Really nice signalling quote coming up in this post so do not skip over it.





That depends on what the objective is. If it is just transcribing this material for future reference - that is taken care of. It should be recognised though, that even that is not as simple as it seems.

When speaking to someone, I always tried to create a situation where it was more of a conversation than an interview. That way, the information that I was given tended to be far more detailed and the speaker had no hesitation in stopping to think about things or to go rambling into an off-topic aside that could often lead in all sorts of valuable directions.

No loaded questions. That was vitally important. If I had to ask a question, I would always rephrase it so that it offered no guidance whatsoever to the answer that I expected.

These are just a few of the rules that I used, but it meant that our conversations included a large amount of shared knowledge that would not always be known by others. For this reason, it has been important to add numerous footnotes to clarify what was being talked about.

I will give a couple of examples from a former locomotive driver:

1. (He is talking about over-running signals). "They was on a cable, see? They wasn't electric. They had an electric light in them. And there used to be a slide, up and down, and you could always tell when it was on. And if you run past it, you could jump out - on that platform like - and hold the wire, and when it was clear it would go through your hand, so you knew it had come off." (laughs)
"I don't say everybody done it." (laughs)

I understand all of that, but does everyone else? Read it again and see if every word makes sense or if there is something that you are guessing at. If you are guessing, are you sure that your assumption is correct?

2. In another interview, there was mention of the 'Tramway Hall'. How many people on this forum would know where that was or what it was without looking it up? How long would it take to find out if it was relevant or not, and how can anyone judge what is relevant to a future reader?

It is so easy to skip over important words or references simply because they are not understood. Footnotes are not what the person said, but they are essential to the understanding and to guide others to alternative sources. I add footnotes and cross-references where I have them, because that is exactly what I wish for when I am reading things.

Note to tut:
All of this assumes that you are asking about the interviews and not about another project, 'The Slightly Larger History of the City & South London Railway'? That is in hand, but it is not a three month job, even if some writers appear to throw books out in that sort of timescale.

Notes to all forum members:
To pre-empt the next question, 'It has been underway for some time.'
And to answer the follow-up question...the answer is, 'No, I do not.'
And for those who cannot work out the questions - you probably do not need to know the answers

Going back to the driver's comment, you'd really need to know how the system worked and the terminology used for it to make any sense.

I suppose a lot of us here could add our anecdotes; to go slightly off the subject but of relevance, when the C stock was being introduced, I jumped one at Acton Town one day towards Hammersmith. the train crew inspector told me they had to make loads of modifications to the cabs before they could enter service; the whistle button on the left had to be moved as if the driver was braking and there were men on the track, he couldn't blow the whistle without dropping the handle..such little things..

But its the only way round now they dont modify the trains they spend millions instead modifying the existing equipment to make there wonderful trains compatible.