Signal Cabins

Of course no railway could run without signals... well it could, but it'd only be safe to operate one train at a time which would rather defeat the purpose of a public transport system. So very early in the history of railways, signaling systems were invented.

There’s a wealth of publications on the topic, but a brief description is appropriate to get a bit of a feel for what we have.

London Underground signals fall into two categories, Automatic and Semi-Automatic. The latter equate to what are known as Controlled signals on the National Rail network.

What's the difference?

Actually quite a lot! Automatic signals are just that, they work by ‘knowing’ when the section they control is occupied going to ‘Danger’ (red). Once the section is clear they go to ‘Clear’ (green). In common with everything on the railway the watchword is ‘Failsafe’, so if there is a technical breakdown and the signal can’t see its section, it goes to Danger and therefore the signal has failed safe.

All signals are identified by a unique number. In the case of automatic signals the letter ‘A’ indicates it as an automatic signal. This is followed by a three digit number unique to that signal.

Semi-Automatic signals are controlled by a Signal Operator either from a Signal Cabin or a Control Centre. There are also Programme Machines which can control some of these signals, so manual intervention isn’t always required. Programme machines are an early form of computer operated signaling system. As renewals take place these will be replaced with fully computerised systems, such as is used on the Central Line. There the signals for the whole line are controlled from Wood Lane.

Ours haven't yet reached this degree of sophistication, so our trains are signalled from a number of different locations. The largest of our signalling centres is located at Earls Court. This controls most of the semi-automatic signals west of Tower Hill. There are a few places it does not cover, but I'll expand on these later.

Signal numbers are again allocated. This time the signal plate will consist of two letters followed by anything up to three numbers. The letters are the ‘Cabin Code’ and the number relates to the lever number for that signal. Of course these codes have long since been replaced in reality by a far reduced number of actual cabins, but at each location there is an Interlocking Machine Room which locally controls the signals and  points in its area. An IMR is really a remotely operated cabin, so it is still appropriate for the Cabin Codes to be retained.

Heading in an eastward direction the following locations control our signalling:

The area between Tower Hill and Aldgate East is controlled by the Control Centre at Baker Street... remember here we are in ‘Metropolitan’ territory as this is Minories Junction.

I mentioned earlier that there are some exceptions to the signaling arrangements at the west end of the line.

The first is the area from Notting Hill Gate to Edgware Roadwhere the controlled signals in this area, which are between Paddington Praed Street Junction and Edgware Road itself) are controlled from the cabin  at Edgware Road... remember again here we're in MetLand!

The other exceptions are from East Putney to Wimbledon and between Gunnersbury and Richmond. Here we are on Railtrack metals and not only are we subject to their Rules and Regulations but their signalling systems too, which have quite a few differences from London Underground’s... so as District Line driver you have to know both!

Earlier I described the failsafe nature of automatic signals. The same applies should a semi or a controlled signal fail. The signal will return to danger and the signal operator won’t be able to clear it. In my diary pages you’ll find a description of how this situation is addressed.

There is often a great deal of misunderstanding between drivers and signal operators. The former thinks the latter is trying to delay him at all costs, whilst the latter thinks the former is trying to bother him when there’s a problem he’s trying to resolve and is under pressure! Often the only time one speaks to the other is when the driver is delayed and uses the signalphone... and when the signaler is often under pressure and the driver gets pretty short shrift! Personally I'd like to spend time with a signaler to understand his job better, and I think it’d do the signalers good to spend some time with drivers. Then perhaps we’d all understand each other a bit better!

I touched earlier on the Control Centre at Earls Court. Not only does this control the signaling for the section of the line described, but is also where the line is run from. The Line Controllers are there, able to ‘see’ the line from the signaling diagrams and, at certain locations, via CCTV too. The Line Controller has the immediate responsibility for the service as he is the one who must react to any situation, perhaps suspending a service, diverting trains and so on. He will send and receive messages by radio to the trains. He will also put into place any emergency procedures necessary in any given situation.

Also at Earls Court is the Duty Operations Manager (DOM). It’s the DOM’s job to look overall at the service, and he is responsible for maximising the train service. That's a pretty simplistic explanation, but gives the right idea at least!

So there we have it... a brief view of the signalling structure of the District Line.

With the exception of the photographs taken in Upminster Signal Cabin, which are District Dave’s own work, all the photographs and captions which appear above have been reproduced from and are with the permission of Anorak Heaven. Although they were all taken some time ago, little has changed in any of the locations, so are quite relevant to today's operations. District Dave’s thanks are extended for the use of these images.