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Signals on the L&M


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  • RMweb Gold

 

 

Also I believe that the whole basis behind the clearing point in mechanical signalling is to provide a safety margin beyond the Home signal governing the exit from a block section and it was thus similar in principle to the 200yard overlap beyond a colour light signal. Thus it is a signalling principle that the signal section must have the section of line between the home signal and the clearing point (440 / 200 yards) free of trains* if a train is permitted to enter the block or signal section the overlap / clearing point.

 

Yes & no.  Firstly the 200yd/300yd standard overlaps in multiple aspect colour light signalling were indeed drawn from the principle of the Clearing Point although in effect they work in a rather different way because they (and the subsequent variations on the original standard) apply at every signal capable of showing a danger indication.  That is rather different from semaphore practice where the Clearing Point only applies in connection with block working (and therefore to the outermost Home Signal) rather than at every stop signal.  Colour light practice in effect makes every signal section an equivalent to a block section whereas semaphore practice doesn't, in the latter there is no need for a Clearing Point at every stop signal - hence keeping the terminology distinct and not confusing the various terms.

 

Thus the terms Block Section and Station Limits each have a very specific meaning within the Rules & Regs and while the term Signal Section can be used in relation to semaphore style signalling it is best kept separate from those basic, and very critical, terms.  A Block Section is indeed also a signal section but the meaning and term which counts, and is totally unambiguous, is 'Block Section' 

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The Clearing Point lies within Station Limits (there wouldn't be much sense to it if that wasn't the case)

Unless, of course, it is in the advance section. And I know The Stationmaster knows that, and was only trying to be succinct, but signalling can be very confusing to the less knowledgeable, including myself. The obvious case here is a box which only has a single stop signal in a particular direction, but you could potentially have a box with home and section signals less than a quarter-mile apart.

 

In fact I'd say that even more than other railway disciplines signalling is one of those areas where "a little knowledge is a dangerous thing", whether it's people generalising from one set of signalling regs to assume all work the same way; assuming that the world works like a particular simulation, or just by making assumptions from partial descriptions. I saw someone state on another forum recently that the reason why, under ETT regs, only one train may enter a crossing loop at once is that the loop points would be within the overlap of the loop exit signal. When I told them, politely, that they had misunderstood and the loop exit signal did not have an overlap as they understood it, I was told I was completely wrong because "every signal has an overlap"!

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  • RMweb Gold

Unless, of course, it is in the advance section. And I know The Stationmaster knows that, and was only trying to be succinct, but signalling can be very confusing to the less knowledgeable, including myself. The obvious case here is a box which only has a single stop signal in a particular direction, but you could potentially have a box with home and section signals less than a quarter-mile apart.

 

In fact I'd say that even more than other railway disciplines signalling is one of those areas where "a little knowledge is a dangerous thing", whether it's people generalising from one set of signalling regs to assume all work the same way; assuming that the world works like a particular simulation, or just by making assumptions from partial descriptions. I saw someone state on another forum recently that the reason why, under ETT regs, only one train may enter a crossing loop at once is that the loop points would be within the overlap of the loop exit signal. When I told them, politely, that they had misunderstood and the loop exit signal did not have an overlap as they understood it, I was told I was completely wrong because "every signal has an overlap"!

We can confuse and confound even more if you like ;)  You are of course absolutely right about the situation where a 'box has only one stop signal (and of course it then doesn't have Station Limits).  You can (definitely 'could') have a 'box where its outermost Home Signal was less than 440 yds from the outermost Home Signal of the next 'box in advance and you could also have a  situation where the Clearing Point was specially modified to take account of, say, a distance of less than 440yards between the Home Signal and SectionSignal (if other factors allowed).   So lots of meat on the bone beyond the basic situation - although I think and find that it is always best to get the basic principle in its simplest form over and understood well before going into the esoteria of such things as mentioned in the post above and this one.  In fact one good way of ensuring you have got the basic principle into someone's head is when they start asking questions about situations like these.

 

Your latter comment is of course absolutely spot on - indeed I wrote something very similar to it into a draft article only a week or so back.  I'm afraid that one of the biggest menaces to helping to get signalling properly and easily understood is those who barge in with half a story, an inaccurate story, or a load of utter nonsense.  I can understand the error Phil made in that sketch as he was starting from the land of colour lights which he is well used to but there are those about who either know little and spout rubbish or who think they know a lot but are ignorant, and alas the internet seems to have helped them to breed.

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Regarding distances between adjacent boxes, I believe that the Lancashire and Yorkshire Railway had slightly more signal boxes than it had route miles of track, and some sections must have been extremely short in consequence. As an example, Between Miles Platting station and Victoria East Junction - a distance of less than 1 1/2  miles - there were no less than FIVE boxes, including the East Junction.

 

I have to agree with ForestPines and Mike regarding 'a little' knowledge' etc., hence my caveat in Post 20. This particular thread, which started with humble beginnings, is starting to stretch my knowledge of signalling. Still, we live and learn!

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 I was told I was completely wrong because "every signal has an overlap"!

 

Even I know that statement is false under mechanical or MAS principles (Hence why I only emphasised the 'overlap' - that isn't an overlap in descriptive terms, but thats what it is functionally speaking - between the home signal and the clearing point on the diagram). The reason for extending the 'block section' beyond the actual home signal up to the clearing point comes from the principle that under normal conditions to allow a train into a block section, the bit between the home signal and the clearing point must be free of trains.

 

Your latter comment is of course absolutely spot on - indeed I wrote something very similar to it into a draft article only a week or so back.  I'm afraid that one of the biggest menaces to helping to get signalling properly and easily understood is those who barge in with half a story, an inaccurate story, or a load of utter nonsense.  I can understand the error Phil made in that sketch as he was starting from the land of colour lights which he is well used to but there are those about who either know little and spout rubbish or who think they know a lot but are ignorant, and alas the internet seems to have helped them to breed.

 

I hope you aren't including me in that last category ;)

 

But in all seriousness I accept I do tend to get things wrong once I step out of the modern MAS signalling or Single line working via Electric Key token with mechanical signalling - the two types of signalling I work with on a regular basis.

 

Oh yes and non SR stuff confuses me too sometimes.

Edited by phil-b259
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Earlier than that - much earlier! The opening of the Warrington and Newton Railway in 1831 and its junction with the L&MR at Newton Junction (Earlestown) soon showed that some system of regulation was needed. There were various methods, including the Policeman (hence 'bobby') standing at ease or attention, to an arrow pointing towards Warrington when the road was set in that direction. Trains were also required to carry targets or lamps at night, the colours and shapes showing the direction they were to take. Everything was on the time interval system, of course, and there were regulations as to how soon one train could follow another.

 

No, the L&MR initiated signalling, and passed its experiences to the Grand Junction Railway, before the two amalgamated.

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Wait a minute this is getting confusing now...

 

If we use only LNWR terms for signalling.

An Intermediate Block Home Signal (IBS) is just another signal on the line, it is the last signal the signal box controls before the block section? It is the signal that prevents movement into the Block Section?

 

And there can be but might not be a distant signal for that IBS and it will be sited within braking distance in rear from the IBS?

And its purpose is to reduce the length of the Absolute Block Section?

 

Basically, if you move the signals further away from the controlling box the block will be smaller and you can get more trains on the track?

 

Because once the train as cleared the starter, the last starter signal, and the bobby has seen the tail lamp he can offer the train forward (to the box in advance) and tell the signal box in rear that the train in clear of the Absolute Block in rear of his OUTER MOST Home signal, so he can accept another train, but he still has a train in section, and it is between the Starter and IBS ?

Edited by ElectroSoldier
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  • RMweb Gold

Wait a minute this is getting confusing now...

 

Answering your comments as raised

 

An IBS is not just another signal on the line - although in form it will be the same as a normal stop signal - different regulations apply to it but fundamentally it still controls (not prevents) movements into a block section.

There could be another IBS in advance of an IBS, several boxes on the WCML controlled multiple IBS, the last one would of course control access to the block section leading to the next box. An IBS terminates and starts a block section - it's akin to a signal box only having one stop signal (not unheard of).

 

All IBS homes have distants associated with them (unless someone knows different ?) - there needs to be a warning to the driver that the stop signal is at danger, and it needs to be braking distance away - the distant.

 

The purpose of an IBS is to break up what would otherwise be a long section - note that "long" frequently means "long time" rather than "long distance" - allowing more trains to be on a given stretch of line (I am avoiding permissive / reg 5 etc, working) but under the control of one box.

Moving them further away will actually means less trains can use a length of railway, occupancy is a function of time and distance, shorter distances between signals means more trains on a given stretch of line. - but there is always the compromise between equipment costs and traffic gains, more signalling means more trains can be dealt with, but at a higher capital and maintenance cost.

 

The signalman can give out of section when he has seen the tail lamp or had it confirmed to him that the train has arrived complete (e.g. by a guard off a freight train), he cannot accept another train unless his clearing point is available but this does NOT mean the train has to have passed the starter, at Hooton for example (a box I visited regularly) we had outer homes, inner homes and then a starter - once the train had passed the box tran out of section could be given to the box in rear, even if the train was to wait at the starter for acceptance, the clearing point was still available so another train could be accepted under normal regulations.

 

A block section runs from the last signal of one box to the first signal of another, when an IBS is provided the block section runs from the last signal in a block section (e.g the starter) to the IBS. If a second IBS is provided then another block sections runs from the first IBS to the second IBS - remember a block section is basically where only one train is normally permitted to be.

 

I hope I haven't confused you even more.

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  • RMweb Gold

No, thank you I understand it now :)

 

I was confused because I didnt realise an IBS marks the block section... for instance if there is an IBS then there are 2 absolute block sections, if there are 2 IBS then there are 3 blocks. Yes?

Not exactly.   If there is an Intermediate Block Section it is indeed another block section and it is also an absolute block section (i.e only one train allowed at a time) but it is worked under rather different Regulations from Absolute Block.  The principle is exactly the same but details are different especially in degraded working situations.

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"A block section runs from the last signal of one box to the first signal of another, when an IBS is provided the block section runs from the last signal in a block section (e.g the starter) to the IBS. If a second IBS is provided then another block sections runs from the first IBS to the second IBS - remember a block section is basically where only one train is normally permitted to be."

 

You are of course correct in your very concise reply above Dave but just to clarify, (and as the Station Master points out in post 19), the Intermediate Block Section runs from the last signal controlled by the box in rear, (the starter), to the Intermediate Block Home, (not the IBS as you typed - abbrieviations can confuse matters). Of course, an Intermediate Block Section can run, (as you quite correctly say), from one Intermediate Block Home to another Intermediate Block Home, thus providing two Intermediate Block Sections, (or more), ahead of the controlling, (or supervising), box.

 

The section of line ahead of an Intermediate Block Home to the first stop signal controlled by the box in advance is the Absolute Block Section.

 

HTH.

 

Sean.

Edited by the penguin of doom
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  • RMweb Gold

I'm definitely sending that invisible ink back because it seems I wrote Post No 19 in either invisible ink or the vacuum of deeper space (or maybe I confused things by using the correct terminology).

 

So whilst I'm about it I would simply point out that (in the most common form of IBS - i.e. in advance of the 'box which controls it - the last (i.e.most advanced) stop signal controlled by that 'box is actually the IBHome and not the Section Signal.  And in the case of IBSections it is a controlling and not a supervising 'box (we'll ignore the somewhat unusual arrangement which at one time existed on the Chiltern Line in LMR days) because the signals are worked by the Signalman (although some might auto replace to danger) and he is responsible for ensuring that the IB Section is clear before allowing a train to enter it by clearing his Section Signal.

 

PS For anyone who doesn't understand this I woiuld suggest they look at the Block Regulations - recent versions are quite considerably simplified (and are actually aimed at a relatively low reading age for reasons which are quite beyond my understanding as I would prefer such work not to be in the hands of those with a poor understanding of English) but the illustrations are also very helpful in trying to get one's head around the terminology and how things area arranged.  

This link is to a discontinued version but the important basics are there and it might save me having to write the same thing several times over in this thread -

 

http://www.rgsonline.co.uk/Rule_Book/Rule%20Book%20Modules/TS%20-%20Train%20Signalling/GERT8000-TS3%20Iss%203.pdf

Edited by The Stationmaster
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  • RMweb Gold

I didn't want anyone confusing IBS's with IBH'S etc later in the thread.....

.

There's information overload in this thread now and its confusing me!!

 

As an aside here used to be an IBH at baschurch, between gobowen and shrewsbury that was controlled by the signalbox in advance, (its now and automatic signal)

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  • RMweb Gold

I'd agree Jim and it was always one subject that flummoxed my students for some reason - that and locomotive running round it's train.....

 

I think everythings explained itself nicely now though.

 

Cheers.

 

Sean.

 

 

The current rulebook has this to say regarding the definition of an IBS "The line between the section signal and the intermediate block home signal worked by the same signal box in the same direction of travel." which unfortunately means we are both wrong to some extent, but I have heard an IBS to mean Intermediate Block Signal - maybe not nowadays.

 

Jim has kindly provided (another) example and I had already mentioned, rear section IBS were also available, although not common and I do note that the rule book says always assume the box in rear controls them - but we haven't narrowed down dates too much.

 

The terminology starter to IB is not right. Stationmaster has suggested (in '#19) that section signal is a better term and that's what I am used to and what the rule book uses - see above quote.

 

At the place in question - Huyton - the main line had a home 1, a home 2 with a bracket arm for the branch but on the main, that was it, the doll had the distant for Huyton Quarry IB below it, no starter was provided on the main. (The branch did have a starter (or starting as the LNWR liked to call them) but it didn't have an IB)

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Ah yes, I see what you're saying Dave.

 

Without access to any rule books, (I handed mine back when I moved on from the railways - and that was some years ago), I was basing my information on the block sections I had worked over here in Yorkshire, (all worked from the box in rear). All the "section" signals I worked were plated up as "starter". Another example of local trends still extant from times gone by.

 

Cheers.

 

Sean.

Edited by the penguin of doom
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  • RMweb Gold

Intermediate block sections in rear of the controlling signalbox appear to be (have been?) peculiar to the LMR and in many respects never seemed to make much sense to me - they really seem to have been a form of intermediate signalling but not wholly Track Circuit Block.

 

As a matter of interest the term 'Section Signal' is now quite old having first appeared - as far as I can trace in my amendments to the 1960 Regulations - 47 years ago, in the 1968 issue of the Tokenless Block Regulations, although the pre-existing Regulations appear not to have seen use of the term until the 1972 reissue of the Block Regulations.  But it was used, where relevant, throughout the whole of the 1972 Regulations and of course has been ever since and certainly figured in block exams from 1972 onwards.  It was no no doubt used to shorten the term 'signal controlling the entrance to the section ahead' which had been used previously in the Block Regulations.  I don't have all my original 1972 Rule Book pages but I'm fairly sure it would be in those as well as the normal course of revision, certainly when I was doing it in the 1980s, was to ensure consistencies of terminology between the Rule Book, Block Regulations, General Appendix, Sectional Appendices and such items as Signalbox Special Instructions  

 

It would not of course appear on lever leads etc as in the case of those the relevant name of the signal would be used and that could therefore be anything from the Home Signal, and every term in between to, finally (I think)  the 'Outer Advanced Starting Signal' although they were more of a Western thing than elsewhere I believe ;) .

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  • RMweb Gold

Thinking about the Banbury line, when there were crossover ground frames and/or IB sections at Fosse Road, Cropredy and Astrop the protecting signals on both lines were controlled from the same box. This rear section IBS on one line and an advance section IBS on the other. The line from the rear signal box Starter to the rear section IBS was track circuited. The reason for retaining Absolute Block was that although some sections were fully track circuited others were not, therefore introducing complications when certain boxes switched out. The operating gurus at Crewe declared that it was not acceptable to work different regulations over a section of line depending on which boxes were switched in.

Edited by TheSignalEngineer
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A block section runs from the last signal of one box to the first signal of another.

I just re-read your post again Dave. I'm sure the "First signal of another" you mention would in most cases, if not all, be a distant signal. It is important to remember that the definition of the first signal to which you are referring is usually the "Home" signal, be it outer or inner etc and would usually be the second signal a driver would come across having entered the block section would it not?

 

Cheers.

 

Sean.

Edited by the penguin of doom
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  • RMweb Gold

I just re-read your post again Dave. I'm sure the "First signal of another" you mention would in most cases, if not all, be a distant signal. It is important to remember that the definition of the first signal to which you are referring is usually the "Home" signal, be it outer or inner etc and would usually be the second signal a driver would come across having entered the block section would it not?

 

Cheers.

 

Sean.

 

I assume that most only want a simple explanation, at least at first, and not something which covers every variation / detail as otherwise I'd have to explain about combined home and distant signals and how a distant is not always the first signal of the next box when boxes are close together, and then we could get into slotted signals which are one boxes starting and another boxes home and even some boxes which had both of the above but ...

 

I try to avoid explaining every single permutation of things at the first ask as otherwise it just seems like I am trying to be clever and confuse the person asking the question.

We've had someone who did that in the past - 509 - , unfortunately not only did he try and cover all sorts of eventualities at the first ask, he frequently made mistakes which meant "The Signalling Mafia*" had to spend lots of time correcting the never-ending stream of mistakes he kept posting, those days are gone fortunately.

 

*TSM were me, Mick Nick, StationMaster and Flyingsignalman apparently - not our name, a name given to us by a.n.other.

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