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Simple Signalling/Section Question - Single Track Line


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Hi all,

 

A simple question: if a double line track's station limits are defined by Home to Most Advanced Starter on the Up line, and the same on the Down line, and these two arrangements overlap but not entirely so, how are the station limits on a single track line defined?

 

Is it from Home to Home either side of the station (being single line I gather there isn't a 'proper' application of the terms 'in rear' and 'in advance')?

 

I can't think it would make sense to be from Home to Most Advanced Starter in the Up direction, and from Home to Most Advanced Starter in the Down direction, as this would give the possibility of 'incursions' to the block sections if the Most Advanced Starter is further out than the Home on that side of the station, and vice versa.

 

TIA

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Station limits is the area under the sole control of one signal box - the extent of line where you don't need to ask somebody else's permission to occupy the line.  Except of course that because of the existence of overlaps,, you may have to Block Back Inside, as you could be fouling the overlap.

 

The term doesn't seem to be used on single lines, where the rules are necessarily a bit different.  In the absence of outer homes, you wouldn't be able to give train out of section when you had a train in both platforms if the line had to be clear for 1/4 mile from the home  - the overlap would not exist, and of course you can't get tokens for the trains for the crossing trains to depart until you have cleared out for their arrival.  So the rules for acceptance and for giving Train out of Section are worded to allow for the possible situations.  And you don't have Blocking Back Inside.  If you want to occupy the single line for shunting purposes you need to exchange Blocking Back signals - you can't do that if there is a train approaching on the single line.

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I think the books I have and websites I've looked at that explain signalling are falling short on describing single track lines and their variations from double track lines. I may need some help in that regard.

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It's a very interesting question and of course the standard definition of Station Limits applies at a signal box on a single line just as much as it does at a signal box on a double line.  But what you need to understand is that Station Limits is not a signalling term per se and on a single line the Station Limits in opposite directions overlap each other (which of course they do at a double line signal box although there they are usually different for each running line).  

 

The thing to remember about Station Limits is that they are really there to separate in operational terms that portion of railway from a block section.  Hence you are allowed to do various things in Station Limits which are not permitted in a block section (e.g. propelling vehicles or moving in the wrong direction is permitted in Station Limits but is prohibited through a block section). As far as signalling concerned all the Signalman needs to be aware of is the sort of operating practices which are permitted in Station Limits - that apart it has nothing at all to do with signalling trains or the Signalling Regulations (where the critical things are the block section and certain signals).

 

It then becomes relatively simple to understand, that the Block Section between crossing station A and crossing station B runs from the most advanced stop signal at A to the rearmost stop signal at B (B is of course in advance of A and A is in rear of B for trains and movements from A to B).  Thinking the opposite way round for the same piece of railway the block section from B to A runs from B's most advanced stop signal to A's rearmost stop signal and for trains and movements in this direction A is in advance of B and B is in rear of A). So to know whicvh way is in advance and which way is in rear on asingle line it depends on the. direction in which a train is being signalled and is moving.

 

Outer Home/Acceptance Home Signals were fairly uncommon on single lines as were Advanced Starting Signals although particular situations, especially at junctions etc, could lead to a requirement for such signals.   Also because of the lack of such additional signals the overlap between Station Limits in opposite directions tended not to be very great anyway.  The very nature of  single line crossing places etc meant that the Regulations for acceptance of trains had to be very different from double lines (and additionally at termini also varied somewhat between the Grouped railway companies) so the normal 440 yard Clearing Point in advance of the outermost Home Signal didn't apply (except when an Outer Home Signal was provided for acceptance purposes).  

 

Shunting into the section/onto the single line was also rather different from the situation on double lines.  Shunting into the forward/advanced section was a procedure that, for those Companies which had used it, a fairly early disappearance while Blocking Back was different in that it applied to 'occupying the single line for shunting purposes outside (i.e. in the rear of) the Home Signal'.     There could be no Blocking back inside the Home Signal because of the way the single Line token Regulations worked in respect of acceptance.  The interesting thing about a block back was that it applied effectively to the signal which protected the single to double line connection and not to an outermost  Home Signal - in other words the Block Back was, as the Regulation was headed, for a movement onto the single line and not for one outside the outermost Home Signal. (unless the signal Box Special Instructions allowed an exception).

 

 

 

 

 

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Thanks for the replies, I will need to reread them several times as I do find worded explanations of signalling (on any type of line) difficult to understand without illustrations. Obviously there are significant differences in terminology usage for single track line operation, and I'll need to get my head round them.

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OK, I have this idea in my mind (in the absence of a clean and clear explanation of single track line working):

 

When a train is moving from box to box, via the block sections, then the signalman in any given box has to accept from the box 'in rear' and request from the box 'in advance' the movement of the train. The station limits are then Home (in rear) and Starter (in advance).

 

However, when coordinating movements 'within station limits' that don't impinge into the block sections either 'in rear' or 'in advance', the for all intents and purposes the 'station limits' are Home (in rear) to Home (in advance), as it is the Home either side of the box that in effect indicates the boundary across which a train would be 'in section' and therefore at risk of colliding with another train from either in rear or in advance. If movement across that boundary is required, then the signalman would have to request control of that block section in order that no trains can be sent in from the box at the other end of that section.

 

Does that make sense? I have no idea if it matches the actuality of practice or regulation.

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No, the Home Signal is not the section boundary.  Rather that serves to protect the facing point where the loop starts (and any siding points).  The train is considered clear of the section (and Train out of Section can be given) once the train is inside the loop, clear of the "fouling point" of the entrance to the loop - in other word sufficiently far past the loop points that another train going the other way could depart without striking the rear of the train.  So that fouling point can be considered to be section/station limits boundary.

 

The single line section begins (and the station limits therefore end) at the starting signal which is positioned such that protects the single line - it is at the end of the loop but in rear of the convergence of the two loops. 

 

So the section is defined by the single line (including the loop points) rather than by the position of signals.

 

The regulations cover four different situations depending on the geography of the station 

A train is considered out of section at a terminus once it has passed the Home SIgnal. 

At a non-crossing place or a junction it is out of section when it is 1/4 mile past the the Home SIgnal, or the junction points have been set the other way behind it and that route is clear.

 

 

 

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47 minutes ago, Michael Hodgson said:

No, the Home Signal is not the section boundary.  Rather that serves to protect the facing point where the loop starts (and any siding points).  The train is considered clear of the section (and Train out of Section can be given) once the train is inside the loop, clear of the "fouling point" of the entrance to the loop - in other word sufficiently far past the loop points that another train going the other way could depart without striking the rear of the train.  So that fouling point can be considered to be section/station limits boundary.

 

The single line section begins (and the station limits therefore end) at the starting signal which is positioned such that protects the single line - it is at the end of the loop but in rear of the convergence of the two loops. 

 

So the section is defined by the single line (including the loop points) rather than by the position of signals.

 

An interesting discussion, given that - by coincidence - I am in the process of trying to clarify exactly this sort of situation for a proposed heritage railway installation and there are a lot of conflicting views! The situation becomes even more muddled when you add in an Advanced Starting signal and then an Outer Home which is the 'clearing point' distance in advance of that AS.

 

I would agree that, for a train approaching a passing-loop, then TOS should not be given until the whole train has passed clear into the loop , as that is what was specified in Block Regulation 6(a)(i). However I would argue that the actual 'end of section' for arriving trains was the Home signal, especially in locations where the Home was sufficiently far in rear of the facing points for a light engine to be able to shunt from one loop to the other without going outside of the Home. I don't see any problem in having a distinction between the nominal 'end of section' and the actual spot that a train has to pass before you can give TES. 

 

But others may disagree...:-)

 

Consider also.... Reg 6(a)(ii) said that at a terminal station the TOS may be given as soon as the train has passed beyond the Home signal. But what is the difference between a passing-loop, where the arriving train must pass "clear onto the loop line" (which seems to be interpreted above as meaning beyond the fouling point of the adjacent loop, presumably so that a train in the other loop can then depart safely), and a terminal station with two roads, where a train which has passed  "beyond the Home signal" may still be fouling the adjacent road when TOS is given?

 

PS: ought not this thread to be in the PW, Signalling & Infrastucture forum?

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So, in a single track line, crossing station scenario, where are the limits for movements within the 'station', and how and what does the signalman have to communicate to the in rear and in advance boxes if the movements are going to go onto the actual block sections? It might be worth using the example of a locomotive using the loop to run round a train of some kind, as going by @Michael Hodgson's description above, the loco would have to cross into both the in rear and in advance sections in order to do so.

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2 hours ago, RailWest said:

An interesting discussion, given that - by coincidence - I am in the process of trying to clarify exactly this sort of situation for a proposed heritage railway installation and there are a lot of conflicting views! The situation becomes even more muddled when you add in an Advanced Starting signal and then an Outer Home which is the 'clearing point' distance in advance of that AS.

 

I would agree that, for a train approaching a passing-loop, then TOS should not be given until the whole train has passed clear into the loop , as that is what was specified in Block Regulation 6(a)(i). However I would argue that the actual 'end of section' for arriving trains was the Home signal, especially in locations where the Home was sufficiently far in rear of the facing points for a light engine to be able to shunt from one loop to the other without going outside of the Home. I don't see any problem in having a distinction between the nominal 'end of section' and the actual spot that a train has to pass before you can give TES. 

 

But others may disagree...:-)

 

Consider also.... Reg 6(a)(ii) said that at a terminal station the TOS may be given as soon as the train has passed beyond the Home signal. But what is the difference between a passing-loop, where the arriving train must pass "clear onto the loop line" (which seems to be interpreted above as meaning beyond the fouling point of the adjacent loop, presumably so that a train in the other loop can then depart safely), and a terminal station with two roads, where a train which has passed  "beyond the Home signal" may still be fouling the adjacent road when TOS is given?

 

PS: ought not this thread to be in the PW, Signalling & Infrastucture forum?

I think I might be able to guess which railway in view of the arrangement of signals which exists at its (truncated extent) terminus.  I would be quite happy to draft an Instruction to deal with that situation should you wish as it wouldn't be the first Regulation ofrSignal Box Special Instruction I have produced over quite a few years.  And yes - we are really in the wrong area of the forum

 

Now let's please get it right and ditch some confusion - for an arriving train at a single line crossing station the end of the block section is the Home Signal because that is where the single line ends and the loop starts (forget for now signal nomenclature applied to Home Signals using the GWR method of naming).   I suspect that the mention of a Home Signal at a terminal station might originally have been done to keep things roughly  in line with the situation at a crossing loop in that in both instances the train has to pass beyond the Home Signal.  But however it was arrived at it goes back a more than a century in the Regulations so whoever decided it will be long gone.  But whatever the logic of it we saw no reason to alter when I was a member of the working party which reviewed the Block Regulations in the mid 1980s so you could possibly blame me, and those who were also on the working party plus the BR Signalling Officers who approved our review, for the fact that we saw no reason to alter it ;)

 

So the single line actually runs from Home Signal (at Box A) to Home Signal at Box B although those two signals apply to trains running in opposite directions.  And of course, as the Regulations have stated for a very long time, at a crossing station or terminus 'Train Out Of Section' can be sent after an arriving has passed beyond that signal (at a terminus) or beyond that signal and is in clear on the loop at a crossing station.  The Starting Signal at the advance end of the loop would mark the end of Station Limits if it was the only stop signal at the loop exit or in advance of it but it will also be the signal which protects the entrance to the single line section.  The role of the Home Signal as marking the end of the single line section is of course confirmed by the Blocking Back arrangement for occupying the single line for shunting purposes etc which clearly states that it is for a movement onto the single line outside the Home Signal.  There is no regulations - and hasn't been for many years, dealing with occupying the single lin advance of the loop starting signal.  It doesn't matter which line the movement  comes from - the key factor is that it will require to go outside the Home Signal.  So clearly it again reinforces the fact that the Home Signal, and only the Home Signal, marks the end of the single line section.

 

But just keep Station Limits out of any debate about block signalling on any line,  double or single, because the term has no direct relevance to the Signalling regulations.  As I explained previously. it is an operational term which permits certain things to be done which are not allowed  through a block section.

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10 minutes ago, Ian J. said:

So, in a single track line, crossing station scenario, where are the limits for movements within the 'station', and how and what does the signalman have to communicate to the in rear and in advance boxes if the movements are going to go onto the actual block sections? It might be worth using the example of a locomotive using the loop to run round a train of some kind, as going by @Michael Hodgson's description above, the loco would have to cross into both the in rear and in advance sections in order to do so.

Dead simple.  If it is necessary to occupy the singe line outside the Home Signal for shunting purposes the equivalent of the double line Blocking Back procedure is used.   So, provided that no train is approaching in that section, Box A would send the bell signal 3-3 to Box B and provided it is acknowledged he would authorise the movement either by clearing a signal or verbally instructing the Driver.  While he is doing that the Signalman at Box B can do exactly same and send the 3-3 to Box A and when it is acknowledged he can also occupy his end of the single line section for shunting purposes.

 

In the past (and possibly there might still be some around today although I think not) special Shunting tokens were sometimes used with different bell signals to achieve the same thing.   Additionally if Box A has a train in the single line section proceeding towards Box B he can make a shunting etc movement into that section without any need to contact Box B.  However if the shunting etc is still going on when he receives Train Out Of section from Box B he must immediately send the 3-3 bell signal and get it acknowledged by Box B.

 

If a loco is running round the same procedure would be applied to each of the sections on either side of Box A.  So the Signalman would first send 3-3 to Box B (the one in advance of the arrival the loco has detached from) and when that has been acknowledged he would authorise the loco to pass the Starting Signal at danger and enter that single line section.  Once it was clear of the points he would change the points and clear the Home Signal to allow the loco to proceed toward the other end of that crossing and once it was in clear on the loop he would send Train Out of Section to Box B. Before authorising the loco to leave the other end of the loop he would send 3-3 to Box X and when it has been acknowledged he would authorise the Driver to pass that Starting Signal at danger and proceed onto the single line clear of the Home signal  and connection towards the loop where the train is standing.  Once clear of the points and they had been changed the loco would be handsignalled (in many cases the Home Signal could legitimately be cleared for the next movement) back onto its train and once it was in clear on the loop the Signalman would send Train Out Of Section to Box X.  Dead  easy and something that went on almost every day at those single line crossing stations where trains reversed while shunting onto the single line using the 3-3 happened at numerous places back in the days when freight trains served almost every station.

 

At a couple of the 'boxes on my patch in the 1970s it was still being done several days a week in order to shunt various sidings.  Putting a shunt in behind a train which has recently departed was probably a lot less common although back in the 1970s I did it one day with a 10 coach loco hauled passenger train and had it propelled back onto the single line not long after a DMU had departed.  Only problem was the Driver's knowledge of Rules & Regs for single lines was somewhat lacking  when it came to the finer detail and in order to get him to move I had to go and get a copy of the General Appendix and read the relevant part out to him.

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Thanks for the replies @The Stationmaster, very enlightening, even though I'm still struggling to get my head round it.

 

My thoughts regarding them are that I'm right in one respect, that the block section is Home (in advance) to Home (in rear), but wrong (and I expect this is where confusion can come in regarding the block sections) with respect to when the line is considered clear (that relies on the train being in a loop or siding out of the way of other traffic).

 

With regards to the terms 'station limits' and 'signalling', when operating a model railway, and for that matter probably the real one too, the signalling and stations limits surely are thought of together?

 

With respect to running round, if the movement can be done entirely inside the Home (in rear) and Home (in advance), would the signalman have to notify either of the boxes either side?

 

To the point of where this thread should sit, I put it here as I thought the Permanent Way, Signalling and Infrastructure section was for modelling Skills and Knowledge, rather than purely for Prototype.

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1 hour ago, Ian J. said:

My thoughts regarding them are that I'm right in one respect, that the block section is Home (in advance) to Home (in rear), but wrong (and I expect this is where confusion can come in regarding the block sections) with respect to when the line is considered clear (that relies on the train being in a loop or siding out of the way of other traffic).

Be a little wary of things like "when the line is considered clear". As I am sure you know, there are different rules for accepting line clear (at passing loops, the line must be clear to the starter) and for giving out of section (at passing loops, the train must be clear into the loop).  It is very common to give out of section and not be in a position to accept a following train.

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4 hours ago, Ian J. said:

Thanks for the replies @The Stationmaster, very enlightening, even though I'm still struggling to get my head round it.

 

My thoughts regarding them are that I'm right in one respect, that the block section is Home (in advance) to Home (in rear), but wrong (and I expect this is where confusion can come in regarding the block sections) with respect to when the line is considered clear (that relies on the train being in a loop or siding out of the way of other traffic).

 

With regards to the terms 'station limits' and 'signalling', when operating a model railway, and for that matter probably the real one too, the signalling and stations limits surely are thought of together?

 

With respect to running round, if the movement can be done entirely inside the Home (in rear) and Home (in advance), would the signalman have to notify either of the boxes either side?

 

To the point of where this thread should sit, I put it here as I thought the Permanent Way, Signalling and Infrastructure section was for modelling Skills and Knowledge, rather than purely for Prototype.

Let's try a bit further - the single line section is between the two opposing Home Signals, i.e the Home Signal at each end of the single line.  The Block section runs from the most advanced stop signal at the 'box in rear to the outermost Home Signal at the 'box in advance.  There is therefore a slight contradiction in terms once we get away from the simple situation of a Home Signal and Starting Signal at a crossing station (the conundrum faced by Railwest I suspect) but it can be resolved for any particular location by suitable  items in the Signalbox Special instructions which can be used to modify or alter the application of the Block Regulations.

 

As far as 'the line being considered clear' Jeremy C has made the critical point - the conditions for accepting at train on a single line are different from those ona double line as are those for giving 'Train Out of Section'.  These differences have been mentioned in various posts above but I can re-list them if you are not clear on how they work.

 

Station Limits are decided by the position of the outermost Home Signal and the most Advanced Starting Signal.  I suppose that it is feasible - but rather unusual in my experience (except in the preservation world) - for those signals to be sited solely to ensure that Station Limits extends over a particular area.  Running signals are normally sited to suit the most efficient through traffic running rather than anything else and the Regulations provided, in various ways, for shunting into a block section while in some circumstances things which were normally not permitted in a block section could be authorised through the Sectional Appendix or by a special Notice.  For example I know of several locations, including one on a single line, where propelling of vehicles was permitted through part of a block section.

 

As far as the running round movement is concerned if it can be done entirely within the Home Signal and without going onto the single line then there is  no need for the procedure I explained.  However I do wonder if there was anywhere where that would have been possible on a single line section other than at a terminus.  

 

Unfortunately in recent years the way preserved/heritage railways have been signalled has tended to confuse things somewhat.  They are far busier in movement terms, including things like shunting and running round, that the original single railways most of them are on.   Thus in some places they have adopted the idea of providing crossing stations, and even more so their termini, with things like Outer Home Signals and Advanced Starting Signals to the extent that the original BR single line Signalling Regulations are no longer wholly suitable for dealing with shunting onto the single line.

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Thanks again.

 

I think I need to be more careful in my use of terminology. 'Train Out of Section' and 'Line Clear' are obviously different things now I think about it. Also, I need to be more careful in my use of Home and Starter.

 

As this is all to help me in my track, signalling and operation of my S&P heritage idea's various 'vignettes', I think I may need to be careful in how I apply 'normal' single line operation. However I'd like to stick as close as possible to normal if I can.

 

@The Stationmaster Is there a reason why Advanced Starters weren't generally used on single track lines to reduce the need for section occupancy when doing shunting manoeuvres? In thinking through what's written above, I wonder if it's something I need to consider for a heritage context, where as you said more running round occurs, so without an Advanced Starter the locos would keep having to occupy the Advance section when going past the Starter at the platform with the loop.

 

At some point I will try and get some simple diagrams done so that it's easier to see how my thinking is in error.

 

Another factor in heritage operation, and probably happened in conventional operation as well, is how trains that are too long for a loop are handled when stopped at such a station? They can't be Train Out of Section, so effectively block the section in rear, and possibly in advance as well?

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>>>Is there a reason why Advanced Starters weren't generally used on single track lines to reduce the need for section occupancy when doing shunting manoeuvres? In thinking through what's written above, I wonder if it's something I need to consider for a heritage context, where as you said more running round occurs, so without an Advanced Starter the locos would keep having to occupy the Advance section when going past the Starter at the platform with the loop......

 

Even with an Advanced Starting signal, you are still outside of the Home signal and therefore occupying the single-line section unless there is an Outer Home which is further out than the AS. Certainly quite a few early L&SWR passing-loops had Advanced Starting signals, many of which were abolished in later years.

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6 hours ago, Ian J. said:

'Train Out of Section' and 'Line Clear' are obviously different things now I think about it.

Personally, I don't think there is anything obvious about it at all, and perhaps this apparent discrepancy is one reason why the regulator seems to have been asking more for outer homes and advanced starters. The Signalman knows far more about this than I do, but as far as I am aware, this discrepancy between Regulation 4 (Line Clear) and Regulation 6 (Train Out of Section) does/did not exist with double lines (I only have a copy of the 1960 Signalling Regulations and have no idea what the current rules are). I can imagine a modern day legally-minded regulator not liking it. Quite honestly I can imagine a modern day heritage railway signaller not liking it either, but Regulation 6 is a wonderful piece of pragmatism.

 

6 hours ago, Ian J. said:

Is there a reason why Advanced Starters weren't generally used on single track lines to reduce the need for section occupancy when doing shunting manoeuvres?

Cost. The only things the usual signalling arrangements prevented you from doing was shunting in front of an approaching train, and following one train with another in the same direction when the first train is still in the loop. Neither of these are common things to want to do at an ordinary passing loop. Most movements can be arranged when the sections either side are empty, or behind a departing train.

 

6 hours ago, Ian J. said:

Another factor in heritage operation, and probably happened in conventional operation as well, is how trains that are too long for a loop are handled when stopped at such a station? They can't be Train Out of Section, so effectively block the section in rear, and possibly in advance as well?

 

Yes, this is entirely possible, and it makes precious little difference if it isn't crossing anything. The signalman will already have obtained line clear from the box in advance, so that side of things is no problem, and although they might have to wait a little bit longer before they give out of section, they could not accept another train from the box in rear till the first train had left even in ordinary circumstances.

 

If trains are crossing, then the rules insist that the "short" train is clear in the loop before the "long" train moves past the starter, and that the "long" train is clear of the fouling point at the other end before the "short" train is allowed to depart, but since these are physical requirements in any case (at least, they are if the starter is close to the fouling point), it seems that the rules are perfectly suited to the purpose.

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  >>> Ian J. said: 'Train Out of Section' and 'Line Clear' are obviously different things now I think about it.

 

35 minutes ago, Jeremy C said:

 

Personally, I don't think there is anything obvious about it at all, and perhaps this apparent discrepancy is one reason why the regulator seems to have been asking more for outer homes and advanced starters. The Signalman knows far more about this than I do, but as far as I am aware, this discrepancy between Regulation 4 (Line Clear) and Regulation 6 (Train Out of Section) does/did not exist with double lines .....

I'm confused here!

 

IMHO 'Line Clear' and 'Train Out of Section' are obviously very different things in signalman's terms.

 

Reg 4 governs when you can give 'Line Clear' to the box in rear to accept a train, Reg 6 deals with when you can give 'Train Out of Section' to the box in rear for that train. I don't understand what is meant by there being any discrepancy between the two Regs, given that - by their nature - they are dealing with two different situations anyway. Some elements of their criteria may bary, but so what?

 

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15 minutes ago, RailWest said:

Reg 4 governs when you can give 'Line Clear' to the box in rear to accept a train, Reg 6 deals with when you can give 'Train Out of Section' to the box in rear for that train. I don't understand what is meant by there being any discrepancy between the two Regs, given that - by their nature - they are dealing with two different situations anyway. Some elements of their criteria may bary, but so what?

On double lines, both Regulation 4 and Regulation 6 make reference to the (same) clearing point, so that in ordinary circumstances, you can send out of section and immediately accept a following train. On single lines, trains do not need to have reached the "clearing point" in order to send out of section, and in general you cannot send out of section and then immediately accept a following train; something else has to happen first.

 

Of course, Regulation 6 has been written to allow trains to cross. The signalman needs to be able give out of section with the train still in the loop to be able to ask is line clear for the crossing train.

 

However, with outer home signals, rules could be written around clearing points in the same way they are for double line signalling, so that out of section could be immediately followed by accepting a following train.

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OK, here's a thing: I've looked up a few signalling diagrams for single track line stations with passing loops, and it appears (though I can't be 100% sure) that quite a few have the Home signals close up to the point at the beginning of the loop.

 

In my mind I've had the impression that there was a decent distance between the Home and the loop point, enough to hold a train or more (say ten carriages or so). I wonder if I'm being confused by heritage practice, and simply don't know enough about 'normal' examples.

 

To quote an example, look up the signalling diagram for Shillingstone (http://www.trainweb.org/railwest/images/sb-diag/shilling-65.jpg) and the 1:10,560 map with Shillingstone on NLS (https://maps.nls.uk/geo/explore/#zoom=16&lat=50.90626&lon=-2.25334&layers=193&b=1)

 

It shows the signal posts for the Homes pretty much at the points. This knowledge significantly affects how I'm interpreting answers, and explains why I was struggling to understand why occupying the block sections while shunting or running round has been such a common theme. I was thinking that most signalling would have been positioned with enough space to do shunting moves without such occupations of the block sections as a norm, but apparently not.

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Here’s a view of Marchwoods Home signal from the Starting signals. 

Marchwood Signalbox 21/3/2001

 

As Mike noted the Station limits purely tells the Signalman where he can allow certain types of movement not how it is signalled. Every type of train is signalled in the same way in theory but certain types of move, such as propelling, have obvious safety implications because the driver doesn’t have as clear a view as normal so there are restriction on how far they can go. Shunting involves propelling usually. 


The Signal would only be placed to danger once the train is clear of the points in the photo, as it is part of the interlocking to stop you changing the points under the train. As the signal is still off you cannot give Train Out of Section until the Signal is at danger to protect the train ahead. Once you have given TOS and put the instrument to normal then either box can ask for Is Line Clear ready for the next move to be agreed. It then has to be repeated back and the instrument placed to Line clear to accept it. 

Edited by PaulRhB
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>>>I've looked up a few signalling diagrams for single track line stations with passing loops, and it appears (though I can't be 100% sure) that quite a few have the Home signals close up to the point at the beginning of the loop.....

 

I would suggest that was the normal practice, for one simple reason. Once a train has started to pass a Home signal which has been 'off', you do not want the signalman to be able mistakenly to replace that signal, unlock the the facing point ahead, and then move the point under the train. The necessary 'route holding' used to be provided by the 'lock bar' for the FPL, which would extend from the point back to the Home, but clearly not the length of a 10-coach train! 

 

Where the Home is some considerable distance back from the facing point, then usually there would either be a track-circuit between the Home and the point that would lock the FPL and point levers and/or a 'running shunt'  at the point itself (the latter can be seen at the Minehead end points of the loop at Blue  Anchor, although it's a WSR adaption of it original use).

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On 23/08/2021 at 20:45, RailWest said:

An interesting discussion, given that - by coincidence - I am in the process of trying to clarify exactly this sort of situation for a proposed heritage railway installation and there are a lot of conflicting views! The situation becomes even more muddled when you add in an Advanced Starting signal and then an Outer Home which is the 'clearing point' distance in advance of that AS.

 

I would agree that, for a train approaching a passing-loop, then TOS should not be given until the whole train has passed clear into the loop , as that is what was specified in Block Regulation 6(a)(i). However I would argue that the actual 'end of section' for arriving trains was the Home signal, especially in locations where the Home was sufficiently far in rear of the facing points for a light engine to be able to shunt from one loop to the other without going outside of the Home. I don't see any problem in having a distinction between the nominal 'end of section' and the actual spot that a train has to pass before you can give TES. 

 

But others may disagree...:-)

 

Consider also.... Reg 6(a)(ii) said that at a terminal station the TOS may be given as soon as the train has passed beyond the Home signal. But what is the difference between a passing-loop, where the arriving train must pass "clear onto the loop line" (which seems to be interpreted above as meaning beyond the fouling point of the adjacent loop, presumably so that a train in the other loop can then depart safely), and a terminal station with two roads, where a train which has passed  "beyond the Home signal" may still be fouling the adjacent road when TOS is given?

 

PS: ought not this thread to be in the PW, Signalling & Infrastucture forum?

In practice, at most stations you wouldn't be able to give TOS until the train was clear into the loop anyway, as most boxes are either on, or at the end of, the platforms, so the rear of the train will be in clear by the time you can see the tail lamp...

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1 hour ago, Ian J. said:

@RailWest Useful info, thanks. I suppose then that's where the Outer Home would come in, as that wouldn't need to be interlocked to the occupancy detector on the point...?

I think what you need to do is ignore the near total irrelevance of Outer Home Signal and Advanced Starting Signals at single line crossing stations.  They certainly seem to have introduced confusion into your mind (and I suspect some confusion in the minds of those who have provided them on various heritage railways many of which are in any case massively over-signalled).    

 

The important thing on traditionally signalled single lines which have fixed signals (i.e. signals fixed at a site) is that a stop signal is needed to protect a point and at a single line crossing station that means there will be a stop signal at the toe end of the loop points (as illustrated in the photo posted by Paul RhB). There will then be a track circuit (or in old days a locking bad) locking the Facing Point Lock for that point in order to prevent the point moving under a train passing over it.  That is also why at a facing point the stop signal applying to that point must not be returned to danger until the entire train has passed clear of the point.

 

Logically at a single line crossing station, or at a terminus, that signal which protects the facing point will also be the Home Signal.  It has to be close to the point to ensure that the locking bar is held 'locked' without giving time for the point to be moved after a train passes the signal.  The distance can in theory be longer if a track circuit is used (as has been the case for the best part of the past 40 years or so) but there's little sense in doing that.   Equally logically that signal would also be the Home Signal - and  a Home Signal is needed to make the Regulations meaningful so if there is one there for safety reasons connected with the point the one signal can carry out both functions.

 

It's probably useful now to look at what an additional Home signal provided for acceptance purposes (i.e. an Outer Home Signal) would actually achieve on a single line and i can see no benefit at all except approaching a junction where it would allow a train to be accepted if another train on a conflicting route have been accepted towards, or was approaching the junction. It would have some, arguable, value at a terminus because since 1960 the various single line Block Regulations have required the line to be clear to the buffer stops in order to accept a train and give 'Line Clear' for it to enter the section.  However assuming the line is not clear to the buffer stops an obvious question would be what happens when the approaching train arrives at the Home Signal?  Only possible answer is that it would then have to be admitted to the already occupied line for which suitable provision would have to be made - but that is the only advantage it would offer.  Ona busy railway which is shotrt of siding space to store vehicles so has to leave some on the platform line that would confer a possible 'handy feature' - but that is all. 

 

If you wanted to make a shunt onto the single line and still be in a position to accept a train then some rather special provisions would have to be made and in my view you would need to provide two additional Home Signals plus an Advanced Starting Signal and write the necessary Regulation to permit what you have in mind.  In my view it wouldn't satisfy a properly conducted risk assessment because it wouldn't make the potential risk as low as reasonably practicable unless all those additional stop signals had some sort of mechanism to prevent a movement passing them at danger.  

 

The methodology for shunting onto a single line has - I'm fairly sure, been changed anyway because it now has little utility on the national network and the heritage railways have in any case got to take account of various very different human factors.  However if they are still using (as some to my knowledge were not very many years back) BR era Block Regulations there is no logical reason at all to provided an Outer Home Signal on a single line with the possible exception of a terminus - but it wouldn't make any difference to the traditional procedure for occupying the single line for shunting purposes because it confers no additional protection at  all.   The only possible advantage of adding an Advanced Starting  Signal if the railway concerned is using the BR era Regulations is that it would serve as a reminder to a Driver etc making a shunt move not to go off into the section - but that is the only advantage it confers.  And in any case under ROGS a heritage etc railway has no legal obligation to provide such additional provided it has taken the necessary action and has the necessary data and paperwork from a Competent Person to support what it is providing.  Hence, for example, what I recommended, as a  Competent Person, to such a railway in terms of provision at a proposed new single line crossing loop is fully supported by all the necessary paperwork and covered by professional indemnity insurance.

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