Colour Light Signalling for Model Railways (Out Now)

[The Stationmaster]

On 06/11/2019 at 17:50, 2mm Andy said:

 

I wasn't aware that the HMRS had published a book on GWR signalling recently. Do you mean the Great Western Study Group book?

 

http://www.gwsg.org.uk/GWSG_Publications.html#

 

Andy

Sorry but yes - that's the one.

[dcordingley]

On 01/11/2019 at 13:01, ColinK said:

Collected the copy I had ordered from the independent Carnforth Bookshop.  From what I’ve read so far it is excellent - clear diagrams, good explainations and well written.  Thanks for producing it Simon, I hope it sells well.

 

PS while there they gave me some info on a new book about Lancaster, Morecambe and Heysham including the old electrics.

 

Do you have any further info on the book which includes material on the Lancaster-Morecambe-Heysham electrics? I ask because I'm currently building a 4mm scale model of one of the 1950s/60s 3-car sets; assembling good photos is a challenge, and as for drawings....

 

David

[charliepetty]

This will be on sale at the Manchester Show from DCKits & Models.

 

Charlie

[St. Simon]

Just now, charliepetty said:

This will be on sale at the Manchester Show from DCKits & Models.

 

Charlie

 

Thanks Charlie, it is much appreciated!

 

Simon

[ColinK]

On 07/11/2019 at 20:28, dcordingley said:

 

Do you have any further info on the book which includes material on the Lancaster-Morecambe-Heysham electrics? I ask because I'm currently building a 4mm scale model of one of the 1950s/60s 3-car sets; assembling good photos is a challenge, and as for drawings....

 

David

 

It is being launched at Carnforth bookshop tomorrow. I’m planning to pick up a copy.

[dcordingley]

10 hours ago, ColinK said:

 

It is being launched at Carnforth bookshop tomorrow. I’m planning to pick up a copy.

 

Many thanks Colin - I'll look out for it. 

 

David

[Not Jeremy]

On 07/11/2019 at 20:28, dcordingley said:

 

Do you have any further info on the book which includes material on the Lancaster-Morecambe-Heysham electrics? I ask because I'm currently building a 4mm scale model of one of the 1950s/60s 3-car sets; assembling good photos is a challenge, and as for drawings....

 

David

www.willowherbpublishing.co.uk

Edited November 9, 2019 by Not Jeremy

[dcordingley]

On 09/11/2019 at 10:27, Not Jeremy said:

www.willowherbpublishing.co.uk

 

Thanks - duly ordered. 

 

David 

[Mike Bellamy]

.

Phil Parker has reviewed this book on his daily blog.

 

See here 

 

http://philsworkbench.blogspot.com/2019/11/book-review-colour-light-signalling-for.html

 

.

[St. Simon]

Hi All,

 

I keep meaning to post this, but I keep forgetting!

 

To anyone who has brought the book (thank you once again if you have), if you wish to provide feedback to me on how it may be improved or if I have something wrong (which I'm sure there is!), I'll be happy to hear it!

 

I'll be helping to operate Dad's Loughborough Road layout at Warley this weekend if you want to come by and talk about the book or ask questions!

 

Simon

[The Stationmaster]

13 hours ago, St. Simon said:

Hi All,

 

I keep meaning to post this, but I keep forgetting!

 

To anyone who has brought the book (thank you once again if you have), if you wish to provide feedback to me on how it may be improved or if I have something wrong (which I'm sure there is!), I'll be happy to hear it!

 

I'll be helping to operate Dad's Loughborough Road layout at Warley this weekend if you want to come by and talk about the book or ask questions!

 

Simon

That sounds to me like an excuse to get out of operating  

 

I presume you have pointed out to the gentleman concerned the error which I pointed out previously?  Note for others - it was not Simon's error.  The WR style NX panel illustrated on page 156 contains a couple of very non WR errors - the signal numbering is incorrect for WR controlled signals and two of the exit buttons (those serving both running and shunt signal routes) are incorrectly coloured.  All based on kit long before Simon's time in signal engineering/before he was born so he couldn't have noticed them when selecting the illustrations.

[St. Simon]

1 hour ago, The Stationmaster said:

I presume you have pointed out to the gentleman concerned the error which I pointed out previously?  Note for others - it was not Simon's error.  The WR style NX panel illustrated on page 156 contains a couple of very non WR errors - the signal numbering is incorrect for WR controlled signals and two of the exit buttons (those serving both running and shunt signal routes) are incorrectly coloured.  All based on kit long before Simon's time in signal engineering/before he was born so he couldn't have noticed them when selecting the illustrations.

 

Hi Mike,

 

Yes, I had great pleasure in telling him that, and to be fair he was gracious in defeat!

 

Simon

[Jack374]

I was fortunate to find a copy of your book under the tree Simon (I had asked...), and it's a very comprehensive guide, which has clearly been written by a railway modeller. I particularly like the track diagrams and references to model products available. The pictures aid the desriptions and it has answered quite a few questions I had with regards to signalling.

 

Many thanks for taking the time to produce this highly useful guide!

 

Jack.

[St. Simon]

3 hours ago, Jack374 said:

I was fortunate to find a copy of your book under the tree Simon (I had asked...), and it's a very comprehensive guide, which has clearly been written by a railway modeller. I particularly like the track diagrams and references to model products available. The pictures aid the desriptions and it has answered quite a few questions I had with regards to signalling.

 

Many thanks for taking the time to produce this highly useful guide!

 

Jack.

Thank you Jack, glad you enjoyed it and found it useful!

 

If there is anything you still have questions on (or anything you think I missed / didn’t cover enough), you’re more than welcome to send me a message!

 

Simon

[Dungrange]

I also received a copy of your book for Christmas from my son (my seven year old daughter thought it was too boring a present for her to hand over when my wife showed her it), but I'm not as quick a reader as Jack.  My overall impression is that it seems to be fairly comprehensive (which is good) but in trying to cover everything, some areas of more interest are perhaps not covered in as much detail as I may have liked and a few more signalled junction examples (like Figure 126) would have been welcome.  Obviously it's always difficult trying to convey terminology heavy text in a form that a lay person can understand and I may need to read the book twice (or more) to fully understand it.

 

Just to check that I've understood what I've read so far, can you confirm that the A and B point numbers at the trailing crossings (301 and 305) are the right way round in the figure below?  I struggled a bit with the text that states "the 'A' end is where a train running in the Down direction (regardless of signalling arrangements) would travel over a point in the facing direction, that is at the end nearest low mileage."  How do you run over a trailing crossover in the facing direction?  It took me a while to realise that I think the "regardless of signalling arrangements" actually means by wrong direction running on the Up line in the example below.

 

Also, going by the principle that you should have as few signals as possible, would it be correct for the Junction Indicators on signal LP 101 to cover diverging routes at both points 303 (to the down loop) and 306 (to a branch) as long as the switch of point 306 is within 800 m of signal LP 101?  I had originally assumed that I'd need a junction indicator three aspect signal where I have the text 'Down Main', but now don't think that's necessary (and LP 101 would actually be off stage, which would simplify the number of main aspect signals required).

 

Finally, as I understand it, there would be no operational restrictions due to a Down train approaching signal LP 101 because the overlap is at the clearance point of trailing crossover 301.  However, in the opposite direction, before the signal in rear of LP 104 can be cleared to allow a train to run up to LP 104, I understand that crossover 305 would have to be locked in the normal position, which means that it would not be possible to drive a train from the Branch to the Up Main whilst also driving a train up to signal LP 104.  However, since I'm happy to forego that combination of moves, it would allow me to place LP 104 at the minimum distance from the clearance point of point 305B - ie 15 m.  If that's correct, then I'll have a think about the various position light signals that I will need and how workable the track plan below actually is.

[St. Simon]

On ‎30‎/‎12‎/‎2019 at 23:19, Dungrange said:

Just to check that I've understood what I've read so far, can you confirm that the A and B point numbers at the trailing crossings (301 and 305) are the right way round in the figure below?  I struggled a bit with the text that states "the 'A' end is where a train running in the Down direction (regardless of signalling arrangements) would travel over a point in the facing direction, that is at the end nearest low mileage."  How do you run over a trailing crossover in the facing direction?  It took me a while to realise that I think the "regardless of signalling arrangements" actually means by wrong direction running on the Up line in the example below.

 

Hi David,

 

Yes, the A and B ends are fine on your layout, my only comment would be that 303 & 304 points and 306 & 307 points might be crossovers as well, although this depends on the length between the two ends of the crossover.

 

On ‎30‎/‎12‎/‎2019 at 23:19, Dungrange said:

Also, going by the principle that you should have as few signals as possible, would it be correct for the Junction Indicators on signal LP 101 to cover diverging routes at both points 303 (to the down loop) and 306 (to a branch) as long as the switch of point 306 is within 800 m of signal LP 101?  I had originally assumed that I'd need a junction indicator three aspect signal where I have the text 'Down Main', but now don't think that's necessary (and LP 101 would actually be off stage, which would simplify the number of main aspect signals required).

 

Whilst there is nothing completely wrong with having a route from LP101 onto the Branch and one from LP101 to LP103, it is quite unusual. In your case, in real life you'd have to be careful of over braking between LP101 and the first signal on the branch and under-braking between LP101 and LP103. There might be some 'drivability' issues with it as the Branch signal would have two different signals acting as 'first caution'. I would only expect that scenario if the either there wasn't enough room between the CP for 305B and the CP for 303 or where the Down Main to Branch connection was much higher speed than the Down Main to Down Loop connection.

 

However, it is still a valid signalling arrangement, I would probably end up using the Position 1 JI for the Loop and Position 2 JI for the Branch Route. 

 

The 800m actual only applies between the signal and first facing point in any forward route from the signal, so in your case, the rule is that LP101 has to be within 800m of the toes of 303 points, but if you apply the rule between LP101 and 306 point toes, then it makes your signalling arrangement more valid (if that makes sense).

 

On ‎30‎/‎12‎/‎2019 at 23:19, Dungrange said:

Finally, as I understand it, there would be no operational restrictions due to a Down train approaching signal LP 101 because the overlap is at the clearance point of trailing crossover 301.  However, in the opposite direction, before the signal in rear of LP 104 can be cleared to allow a train to run up to LP 104, I understand that crossover 305 would have to be locked in the normal position, which means that it would not be possible to drive a train from the Branch to the Up Main whilst also driving a train up to signal LP 104.  However, since I'm happy to forego that combination of moves, it would allow me to place LP 104 at the minimum distance from the clearance point of point 305B - ie 15 m.  If that's correct, then I'll have a think about the various position light signals that I will need and how workable the track plan below actually is.

 

Yes, that it is correct. If allowing a train up to LP104 whilst a train departed the branch were required, but you didn't have enough room for a full overlap clear of 305 crossover, you would look at providing a Restricted Overlap (ROL) on LP104 and a Warning route upto to LP104. If you didn't have enough room for a ROL between LP104 and 305 crossover, you could just route a train from the Branch into the Down Loop and then onto the Up Main via 301 crossover.

 

I hope that all helps. I'll look at adding in more examples in a second edition, or possible a follow up supplement of worked examples.

 

Simon

Edited January 4, 2020 by St. Simon

[Dungrange]

Happy New Year Simon,

 

On 31/12/2019 at 14:02, St. Simon said:

I'll look at adding in more examples in a second edition, or possible a follow up supplement of worked examples.

 

A supplementary book of worked examples would be good, although as you say, it would be a million page book if you were to cover every conceivable arrangement.  However, I usually find a few good worked examples aid understanding.  I guess you just need to wait and see how well the first edition has sold before thinking about the future.

 

On 31/12/2019 at 14:02, St. Simon said:

Yes, the A and B ends are fine on your layout, my only comment would be that 303 & 304 points and 306 & 307 points might be crossovers as well, although this depends on the length between the two ends of the crossover.

 

Thanks, but that now gives me a follow on question.  Is there an operational or design benefit in operating pairs of points as a crossover (ie as 303A / 303B rather than 303 and 304)?  My rational for labelling 303 and 304 separately was that I'd only need to reverse points 304 to access the oil sidings, whereas I'd need to reverse points 303 for any train arriving in the Down Loop.  This would include loaded fuel for the oil siding, but would also include Down trains destined for the Yard on the Up side and some Down trains heading for the Branch.  Therefore to avoid unnecessarily throwing points, I'd assumed that these would not be a crossover (ie I assumed that keeping them separate would reduce wear in the point motor for 304 in real life).

 

However, having given this some thought, I think I can see a benefit in changing the natural lie of point 304 and making it 303B as this would allow it to perform a trap function to stop a rake of wagons in the loop rolling back onto the Down Main during a run-round operation.

 

On 31/12/2019 at 14:02, St. Simon said:

Yes, that it is correct. If allowing a train up to LP104 whilst a branch departing the branch were required, but you didn't have enough room for a full overlap clear of 305 crossover, you would look at providing a Restricted Overlap (ROL) on LP104 and a Warning route up to to LP104. If you didn't have enough room for a ROL between LP104 and 305 crossover, you could just route a train from the Branch into the Down Loop and then onto the Up Main via 301 crossover.

 

I assume that Railway Group Standards GK/RT0064 Provision of Overlaps and Trapping Protection (Railtrack PLC, 2000) (https://catalogues.rssb.co.uk/rgs/standards/GKRT0064 Iss 1.pdf) is the suitable further reading on this subject, which seems to distinguish between "Reduced Overlaps" and "Restricted Overlaps".  I assume that you are referring to Reduced Overlaps when you state in your book that "Under some circumstances this can be further reduced, to provide operational flexibility down to an absolute limit based on the approach speed of the signal" (page 91) - ie the figures in Table 2 of the above standard would apply, so if the line speed were reduced to say 50 mph, then the 180 m full Overlap can be reduced to 105 m subject to a Risk Assessment.

 

I'll give this some more thought as the left side of my track plan is a bit more fluid than the right.  I can see merit in simply removing crossover 305 and routing all branch trains along the line of the Down Loop to use crossovers 301 and 303 (ie fewer points).  It would also get rid of the differential braking issue that you highlighted.  The downside of that layout would of course be that Down trains heading for the Branch would have to wait on the Down Main if there was an Up train still on the Branch, whereas the layout I've shown would permit these to clear to Down Main whilst waiting for a Up train on the Branch.   Deciding on the best track layout and signal plan is not a straight forward task.

 

Anyway, thanks for writing the book.  I hope it sells well.

[ruggedpeak]

Simon

 

Bought the electronic version of your book, skimmed it so far but loads to read in due course. Great addition to the digital bookcase.

 

Looking to signal my micro layout, lots to think about.

 

All the best

 

Tony

[St. Simon]

On ‎01‎/‎01‎/‎2020 at 18:42, Dungrange said:

Thanks, but that now gives me a follow on question.  Is there an operational or design benefit in operating pairs of points as a crossover (ie as 303A / 303B rather than 303 and 304)?  My rational for labelling 303 and 304 separately was that I'd only need to reverse points 304 to access the oil sidings, whereas I'd need to reverse points 303 for any train arriving in the Down Loop.  This would include loaded fuel for the oil siding, but would also include Down trains destined for the Yard on the Up side and some Down trains heading for the Branch.  Therefore to avoid unnecessarily throwing points, I'd assumed that these would not be a crossover (ie I assumed that keeping them separate would reduce wear in the point motor for 304 in real life).

 

However, having given this some thought, I think I can see a benefit in changing the natural lie of point 304 and making it 303B as this would allow it to perform a trap function to stop a rake of wagons in the loop rolling back onto the Down Main during a run-round operation.

 

Hi David,

 

Having read your reasoning, it is sound, but your point in the second paragraph would be why I would expect them to be a cross-over. Also, by making them a cross-over pair it provides flank protection of trains both on the Down Main and Down Loop as they would be motored together, where as if they were two single numbers, then there is potential for one set to be reverse and one to be set normal.

 

On ‎01‎/‎01‎/‎2020 at 18:42, Dungrange said:

I assume that Railway Group Standards GK/RT0064 Provision of Overlaps and Trapping Protection (Railtrack PLC, 2000) (https://catalogues.rssb.co.uk/rgs/standards/GKRT0064 Iss 1.pdf) is the suitable further reading on this subject, which seems to distinguish between "Reduced Overlaps" and "Restricted Overlaps".  I assume that you are referring to Reduced Overlaps when you state in your book that "Under some circumstances this can be further reduced, to provide operational flexibility down to an absolute limit based on the approach speed of the signal" (page 91) - ie the figures in Table 2 of the above standard would apply, so if the line speed were reduced to say 50 mph, then the 180 m full Overlap can be reduced to 105 m subject to a Risk Assessment.

 

It is, although the industry has now gone through a principles review of overlaps which has changed things some what. You are correct in that it is reduced overlaps I'm referring to and your reading of the standard is correct, the only thing on that to add is that the minimum length of a Restricted Overlap is 45m.

 

I didn't want to go into the different overlaps you can have (Full, Reduced, Phantom, Restricted, Restricted Phantom, Shunt, Shunt Phantom and Block Acceptance. EDIT: I forgot about Preferred, Non-Preferred, Forward Route Set / Non Called!), as these really only apply to how the interlocking is done and the actual operation of the railway, which I thought a lot of people won't be too excited about!

 

The difference between a reduced overlap and a restricted overlap is only very slight and can be confusing. A Restricted overlap is effectively a second overlap (as well as the full overlap) provided for a signal for operational reasons and it requires a Warner Route to be provided on the previous signal. If the normal overlap for a signal is reduced to below 180m to get around IRJ constraints, then it is called a Reduced Overlap. That's a very simplistic differential between the two, but without taking you all on an AST course, it will do!

 

On ‎01‎/‎01‎/‎2020 at 18:42, Dungrange said:

I'll give this some more thought as the left side of my track plan is a bit more fluid than the right.  I can see merit in simply removing crossover 305 and routing all branch trains along the line of the Down Loop to use crossovers 301 and 303 (ie fewer points).  It would also get rid of the differential braking issue that you highlighted.  The downside of that layout would of course be that Down trains heading for the Branch would have to wait on the Down Main if there was an Up train still on the Branch, whereas the layout I've shown would permit these to clear to Down Main whilst waiting for a Up train on the Branch.   Deciding on the best track layout and signal plan is not a straight forward task.

 

You're now getting into the mind of a signalling designer, but luckily you have less people to please than I do most of the time!

 

Simon 

Edited January 4, 2020 by St. Simon

[St. Simon]

1 hour ago, ruggedpeak said:

Simon

 

Bought the electronic version of your book, skimmed it so far but loads to read in due course. Great addition to the digital bookcase.

 

Looking to signal my micro layout, lots to think about.

 

All the best

 

Tony

 

Hi Tony,

 

Thank you, I hope you find it useful and if you have any questions please ask!

 

Simon

[airvisual]

Just what I was looking for, well done that man !! 

[St. Simon]

On ‎23‎/‎01‎/‎2020 at 19:33, airvisual said:

Just what I was looking for, well done that man !! 

 

Hi,

 

Thank you, I'm glad you've found it useful!

 

Simon

[Dungrange]

Simon,

 

Another question from me, although I'm not sure whether or not it's a design question.    On pages 92-93, you "suggest train length as a minimum length between signals" on a model, but then state that "Of course, it may be difficult if you model the jumbo stone trains of the Western or the Drax Biomass trains, which sometimes are longer than some signalling sections in real life."

 

This prompts the question of who is responsible for 'managing' the potentially adverse impacts of running 'long' trains: drivers, signallers or someone else - ie the signal designer?  I don't intend running either jumbo stone trains or Biomass trains, but I do want to run some reasonably long freight trains by model standards.

 

In the diagram below, I plan to run trains in the Up direction (left to right) from the branch (bottom left), which will be longer than the distance between signal LP104 and the Clearance Point of point 305A on the Up Main.  This therefore means that if the branch signal LP110 was pulled off and showed a yellow aspect (indicating that LP104 shows a red aspect), a 'long' train proceeding to cross the Down Main would end up blocking the Down Main when it has to stop at LP104 (because crossover 305 will remain locked).  Therefore for operational reasons, it would seem to make sense to hold a 'long' train at signal LP110 until the Up Main is clear as far as the end of the Overlap for Signal LP102.

 

 

Would such a scenario be handled by the driver (through the combination of his route knowledge and knowledge of the train he was hauling) waiting for LP110 to display a green aspect before proceeding to cross the Down Main (ie the driver ignores the yellow aspect - possibly phoning the signalman), or would the signaller 'know' that particular train was 'over-length' and therefore keep LP110 at red until the Up Main is clear to the end of the Overlap for Signal LP102 (ie manually overriding the ability of Signal LP110 to display a yellow aspect), or would the signal designer, presumably through the use of Track Circuits to determine whether a train exceeds a certain length, design 'something' that would automatically only permit Signal LP110 to display a cautionary aspect if a train is less than x metres long (ie if a Track Circuit x metres in rear of the signal is occupied then the signal is unable to display a cautionary aspect). 

 

My guess is that if long trains are anticipated, then the signal designer will design the system to accommodate them and their consequences during the design process, but if trains of a particular length weren't envisaged when the signalling system was installed, then I'm not sure.

[guzzler17]

11 hours ago, Dungrange said:

In the diagram below, I plan to run trains in the Up direction (left to right) from the branch (bottom left), which will be longer than the distance between signal LP104 and the Clearance Point of point 305A on the Up Main.  This therefore means that if the branch signal LP110 was pulled off and showed a yellow aspect (indicating that LP104 shows a red aspect), a 'long' train proceeding to cross the Down Main would end up blocking the Down Main when it has to stop at LP104 (because crossover 305 will remain locked).  Therefore for operational reasons, it would seem to make sense to hold a 'long' train at signal LP110 until the Up Main is clear as far as the end of the Overlap for Signal LP102.

 

 

 

 

Alternatively would it, in your world, be possible to hold the long freight at LP106 therefore completely clear of the down main?  When a suitable gap appears the freight would cross via 304 and 301 and be on its way.  If the next down service was headed for the branch it could be held at LP101 rather than at LP103 which might foul the 304 points.

 

However for what you're suggesting, hold at LP110, there is an example in real life and that's the exit from Angerstein Wharf.  After several derailments being caused by a departing train sitting part on and off the main line the working practice was altered so that the train only proceeded off the branch on a green signal.  I got this from an RAIB report after the second derailment.

[St. Simon]

18 hours ago, Dungrange said:

Simon,

 

Another question from me, although I'm not sure whether or not it's a design question.    On pages 92-93, you "suggest train length as a minimum length between signals" on a model, but then state that "Of course, it may be difficult if you model the jumbo stone trains of the Western or the Drax Biomass trains, which sometimes are longer than some signalling sections in real life."

 

This prompts the question of who is responsible for 'managing' the potentially adverse impacts of running 'long' trains: drivers, signallers or someone else - ie the signal designer?  I don't intend running either jumbo stone trains or Biomass trains, but I do want to run some reasonably long freight trains by model standards.

 

In the diagram below, I plan to run trains in the Up direction (left to right) from the branch (bottom left), which will be longer than the distance between signal LP104 and the Clearance Point of point 305A on the Up Main.  This therefore means that if the branch signal LP110 was pulled off and showed a yellow aspect (indicating that LP104 shows a red aspect), a 'long' train proceeding to cross the Down Main would end up blocking the Down Main when it has to stop at LP104 (because crossover 305 will remain locked).  Therefore for operational reasons, it would seem to make sense to hold a 'long' train at signal LP110 until the Up Main is clear as far as the end of the Overlap for Signal LP102.

 

 

Would such a scenario be handled by the driver (through the combination of his route knowledge and knowledge of the train he was hauling) waiting for LP110 to display a green aspect before proceeding to cross the Down Main (ie the driver ignores the yellow aspect - possibly phoning the signalman), or would the signaller 'know' that particular train was 'over-length' and therefore keep LP110 at red until the Up Main is clear to the end of the Overlap for Signal LP102 (ie manually overriding the ability of Signal LP110 to display a yellow aspect), or would the signal designer, presumably through the use of Track Circuits to determine whether a train exceeds a certain length, design 'something' that would automatically only permit Signal LP110 to display a cautionary aspect if a train is less than x metres long (ie if a Track Circuit x metres in rear of the signal is occupied then the signal is unable to display a cautionary aspect). 

 

My guess is that if long trains are anticipated, then the signal designer will design the system to accommodate them and their consequences during the design process, but if trains of a particular length weren't envisaged when the signalling system was installed, then I'm not sure.

 

Hi,

 

We never expect the driver to manage a situation like that, they don't have enough information to make that decision efficiently.

 

Most of the time, it would be managed by providing a suitable path that meant LP104 would be 'OFF' when the long train needed to come off the branch, this could either be done by the timetabling people when creating the path or by the signaller 'manually' holding it on the branch until a suitable opportunity. Of course, you might say that in those cases, you would send it along the Down Loop instead, assuming that LP105 to LP106 is the correct distance.

 

However, if it was every signal train was to be 'over-length', then we might looking at doing something in the design. The first thing we do is do the initial design to the longest regular train we can, and then if anything was longer then we tend to leave it to the operations department to sort. If the Ops came back and said it was operational imperative that you can't let a long train off the branch until LP104 is off, you could look at adding a interlocking controls.

 

The first would be a form of ‘tunnel’ or ‘closing up’ controls within the route level of the interlocking. To help explain, I’ve add some track circuits onto your diagram:

 

 

These controls are controls that allow a train that would block a junction up to a signal showing red only when we are pretty sure that the signal will clear up to a proceed aspect quickly (preferably before the train gets to it). So in the case above, we would prove that the section from LP104 to LP102 is clear of a train or that LP102 is OFF (which means the a train between LP104 and LP102 won’t stop and will keep going). So, we add an additional control to the route level that says:

 

LP110 A(M) route also requires [(‘A’ Clear & ‘B’ Clear & ‘C’ Clear) OR (LP102 OFF)]

 

However, this would prevent you sending a short train out to LP104 to wait until that clears so you can clear the branch a bit quicker. For this you could add Lime Street Controls, this involves providing two track circuits on approach to LP110:

 

 

As in the diagram above, it ‘E’ track circuit would be the same length as ‘D’, where as ‘F’ track can be any length you want. This now means that if ‘E’ track was occupied and ‘F’ was clear, the signalling system knows that the train will definitely fit between LP104 and 305A point toes. So the route control would be:

 

LP110 A(M) also route also requires [(LP104 ‘OFF’) OR (‘E’ Occupied & ‘F’ Clear)].

 

Now, if you are following it, the LP104 OFF condition could be satisfied by the tunnel controls. So, the whole statement would be:

 

LP110 A(M) route also requires [(‘A’ Clear & ‘B’ Clear & ‘C’ Clear) OR (LP102 OFF) OR (‘E’ Occupied & ‘F’ Clear)]

 

Some would argue that the above should be an aspect level control rather than a route level control, but I think route level is better as it prevents you setting the route and locking by the junction which then is never used as the signal won’t pull off.

 

I hope that makes sense.

 

As you can probably tell, these sorts of interlocking controls add great complexity and, in the case of the Lime Street Controls, problems when short trains might stop back too far and occupy ‘F’ track. So, we tend to control an over length train through procedure and other means.

 

Simon

Edited January 31, 2020 by St. Simon