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What is the colour light signaling equivalent of a "Shunt Ahead" signal?


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Thanks for everyone's input on this.

 

If I understand all the comments correctly, the bottom line is that modelling a colour light scheme there is no need for the "Shunt Ahead" signal. All that is required are the normal ground signals for operating the crossover.

 

This is good from my point of view as it makes the colour light version of the starter a simpler beast to make without the complications of a ground type signal on the same pole!

 

Best regards

Paul

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On 23/10/2020 at 12:54, DY444 said:

 

I can't say how widespread it was across the WR but there were certainly some routes on Bristol PSB which could be cleared as either main or sub. 

There were numerous places on the WR where routes could be cleared as main or sub route BUT the critical thing then is what sort of sub route?  And off hand I can't think of many where a sub route meant the same route setting conditions as the main route.  Although there were many which were nothing other than the equivalent of  what amounted to a calling on sub because it came with an indication of route (using a stencil indicator in conjunction with the sub if it was over a main route where there was no indication of route with the main aspect (if that makes sense?). 

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1 hour ago, The Stationmaster said:

There were numerous places on the WR where routrs could be cleared as main or sub route BUT the critical thing then is what sort of sub route?  and off hand I can't think of any where a sub route going teh same way as the main route was anything other than the equivalent of e what amounted to a calling on bev cause it came with an indication of route (using a stemcil indicator in conjunction with the sub if it was over a main route where there was no indication of route with the main aspect (if that makes sense?). 

 

Not sure if it makes sense or not.  Either way consider the east end of Temple Meads.  There were routes from some of the platform signals to the east gantry which could be cleared as either main or sub.  Take B45 at the east end of P7 for example.  It had routes to B57 and B59 on the east gantry.  According to the route tables the main routes cleared with RIs of "UF" and "DF" respectively whilst the sub routes did not display a RI at all.  I presume this was because there was an implicit assumption that the sub route on B45 would only be called for a movement that was intended to reverse behind the Dn direction GPLs B566 or B560 and not proceed right up to the east gantry.

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3 minutes ago, DY444 said:

 

Not sure if it makes sense or not.  Either way consider the east end of Temple Meads.  There were routes from some of the platform signals to the east gantry which could be cleared as either main or sub.  Take B45 at the east end of P7 for example.  It had routes to B57 and B59 on the east gantry.  According to the route tables the main routes cleared with RIs of "UF" and "DF" respectively whilst the sub routes did not display a RI at all.  I presume this was because there was an implicit assumption that the sub route on B45 would only be called for a movement that was intended to reverse behind the Dn direction GPLs B566 or B560 and not proceed right up to the east gantry.

Hope the rest of you can follow this, he has lost me!!

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18 minutes ago, DY444 said:

 

Not sure if it makes sense or not.  Either way consider the east end of Temple Meads.  There were routes from some of the platform signals to the east gantry which could be cleared as either main or sub.  Take B45 at the east end of P7 for example.  It had routes to B57 and B59 on the east gantry.  According to the route tables the main routes cleared with RIs of "UF" and "DF" respectively whilst the sub routes did not display a RI at all.  I presume this was because there was an implicit assumption that the sub route on B45 would only be called for a movement that was intended to reverse behind the Dn direction GPLs B566 or B560 and not proceed right up to the east gantry.

 

That seems a strange and complicated way of signalling trains (but then it is the Western Region !). If the route is clear to the next main aspect, why not just clear the main aspect; The Driver of a reversing move will know where to stop ? 

 

Regarding position light signals (PLS), many years ago a train approaching Glasgow Central (then an extremely complex layout, slightly less complex today) passed a main aspect at danger but rather than stop, continued into the platform passing several PLS at danger too. When asked why afterwards, the Driver said that after passing the first signal at danger he thought it best to continue and get clear in the platform ! Fortunately, IIRC, no points were run through as a result. 

 

 

 

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14 minutes ago, Tallpaul69 said:

Hope the rest of you can follow this, he has lost me!!

Don't worry about it because we are now in very different territory from the question you asked and the answer needed. - which you've already got to in your previous post.

 

What the post  below talks about is a subsidiary position light at a colour light signal reading to an intermediate ground position light (GPL) signal in advance of it because of other pointwork which allows a shorter shunt route instead of the main signal route.  Very different circumstances from the question you asked where the signal you have is protectinga trailing point and simply carries on over plain line beyond the trailing crossover joining the line it is protecting

 

25 minutes ago, DY444 said:

 

Not sure if it makes sense or not.  Either way consider the east end of Temple Meads.  There were routes from some of the platform signals to the east gantry which could be cleared as either main or sub.  Take B45 at the east end of P7 for example.  It had routes to B57 and B59 on the east gantry.  According to the route tables the main routes cleared with RIs of "UF" and "DF" respectively whilst the sub routes did not display a RI at all.  I presume this was because there was an implicit assumption that the sub route on B45 would only be called for a movement that was intended to reverse behind the Dn direction GPLs B566 or B560 and not proceed right up to the east gantry.

So we're actually talking about rather different circumstances from the original question  because we aren't looking at signals reading into a stretch of plain line beyond the point they are protecting but are reading to a variety of routes.   And we are looking at a different reason for the subs.  

 

Thus the subs on all the east end platform starting signals read to the east gantry but in every case there was a GPL part way to the gantry at which they could reverse to come back on another line.  So we are not looking at non route indicated subs leading onto plain line but in all cases to lines where there are opportunities to reverse before reaching the east gantry (am nd probably not l needing a clear overlap track circuit beyond the gantry.  This made them all directly compatible with the GPLs reading from thehtwo middle spurs and the loco depot inwards and outwards lines.  But what we are talking about is a major station with a considerable amount of loco changing taking place and a need to move engines around smartly with minimum impact on other moves.  

 

Thus the sub on B57 with no indication of route ran only to GPL 569 which allowed a short shunt - especially a loco - to pass the gantry and then get itself in rear of B26 to go back to wherever it needed to go.  

 

 

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20 minutes ago, caradoc said:

 

That seems a strange and complicated way of signalling trains (but then it is the Western Region !). If the route is clear to the next main aspect, why not just clear the main aspect; The Driver of a reversing move will know where to stop ? 

 

Regarding position light signals (PLS), many years ago a train approaching Glasgow Central (then an extremely complex layout, slightly less complex today) passed a main aspect at danger but rather than stop, continued into the platform passing several PLS at danger too. When asked why afterwards, the Driver said that after passing the first signal at danger he thought it best to continue and get clear in the platform ! Fortunately, IIRC, no points were run through as a result. 

 

 

 

Bristol was I think somewhat exceptional in this respect although I suspect similar moves might have been possible in places at Paddington.  But as I said we are looking at a large station with - back in those days - lots of engine movements which needed to be done pretty sharply at busy times and kept to the shortest possible distance.  An  interesting feature of the MAS scheme arrangements at Bristol was that they precisely replicated what had been available in the 1930s resignalling - when engine changes and short distance shunts had been far more prevalent than they were even when MAS arrived in 1970.

 

If a main aspect had to be cleared at the platform end that would need a clear overlap track circuit at the next running signal in advance and that would no doubt conflict with other potential movements whereas using the sub wouldn't need the overlap (or certainly would need all of it so possibly a reduced overlap might have been used instead of no overlap at all.  

 

Comparison with Glasgow Central is interesting because it might high light differences in Regional practice although I noticed there in 2003 (and have just checked my photos to confirm) that below some of the platform 'starting signals' there were subs which didn't have an associated route indicator while others definitely did have stencil indicators.

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59 minutes ago, The Stationmaster said:

Comparison with Glasgow Central is interesting because it might high light differences in Regional practice although I noticed there in 2003 (and have just checked my photos to confirm) that below some of the platform 'starting signals' there were subs which didn't have an associated route indicator while others definitely did have stencil indicators.

Wasn't the practice at the time to illuminate the main route indicator (if one was applicable) for a subsidiary route that went to, or towards, the same exit signal?  The sub could also be offset to the left or right if its only route diverged in that direction, although I'm not sure if that would be done for complex signals in a major station.  

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19 hours ago, Tallpaul69 said:

Hope the rest of you can follow this, he has lost me!!

 

Sorry!  I guess many of us have a rivet counting tendency on one particular aspect of railways or another.  Mine happens to be the minutiae of BR era power signalling schemes.  :o

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On 24/10/2020 at 14:41, Edwin_m said:

Wasn't the practice at the time to illuminate the main route indicator (if one was applicable) for a subsidiary route that went to, or towards, the same exit signal?  The sub could also be offset to the left or right if its only route diverged in that direction, although I'm not sure if that would be done for complex signals in a major station.  

 

Yes except where it wasn't! 

 

The Bristol PSB and Derby PSB schemes were designed at roughly the same time and commissioned within a few months of each other.  For some routes at Bristol, as in the example I gave, the route indicator was lit for the main route but not the sub route to the same signal.  As far as I can see this appeared to be the case for sub routes where the exit of the route was thought to be irrelevant as movements were intended to stop short of that exit and reverse back.  By contrast, for routes with the same characteristics at Derby the main route indicator was always lit. 

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1 hour ago, DY444 said:

 

Yes except where it wasn't! 

 

The Bristol PSB and Derby PSB schemes were designed at roughly the same time and commissioned within a few months of each other.  For some routes at Bristol, as in the example I gave, the route indicator was lit for the main route but not the sub route to the same signal.  As far as I can see this appeared to be case for sub routes where the exit of the route was thought to be irrelevant as movements were intended to stop short of that exit and reverse back.  By contrast, for routes with the same characteristics at Derby the main route indicator was always lit. 

Where the routes "stopped short", would either Bristol or Derby have provided a preset/running shunt signal to mark the limit of the subsidiary route?  

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38 minutes ago, Edwin_m said:

Where the routes "stopped short", would either Bristol or Derby have provided a preset/running shunt signal to mark the limit of the subsidiary route?  

Certainly not the case at Bristol however there is what could be interpreted as an exception on B57 (Up direction on the east gantry) where the sub route without an indication ran to GPL 569 which was also in two of the running routes from B57.  Again the purpose here was solely to get a sgunt movement (a relatively short one so probably no much more than a loco past the gantry so that it could set back from a gantry signal or possibly past a GPL in rear of B57 should it be too long to be accommodated in rear of that signal.  Again thsi more or replicated a provision that had ne been made in the 1930s resignalling although the track layout had been considerably rationalised.

 

The DA (Draw Ahead subsidiary) on B57 had two routes - one, without indication of route, to GPL 569 and the other, with indication of route by the letter 'K' on a stencil indicator, to Kingsland Road sidings.

 

WR practice in respect of route indication for Draw Ahead subsidiaries was relatively consistent -

1. An indication of route in conjunction with a theatre route indicator or JI was only given if the route was into a line which might be occupied or was occupied by another train or if the route was for a running movement but did not lead to a signal capable of showing a red main aspect.  Effectively it meant the route was subsidiary to what would otherwise be a main aspect route except if it read to a GPL on a goods or reception line.

2. If the main aspect was displayed without an indication of route and a Draw Ahead route was provided for passenger trains a separate stencil indicator would be provided to clear with the DA.

 

Both of these situations meant that if a DA illuminated for a passenger line with an indication of route it could be passed, with appropriate caution etc, by a passenger train.  If it illuminated without an indication of route it could not be passed by a passenger train, i.e. it was purely a shunt route.

 

3. In all other situations route indications were not provided on the WR for DA subsidiaries (and they weren't provided at all for GPLs or elevated PLs although the latter was slightly relaxed in 1978 when it was decided that where traffic conditions demanded a route indicator could be provided for a PL reading from a yard or sidings if it would be used to signal a departing train movement; thus one was provided for the Down yard at Westbury - that was the first example on the Region).

 

One of the drawbacks under No.1 was that if a signal read into a goods line etc and the next signal was a STOP board or GPL the route would be signalled by the DA with an indication of route - by either a JI or theatre route indicator (e.g. entering the Up Goods Line at Scours Lane at Reading) which in turn meant an approaching train would be virtually brought to a stand (or to a stand) before the signal cleared.  This greatly increased the amount of time a train would take to clear passenger running lines hence when the connections into Southall yard were altered, with higher speeds, at the time of the Heathrow scheme I specified that all the routes into the yard had to lead to red main aspects (including providing fixed reds on lines which were simply intended to receive trains and not loop them).   The idea was that with more trains on the Mains to serve LHR any freight going into the yard would clear the Mains more quickly without being brought right down in speed.

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28 minutes ago, Tallpaul69 said:

So getting back to the original strand of this thread.......

Can any one point me in the direction of a good photo of a starter semaphore with a "shunt ahead" or "calling on" arm?

Many thanks

Paul 

Have a look at my photos on pages 2, 3, & 4 of this thread -

 

https://www.rmweb.co.uk/community/index.php?/topic/48504-gwr-signals-and-where-they-go/page/2/

 

Between them they show the standard GWR pattern Shunt Ahead arm (albeit in preservation and incorrectly used!!); the old pattern GWR Calling On arm with the letters CO on it;  The new (standard style of subsidiary arm used initially only on Calling On subsidiaries by the GWR  but then for Shunt Ahead and Warning purposes  - from some date in the 1930s.  

 

As far as I can ascertain there was no fixed subsidiary arm signal used for Warning purposes on the GWR until the red/white/red style arm was introduced (and even then they were quite rare until BR days).  GWR pattern Shunt Ahead sub arms could still be found well into the 1960s in some cases even on main line routes but they were never used on signals with tubular steel posts so theoretically began to disappear from the late 1930s onwards.

 

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On 25/10/2020 at 07:25, DY444 said:

 

Sorry!  I guess many of us have a rivet counting tendency on one particular aspect of railways or another.  Mine happens to be the minutiae of BR era power signalling schemes.  :o

Please may I join your club?  Actually, I think I’m already in it!

Paul.

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On 24/10/2020 at 12:46, caradoc said:

That seems a strange and complicated way of signalling trains (but then it is the Western Region !). If the route is clear to the next main aspect, why not just clear the main aspect; The Driver of a reversing move will know where to stop ? 

To give some ‘other region’ practice, ScR and LMR installations regularly has a shun aspect to the same destination as the main signal, even onto just plain line where there were no overlap considerations to worry about.  (Specifically Edinburgh PSB late 70s, Queen St mid 60s.). The theory was that it told the driver to expect to shunt back after their move.  (Others took the view that if the driver didn’t understand the move to be made then something more fundamental was wrong.).  At that time though, shunt routes did not prove track circuits clear so could (technically at least) be used to signal out behind a departing train before it had cleared the section.  I don’t know if this was a factor in the design application.

From early 80s (e.g. Westbury and Exeter), shunt signals generally prove tracks clear too so there is no benefit to having both types of route to the same destination and current practice is main route only.

Paul.

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On 23/10/2020 at 12:00, The Stationmaster said:

The Regulation allowed a shunt into the forward section if the block indicator was at 'Train on Line' but other Regulations effectively prevented two movements  to take place simultaneously in the same direction in an Absolute Block section.  So the block being at ToL  could be because the Clearing Point at the next 'box in advance was fouled for some reason (which might be a train which had arrived and was within the protection of signals or a Block Back had been put on).   There was nothing in the Regulations, except in very short section, to prevent a shunt being made into the advance section if there was a Block Back already in operation in the section (and vice versa).  So in that respect it was broadly equivalent to the single line Block Regulations which allowed shunts to be made simultaneously into both  ends of a single line section.

Thanks Mike.  I had wondered if a Shunt Ahead arm would be locked by the block (my gut feeling was ‘No’) but this answers it definitively.

Paul.

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I was surprised after a gap of nearly 2 months to see some postings on this thread!

I think my query in the original posting has been answered and the discussion has wandered into a number of quite specific (and some non WR) side issues.

 

So the time has come I think to wind this thread down. Thanks to all the contributers.

Stay safe everyone, and lets hope we have the chance to get back to exhibitions, club meetings and other face to face formats before too much of 2021 has disappeared

Best regards

Paul 

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21 hours ago, 5BarVT said:

To give some ‘other region’ practice, ScR and LMR installations regularly has a shun aspect to the same destination as the main signal, even onto just plain line where there were no overlap considerations to worry about.  (Specifically Edinburgh PSB late 70s, Queen St mid 60s.). The theory was that it told the driver to expect to shunt back after their move.  (Others took the view that if the driver didn’t understand the move to be made then something more fundamental was wrong.).  At that time though, shunt routes did not prove track circuits clear so could (technically at least) be used to signal out behind a departing train before it had cleared the section.  I don’t know if this was a factor in the design application.

From early 80s (e.g. Westbury and Exeter), shunt signals generally prove tracks clear too so there is no benefit to having both types of route to the same destination and current practice is main route only.

Paul.

Your final sentence has reminded me of a somewhat unusual conversation I had in the early 1990s.  When I planned the track layout for the Bristol Bulk Haling Terminal (BBHT) I also wrote a full signalling spec for the S&T Scheme Development folk at Reading and went though it signal by signal with John Wagstaffe.  John was an excellent bloke to work with on schemes because he understood operating and he also understood some of my views on signalling (he knew, for example I was firmly in favour of fixed reds to allow use of main aspect routes wherever possible going into yards etc).

 

Anyway part way through developing the scheme the Regions vanished and I became part of TLF and TLFs Rules people were the former ER folk at York who had some rather odd ideas.  In this particular area it took a lot of effort to convince them that all the subs I had specified at BBHT were needed - how else would you get engines onto trains?

And what were the fixed reds for?

 

Somewhat differently they got rather upset when on an Inspection Special we were approaching Claydon LNE Jcn from the Oxford direction and we went past a retroreflective distant board before coming to a colour light 'Home Signal'.  Instant cries of you can't use a board like that for a colour light signal so I pointed out that it was not unusual practice on the WR and I could show them a passenger line where exactly the same arrangement applied - why bother spending extra money when all you needed was the equivalent of a fixed yellow with relatively low lines speeds?

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7 hours ago, Edwin_m said:

Possibly a rhetorical question:

 

If you can have a yellow distant board instead of a colour light distant, why can't you have a red stop board instead of a fixed red?  


Hi,

 

No reason really, Stopboards have more ‘functionality’ than Fixed Reds, in that they can be used to provide more detail instructions to the driver (if required) than a fixed red.

 

I can only assume the reason for a fixed red over a Stop board (as I can’t remember any official guidance on one way or the other when it’s a 50:50 choice) is that the additional instructions aren’t necessary or to be consistent with other signalling in the areas make it more ‘driveable’

 

Simon

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On 21/12/2020 at 12:28, Edwin_m said:

Possibly a rhetorical question:

 

If you can have a yellow distant board instead of a colour light distant, why can't you have a red stop board instead of a fixed red?  

I suspect the simple reason is that a STOP board can't be proved in the control circuitry so you can't have a main aspect reading to it. (apart from any overlap considerations).  Thus the only aspect which can read to it is a sub and the controls will mean that does not clear until very late during the approach of a train towards it.  That in turn reduces the junction speed of the approaching train so by havinga fixed red you clear the running lines more quickly.

 

Thatw as why I specified them at Southall when the layout was considerably simplified and resignalling was carried out at the time of HEX electrification the idea being - in particular - to minimise the delay to freights crossing into the yard and Avoiding Lines from the Relief Lines because of the increased line occupation on the Mains once HEX started running.

 

I'd seen the time cost impact of running in towards a STOP board all too starkly when I ran a trial train checking the various run round options for the imported coal from BBHT to Didcot.  The other 'wizard wheeze' I adopted for that scheme was rather different and that was to have the Up Relief Line between Foxhall Junction and Ddcot West End turned into a two way Goods Loop where the coal trains could run round before entering and after leaving the power station.  They could have run round on the Up Relief witha few monor signalling alterations but that would still have left in place a restrictive overlap situation at Didcot West end so I broke that hurdle and restriction on teh speedy handling of the coal trains by having trap points installed on what became the Good s Loop.

 

Fortunately the loop that was created at Didcot fitted the overall train length that I was building into the trainplan but that train length also meant the terminal at the other end not only fitted the available site but also meant there was no need for trains loading at the terminal to foul St Andrews level crossing when trains were loading.  My back of a sheet of scrap paper fitted the site at Avonmouth with c.60 feet to spare.  Which also meant i don't need to recalculate the train lengths I had already used to meet the contract tonnage and rate of loading specs.

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6 minutes ago, The Stationmaster said:

I suspect the simple reason is that a STOP board can't be proved in the control circuitry so you can't have a main aspect reading to it.

But then you can't prove a yellow distant board either.

 

Actually either type of board could be proved if you really wanted to. ie you could install wiring to the board that would break if it was stolen or demolished, more complex of course the longer your list of possible situations.

But then a fixed red is not immune to having a bag over it or the mast knocked down  etc.

All gets back to the hazard analysis.

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4 hours ago, The Stationmaster said:

I suspect the simple reason is that a STOP board can't be proved in the control circuitry so you can't have a main aspect reading to it. (apart from any overlap considerations).  Thus the only aspect which can read to it is a sub and the controls will mean that does not clear until very late during the approach of a train towards it.  That in turn reduces the junction speed of the approaching train so by havinga fixed red you clear the running lines more quickly.

 

 

Isn't a stop block with its big red buffer beam effectively a fixed stop signal, and fitted with lamps which can be proved?

 

I love Yardman's call-on signal.

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