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Distant signals in a very short section.


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Once again, I'm not sure if this should be here, or in the prototype section, but it's definitely signalling.

I'm well aware of the practice of placing a distant under the section signal of the box in rear, and slotting the two together.

But what if the 2 boxes were so close together that the "box B" distant needed to be well before A's starter.  Were both distant signals combined and slotted so both A and B distant levers had to be pulled before the signal came off, or was some other arrangement used?

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It is my understanding that if the signals are on the same post then they are either:

 

Slotted so the distant cannot show clear until the box in the rear has cleared the home signal.

 

If not slotted then because the boxes are close together the distant for the box in advance will be fixed at caution. Talyllyn  junction having a fin example of such an arrangement

image.png.2aac98652a1efdc3ffe48d7f6838c36b.png

 

These are the signals made by Jon Fitness for Jinty and can be seen on the Talyllyn Junction thread within the  7mm modelling area.

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The link below to the Knowle & Dorridge accident report describes one method of achieving this, and how it contributed to the accident.  Slotted distants (requiring both boxes to reverse their distant levers, not just slotted with the stop arm above them) were also used - they were also contributory to an accident but I don't immediately recall where or when.  

http://www.railwaysarchive.co.uk/documents/MoT_Knowle1963.pdf

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2 hours ago, Edwin_m said:

The link below to the Knowle & Dorridge accident report describes one method of achieving this, and how it contributed to the accident.  Slotted distants (requiring both boxes to reverse their distant levers, not just slotted with the stop arm above them) were also used - they were also contributory to an accident but I don't immediately recall where or when.  

http://www.railwaysarchive.co.uk/documents/MoT_Knowle1963.pdf

First to the OP and the answer is that where there is a short section the signal box in advance has to exercise some method of control over the distant signal (s) of the signal box in rear in order to create sufficient braking distance for approaching trains.  This can be done by slotting (which might not always be possible due to the distance involved) or by an electrical control (i.e. what amounts to an electric slot) or it can be done by Special Instruction to the signal boxes involved, or it can be done - as on the GWR - by a general Signalling Regulation included within the normal book of Block Signalling Regulations and was used where no other controls were in place.  Whichever is used the purpose is to ensure that the outermost distant signal - i.e. the one of the signal box is rear - is not cleared until the line is clear and all stop signals are cleared at both signal boxes.   It can get quite complicated when there is a whole a succession of short block sections although that is unusual nowadays but was once commonplace.

 

Where signal boxes are even closer together and the outermost Home Signal of the signal box in rear is less than 440yds in rear of the outermost  Home Signal of the next signal box then there is an additional imposition on the Signalman at the rearmost signal box and he is not allowed to accept a train until he has received Train Out of Section from. the signal box in advance because the section has to be clear in order to create a 440yd Clearing Point.

 

Coming back to the Knowle & Dorridge collision Report  a read through makes it clear that the basic cause of the accident was dangerous working on the part of the Knowle & Dorridge Signalman.  And this was not helped by the Station Master failing to notice TRB irregularities during his signal box visits (I can, unfortunately, guess exactly how those visits were conducted and why blank entries were missed).    Whatever else might be said there is no getting away from that fact and in some respects it makes no difference whether he accepted the train under Regulation 4 or Regulation 4A because both required the line to be clear to the Clearing Point, and that Clearing Point was well and truly fouled after the train had been accepted.  I am absolutely amazed that the number of missing times in the TRB at Knowle had seemingly passed without coming being notice when they averaged nearly 5 per day.   Anyone conducting a signal box visit would be either blind or incompetent to miss that level of errors especially if they were all down to one Signalman - and it's a sad. fact that sloppy booking is often indicative of a poor, and sloppy, Signalman in need of having his fortune told.  It's hardly difficult to pick up from a TRB check during a routine signal box visit that a train has not been accepted under the correct Regulation - in fact it's just what someone should be looking for if there is evidence of poor booking.

 

ABR 4A is a perfectly safe method of working where controlled distant signals are not used and in fact is still in use today in one location (I think now only one) on NR. The only real change to ABR 4A, made two years after the collision was to add the words that stated it was only to be applied where authorised which effectively relieved  Signalmen of the need to know to look at the gradient chart displayed in his signal box when it came to applying this Regulation (a competent Signalman should in any case hardly need to look at the gradient chart once he had 'signed' to work a particular signal box).

 

 

 

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>>>Slotted so the distant cannot show clear until the box in the rear has cleared the home signal

Not relevant if (say) the distant was underneath the Starting or Advanced Starting signal.

 

>>>>If not slotted then because the boxes are close together the distant for the box in advance will be fixed at caution. Talyllyn  junction having a fin example of such an arrangement.

I would suggest that is a misconception. The distants are not slotted with the stop arms above them because they are 'fixed'. The reason they are 'fixed' would be related to the circumstances at the box ahead (eg slow speed limit etc).

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There has been a description on here of Wrexham or Oswestry or some such place (Mike @Stationmaster corrected me on the details once before) with five or so signal boxes in short succession. Each successive box would clear its home and starting signals (some presumably doubling up and slotted); only once the box furthest in advance had cleared its starter would the slotting allow the distants to clear - so, one would see the stop arms come off one after another in the direction of travel, then the distants come off one after another in the other direction. Or something like that. 

 

i await correction!

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13 hours ago, Compound2632 said:

There has been a description on here of Wrexham or Oswestry or some such place (Mike @Stationmaster corrected me on the details once before) with five or so signal boxes in short succession. Each successive box would clear its home and starting signals (some presumably doubling up and slotted); only once the box furthest in advance had cleared its starter would the slotting allow the distants to clear - so, one would see the stop arms come off one after another in the direction of travel, then the distants come off one after another in the other direction. Or something like that. 

 

i await correction!

Something like that!.

 

In short sections there are three basic constraints/factors which have to be taken into account in block working and the working of signals.

1. Outermost Home Signals at successive signal boxes being less than 440yds apart.

2. The need to ensure sufficient braking distance to the outermost Home Signal of any signalbox when that signal is less than required braking distance from a lower arm distant underneath the outermost Home Signal at the signal box next in rear (e.g. the situation at Knowle & Dorridge where its Up Distant Signals did not have sufficient braking distance from their position beneath Bentley Heath Crossing's Up Home Signals), and 

3. The need to keep trains moving under clear signals which normally meant signal boxes immediately offering a train forward to the next box in advance on receipt of the Is Line Clear?  (ILC) bell; signal.  However to allow some flexibility this has to be controlled to avoid 'asking forward' too far at a time and this is done using another bell signal known as 'Train Approaching' (1-2-1)

 

We can see items 2 & 3 in action in the Knowle & Dorridge Collision Report.   In that case there was only one short section - between Bentley Heath Crossong and Knowle & D but it can illustrate one way in which things were worked in order to take account of both the short section and avoid delay to trains while still allowing some flexibility.   It worked like this -

 

A train was asked forward (i.e. ILC?) in the normal way from Solihull to Bentley Heath with the appropriate ILC? bell signal and provided he had a Clearing Point (440yds in advance of his Home Signal) Bentley Heath would accept the train.  With boxes a normal distance apart  Bentley Heath would not offer the train forward until he received the Train Entering Section (TES) but because the section to Knowle was short and there was the other restraint imposed by the lack of braking distance plus a further restraint at Knowle that might not necessarily work so to give a bit of flexibility Bentley Heath asked ILC? forward to Knowle after he received the 1-2-1 bell signal from Widney Manor (which meant the train was just passing Solihull).

 

Regulation 4A applied between Bentley Heath and Knowle which meant that in order to clear his signals the Signalman at Bentley Heath had to receive a full 'Line Clear' (i.e repetition of the ILC? bell signal) from Knowle.  If he only received the bell signal 'Line Clear to Clearing Point Only' (2-2-2) the Bentley Heath Signalman was supposed to keep his stop signals at danger until he was sure that the train had passed his Distant Signal (which would be at caution and the train had therefore slowed so would have sufficient braking distance from Knowle's Distant Signal below Bentley Heath's Home Signal (902 yds from Knowle's Home Signal).

 

There was a further constraint on the Knowle Signalman because he had to have received a full Line Clear (or a 2-2-2 acceptance) from Lapworth before he could accept a train under full Line Clear from from Bentley Heath.  So on receiving ILC? from Bentley Heath the Knowle Signalman should immediately offer the train forward to Lapworth before responding to the  Bentley Heath ILC? bell signal. (alternatively he could send 2-2-2 and then a full Line Clear after receiving Line Clear from Lapworth).  This might seem a bit odd because the section between Knowle and Lapworth was 2.5 miles long so definitely not 'short'.  However the full Line Clear was needed to allow Knowle to immediately clear his signals - if the Knowle Signalman did not have that full Line Clear he could not immediately clear his stop signals which meant that he couldn't clear his Distant Signal so under Regulation 4A the Signalman at Bentley Heath couldn't clear his Distant Signal either.   Even more so if Knowle hadn't received any sort of Line Clear from Lapworth it meant he had to keep his stop signal s at f danger until he was sure that the Driver of an approaching train had reduced speed sufficiently to be able to stop at that signal.

 

This incidentally is why I expressed concern regarding the Station Master's signal box visits because it is not difficult - from a properly kept TRB (Train Register Book) - to check that block bell signals and acceptances were being used correctly and it was an important part  of the Station Master's duty during a signal box visit to check things like that.  The district Inspector was seemingly also lacking when it came not only to his (less frequent) signal box visits but clearly so when it came to TRB cross checks.  The irregularities noted in the collision Report were hardly likely to have been some sort of sudden outbreak but were clearly a symptom of persistent sloppy working.  

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Thanks for all your replies.

Interestingly, this has simultaneously popped up on FB on an almost identical situation...

https://www.facebook.com/groups/168118503304604/permalink/3057837930999299

 

So it seems that there are 3 ways of dealing with this particular situation (signal boxes "A", "B" and "C", section A-B too short for full braking distance)

1 - A slot (mechanical or electric) on the distant of A so both A & B have to pull their distant levers for the signal to come off

2 - An electric lock to release the distant lever in A, with an alert buzzer if B has returned his distant lever to on.

3 - Special intructions requiring line clear (at least to home signal if not to clearing point) to be received from C before giving line clear from B back to A, with A not clearing distant until full line clear recieved from B.

 

If I do end up applying this on a model (actually having space for a distant signal being the problem!) it will be using option 1...

 

Thanks again

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Your No.3 would not apply because it requires the stop signals at B to be kept at Danger because the train would have been accepted by C under the Warning  - Regulation 5, Warning Acceptance (using in 1960/72 Block Regulations numbering).  Therefore because B has to keep his stop signals at danger and that will include his outermost Home Signal so he obviously cannot clear his Distant Signal.   Under Western Regulations with A - B a short section it would either be a 2-2-2 acceptance or a full Line Clear acceptance if B controls A's Distant signal.

 

In order for B to clear his stop signals he has to have received a Line Clear acceptance of some sort from C which shows the line is clear as far as C's Clearing Point and not a Warning Acceptance which tells him the line is clear only as far as C's Home Signal.

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  • 3 years later...

I have just been looking at the George Pryer diagrams for the Truro area and have noticed that Truro West only had one distant arm for the up line (fixed at caution on  the same post as the Penwithers Junction Up section signal).  This however is shown to have been at a distance of 590 yards in rear of Truro West box, with the Up Main Home at 189 yards in rear leaving  only 401 yards from distant to home.  This would suggest that regulation 4A would have been required for every train but that would make it pointless for Penwithers Junction to have a worked  Up Main Distant at all if it could never be cleared.  There were also two other stop  signals in rear of the section signal which could have had distant arms below them to more braking distance but for some reason did not. 

 

There does not appear to have been a speed restriction at Penwithers Junction or a severe rising gradient towards Truro so would the driver have been expected to have known to expect Truro West box Up Home to be at danger even though the fixed distant would have been located after the point at which they would have needed to start braking?  There was I believe a speed limit through Truro station but the braking point for that would have been later.

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4 hours ago, Zoe said:

I have just been looking at the George Pryer diagrams for the Truro area and have noticed that Truro West only had one distant arm for the up line (fixed at caution on  the same post as the Penwithers Junction Up section signal).  This however is shown to have been at a distance of 590 yards in rear of Truro West box, with the Up Main Home at 189 yards in rear leaving  only 401 yards from distant to home.  This would suggest that regulation 4A would have been required for every train but that would make it pointless for Penwithers Junction to have a worked  Up Main Distant at all if it could never be cleared.  There were also two other stop  signals in rear of the section signal which could have had distant arms below them to more braking distance but for some reason did not. 

The Penwithers Jn diagram shows the same post with a worked distant so one of them is wrong. It would be more logical if Penwithers was right.

Paul. 

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14 minutes ago, 5BarVT said:

The Penwithers Jn diagram shows the same post with a worked distant so one of them is wrong. It would be more logical if Penwithers was right.

Paul. 

But the diagram for Penwithers Jcn would not show whether the distant belonging to another box was fixed or not - that would be shown only on the diagram of the other box.

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1 hour ago, RailWest said:

But the diagram for Penwithers Jcn would not show whether the distant belonging to another box was fixed or not - that would be shown only on the diagram of the other box.

Every day is a school day!  Didn’t know that.

Paul.

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2 hours ago, 5BarVT said:

Every day is a school day!  Didn’t know that.

Paul.

I've looked at the SRS diagrams (pre-1971).

 

Unless I'm misreading something, both Truro West Up Distant (mounted on Penwithers Junction Up Starting post) and Truro East Up Distant (mounted on Truro West Up Home post) appear to be fixed.

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By my understanding of Reg 4A, if that was used for Up trains between Penwithers Jcn and Truro West and West accepts Line Clear to Clearing Point only, then Penwithers would have to keep his Up stop signals (2, 6 and 7) at danger until the train has passed within his distant (1) and only then cleared.  This means Penwithers' Distant must be held at caution and so trains will already have been slowed approaching Penwithers well before seeing Truro West's fixed Caution signal. 

 

But Truro West and East are pretty close, so I would expect West to offer immediately to East box immediately it is offered to him.  Provided the train has been accepted by East box, I see no reason why Truro West can't then accept at full Line Clear rather than 2-2-2, in which case Penwithers could clear all his signals including his own distant.  In this case, the line must be clear as far as the platform, so West box will be able to clear his Home Signal to admit the train to the platform as it approaches, even if East isn't yet able to pull off.

 

Or to put it another way, Penwithers distant (1464 yds) effectively acts as distant for Truro, and is at adequate braking distance.

 

But if I've misuderstood this strange GWR practice, no doubt the Stationmaster will be along shortly with the right version!

 

 

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Right first of all I shall clarify the situation with Truro West's Up Distant - it was Fixed at Cautiony, no doubt, because there was a permanent restriction of speed to 15 mph over the Up Platform Line at Truro - so that alone would mean that a worked distant could not be used.   That is the simple bit.  

 

The lines between the platforms at Truro were restricted to 30 mph so there was no need for a speed related Fixed Distant for Truro West in the Down direction however very few trains would be passing through on the Down main Line without stopping and speed was in any case restricted.   But it is noticeable - according to George's diagrams - that the Section Signals in both directions had 'Calling On' subsidiaries so had seemingly never been updated  - as elsewhere in such situations - to have either 'Warning' or 'Shunt Ahead' (or both) indications added.  

 

The lack of 'Warning'  subsidiaries, related also to the low speeds (which seem to have remained in place until the 1971 resignalling when they were raised to 60mph)  makes me wonder if the two Truro 'boxes had Modified Clearing Points when it came to accepting trains from each other?  Which makes the use of fixed distants between them more plausible.

 

Short Section working in the normal sense would not have applied between the two Truro 'boxes because their respective (outermost) Home Signals in both directions were more than 440 yards apart.  However Truro West's Down Distant was not out far enough when related to the steep falling gradient (even with 60 mph line speed) and equally it's Up Distant, even allowing for permanent restriction of speed, was not out far enough either.  So Regulation 4A would have inevitably applied in both directions between the two Truro boxes and in the Up Direction between Penwithers Jcn and Truro West.

 

Although short section working did not apply the respective main lines' Clearing Points for trains approaching Truro were in both cases part way along the station platforms and the platforms were also in the block sections so not in Station Limits at  either 'box.  So it was probably the case that both East and West were required in the 'Box Instructions to ask 'Is Line Clear?' forward at a specified time.  This might have been on receipt of 'Is Line Clear?' from the 'box in rear although in view of the length of the sections involved further out from Truro it might have possibly been on receipt of the  'Train Approaching' bell signal.  It would need a look at running times to establish that with greater clarity but again the fact that most trains stopped at Truro would have a bearing on that as would the fact that arriving branch traisn at teh west end would foul West box's Down Clearing Point.

 

So some questions will remain unless somebody happens to come across a copy of the Signal Box Special Instructions.  i know for a fact that the original office copies are long gone and were probably dumped at the time of the 1971 resignalling.  But someone might have saved something from one of the 'boxes at that time?

 

Lots of fascinating stuff involved but at least the original question from Zoe was the simple bit as it was part of standard GWR practice for Distant Signals.

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5 hours ago, The Stationmaster said:

 

Lots of fascinating stuff involved but at least the original question from Zoe was the simple bit as it was part of standard GWR practice for Distant Signals.

What I'm still not sure about though is why Penwithers Junction had a worked distant on the Up Main at all.  If all trains were accepted by Truro West under regulation 4A then it could never have been cleared. 

 

Looking at the diagram for Truro  East, it shows a worked distant on the Down Main which  could never have been be cleared if Truro West had to  accept under regulation 4A unless the 30 mph PSR through the platforms could have avoided this situation but it seems that the platforms were not long enough.

 

It would appear then that both Penwithers Junction and Truro East had worked distants which could never have been cleared.

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5 hours ago, Zoe said:

What I'm still not sure about though is why Penwithers Junction had a worked distant on the Up Main at all.  If all trains were accepted by Truro West under regulation 4A then it could never have been cleared. 

My understanding from @The Stationmaster 's post is that Truro West could accept trains from Penwithers Junction under full line clear, although it might not be entirely clear how this was done.

 

One possibilty might be that Penwithers Junction offers a train to Truro West, Truro West offers it to Truro East, Truro East accepts, Truro West (perhaps after first clearing his signals - but see below) then accepts the train from Penwithers Junction. This then allows Penwithers Junction to clear his signals including the distant, and the fact that Truro West distant is at caution (because of the speed limit through the platform) is irrelevant.

 

However, the Knowle and Dorridge accident report implies that Regulation 4A would also apply to Truro East (<1000 yards from distant to home on a falling gradient), and if Truro East only gave a 2-2-2 acceptance then Truro West could not clear his signals till the train had passed the Truro West distant, so I wonder if that allows Truro West to give full line clear acceptance to Penwithers Junction (on the face of it I don't see why not, but it does mean that a driver could find the Penwithers Junction distant pulled off but the Truro West home at danger). Perhaps Truro East had to offer the train to Probus and have it accepted before accepting the train from Truro West under full line clear.

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12 hours ago, bécasse said:

Given the conundrum over worked distants that could never have been cleared, I wonder if either or both of the station boxes could switch out?

I looked at the 1949 Service Time Table to get the opening times (thanks Michael Clemens Railways website).

 

Truro East and West SBs - open continously with no closing switch.

 

Penwithers Junction SB 

5.40am-10.55pm Mon-Fri 

5.40am-11.10pm Sat

7.20am-9.35pm Sun

With a closIng switch.

 

Will

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What happens in respect of Regulation 4A at Truro West when Penwithers Junction switches out?

 

I suppose Penwithers Junction keeps his up distant at caution when switching out, and that Truro West then sends full line clear to Baldhu (or wherever).

 

I wonder what instruction was issued to drivers.

On 22/10/2023 at 01:12, Michael Hodgson said:

Or to put it another way, Penwithers distant (1464 yds) effectively acts as distant for Truro, and is at adequate braking distance.

It must have been part of drivers' route knowledge to know that certain boxes were "paired" in this way, for otherwise the provision appears to lose most of its purpose.

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4 hours ago, Jeremy Cumberland said:

What happens in respect of Regulation 4A at Truro West when Penwithers Junction switches out?

 

I suppose Penwithers Junction keeps his up distant at caution when switching out, and that Truro West then sends full line clear to Baldhu (or wherever).

 

 

That was certainly the case at Taunton West Station, the box instructions (available from the SRS  website at https://www.s-r-s.org.uk/html/gwe/S732.htm) show that Taunton West Junction's Up distants were maintained at caution when that box was out of circuit with regulation 4A then not applying.

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On 22/10/2023 at 16:24, Zoe said:

What I'm still not sure about though is why Penwithers Junction had a worked distant on the Up Main at all.  If all trains were accepted by Truro West under regulation 4A then it could never have been cleared. 

 

Looking at the diagram for Truro  East, it shows a worked distant on the Down Main which  could never have been be cleared if Truro West had to  accept under regulation 4A unless the 30 mph PSR through the platforms could have avoided this situation but it seems that the platforms were not long enough.

 

It would appear then that both Penwithers Junction and Truro East had worked distants which could never have been cleared.

This might well come back to any modfied Clearing Points at Truro East and West and that PROSs through the station and when the two station 'boxes asked 'Is Line Clear?' forwards between each other' and the strong probability that 2-2-2 acceptances were also used

 

Let's assume for a moment that Truro West asked forwards on receiving the ILC? from Penwithers Jcn   If that was acknowledged and 'Line Clear' was pegged up by Truro East then West  could accept under full 'Line Clear' from Penwithers Jcn and the Penwithers Jcn Signalman could clear all his relevant Up direction signals including the distant.  If Truro East could not accept the train then West would implement Regulation 4A  (provided the line was clear to his Clearing Point) and the Penwithers Jcn Signalman would keep his Up Distant Signal at Caution  So there was clearly a situation in which Penwithers Jcn Signalman could clear his Up Main. Distant.

 

In the opposite direction things were different because Truro East had a full Clearing Point between his Down Main Home and his Inner  Home with the distant a very long way back from the Home.  So no restriction on acceptance from Probus (or Burngiullow when Probus was switched out or after it had been closed for good in 1965)  provided East's Clearing Point was not fouled.  But he could not clear all his Down Main stop signals and clear his Distant until the train had been accepted by Truro West under a full 'Line Clear.  So even if West accepted by 2-2-2 East could still accept under full Line Clear from Probus/Burngullow because his Distant had more than adequate braking distance to the Home Signal

 

In the Up direction if East accepted a train under Regulation 4A from West that still gives West a full Clearing Point so he could accept from Penwithers Jcn under a full 'Line Clear'.  It's interesting to note that according to George Pryer's diagram West did not have a two shot detonator placer on the Up Main Line but did have one on the Up Branch Line (the one between the two platforms which is nowadays the Up Main).  I suspect the reason for that was the very low PROS on the Up Main.

 

The big question which we don't know the answer to is what the Clearing Points were at both station 'boxes and if my assumption about possible Modified Clearing Points is correct or whether they had 4A acceptances between each other instead?  But even if West accepted 4A from East that would not affect East's acceptance from Probus and East would keep his Distant Signal at caution  As I said above an awful lot of this depends on what was in those Signal Box Instructions - West clearly had a potentially very short Clearing Point on the Down Main in any event.

 

Incidentally prior to the Knowle & Dorridge collision  (which involved the failure of a Signalman to properly apply Regulation 4A( application of the Regulation was effectively left entirely to the knowledge of the Signalman.  One of the consequnces of that collsion and the Inspecting Officer's Report was that its use was subsequently noted in the Signal Box Soecial Instructions at all places where it applied.  

 

Regulation 4A was amended in late 1965 and was removed completely from the Regulations booklet in the 1972 reissue.  However it did not disappear and was cinrinued in Signalbox Soecial Instrux ctions at those places were it still had any application.  This led to the strange situation of it no longer applying anywhere on the WR but still applying in at least one place which had been transferred frim the WR to the LMR.  Thus when i visited the 'boxes in the immediate Shrewsbury area c.30 years ago what had been GWR AB Regulation 4A was still in use and I even heard a 2-2-2 acceptance bell signal.  As little has changed at Shrewsbury since then it could wel be still in use there - 50 tears after it disappeared from the Absolute Block Regulations.

 

BTW. Oenwithers Jcn' Down was only 44o yds i. rear of the Home Signal so 4A presumably also applied there although the switchback gradient, albeit steep,. might have been considered to decide that it was not necessary.

Edited by The Stationmaster
oops, minor error - thks Michael Hodgson for pointing it out
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15 minutes ago, The Stationmaster said:

 

 

In the opposite direction things were different because Truro East had a full Clearing Point between his Down Main Home and his Inner  Home with the distant a very long way back from the Home.  So no restriction on acceptance from Probus (or Burngiullow when Probus was switched out or after it had been closed for good in 1965)  provided East's Clearing Point was not fouled.  But he could clear all his Down Main stop signals and clear his Distant until the train had been accepted by Truro West under a full 'Line Clear.

Is there a "not" missing from the last sentence above?

 

 

My impression of the use of distant signals at stations big enough to have two (or more) boxes is that in practice distant off generally tells the driver of a train not booked to stop that he has a clear run right through the whole station, not just past the first box.  Other railways didn't use 2-2-2 but they often had other means (for example a mechanical or electrical indicator or slotting) of getting a box in rear to keep his distant on until they were ready for the train to proceed.

 

 

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