Signalling for modellers who don't know much about signalling

[RailWest]

>>> This signal, despite appearances, is not junction signal; it is sited 'in advance of' (I think?!) the series of trailing connections immediately ahead of it....

 

NO. The pointwork is 'in advance' of the signal, hence the signal is 'in rear' of the pointwork.  For your homework tonight, please read Lesson 1 again..:-)

[TheSignalEngineer]

Well, in for a penny, in for a pound, as they say...

 

.....................................

Down Main_04.jpg

As the train passes, Yard Box returns his signal to danger. The slotting arrangement automatically causes the distant to also return to danger. North's signal remains cleared however, as the train has yet to pass that. Once it does, North can return his signal to danger and we're back to photo 1.

 

In reality, the signal featured was more complex at Grantham itself as it had additional miniature signals (which I think were 'calling on' arms I this case) but, as others have already pointed out, modelling almost always involves compromise so I haven't included them.

 

Hope that is of some interest to some. I can happily do more of these although I might need to do some fresh photography as this is the only signal for which I have a sequence of photos like this. I hasten to add that these pictures were taken some years ago; the scenery is somewhat more developed these days!

Hope you don't put the signal back to danger until the train has passed over all of the points in the route. That was the way of ensuring that a conflicting route wasn't set before the train was clear.

[PatB]

Hope you don't put the signal back to danger until the train has passed over all of the points in the route. That was the way of ensuring that a conflicting route wasn't set before the train was clear.

Doing this, combined with a small but crucial inadequacy in the interlocking and a possibly once in a lifetime mistake by another signalman who pulled the wrong lever, led to the 1927 Hull Paragon crash. A classic example of a series of individually minor failures leading to a major accident.

[beast66606]

Doing this, combined with a small but crucial inadequacy in the interlocking and a possibly once in a lifetime mistake by another signalman who pulled the wrong lever, led to the 1927 Hull Paragon crash. A classic example of a series of individually minor failures leading to a major accident.

 

The crash was caused by a signalman replacing a signal before the train had fully passed which meant it had not reached a locking bar.  The replacement of the signal level and the train not on the locking bar allowed a second signalman to accidentally pull a wrong lever, There was no problem with the interlocking.

[LNER4479]

>>> This signal, despite appearances, is not junction signal; it is sited 'in advance of' (I think?!) the series of trailing connections immediately ahead of it....

 

NO. The pointwork is 'in advance' of the signal, hence the signal is 'in rear' of the pointwork.  For your homework tonight, please read Lesson 1 again..:-)

Aarrghh! Thanks for pointing out. Text in the posting amended...

[PatB]

The crash was caused by a signalman replacing a signal before the train had fully passed which meant it had not reached a locking bar.  The replacement of the signal level and the train not on the locking bar allowed a second signalman to accidentally pull a wrong lever, There was no problem with the interlocking.

 

I would argue that the interlocking, although working as designed, failing to prevent the wrong lever pull in the (let's face it, quite likely) event of the signal being replaced prematurely represents a very serious problem with the interlocking, hence my choice of the word "inadequacy" rather than "fault". Particularly since this occurred in the late 1920s when signalling and interlocking systems were a mature technology rather than the C19th when the railway companies and signal engineers were still in the learning phase.

[micknich2003]

The MoT report for the Paragon accident can be down loaded off the 'net. The Railways Archive The Inspecting Officer found nothing wrong with the interlocking. A Track Circuit would have "Held the Road" and prevented the accident, and following his recomendations they were provided. The story about faulty interlocking is nomore then "Local FolK Lore", and is still occasionaly perpetuated today.

 

Anyone who wants to know more, and is in the Hull area this Saturday will find the attached talk of interest. Neil has done a lot of research, and to further demonstrate, he will have with him part of an EP frame as used at Paragon.

[beast66606]

I would argue that the interlocking, although working as designed, failing to prevent the wrong lever pull in the (let's face it, quite likely) event of the signal being replaced prematurely represents a very serious problem with the interlocking, hence my choice of the word "inadequacy" rather than "fault". Particularly since this occurred in the late 1920s when signalling and interlocking systems were a mature technology rather than the C19th when the railway companies and signal engineers were still in the learning phase.

 

The interlocking did exactly as it was supposed to do. Interlocking (mechanical) cannot differentiate between a signal being returned before a train has passed and a signal being returned after a train has passed - thats what the locking bar on the ground is for and these have been gradually replaced by track circuits over the years (now the norm of course).

 

Edit :

Mick has added some further information while I was typing this.

[PatB]

No, the equipment was not faulty. Yes, it functioned exactly as designed. It was, however, manifestly inadequate. Had it not been, the crash would not have happened.

[micknich2003]

Here is the final page of the 1927 Paragon Accident report.

[beast66606]

No, the equipment was not faulty. Yes, it functioned exactly as designed. It was, however, manifestly inadequate. Had it not been, the crash would not have happened.

 

The locking frame was not inadequate - it doesn't matter how many times you express this view, it was not put forward in the accident report as Mick has shown so unless you have some great insight that was missed at the time then perhaps it's time to move on.

 

Perhaps people can see why such a thread will never get very far off the ground and why I rarely assist in signalling questions any more.

[PatB]

The Inspector's report clearly recommends the installation of a track circuit to guard against the possibility of a reoccurence of the circumstances leading to the crash. IOW the equipment at the time of the crash was not as comprehensive as it could have been. Regardless of whether the inadequacy lay in the frame itself (granted not so) or in the provision, omission, siting or  function of subsidiary equipment, the system as a whole failed to guard against a forseeable human error. My use of the word "interlocking" in my first post was intended to refer to this overall system and not be strictly confined to the locking frame under the signal box. I admit that this may have led to confusion.

 

However, I fail to understand why pointing out a fairly obvious hole in the system has caused others to take umbrage. I apologise for any offence caused and would appreciate a clear explanation from those more knowlegable than myself of why a locking bar, a track circuit etc. does not constitute part of the interlocking system (as opposed to part of the locking frame itself).

[beast66606]

The Inspector's report clearly recommends the installation of a track circuit to guard against the possibility of a reoccurence of the circumstances leading to the crash. IOW the equipment at the time of the crash was not as comprehensive as it could have been. Regardless of whether the inadequacy lay in the frame itself (granted not so) or in the provision, omission, siting or  function of subsidiary equipment, the system as a whole failed to guard against a forseeable human error. My use of the word "interlocking" in my first post was intended to refer to this overall system and not be strictly confined to the locking frame under the signal box. I admit that this may have led to confusion.

 

However, I fail to understand why pointing out a fairly obvious hole in the system has caused others to take umbrage. I apologise for any offence caused and would appreciate a clear explanation from those more knowlegable than myself of why a locking bar, a track circuit etc. does not constitute part of the interlocking system (as opposed to part of the locking frame itself).

 

You are blaming an interlocking failure / shortfall which is simply not the case - imagine if I entered your sphere of knowledge and started using the wrong terminology and ignored any attempt to correct it and persisted with my statement of "facts".

 

This is getting like the "in advance" and "in rear" discussion - interlocking (used to be interlocking apparatus) is between levers (or their modern equivalent such as routes) and not the outside world.

A locking bar will, mechanically, feed information back to a lever (yes you can move, no you can't because I've got a loco on me) as will a track circuit, axle counter or other devices - but they do not lock the other levers, they allow one lever/route/... to move/not move which is then used in the interlocking in the frame / panel / computer / ...

[LNERGE]

Well, in for a penny, in for a pound, as they say...

 

As this fascinating thread was (I think?) related to signals on model railways, I thought I'd post this sequence of photos from my Grantham layout. There are a total of 13 working signals so far (with more to add), interlocked with the points and the control system so thought it might be of interest if I outlined how each one is positioned, what it 'means' and how it operates. Happy for the experts to point out the shortcomings (seriously!) but hopefully not too many 'howlers'.

 

Down Main_01.jpg

The prominent signal in the foreground is controlled by Yard Box and applies to both the down main (to its right) and the down relief (to its left). I'll say straightaway that Grantham is by no means the best 'typical' example of a traditional steam age signalling system, but let's see how we go. This signal, despite appearances, is not junction signal; it is sited 'in advance of' (I think?!) before the series of trailing connections immediately ahead of it and thus provides protection for mainline trains from those points. This pointwork allows a variety of shunting moves to take place at the south end of the station. If any of these points are changed (reversed) to be set for a shunting move then the interlocking system doesn't allow the signals to be pulled 'off'.

 

Down Main_02.jpg

A northbound express is due. Having checked with the next box that the route ahead is clear, the signalman at Yard Box (the actual signalbox can be seen behind the Gresley A1) clears the down main signal. Note that, at this stage the distant signal below it doesn't clear, as the signal in the distance is still 'on' (at danger). Due to the close proximity of the signalboxes at either end of the station, the length of the block section is quite short hence the distant for the next signal box is mounted on this signal. He doesn't have separate 'home' and 'starter' signals; this is his only 'stop' signal which must, therefore. make it the section signal (experts please confirm!)

 

Down Main_03.jpg

At the north end of the station lies North Box and, having checked the line ahead is clear to the next box (in reality Barrowby Road, but not included on the model), the signalman at North box pulls 'off' his corresponding signal. In this case it is an older somersault type so it lowers but means the same thing. This now causes the distant signal to clear so that the driver knows that the route right through the station is clear. In reality, North would have separate levers for these (red for his stop signal and yellow for this distant, which he controls); on the model, the control system logic automatically pulls of the distant, via a snazzy little 5 second delay timer unit my clever electronix mate knocked up for me.

 

Down Main_04.jpg

As the train passes, Yard Box returns his signal to danger. The slotting arrangement automatically causes the distant to also return to danger. North's signal remains cleared however, as the train has yet to pass that. Once it does, North can return his signal to danger and we're back to photo 1.

 

In reality, the signal featured was more complex at Grantham itself as it had additional miniature signals (which I think were 'calling on' arms in this case) but, as others have already pointed out, modelling almost always involves compromise so I haven't included them.

 

Hope that is of some interest to some. I can happily do more of these although I might need to do some fresh photography as this is the only signal for which I have a sequence of photos like this. I hasten to add that these pictures were taken some years ago; the scenery is somewhat more developed these days!

Not wishing to complicate matters but those two stop arms are shared as Grantham Yard's homes and Grantham South's starters. I bet there was a bit of distant indicator working too.

[The Stationmaster]

No, the equipment was not faulty. Yes, it functioned exactly as designed. It was, however, manifestly inadequate. Had it not been, the crash would not have happened.

 

The equipment was completely adequate provided that the Rules were complied with by those operating it, it really was as simple as that, as stated in Colonel Pringle's conclusions.  The requirement, in Rule 61 in the NER Rule Book, not to return a signal to danger until the whole of a train passing it had passed over any facing points which it protected was in existence before the design of the Hull Paragon power resignalling scheme and of course some early power signalling schemes made little or no use of track circuits, particularly for locking facing points in lieu of facing point locking bars.

 

As ever it is all too easy to judge the past by the standards of today where irrespective of the Rule Book requirement a 'belt & braces' approach means that facing points protected by fixed signals are invariably locked by track circuits including in many cases approach track circuits even where semaphore signals are in use - exactly as recommended at Hull by Colonel Pringle.

Edited November 2, 2017 by The Stationmaster

[micknich2003]

For interest only, interior view of Park Street signalbox showing the lever frame from were the "Deed was Done". Of further interest is the verticaly arranged "Hamby's Cross Locking".

[Dave John]

Oh, keep quibbleing chaps , I'm learning a lot from all this detailed stuff. 

 

The thread started as "signalling for modellers who don't know much about signalling" and has ended up as a highly technical discussion amongst folk that do it for a living and know a fair bit about it. This is actually a good thing, it means the rest of us might get a decent amount of our model signalling right. Then again I am still wondering how the caley managed to signal a main line as a headshunt in a tunnel. A calling back stevens pattern tunnel signal with a purple glass? Really if anyone knows I'd be interested. 

 

 

Mind you if I ever sign a letter "I have the honour to be Sir, your obedient servant ", feel free to shoot me. 

 

[The Stationmaster]

 

Oh, keep quibbleing chaps , I'm learning a lot from all this detailed stuff. 

 

The thread started as "signalling for modellers who don't know much about signalling" and has ended up as a highly technical discussion amongst folk that do it for a living and know a fair bit about it. This is actually a good thing, it means the rest of us might get a decent amount of our model signalling right. Then again I am still wondering how the caley managed to signal a main line as a headshunt in a tunnel. A calling back stevens pattern tunnel signal with a purple glass? Really if anyone knows I'd be interested. 

 

 

Mind you if I ever sign a letter "I have the honour to be Sir, your obedient servant ", feel free to shoot me. 

 

 

 

Where was that?  Sounds like it might actually be a straightforward use of a running line to shunt, as at Buchanan Street Tunnel for example - but on the other hand ...

[micknich2003]

Dave, if you have not seen it, a few years ago a book was published on Caledonian Rly signalling. I have it here, and I can dig it out.

[PatB]

I'm posting on my phone and so can't easily quote all the stuff I'd like to address, but hopefully I can make myself adequately clear (perhaps not a given). Firstly, thanks to Beast, Stationmaster, Mick et al for clarification of correct terminology and providing me with informational resources I didn't previously know about. Very useful.

I confess to approaching the Hull crash from the perspective of a C21st engineer with some experience in safety systems rather than as an expert in railway signalling and operation either historic or contemporary, so yes, I'm probably guilty of a degree of projection of current standards to a different era. However, even allowing that the Swiss Cheese Model and the Hierarchy of Controls were many decades into the future at the time, I find myself surprised that the system in place met the legislation in force both at the time and subsequently. That it did is clear both from the lack of censure from the Inspector and the fact that it remained in place afterwards. Even without the frameworks developed later I remain surprised that an administrative control (a rule) was considered adequate when an engineering control (a track circuit or an extended/repositioned locking bar) would have provided a more robust safeguard. This particularly in the context of a busy station, a large and complex signalling system and multiple signalmen working under considerable pressure of time; all factors increasing the likelihood of errors.Even allowing for strict adherence to the Rule Book, wouldn't, for example, a light engine (obviously much shorter than the train involved) have shaved any margin of safety in the system very thin indeed?

Anyhow, consider me educated, which is, after all, the point of this thread.

I suspect that what might have come across as dogged insistence that I knew better than the experts was more an internet filtered manifestation of my astonishment that such a fragile system remained in place so late. Especially given that the railways and those overseeing them were probably the leading pioneers in the development of effective, fail-safe safety systems from a very early date.

Edited November 3, 2017 by PatB

[Colin_McLeod]

A super post PatB. I too shared your surprise that such a system was permitted.

[beast66606]

A super post PatB. I too shared your surprise that such a system was permitted.

 

When I was at school we used to have little pots of mercury, we made TNT in chemistry and grew copper sulphate crystals - all highly dangerous in their own ways.

 

Even with safeguards in place it's possible to defeat them and cause an accident

[LNER4479]

Not wishing to complicate matters but those two stop arms are shared as Grantham Yard's homes and Grantham South's starters. I bet there was a bit of distant indicator working too.

Thanks for that. I genuinely did not know that and find that really interesting.

 

That having been said, my approach to this so far as my modelling goes is to get it as 'right' as it needs to be to give a good representation of the working railway to the viewing public. What the public see is the sequence of signals being operated as described which is what they would have seen were they to have been one or around the station c.1938. They (the public) don't actually see the interlocking working (its electrical anyway whereas it should be mechanical to be prototypical) but they do see the effects of it in terms of signals only showing for correct routes and not being pulled if the points aren't set (and vice versa). The ultimate effect of that is that we don't (often) have trains crashing into each other which is also - I believe - prototypical(!)

 

As I say, that's my approach but utmost respect to those who go further in replicating some of the more detailed nuances of the real thing.

[Ray H]

It must be remembered that the railway companies of old didn't spend more money than necessary on anything. They were of the view that their rules were enough to provide a safe system. I suspect that we might still be using policemen ("Bobbies") with flags to signal trains on a time interval system had not this method prove to be flawed by several accidents. Likewise, fouling bars were no doubt introduced because someone accidentally (or otherwise) changed the points under a passing train.

 

Reading railway accident reports will reveal numerous safeguards that at the time of the incidents weren't in place and I hate to say this but as sure as eggs is eggs there'll still be some that are missing today. As long as there are human beings involved, there will be the chance of accidents even if the chance is in the millions to one quantity.

[LNER4479]

I'm posting on my phone and so can't easily quote all the stuff I'd like to address, but hopefully I can make myself adequately clear (perhaps not a given). Firstly, thanks to Beast, Stationmaster, Mick et al for clarification of correct terminology and providing me with informational resources I didn't previously know about. Very useful.

 

I confess to approaching the Hull crash from the perspective of a C21st engineer with some experience in safety systems rather than as an expert in railway signalling and operation either historic or contemporary, so yes, I'm probably guilty of a degree of projection of current standards to a different era. However, even allowing that the Swiss Cheese Model and the Hierarchy of Controls were many decades into the future at the time, I find myself surprised that the system in place met the legislation in force both at the time and subsequently. That it did is clear both from the lack of censure from the Inspector and the fact that it remained in place afterwards. Even without the frameworks developed later I remain surprised that an administrative control (a rule) was considered adequate when an engineering control (a track circuit or an extended/repositioned locking bar) would have provided a more robust safeguard. This particularly in the context of a busy station, a large and complex signalling system and multiple signalmen working under considerable pressure of time; all factors increasing the likelihood of errors.Even allowing for strict adherence to the Rule Book, wouldn't, for example, a light engine (obviously much shorter than the train involved) have shaved any margin of safety in the system very thin indeed?

 

Anyhow, consider me educated, which is, after all, the point of this thread.

 

I suspect that what might have come across as dogged insistence that I knew better than the experts was more an internet filtered manifestation of my astonishment that such a fragile system remained in place so late. Especially given that the railways and those overseeing them were probably the leading pioneers in the development of effective, fail-safe safety systems from a very early date.

Well, little did I know that my 'let's look at some modelling' post would have spawned such a discussion.

 

Pat B - as a railway industry safety assurance professional I could write a PhD dissertation in response to your posting. I don't have the time today(!) so I will limit myself to the following:

 

The Hull Paragon accident was in 1927, 90 years ago.

 

Most railway historians regard the Armagh accident in 1889 as the 'seminal' moment in the history of railway safety, when railway companies were forced to adopt fundamental safety controls to prevent accidents. The working methods in place on that day would be comical were their consequences not so tragic.

 

Using a crude bit of maths, Hull Paragon is somewhat closer to Armagh 1889 than the present day (2017). So on that - admittedly rather unscientific - basis, comparisons with contemporary safety thinking such as hierarchy of control and Swiss cheeses is perhaps a little disingenuous. (as indeed you do acknowledge)

 

Sadly, but perhaps inevitably, advances in safety on the railway have often been spurred on by accidents which expose weaknesses in the incumbent systems. I have more than a suspicion that the railway industry might not be unique in this regard? Two classic examples illustrate the point.

 

Harrow 1952 brought about the widespread adoption of AWS (the cab warning system that advises the driver of signal aspects and applies the brakes if he doesn't react to an adverse signal). The rail industry had been toying with that idea for at least the previous 30 years and an equivalent system was already in use on the former GWR. Contemporary safety thinking would have it that the industry should have assessed the risk, determined it to be intolerable (or at the very least not ALARP) and fitted the system before such an accident occurred. But it didn't (two world wars didn't exactly help, to be fair!)

 

Bringing the story more up to date, a spate of bad accidents in the 1990's, notably Southall (1997) and Ladbroke Grove (1999) highlighted that, good as it was, AWS was not infallible and so nowadays we have TPWS, an overlay which prevents* the driver overriding the warning should the TPWS trap be 'tripped' and thus bringing train safely to a stand. It is now beyond reasonable doubt that this initiative is a major factor (in my view THE major factor) as to why we have not had a fatal train accident in the UK for over 10 years now, an unprecedented record. (*feel free to cite the circumstances behind the Wootton Bassett SPAD by all means, if you must...)

 

Rail industry a leader in its approach to safety? Hmm... People I work with certainly don't think of it like that and we are constantly looking over our shoulder and comparing ourselves with other industries wondering whether we could do more. And I haven't even 'gone there' in terms of human factors and organisational culture.

 

Next post back to modelling - promise!

Edited November 3, 2017 by LNER4479