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Incident at Chalfont & Latimer (21/06/20)

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bramling

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Would I be correct in thinking that had the LU service departed Chalfont & Latimer some time earlier (possibly even seconds) then the LU driver would not have seen the signal revert back to danger and thus would not have had any indication of anything being amiss until they spotted the Chiltern service heading towards them?

If so I'd imagine RAIB may well comment on this possibility and the good fortune that it hadn't already departed.

Exactly right. My understanding is the LU driver was just starting to move when the signal returned to danger. A couple of seconds earlier and he’d have been on his way. There is the possibility that this might have given the Chiltern driver more of a cue that something was amiss.
 
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SlimJim1694

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It could be (arguably) said that the Chiltern driver was unlucky as had the Chesham train moved he would have realised his error and acted differently.
Also the Chiltern driver would probably have braked earlier if they had seen the Underground train crossing in front.

There are a lot of assumptions here that the Chiltern driver would have reacted in a certain way if the Chesham train had moved, but the evidence suggests that he failed to react to a signal displaying a double yellow, he failed to react to a signal displaying a single yellow, and he failed to react to a signal displaying a red. He also failed to suspect the most obvious reason for being "tripped", eg: a SPAD, especially when his route knowledge should have told him that he was approaching a conflicting junction, and he failed to do the most obvious thing and contact the signaller to advise him/check. If the Chiltern driver failed to react to all of those things - why are people so certain that he would have reacted to the Chesham train pulling away? If he was paying attention he'd have still been sitting back at the red signal twiddling his thumbs.

I don't know how he could have missed all those cues (although I do think it's crazy there is no AWS up there), but to suggest he was paying enough attention to have stopped when the Chesham moved is making a very big leap of faith.
 

bramling

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There are a lot of assumptions here that the Chiltern driver would have reacted in a certain way if the Chesham train had moved, but the evidence suggests that he failed to react to a signal displaying a double yellow, he failed to react to a signal displaying a single yellow, and he failed to react to a signal displaying a red. He also failed to suspect the most obvious reason for being "tripped", eg: a SPAD, especially when his route knowledge should have told him that he was approaching a conflicting junction, and he failed to do the most obvious thing and contact the signaller to advise him/check. If the Chiltern driver failed to react to all of those things - why are people so certain that he would have reacted to the Chesham train pulling away? If he was paying attention he'd have still been sitting back at the red signal twiddling his thumbs.

I don't know how he could have missed all those cues (although I do think it's crazy there is no AWS up there), but to suggest he was paying enough attention to have stopped when the Chesham moved is making a very big leap of faith.

The lack of AWS shouldn’t be a major problem as, unlike on Network Rail, every signal has a full-speed overlap and train stop - so providing everything works as designed even completely disregarding the signal should result in the train stopping before it reaches harm’s way.

The only scenario I can think of for missing all the cues is that he either thought the double yellow and single yellow took him all the way through to Chalfont (still doesn’t fully explain why he missed the red though), or that he lost awareness perhaps through falling asleep, then when he regained awareness saw clear signals ahead of him.
 

357

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S Stock do have hazard warning lights.

Ah, thanks for info! I've not been in an S stock cab for a long time - are they the only stock that has them?

From RAIB:

This suggests the original SPAD was what caused the signal to go to red. If the Underground train had passed the signal before that happened then it would probably have got clear onto the Chesham branch in the time it took the Chiltern train to stop, restart and reach the crossover. Also the Chiltern driver would probably have braked earlier if they had seen the Underground train crossing in front.

I can understand your train of thought and you have a valid point - however in my opinion it's relying on the attention to detail of the Chiltern driver (who it already seems has reset-and-go).

He could have stopped in time, he could just as easily have gone into the front of the LUL train, or even worse into the side of it.

It's still far too close to a potentially fatal incident for my liking.

Everything now seems to be coming down to one question - why did the driver move the train after being tripped?

Be it in violation, error, or possibly even following a Chiltern procedure we know nothing about - from what has been established already there would have been no risk of a collision had the train remained where it was until given authority to move.
 

SlimJim1694

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The lack of AWS shouldn’t be a major problem as, unlike on Network Rail, every signal has a full-speed overlap and train stop - so providing everything works as designed even completely disregarding the signal should result in the train stopping before it reaches harm’s way.

The only scenario I can think of for missing all the cues is that he either thought the double yellow and single yellow took him all the way through to Chalfont (still doesn’t fully explain why he missed the red though), or that he lost awareness perhaps through falling asleep, then when he regained awareness saw clear signals ahead of him.

I understand that the LU system mitigates against collisions resulting from SPADs, but AWS mitigates against the SPADs themselves (TPWS, where fitted, mitigates against the collision).

If there was AWS on the double yellow, single yellow and red the Chiltern driver would have been forced to cancel the warnings or been stopped way back. If he'd fallen into micro sleep the AWS would have woken him up. I appreciate that it's an LU signalling area and they don't "do" AWS but I do wonder if it had been on a Network Rail section fitted with AWS whether the driver would have still got that far after having at least 3 AWS reminders of what he was getting himself into.
 

bramling

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I understand that the LU system mitigates against collisions resulting from SPADs, but AWS mitigates against the SPADs themselves (TPWS, where fitted, mitigates against the collision).

If there was AWS on the double yellow, single yellow and red the Chiltern driver would have been forced to cancel the warnings or been stopped way back. If he'd fallen into micro sleep the AWS would have woken him up. I appreciate that it's an LU signalling area and they don't "do" AWS but I do wonder if it had been on a Network Rail section fitted with AWS whether the driver would have still got that far after having at least 3 AWS reminders of what he was getting himself into.

As you say, it’s simply the way LU works. Likewise they don’t have things like lamp proving, so it’s possible for a driver to encounter a signal displaying no aspect when it should be red, again the presence of a trainstop and full-speed overlap being the mitigation.

Yes you’re right the driver would have had to acknowledge 3x AWS warnings, however there have been cases where a driver has done exactly that and still had a SPAD and collision - Watford Junction in 1996 comes to mind.

The LU system is better, however as line speed increases the viability of full-speed overlaps reduces. 60 mph is already starting to push this to the limits of viability, especially in the open. It’s not that they don’t work, but that they become so long it makes it difficult to design a viable signal layout that can meet the train throughout requirements.
 
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lonogrol

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I understand that the LU system mitigates against collisions resulting from SPADs, but AWS mitigates against the SPADs themselves (TPWS, where fitted, mitigates against the collision).
As you say, it’s simply the way LU works. Likewise they don’t have things like lamp proving, so it’s possible for a driver to encounter a signal displaying no aspect when it should be red, again the presence of a trainstop and full-speed overlap being the mitigation.
Agreed with Bramling. Worth mentioning also that because of this a S.P.A.D is not treated as harshly on L.U as it is on the main - line, because the consequences are not as great. This is not to say they are accepted, but the whole management of the process is carried out to a lesser extent (no forms completed by signaler there and then for instance), and drivers can potentially have a greater number of safety related incidents than their main line counter parts before more formal action is taken. This is not to say procedures are lax - it still takes up a lot of management time dealing with such incidents - and any T/ops would be subject to some sort of action plan under the competence management afterwards.
 

SlimJim1694

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AWS ramps incompatible with the 4th rail in the centre. That's why they have tripcocks instead.
Intrigued by this statement I looked at a drivers eye video of the Bakerloo line Network Rail section. They have AWS magnets on there. The 4th rail has breaks in it to accommodate them.
 

Domh245

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AWS ramps incompatible with the 4th rail in the centre. That's why they have tripcocks instead.

It's not impossible to work around this - AWS is fitted to signals between Wimbledon and East Putney with interruptions in the fourth rail where necessary (the signals are also protected with tripcocks) - the difference being the ownership of the line!
 

Mojo

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It's not impossible to work around this - AWS is fitted to signals between Wimbledon and East Putney with interruptions in the fourth rail where necessary (the signals are also protected with tripcocks) - the difference being the ownership of the line!
Probably a bad example as Wimbledon to East Putney is owned by London Underground! But yes the sentiment is right, you can have fourth rail and AWS or TPWS grids in the 4 foot, as shown on Wimbledon and Richmond branches as well as the DC lines
 

Surreytraveller

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AWS ramps incompatible with the 4th rail in the centre. That's why they have tripcocks instead.
That's not why they have tripcocks instead. There's no requirement for AWS because there are tripcocks, and trains operating on the line are required to have train stops
 

edwin_m

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There are a lot of assumptions here that the Chiltern driver would have reacted in a certain way if the Chesham train had moved, but the evidence suggests that he failed to react to a signal displaying a double yellow, he failed to react to a signal displaying a single yellow, and he failed to react to a signal displaying a red. He also failed to suspect the most obvious reason for being "tripped", eg: a SPAD, especially when his route knowledge should have told him that he was approaching a conflicting junction, and he failed to do the most obvious thing and contact the signaller to advise him/check. If the Chiltern driver failed to react to all of those things - why are people so certain that he would have reacted to the Chesham train pulling away? If he was paying attention he'd have still been sitting back at the red signal twiddling his thumbs.

I don't know how he could have missed all those cues (although I do think it's crazy there is no AWS up there), but to suggest he was paying enough attention to have stopped when the Chesham moved is making a very big leap of faith.
I can understand your train of thought and you have a valid point - however in my opinion it's relying on the attention to detail of the Chiltern driver (who it already seems has reset-and-go).

He could have stopped in time, he could just as easily have gone into the front of the LUL train, or even worse into the side of it.
Maybe I should have said "possibly" rather than "probably". I was going by many accident reports where the driver didn't react to a signal but did react when he saw a train in front.

It's relatively common to get a sudden unexpected sudden stop on Sprinters and Turbostars, which I think is down to the Drivers Safety Device or one of the other systems either not being responded to quickly enough or having a glitch in the circuit. So drivers may be accustomed to this happening now and then and being able to reset and continue. Is the tripcock reset similar to this or does it need a specific action.
 

rebmcr

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he failed to react to a signal displaying a double yellow, he failed to react to a signal displaying a single yellow, and he failed to react to a signal displaying a red.
If there was AWS on the double yellow, single yellow and red the Chiltern driver would have been forced to cancel the warnings
Yes you’re right the driver would have had to acknowledge 3x AWS warnings

I was under the impression that LU signalling is not 4-aspect.
 

Surreytraveller

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Probably a bad example as Wimbledon to East Putney is owned by London Underground! But yes the sentiment is right, you can have fourth rail and AWS or TPWS grids in the 4 foot, as shown on Wimbledon and Richmond branches as well as the DC lines
Although its obviously down to the historical ownership of line, as although owned by LU, it is operated by Network Rail as historically it was owned by British Rail
 

357

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I was under the impression that LU signalling is not 4-aspect.

This section is indeed 4 aspect.

It's relatively common to get a sudden unexpected sudden stop on Sprinters and Turbostars, which I think is down to the Drivers Safety Device or one of the other systems either not being responded to quickly enough or having a glitch in the circuit. So drivers may be accustomed to this happening now and then and being able to reset and continue. Is the tripcock reset similar to this or does it need a specific action.

To isolate any safety systems on my traction requires the drivers master key to be used, and needs another reset key to reset it.

If the DSD or AWS is not responded to and applies the brakes, simply respond to it and the brakes will release (eventually). I wouldn't expect either of these to be a common occurrence and any respectable driver would ensure they know why they have stopped before starting again and not isolate things without authorisation on an assumption that there is a defect. That would be a serious meeting with management.

Unfortunately we might never understand the truth of what was going through that drivers head at the time.
 

greatkingrat

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That's what I said earlier in the thread, but apparently up there it is!

If Simsig Marylebone is accurate there are some 4 aspect ignals in the Amersham area. So the driver would have got a double yellow leaving Amersham station, then the single yellow between Amersham and Chalfont, then the red protecting the junction.
chalfont.JPG
 

SlimJim1694

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If the DSD or AWS is not responded to and applies the brakes, simply respond to it and the brakes will release (eventually). I wouldn't expect either of these to be a common occurrence and any respectable driver would ensure they know why they have stopped before starting again and not isolate things without authorisation on an assumption that there is a defect. That would be a serious meeting with management.
100% agree with this.
 

bramling

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If Simsig Marylebone is accurate there are some 4 aspect ignals in the Amersham area. So the driver would have got a double yellow leaving Amersham station, then the single yellow between Amersham and Chalfont, then the red protecting the junction.
View attachment 80553

Looks right to me. LU has multi-aspect signalling on the main lines only between Harrow and Amersham / Chesham. Unlike Network Rail there is less of a strict demarcation between 3 and 4 aspects so the fourth aspect is not always provided.

Unlike the rest of LU a red aspect will always be preceded by at least one yellow aspect. Fog repeaters are yellow/lunar white in order to differentiate them more clearly from running signals.
 
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bramling

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This section is indeed 4 aspect.



To isolate any safety systems on my traction requires the drivers master key to be used, and needs another reset key to reset it.

If the DSD or AWS is not responded to and applies the brakes, simply respond to it and the brakes will release (eventually). I wouldn't expect either of these to be a common occurrence and any respectable driver would ensure they know why they have stopped before starting again and not isolate things without authorisation on an assumption that there is a defect. That would be a serious meeting with management.

Unfortunately we might never understand the truth of what was going through that drivers head at the time.

Not disagreeing, however as I posted upthread there’s nothing in LU’s rule book which actually states how to respond to an unexpected tripcock activation, there seemingly being an assumption that a driver would know if they’ve overrun a signal.

I’d say it’s rather likely this will be an area RAIB focus on.

Whether there’s anything in Chiltern’s TOC-specific instructions or training is another matter of course.
 

357

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Indeed @bramling - I've never known a false TPWS activation but the mainline policy of always calling up would avoid a situation where a driver didn't know they had a SPAD or overspeed.
 

bramling

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Indeed @bramling - I've never known a false TPWS activation but the mainline policy of always calling up would avoid a situation where a driver didn't know they had a SPAD or overspeed.

False tripcock activations aren't uncommon, the favourite suspects being objects like footballs or dead animals (or sometimes live ones!). I guess in olden times it would have been difficult to have a policy of "you must not move until you have reported", as this could cause quite a delay if unable to get through to anyone. Nowadays communications are rather better so this is less of an issue, perhaps the rules haven't quite caught up.

The Kilburn accident in 1984 springs to mind as a comparison - in that instance a Met Line driver had overrun a signal in thick fog. On that occasion it was an automatic signal, he reset and continued and on that occasion collided with the train which was stopped in front of him, tragically with fatal consequences. In those days LU trains had no device regulating speed after a tripcock activation, indeed it's surprising to read on here that Chiltern trains apparently aren't fitted with such a feature.

There will certainly be some learning points here I suspect.
 

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Quite a few posters have mentioned other areas where LU and NR trains share track and have TPWS and/or AWS.

I'm assuming that there are historical reasons why the area in question is not equipped and if so is anyone able to shed some light on why? Thanks
 

AndyPJG

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Broadly depends on who 'owns' the track.
eg Here LU own the track and Chiltern are the 'visitors' so LU systems/rules (tripcocks etc), whereas Wimbledon to Putney is NR and LU the 'visitors' hence NR rules (AWS/TPWS) and tripcocks only required on LU trains.
 

bramling

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Thank you for explaining that.

Although RAIB might suggest things to mitigate any reoccurrence I think that they wouldn't go so far as the installation of TPWS or AWS.

I doubt there will be any need for infrastructure changes. The trainstop system is equivalent to AWS/TPWS, in fact in this application it’s better as providing everything works as calculated it should eliminate any risk of collision if the driver totally disregards the signalling, which neither AWS nor TPWS guaranteed to do. Also bear in mind this signalling is in its twilight years, in fact it should already have been resignalled some years ago, so it will be hard to justify any changes which aren’t absolutely critical.

I suspect we’ll be looking at scrutiny of procedures, both LU and Chiltern, human factors, and perhaps how the tripcock functions on Chiltern trains, in particular how a tripcock activation presents itself to a driver, reset process, and perhaps whether there should be speed control afterwards.

As a wild card, given how far the train travelled, there could be scope to consider whether there could be a SPAD alarm and to what extent a signaller might be realistically able to make an emergency stop radio broadcast.
 
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