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Collision and derailment near Salisbury (Fisherton Tunnel) 31/10/21

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bahnause

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Worth noting that, again as per the RAIB report, SWR instructors stated that they would expect a driver aware of potential low adhesion to be braking “no later than SY29R”, which seems to tie in with the general consensus on this thread.
Is this reflected in the SWR driving policy? Because one of the other downloaded trains didn't brake before SY29R either. Is there a difference between what is expected in hindsight and how it is instructed?
 
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The Ham

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All this pre-occupation with the driver, yet it was the presence of trees and their leaves that caused all of this. A tree can't fall across the line if it isn't there, which it shouldn't have been. Likewise, the leaves, mostly from the forest above the junction, which shouldn't be there either. Oddly, other tunnel locations have been cleared of trees in recent years, although I don't know if it has been maintained. Whiteball, Dainton and Honiton, on this very route.

I suspect that most would (and given the account of discussion about vegetation clearance and the costs) recognise that this is a (if not the) major factor. However, it's also reasonable to question why the driver did some questionable things.

For example, (and whilst I don't drive trains I do drive cars - and yes I know they are very different to drive but the laws of physics aren't) why when it was known that there was low grip that they didn't start to lose speed over a longer period.

In a car you assume a 2 second breaking distance to the car in front, unless it's wet and then you double that and if it's icy you double it again.

I do have a question, on the deceleration graphs there's a note about a 50mph PSR warning board, whilst one of the trains does go through at below that speed, the other two don't - is that a speed limit (in which case why were the other two too fast) or guidance (in which case or should raise questions of any driver which didn't follow that guidance who then was involved in an incident), a warning of a speed limit (again why not use that to start to slow the train with the lightest of break use, maybe even intermittent breaking, which appears to be what one of the trains did) or something else?

As I said, clearly without the trees things would be different, but in a lot of road accidents there's factors which make things worse than they should be (for example leaves blocking drainage) and whilst they should be the main focus that doesn't mean that people can't question the decisions of the driver (for example if driving a car on a road with excess water due to blocked drains, if you're approaching a point of conflict it would be good practice to reduce your speed more than normal, if someone didn't do that and then had a crash, it's reasonable for people to ask what were they doing?).

From what's been said, that's the tone of the posts about this (i.e. curious about their choices rather than, say, suggesting that the driver shouldn't have been driving). There's a lot of respect for drivers (you can generally ignore those who moan about how well paid they are, especially if it's about how they've broadly maintained their pay against inflation when others haven't) and this appears to be reflected in the tone of the discussions on here.
 

edwin_m

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I do have a question, on the deceleration graphs there's a note about a 50mph PSR warning board, whilst one of the trains does go through at below that speed, the other two don't - is that a speed limit (in which case why were the other two too fast) or guidance (in which case or should raise questions of any driver which didn't follow that guidance who then was involved in an incident), a warning of a speed limit (again why not use that to start to slow the train with the lightest of break use, maybe even intermittent breaking, which appears to be what one of the trains did) or something else?
It's a warning of a speed restriction ahead, placed so there is normally enough distance to decelerate from the speed permitted at the warning to the speed of the actual restriction where it starts. Strictly speaking it shouldn't be necessary, as drivers should know the restrictions as part of route knowledge, but there have been serious accidents over the years arising from drivers losing concentration or becoming unwaware of their position, so the warning and associated AWS magnet provides an extra safeguard. In poor adhesion conditions a driver may decide to start their braking before the warning board.
 

Railwaysceptic

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Here in Italy....more so than it used to be - but nothing like the extent that it has become in the UK.
I haven't noticed London Underground's railway where it runs in the open being as overgrown with vegetation as the main railway network.
 

dctraindriver

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74 is a fine old age. Were checks done to ensure the driver was in suitable health to drive? :)
A medical is a yearly requirement once you hit 55 as a driver so at his last medical he was passed fit to drive. Not many in the seat at that age for sure.
 

Towers

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He wouldn’t have been in the seat if he wasn’t in a fit state, one area the railway really doesn’t take risks is with medical fitness!
 

Nicholas Lewis

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No matter how many times I read this report, I still can’t make much sense of what this driver was doing. I find it bordering on incredulous that a driver would be scouring the line (at nearly 90 mph) in the pitch dark for a fallen tree to use as a braking marker, when he had a perfectly good braking marker in the form of the double yellow aspect, even if this meant the red aspect was heavily overbraked. If worried about adhesion, why would anyone not simply brake earlier, even if just getting the train down a more manageable speed? If the driver wasn’t concerned about adhesion then why change braking points in the first place?

I suspect this is going to be added to the list of incidents where we we will probably never know the true cause. It would neatly fit in to the box of commonly seen caution aspect, no need to react immediately (especially in this case with the extra distance), lose concentration (in this case possibly wondering about the fallen tree), and then the brown stuff moment - except in this case the driver still applied light braking. To me the whole thing made little sense in the first version of the report, and it still doesn’t.
Im surprised RAIB haven't made more of SY29R being significantly overbraked along with potentially daily occurrences of receiving a YY here leads to normal behaviour to run considerably past SY29R before initiating braking. Even 1L43 ran on for 3/4 mile before starting barking. Also worrying is how ineffective the braking and sanding equipment was with the train on several occasions seeing its speed increase once from 60 to nearly 80mph whilst in full emergency. RAIB have made recommendations on this but the industry needs to get on and fit variable rate sanders as the low adhesion isn't going away and we dont want another reason to impose blanket speed restrictions to cover the risk.
 

GC class B1

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Im surprised RAIB haven't made more of SY29R being significantly overbraked along with potentially daily occurrences of receiving a YY here leads to normal behaviour to run considerably past SY29R before initiating braking. Even 1L43 ran on for 3/4 mile before starting barking. Also worrying is how ineffective the braking and sanding equipment was with the train on several occasions seeing its speed increase once from 60 to nearly 80mph whilst in full emergency. RAIB have made recommendations on this but the industry needs to get on and fit variable rate sanders as the low adhesion isn't going away and we dont want another reason to impose blanket speed restrictions to cover the risk.
My understanding is that class 158 and 159 have an older design of WSP that is not as effective as modern WSP systems.
I haven’t seen anywhere in the report that the train speed increased on several occasions and once from 60 to nearly 80 MPH. This would be an extremely strange occurrence with an Emergency brake application and would probably require brake release and traction to be applied. Can you quote where this is stated in the report. It may be that you have read the wheelset rotational speed in the OTDR download as being the train speed. I think the speedometer wheelset may have slowed to 60 MPH while the train speed was almost 80 MPH and when the WSP released the brake on that wheelset then the wheel rail adhesion was sufficient for the wheelset to increase speed to match the train speed.
 
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chuff chuff

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I've seen a speed increase quite a few times after releasing the brake and allowing the wheels to turn at the real speed of the train.
 

Nicholas Lewis

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My understanding is that class 158 and 159 have an older design of WSP that is not as effective as modern WSP systems.
I haven’t seen anywhere in the report that the train speed increased on several occasions and once from 60 to nearly 80 MPH. This would be an extremely strange occurrence with an Emergency brake application and would probably require brake release and traction to be applied. Can you quote where this is stated in the report. It may be that you have read the wheelset rotational speed in the OTDR download as being the train speed. I think the speedometer wheelset may have slowed to 60 MPH while the train speed was almost 80 MPH and when the WSP released the brake on that wheelset then the wheel rail adhesion was sufficient for the wheelset to increase speed to match the train speed.
Argh your correct the fluctuating speed is of course whats measured on the wheelset not the physical speed of the train. Mind you seems odd how differently 1L45 behaved under WSP compared to 1L53 where the former has a rapid fluctuation of WSP where as 1L53 WSP was much slower although the RAIB report doesn't have the data for what the brake pressure was actually doing and may not be measured.
 

GC class B1

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Argh your correct the fluctuating speed is of course whats measured on the wheelset not the physical speed of the train. Mind you seems odd how differently 1L45 behaved under WSP compared to 1L53 where the former has a rapid fluctuation of WSP where as 1L53 WSP was much slower although the RAIB report doesn't have the data for what the brake pressure was actually doing and may not be measured.
Class 158 and 159 have a three step energise to release ep brake and not an analogue brake control. I have studied the OTDR traces and concluded that 1L43 and 1L45 were both braking in step 1. 1L53 was braking in step 3/emergency. This probably explains why the WSP on 1L53 didn’t seem to be as effective as the WSP dump valves would take longer to vent the brake cylinder pressure. As a result the wheelset deceleration would occur over a longer interval and therefore the wheelsets would have slowed down more than the step 1 brake application of the two previous trains over the low adhesion areas.
 

bahnause

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Class 158 and 159 have a three step energise to release ep brake and not an analogue brake control. I have studied the OTDR traces and concluded that 1L43 and 1L45 were both braking in step 1. 1L53 was braking in step 3/emergency. This probably explains why the WSP on 1L53 didn’t seem to be as effective as the WSP dump valves would take longer to vent the brake cylinder pressure.
The WSP dump valves are activated when wheelslip occurs. This occurs at the same brake cylinder pressure, regardless of the position of the brake.
I suspect completely different rail conditions here and therefore different behavior of the WSP.
 

The Ham

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It's a warning of a speed restriction ahead, placed so there is normally enough distance to decelerate from the speed permitted at the warning to the speed of the actual restriction where it starts. Strictly speaking it shouldn't be necessary, as drivers should know the restrictions as part of route knowledge, but there have been serious accidents over the years arising from drivers losing concentration or becoming unwaware of their position, so the warning and associated AWS magnet provides an extra safeguard. In poor adhesion conditions a driver may decide to start their braking before the warning board.

Thanks.
 

GC class B1

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The WSP dump valves are activated when wheelslip occurs. This occurs at the same brake cylinder pressure, regardless of the position of the brake.
I suspect completely different rail conditions here and therefore different behavior of the WSP.
I don’t understand this. In simple terms the dump valve has to vent the brake cylinder pressure to a low value in order for the wheelset to recommence rotating. In step 3 the brake cylinder pressure will be roughly three times the value in step 1 so in order to vent this pressure to the same value that would be needed in step 1 much more air needs to be vented which will take longer.
 

bahnause

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In step 3 the brake cylinder pressure will be roughly three times the value in step 1 so in order to vent this pressure to the same value that would be needed in step 1 much more air needs to be vented which will take longer.
Brake cylinder pressure will never reach the higher pressure. Let's say step 1 equals 1bar brake cylinder pressure, step 2 equals 2bar and step 3 equals 3bar. If Wheelslip occurs at 05.bar WSP will always activate when brake cylinder pressure reaches 0.5bar. It will not wait until the brake is fully applied with 3bar.
 

GC class B1

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Brake cylinder pressure will never reach the higher pressure. Let's say step 1 equals 1bar brake cylinder pressure, step 2 equals 2bar and step 3 equals 3bar. If Wheelslip occurs at 05.bar WSP will always activate when brake cylinder pressure reaches 0.5bar. It will not wait until the brake is fully applied with 3bar.
Thank you. I now understand the reasoning for your post. However the evidence from the OTDR trace is that the wheel slide occurred over a longer interval on 1L53 and the deceleration rate was faster. The brake cylinder pressure would rise very quickly and my understanding is that this older WSP is slower reacting than modern WSP systems. Also when the dump valve reclosed in your example it would have 3 bar air to immediately admit to the brake cylinders.
 

bahnause

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Thank you. I now understand the reasoning for your post. However the evidence from the OTDR trace is that the wheel slide occurred over a longer interval on 1L53 and the deceleration rate was faster. The brake cylinder pressure would rise very quickly and my understanding is that this older WSP is slower reacting than modern WSP systems. Also when the dump valve reclosed in your example it would have 3 bar air to immediately admit to the brake cylinders.
The speed curve of 1L53 is lacking the littel "spikes" shown for 1L45 in step 2. Even a complete release of the brake wouldn't take as long as it is shown on the graph. This graph - in my opinion - shows a WSP unaware of the actual amount of wheelslip occuring. Do the trains use the same WSP or are there differences? Does the WSP behave differently depending on the brake step used?
 

GC class B1

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The speed curve of 1L53 is lacking the littel "spikes" shown for 1L45 in step 2. Even a complete release of the brake wouldn't take as long as it is shown on the graph. This graph - in my opinion - shows a WSP unaware of the actual amount of wheelslip occuring. Do the trains use the same WSP or are there differences? Does the WSP behave differently depending on the brake step used?
I am also surprised at the differences between 1L53 and the two previous trains. The report does say what the consist of the previous trains were. As far as I am aware all class 158 and 159 units have the same WSP system. If they were Turbostar units or similar then I think the WSP systems would be a more modern design which monitor the speed of an unbraked wheelset and act quickly so that the wheelsets never stop rotating and optimise braking. I suspect that the WSP on 1L53 wasn’t performing as well as the systems on the previous trains but this isn’t considered in the report. There may be a number of reasons for this.
 

bahnause

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I suspect that the WSP on 1L53 wasn’t performing as well as the systems on the previous trains but this isn’t considered in the report. There may be a number of reasons for this.
I agree. The more I look into the report, the more disappointed I am with it. It raises questions that it should actually answer.
 

Tomnick

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Class 158 and 159 have a three step energise to release ep brake and not an analogue brake control. I have studied the OTDR traces and concluded that 1L43 and 1L45 were both braking in step 1. 1L53 was braking in step 3/emergency. This probably explains why the WSP on 1L53 didn’t seem to be as effective as the WSP dump valves would take longer to vent the brake cylinder pressure. As a result the wheelset deceleration would occur over a longer interval and therefore the wheelsets would have slowed down more than the step 1 brake application of the two previous trains over the low adhesion areas.
In my experience, both of driving them and of looking at post-incident download data, the WSP is indeed less effective in step 3 than step 2 in moderate wheelslide conditions – and, on 170s, less effective again in emergency (which, unlike 158s, provide higher brake cylinder pressure in emergency than in step 3). It was quite striking on one particular download, from a 170 approaching a signal at danger – you could see the time/speed curve flatten as the driver selected step 3, and again as he selected emergency. Personally, I'm pretty sure that the driver in that case would've stopped comfortably on the right side of the signal if he'd left it in step 2, which unfortunately goes against everything that we're trained nowadays. Not sure it'd have made any difference at Salisbury though, where it's clear that the WSP wasn't really serving to get the wheels rotating again each time.
 

Dan G

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My impression is that step 2 or even step 1 would have reduced speed more than step 3/emergency. Perhaps even enough to have a very, very near miss instead of a collision with the other train
 

GC class B1

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My impression is that step 2 or even step 1 would have reduced speed more than step 3/emergency. Perhaps even enough to have a very, very near miss instead of a collision with the other train
I think you may be right based on the braking performance of 1L43 and 1L45. This is assuming that the available adhesion for 1L53 was similar to that for the 1L43 and 1L45 and the WSP performance for all three units was similar. Unfortunately there is no way of determining now whether this was the case.
 
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Dan G

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Adhesion for 1L53 was definitely lower as it was the first service to run after the light drizzle had wetted the leaf build-up on the rails, but yes it was those charts that led me to consider this. I do think the WSP would have been able to make more use of the adhesion available if it wasn't going back and forth all the way to L3/E pressure each cycle – if that's indeed how it works on the system fitted to the units.

Also it's disappointing that RAIB didn't look into whether Network Rail's decisions to delay taking action on the excessive vegetation were reasonable given the lack of staff ("resource"). If there had been deaths I'm sure they would have.
 

norbitonflyer

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I think you may be right based on the braking performance of 1L43 and 1L45. This is assuming that the available adhesion for 1L53 was similar to that for the 1L43 and 1L45 and the WSP performance for all three units was similar. Unfortunately there is no way of determining now whether this was the case.
All other things being equal, 1L43, being a six-car formation, might be expected to have better braking in wet conditions than the two subsequent trains, which were both three-car, as the rear unit would benefit from having the rails cleaned by the front one.
Of course all other things would not necessarily have been equal - dampness of the track, number of passengers and therefore weight of tbe train, amount of wear on the brakes, could all have had an effect.
 

Stigy

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My impression is that step 2 or even step 1 would have reduced speed more than step 3/emergency. Perhaps even enough to have a very, very near miss instead of a collision with the other train
I believe it may be different with SWR, but not sure if it was at the time of this incident, but our step 1 on a 158 (GWR) is usually terrible. Admittedly, it may be better than a slide though. We’re told if we go in to an all wheel slide, to just throw it all in, as recovering one would usually be impossible.

Step 3 on our 158s is also the same (brake pressure wise) as emergency. Again, that may be different for other TOCs?
 

ainsworth74

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Step 3 on our 158s is also the same (brake pressure wise) as emergency. Again, that may be different for other TOCs?
If the RAIB are to be believed it's the same on all 158s and 159s but on more modern units emergency will have a higher level of breaking applied:

39 The braking system fitted to class 158 and class 159 units decelerates the train by supplying air to brake cylinders mounted on the train’s bogies. These brake cylinders apply friction pads to brake discs mounted on the wheelsets. A driver can apply three levels of braking in normal service. Step 1 brake provides the lowest level of braking, while step 3 (known as ‘full service braking’) provides the maximum braking effort. A driver can also make an emergency brake application. This applies the same level of retardation* as step 3 but uses a different control system to normal service braking so the train can still be braked in the event of a failure of that system.

*More recent multiple unit passenger trains are fitted with enhanced emergency brakes, which apply a higher level of retardation than full service braking. The relevant standard does not require class 158 and class 159 trains to have this capability.
 

GC class B1

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If the RAIB are to be believed it's the same on all 158s and 159s but on more modern units emergency will have a higher level of breaking applied:
All class 158 and 158 and in fact all sprinters have the same deceleration rate in Full Service and Emergency. The brake control is by ‘energise to release’ so that in the event of loss of power or train division the Full Service application will be initiated. Release is obtained by energising two of the three brake control wires. The third wire is the return wire. Release will be when both signal wires are energised. Steps 1 and 2 will be alternate signal wires energised and Full Service will be both signal wires deenergised. In Emergency all brake control wires are grounded to earth so that any faults cannot energise any brake control wires.
The brakes steps should give a nominal 3%, 6% and 9% g deceleration rates respectively. In a properly maintained unit step 1 (3% g) should give a noticeable deceleration.

I believe it may be different with SWR, but not sure if it was at the time of this incident, but our step 1 on a 158 (GWR) is usually terrible. Admittedly, it may be better than a slide though. We’re told if we go in to an all wheel slide, to just throw it all in, as recovering one would usually be impossible.

Step 3 on our 158s is also the same (brake pressure wise) as emergency. Again, that may be different for other TOCs?
I am not sure that ‘throw it all in’ is the correct approach. Figure 34 in the report shows an extended recovery time for the WSP in step 3 compared with step 2. In a step 2 slide it is possible that the stopping distance would be shorter in step 2 than on step 3.
 
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