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

[Wilts Wanderer]

While on this occassion it was only due to late running of the GWR service that both trains reached tunnel junction around the same time, it is quite common (at least was when I used to often travel on this route as a passenger a few years ago that the Waterloo to Exeter service would be held before tunnel juncton for a Portsmouth to Cardiff service as it was a scheduled connection from Portsmouth to Cardiff service to the Exeter Service at Salisbury. If the Portsmouth to Cardiff was running a few minutes late the Exeter Service would sometimes enter Salisbury ahead of it (presumably where doing so would not delay the Cardiff service further) but would then be held as Salisbury while the Cardiff service arrived and departed. On this occassion by delaying the Exeter at Tunnel Junction makes sense as by not doing so would have further delayed both services leaving Salisbury.

Although this incident occurred on a Sunday, when the patterns are different, it’s worth noting that the standard weekday and Saturday timetables have both up and down Portsmouth-Cardiff trains crossing Tunnel Junction about 3 mins ahead of the Waterloo-Exeter and therefore signal checks to the latter service will be extremely common.

 

[niggill617@gma]

Ditto. And driving using this technique doesn't result in delays; at least not on the services I drive.

On this point, however, there is a nagging thought I have in the back of my mind about low adhesion driving that I thought I'd air for discussion.

I recall having a conflab with a driver manager at my former TOC some years back about low adhesion driving. He was banging the drum, telling me that if I thought I was about to slide through somewhere that I should bang the brake straight into emergency. To me this really didn't make a huge amount of sense except on the basis that it ticked a box.

My thinking was that if you were already in a slide it meant that the amount of brake force you were trying to use had already exceeded the limit of adhesion afforded by the conditions, so how would attempting to use even more brake force help you to stop any faster? Surely all you'd do is exacerbate the slide and, by selecting emergency, lose control over the train. I'd shared this thought process with him, but he wasn't going to be distracted from pushing the party line and so I agreed that, yes, if I found myself in a situation like this I would do as he demanded so that he could put it on his form.

I'd parked these thoughts for a while, but the overrun at Stonegate back in November 2010 caused them to resurface. For those who don't recall, this was when a SET service slid for over 3 miles due to a combination of poor railhead conditions and a lack of sand in the leading end of the train. The driver had been using the updated low adhesion driving technique of applying Step 2 brake in order to get the assistance of the sanders but found himself in difficulty approaching Stonegate. The RAIB report into the overrun notes the following;







I found it very interesting that, even without sand, going back to the former instructions of "earlier and lighter" the driver was able to make the next three stations without difficulty (no doubt aided in part by the rising gradient). Here was some vindication of my earlier thoughts regarding low adhesion.

Now obviously it's not appropriate to drive like this everywhere on the network. Clearly you can't be doing this on a busy inner-suburban network, but where I work now it does seem that a driver can still utilise this technique without any apparent performance penalties. No doubt this could be replicated elsewhere also.

Thoughts...?

Ditto. And driving using this technique doesn't result in delays; at least not on the services I drive.

On this point, however, there is a nagging thought I have in the back of my mind about low adhesion driving that I thought I'd air for discussion.

I recall having a conflab with a driver manager at my former TOC some years back about low adhesion driving. He was banging the drum, telling me that if I thought I was about to slide through somewhere that I should bang the brake straight into emergency. To me this really didn't make a huge amount of sense except on the basis that it ticked a box.

My thinking was that if you were already in a slide it meant that the amount of brake force you were trying to use had already exceeded the limit of adhesion afforded by the conditions, so how would attempting to use even more brake force help you to stop any faster? Surely all you'd do is exacerbate the slide and, by selecting emergency, lose control over the train. I'd shared this thought process with him, but he wasn't going to be distracted from pushing the party line and so I agreed that, yes, if I found myself in a situation like this I would do as he demanded so that he could put it on his form.

I'd parked these thoughts for a while, but the overrun at Stonegate back in November 2010 caused them to resurface. For those who don't recall, this was when a SET service slid for over 3 miles due to a combination of poor railhead conditions and a lack of sand in the leading end of the train. The driver had been using the updated low adhesion driving technique of applying Step 2 brake in order to get the assistance of the sanders but found himself in difficulty approaching Stonegate. The RAIB report into the overrun notes the following;







I found it very interesting that, even without sand, going back to the former instructions of "earlier and lighter" the driver was able to make the next three stations without difficulty (no doubt aided in part by the rising gradient). Here was some vindication of my earlier thoughts regarding low adhesion.

Now obviously it's not appropriate to drive like this everywhere on the network. Clearly you can't be doing this on a busy inner-suburban network, but where I work now it does seem that a driver can still utilise this technique without any apparent performance penalties. No doubt this could be replicated elsewhere also.

Thoughts...?

Interesting how some members state brake steps, and others units of deceleration i.e. percent g. I know of driving instructors and competence managers, that simply don't understand the basic mathematical physics of motion, and friction.

I believe the industry is non-compliant to U.K. law in the form of S.I. 1798 attached re: Schedule 3 paragraphs 1. , 6. (e) , 8. (a) (b) and just for the sake of it (c). The other attachment is from the RDG guidance notes and elaborates on the subject matter.

The ORR stated to me calculation is for TOPS, and that many drivers would not understand the basic theory per se. Most skilled jobs are a combination of theory and practice, not purely the arcane. A senior training manager put it all down to lost in translation, from Euro English, and dismissed it from continuation / ab initio training. The RAIB fail to highlight this training requirement.

 

[GC class B1]

Interesting how some members state brake steps, and others units of deceleration i.e. percent g. I know of driving instructors and competence managers, that simply don't understand the basic mathematical physics of motion, and friction.

I believe the industry is non-compliant to U.K. law in the form of S.I. 1798 attached re: Schedule 3 paragraphs 1. , 6. (e) , 8. (a) (b) and just for the sake of it (c). The other attachment is from the RDG guidance notes and elaborates on the subject matter.

The ORR stated to me calculation is for TOPS, and that many drivers would not understand the basic theory per se. Most skilled jobs are a combination of theory and practice, not purely the arcane. A senior training manager put it all down to lost in translation, from Euro English, and dismissed it from continuation / ab initio training. The RAIB fail to highlight this training requirement.

I find your post very interesting. I have had reason to carefully consider and understand both SIs and EN standards with regard to the braking design and performance requirements for Rolling Stock in Britain. I have found that there are instances where the translation from the EU documents has resulted in the text of some requirements not being self explanatory and require careful consideration. However when taken in context I have found the technical requirements to be logical and generally represent best practice.

With regard to your point about possible non compliance with UK law, do you have any evidence to support this.

 

[niggill617@gma]

I find your post very interesting. I have had reason to carefully consider and understand both SIs and EN standards with regard to the braking design and performance requirements for Rolling Stock in Britain. I have found that there are instances where the translation from the EU documents has resulted in the text of some requirements not being self explanatory and require careful consideration. However when taken in context I have found the technical requirements to be logical and generally represent best practice.

With regard to your point about possible non compliance with UK law, do you have any evidence to support this.

I retired from driving back in May, the requirement to calculate braking performance was September 2018, for existing drivers I think? I was never trained how to calculate a braking performance / distance, as part of continuation training. I therefore believe the industry non-compliant. My basic knowledge just comes from O level physics.

I would like to stress that driving must be intuitive not by numbers. This issue is General Professional Knowledge not a procedure.

 

[Val3ntine]

I understand that with current systems you can not know exactly where a train is, especially on very long sections.

Likewise you should never bring in a system which overrides the signals.

However I may not have been overly clear.

First up the system would only ever provide a guide to train speed, which would never set the speed faster than a suitable speed for the section of line based on the current signal conditions. For a specific example it may, at the first non green signal (or possibly even before that), have advised the driver to reduce speeds to a maximum of 75mph. This would be a lower maximum speed than the line speed. It's there anything in that which is misleading the driver? Does that stop the driver from thinking, I know that conditions are bad and so I'll go a bit slower than the maximum speed which I've been advised.

It's like if there's a 50mph limit on a smart motorway, if there's thick freezing fog that doesn't stop a car or lorry driver going slower.

Whilst the system may not know the exact location of the trains within the junction the distances are likely to be fairly short and movement times are likely to be fairly similar. However even if something doesn't work out (say a train stops for whatever reason), then the system would update new maximum speeds to the point where a driver comes to a stop at the signal controlling a junction.

On longer run sections the system would know the likely profile of the leading train and advise the following one accordingly. For instance a class 80x following a class 158 would be advised to run at a maximum of 90mph even if the line speed was 125mph.

Of course the above also could be made more accurate by the advisory speed system being aware of which tablets are using it and their locations.

The system wouldn't be a replacement for the driver's skill, rather a maximum speed advisory system. It's goal would be reduced the need for trains to stop at signals and in doing so reduce the energy requirements of the railways (from reducing the account of acceleration which is undertaken). However drivers, much like lorry drivers on variable speed limit roads, still have to be aware of other factors (signals, weather conditions, etc.).

Yes the system isn't going to make it that no train is ever going to stop away from a platform, however by knowing that a train movement is currently underway which prohibits the signal at red from giving clearance for the train approaching to proceed and that it's likely that it'll not do so for at least another 3 minutes and that under normal conditions the train on approach will take 2 minutes to get to the signal. As such it would advise the train to slow to a maximum speed so it then takes 3 minutes 20 seconds to get there.

Now if the train movement underway takes 4 minutes to undertake the movement, the approaching train will still stop at the signal as the driver will still follow the instructions of the signals (like a car should still stop in a 40mph limit of the traffic lights are red). However if it clears it in 3 minutes then the protecting signal (assuming everything is lined up to allow it to do so) would then allow the approaching train to proceed, potentially without the train stopping (although it would still have slowed significantly).

The training behind such a system would be that it's guidance, however if you fail to stop at a signal that would be the same as if you were following it's guidance or not. Likewise if you exceed the maximum speed guidance and something goes wrong then you'd have to have a fairly good reason for doing so (for instance poor braking conditions). Likewise you should know the maximum linespeed and of it advises you to go faster than that, then it should be reported and the linespeed limit adhered to (as systems are only as good as the people programming them and this is only a secondary system).

What you basically describe here is a form of ETCS. Maximum speed, target speed. At this point you might as well replace the signals with MA (Movement Authority) via in cab signalling.

 

[O L Leigh]

I understand that with current systems you can not know exactly where a train is, especially on very long sections.

Likewise you should never bring in a system which overrides the signals.

However I may not have been overly clear.

First up the system would only ever provide a guide to train speed, which would never set the speed faster than a suitable speed for the section of line based on the current signal conditions. For a specific example it may, at the first non green signal (or possibly even before that), have advised the driver to reduce speeds to a maximum of 75mph. This would be a lower maximum speed than the line speed. It's there anything in that which is misleading the driver? Does that stop the driver from thinking, I know that conditions are bad and so I'll go a bit slower than the maximum speed which I've been advised.

It's like if there's a 50mph limit on a smart motorway, if there's thick freezing fog that doesn't stop a car or lorry driver going slower.

Whilst the system may not know the exact location of the trains within the junction the distances are likely to be fairly short and movement times are likely to be fairly similar. However even if something doesn't work out (say a train stops for whatever reason), then the system would update new maximum speeds to the point where a driver comes to a stop at the signal controlling a junction.

On longer run sections the system would know the likely profile of the leading train and advise the following one accordingly. For instance a class 80x following a class 158 would be advised to run at a maximum of 90mph even if the line speed was 125mph.

Of course the above also could be made more accurate by the advisory speed system being aware of which tablets are using it and their locations.

The system wouldn't be a replacement for the driver's skill, rather a maximum speed advisory system. It's goal would be reduced the need for trains to stop at signals and in doing so reduce the energy requirements of the railways (from reducing the account of acceleration which is undertaken). However drivers, much like lorry drivers on variable speed limit roads, still have to be aware of other factors (signals, weather conditions, etc.).

Yes the system isn't going to make it that no train is ever going to stop away from a platform, however by knowing that a train movement is currently underway which prohibits the signal at red from giving clearance for the train approaching to proceed and that it's likely that it'll not do so for at least another 3 minutes and that under normal conditions the train on approach will take 2 minutes to get to the signal. As such it would advise the train to slow to a maximum speed so it then takes 3 minutes 20 seconds to get there.

Now if the train movement underway takes 4 minutes to undertake the movement, the approaching train will still stop at the signal as the driver will still follow the instructions of the signals (like a car should still stop in a 40mph limit of the traffic lights are red). However if it clears it in 3 minutes then the protecting signal (assuming everything is lined up to allow it to do so) would then allow the approaching train to proceed, potentially without the train stopping (although it would still have slowed significantly).

The training behind such a system would be that it's guidance, however if you fail to stop at a signal that would be the same as if you were following it's guidance or not. Likewise if you exceed the maximum speed guidance and something goes wrong then you'd have to have a fairly good reason for doing so (for instance poor braking conditions). Likewise you should know the maximum linespeed and of it advises you to go faster than that, then it should be reported and the linespeed limit adhered to (as systems are only as good as the people programming them and this is only a secondary system).

We have become so inured to solutions being technological that we fail to see it's limitations.

The problem with that is that the driver still has to decide where to apply the brake to slow/stop the train by a certain point, and this for me is the crux of the problem. The SWR driver was incredibly experienced an no doubt knew the route inside out, and yet still got caught out.

The issue is not adhering to pre-defined deceleration curve but finding yourself suddenly on an unexpectedly bad section of rail. No amount of technology is going to be able to tell the driver that this is about to happen.

== Doublepost prevention - post automatically merged: 25 Feb 2022 ==

I’ve always found the regimental nature of (some) PDPs unfortunate, and this manifested itself in the Stonegate driver feeling the need to operate the train in a way which was against their better judgement out of concern for something flagging up on a potential download. That is extremely undesirable.

I think you might be perhaps inferring something about the actions of the SET driver involved in the Stonegate incident. I don't know if he felt that he had to drive the train in a certain way in order to satisfy the TOC's PDP or whether this was his normal braking technique. I'm sure that the train would have stopped OK provided it had had sufficient sand onboard.

However, on your broad points I do agree. My own feeling is that it doesn't really matter what I do because, as long as I don't mess it up, it doesn't matter what goes on the OTMR.

Interesting how some members state brake steps, and others units of deceleration i.e. percent g. I know of driving instructors and competence managers, that simply don't understand the basic mathematical physics of motion, and friction.

Some trains have a stepless brake controller, hence giving braking inputs as a percentage (as displayed to the driver in the cab).

But yes, I think this basic misunderstanding was what was behind the discussion I had.

 

[niggill617@gma]

We have become so inured to solutions being technological that we fail to see it's limitations.

The problem with that is that the driver still has to decide where to apply the brake to slow/stop the train by a certain point, and this for me is the crux of the problem. The SWR driver was incredibly experienced an no doubt knew the route inside out, and yet still got caught out.

The issue is not adhering to pre-defined deceleration curve but finding yourself suddenly on an unexpectedly bad section of rail. No amount of technology is going to be able to tell the driver that this is about to happen.

== Doublepost prevention - post automatically merged: 25 Feb 2022 ==



I think you might be perhaps inferring something about the actions of the SET driver involved in the Stonegate incident. I don't know if he felt that he had to drive the train in a certain way in order to satisfy the TOC's PDP or whether this was his normal braking technique. I'm sure that the train would have stopped OK provided it had had sufficient sand onboard.

However, on your broad points I do agree. My own feeling is that it doesn't really matter what I do because, as long as I don't mess it up, it doesn't matter what goes on the OTMR.



Some trains have a stepless brake controller, hence giving braking inputs as a percentage (as displayed to the driver in the cab).

But yes, I think this basic misunderstanding was what was behind the discussion I had.

I drove class 800s for a few years. The TOC instructions stated, we must not use the percent gauge. I always braked using 30 percent on the gauge. This would be 0.36 m/s/s, I found it worked very well in practice, never lost time because of my braking style. In fact I would often make up time, re built in get back, and consist excellent acceleration.

The anti - skid light would often illuminate, even at this rate of retarding force. The basic maths ( rotation/linear velocity) from my technician days, meant I need not get concerned, just be aware.

 

[bramling]

I think you might be perhaps inferring something about the actions of the SET driver involved in the Stonegate incident. I don't know if he felt that he had to drive the train in a certain way in order to satisfy the TOC's PDP or whether this was his normal braking technique. I'm sure that the train would have stopped OK provided it had had sufficient sand onboard.

However, on your broad points I do agree. My own feeling is that it doesn't really matter what I do because, as long as I don't mess it up, it doesn't matter what goes on the OTMR.

RAIB allude to it in the Stonegate report.

“At Crowhurst, the driver, after making an initial brake application in step one, reverted to the current driving policy, because he was concerned that the OTDR data would be analysed and his non-compliance identified. Here, the train experienced significant WSP activity, and the driver had to use the emergency brake to stop correctly in the platform.”

 

[O L Leigh]

I drove class 800s for a few years. The TOC instructions stated, we must not use the percent gauge. I always braked using 30 percent on the gauge. This would be 0.36 m/s/s, I found it worked very well in practice, never lost time because of my braking style. In fact I would often make up time, re built in get back, and consist excellent acceleration.

The anti - skid light would often illuminate, even at this rate of retarding force. The basic maths ( rotation/linear velocity) from my technician days, meant I need not get concerned, just be aware.

Why wouldn't you be allowed to use the brake gauge? That seems quite odd. I think that every driver knows that it's a display showing the amount of brake force you're applying rather than the rate of deceleration.

I think I'd rather be able to stop a train on the mark than to be able to mathematically calculate braking distances. The formula I use is; what I see out of the window x what I feel through my backside + experience.

RAIB allude to it in the Stonegate report.

“At Crowhurst, the driver, after making an initial brake application in step one, reverted to the current driving policy, because he was concerned that the OTDR data would be analysed and his non-compliance identified. Here, the train experienced significant WSP activity, and the driver had to use the emergency brake to stop correctly in the platform.”

My apologies. I didn't spot that in the report.

I wonder what might have happened had the driver stuck with his first impulse.

 

[niggill617@gma]

Ditto. And driving using this technique doesn't result in delays; at least not on the services I drive.

On this point, however, there is a nagging thought I have in the back of my mind about low adhesion driving that I thought I'd air for discussion.

I recall having a conflab with a driver manager at my former TOC some years back about low adhesion driving. He was banging the drum, telling me that if I thought I was about to slide through somewhere that I should bang the brake straight into emergency. To me this really didn't make a huge amount of sense except on the basis that it ticked a box.

My thinking was that if you were already in a slide it meant that the amount of brake force you were trying to use had already exceeded the limit of adhesion afforded by the conditions, so how would attempting to use even more brake force help you to stop any faster? Surely all you'd do is exacerbate the slide and, by selecting emergency, lose control over the train. I'd shared this thought process with him, but he wasn't going to be distracted from pushing the party line and so I agreed that, yes, if I found myself in a situation like this I would do as he demanded so that he could put it on his form.

I'd parked these thoughts for a while, but the overrun at Stonegate back in November 2010 caused them to resurface. For those who don't recall, this was when a SET service slid for over 3 miles due to a combination of poor railhead conditions and a lack of sand in the leading end of the train. The driver had been using the updated low adhesion driving technique of applying Step 2 brake in order to get the assistance of the sanders but found himself in difficulty approaching Stonegate. The RAIB report into the overrun notes the following;







I found it very interesting that, even without sand, going back to the former instructions of "earlier and lighter" the driver was able to make the next three stations without difficulty (no doubt aided in part by the rising gradient). Here was some vindication of my earlier thoughts regarding low adhesion.

Now obviously it's not appropriate to drive like this everywhere on the network. Clearly you can't be doing this on a busy inner-suburban network, but where I work now it does seem that a driver can still utilise this technique without any apparent performance penalties. No doubt this could be replicated elsewhere also.

Thoughts...?

An HST 2 plus 8 went past a signal by 260 m a number of years ago, within a low rail adhesion zone. At the time I was learning the said traction, having moved from sprinters. I asked for the timeline from the download, so I may analyse and learn from this incident. Notwithstanding data protection, I was given a redacted part copy of the 72 hrs review.

The driver was braking light from initial, then step 2 shortly followed by 3 and 4. When the brake force is established the anti-skid system kicks in, at about step 2. Note sand system isn't fitted to class 43 or stock. The driver follows up with sequential brake steps finishing with emergency. The consist is out of control and the signal is passed exceeding the safety overlap.

When I scrutinised the numbers I found the consist was in control right up to step 5, the anti-skid was simply doing the job perfectly well. Control was lost when full service was selected, and static friction hit the rubicon. The investigation stated the incident was unavoidable. In my opinion and basic calculation the incident was easily avoidable, but more importantly no lesson have been learnt.

I would generally say especially with modern traction, if in a tricky situation get emergency selected sooner rather than later. As you also suggest, its a bit like deciding when to hit the REC red button, best to stop all trains, hopefully away from the collision point?

Aside 05/03/22, post script just to clarify last sentence. Note "generally" and "modern traction" all in the interest of widely accepted best practice.

 

[O L Leigh]

When I scrutinised the numbers I found the consist was in control right up to step 5, the anti-skid was simply doing the job perfectly well. Control was lost when full service was selected, and static friction hit the rubicon. The investigation stated the incident was unavoidable. In my opinion and basic calculation the incident was easily avoidable, but more importantly no lesson have been learnt.

I would generally say especially with modern traction, if in a tricky situation get emergency selected sooner rather than later, as you also suggest. Its a bit like deciding when to hit the REC red button, best to stop all trains, hopefully away from the collision point?

It's possible that there's a key detail that I've missed. In the incident you cite, your analysis disagreed with the official findings in that the incident could have been avoided. Presumably this means that you felt that, had the driver held the brake in Step 5, the train would have stopped on the correct side of the signal, thereby preventing the SPAD. This being the case, surely it would not be the correct thing to have selected Emergency sooner rather than later but rather to have held the brake in a step where control could be maintained.

On the side issue of hitting the red button, I have always been conscious that there may be situations where this is not desirable. If you're out of control and catching something up the last thing you would want it to do is to stop suddenly, which is what would happen if you made a red button call. Under those circumstances I would prefer to make the emergency call via the yellow button.

 

[Annetts key]

With regards to braking systems, a driver really needs to know how the system(s) operate at each step/mode. Especially if there are differences in operation between different step/modes.

For traction which has regenerative braking, there will be even more differences.

Braking is always about converting kinetic energy (velocity combined with mass) into a different form (heat for conventional brakes). A wheel that is locked due to the brakes applying more force than needed may not be as effective as a wheel that is rotating and transferring energy to the brake pad/shoe or via electro-magnetic means.

And obviously in order for the wheel to rotate while it’s rotation is being resisted by the braking system, it must have enough grip with the surface of the rail.

 

[O L Leigh]

With regards to braking systems, a driver really needs to know how the system(s) operate at each step/mode. Especially if there are differences in operation between different step/modes.

Precisely.

I will defer to someone closer to the situation who may be able to correct any misapprehension on my part, but not many years ago GA were on the point of running out of DMUs because the drivers were turning their wheels into 20p pieces. My own interpretation of this was that this was due to having a one-size-fits-all "just bang it into emergency" driving policy. When I did my skidpan training as a new driver, my Sprinter driving colleagues from the Anglia depots were being told how to drive the unit (a Cl153 in this case) out of a slide. Quite when this changed I cannot say.

For those of us who drove disc-braked units with WSP and sanders it was just a jolly and didn't really teach us much of anything except for what it felt like to get into a slide.

 

[niggill617@gma]

With reference to the interim RAIB report, and hopefully sticking to absolute facts, dare I say physics. The braking point allowing for 3 seconds freewheel/inertia is 0.54 m/s/s, nominal step 2. Three seconds freewheel would mean the driver made his decision in 2 seconds, assessing the anti-skid system was not coping. As mentioned before the sooner DVRS are widespread the better.

The tribometry from RAIB is albeit both ends of the spectrum. The initial and collision speeds would suggest average mu would sustain step 1, notwithstanding unknown gradient.

I hope I have left my ego at the door, just trying to highlight its not all about brake at the white house, or me wheels picked up. TDLCR states understand performance calculation and basic principles of friction inter alia. So when RAIB release the final report lessons are learnt.

When I read RAIB reports I would say lessons are not being learnt regards various issues, do operational undertakings actually read them, or more importantly understand them?

 

[hwl]

With reference to the interim RAIB report, and hopefully sticking to absolute facts, dare I say physics. The braking point allowing for 3 seconds freewheel/inertia is 0.54 m/s/s, nominal step 2. Three seconds freewheel would mean the driver made his decision in 2 seconds, assessing the anti-skid system was not coping. As mentioned before the sooner DVRS are widespread the better.

The tribometry from RAIB is albeit both ends of the spectrum. The initial and collision speeds would suggest average mu would sustain step 1, notwithstanding unknown gradient.

Gradient 1:140 to 1:240 downhill.
Putting all this altogether suggests the coefficient of friction was at the lower end of the RAIB range most of the time after starting to brake. Agreed on step 1 being around / or mostly just under the limit of what was achievable.
The coefficient of friction effectively being lower than teflon on teflon is not a good place to be.

I hope I have left my ego at the door, just trying to highlight its not all about brake at the white house, or me wheels picked up. TDLCR states understand performance calculation and basic principles of friction inter alia. So when RAIB release the final report lessons are learnt.

When I read RAIB reports I would say lessons are not being learnt regards various issues, do operational undertakings actually read them, or more importantly understand them?

 

[GC class B1]

Gradient 1:140 to 1:240 downhill.
Putting all this altogether suggests the coefficient of friction was at the lower end of the RAIB range most of the time after starting to brake. Agreed on step 1 being around / or mostly just under the limit of what was achievable.
The coefficient of friction effectively being lower than teflon on teflon is not a good place to be.

From the RAIB interim report distances, I have calculated the average wheel/rail coefficient of friction over the stopping distance to be around 0.027 - depending on the effectiveness of the WSP system. If the WSP was not optimum (Class 158 and 159 are now quite old) the coefficient of friction value may have been higher but the WSP controlled brake release and reapply could have extended the stopping distance compared to a unit with optimised WSP. Some areas would have had a higher coefficient and some areas lower so I surmise that the WSP would have been applying and releasing the brake as the coefficient changed. For reference, Step 1 would require a coefficient of friction of about 0.03 and it is therefore borderline whether the coefficient of friction was sufficient even for step 1 braking. I do not know whether Step 1 braking would have changed the outcome significantly and the driver would need to have initiated a Step 1 application on passing the double yellow at signal SY29R. I understand that this is not in accordance with the normal practice.

 

[millemille]

I have a suspicion that there may be a characteristic of the class 159 WSP system, when encountering a prolonged slide of all 4 axles on the same vehicle and the reference speed drops to zero because the brake release period isn't enough for the axle rotational speed to recover to true speed over ground, which causes the WSP system to time out (because the system assumes, after a period of time, that the train must have come to a stop) and WSP activity to cease and in turn sander operation to stop (because the sander relies on WSP activity to be triggered) even though the train is still moving/sliding.

This is why on some stock it is possible for the speedo to drop to zero when prolonged WSP activity occurs, even though the train is moving at speed

Later WSP systems fully release the brakes on one axle, when all 4 axles are detected as sliding, so that you've got one axle giving true speed over ground

I may be wrong, but I wouldn't be surprised if this turns out to be a contributory factor.

 

[hwl]

I have a suspicion that there may be a characteristic of the class 159 WSP system, when encountering a prolonged slide of all 4 axles on the same vehicle and the reference speed drops to zero because the brake release period isn't enough for the axle rotational speed to recover to true speed over ground, which causes the WSP system to time out (because the system assumes, after a period of time, that the train must have come to a stop) and WSP activity to cease and in turn sander operation to stop (because the sander relies on WSP activity to be triggered) even though the train is still moving/sliding.

This is why on some stock it is possible for the speedo to drop to zero when prolonged WSP activity occurs, even though the train is moving at speed

Later WSP systems fully release the brakes on one axle, when all 4 axles are detected as sliding, so that you've got one axle giving true speed over ground

I may be wrong, but I wouldn't be surprised if this turns out to be a contributory factor.

Ground speed radar is also as used on some stock is possibly a useful extra tool in this regard as it provides a source of speed info independent of the wheels.

 

[millemille]

Ground speed radar is also as used on some stock is possibly a useful extra tool in this regard as it provides a source of speed info independent of the wheels.

I know some locomotives use doppler radar for low speed control but as far as I'm aware there's nothing certified in the uk for brake control?

 

[niggill617@gma]

From the RAIB interim report distances, I have calculated the average wheel/rail coefficient of friction over the stopping distance to be around 0.027 - depending on the effectiveness of the WSP system. If the WSP was not optimum (Class 158 and 159 are now quite old) the coefficient of friction value may have been higher but the WSP controlled brake release and reapply could have extended the stopping distance compared to a unit with optimised WSP. Some areas would have had a higher coefficient and some areas lower so I surmise that the WSP would have been applying and releasing the brake as the coefficient changed. For reference, Step 1 would require a coefficient of friction of about 0.03 and it is therefore borderline whether the coefficient of friction was sufficient even for step 1 braking. I do not know whether Step 1 braking would have changed the outcome significantly and the driver would need to have initiated a Step 1 application on passing the double yellow at signal SY29R. I understand that this is not in accordance with the normal practice.

The RDG document attached advocates early braking, during leaf fall, as will the professional driving policy, for sure. As you state right on the cusp for step 1 braking from SY29R. I notice in another thread a driver claims a rate of deceleration of 1.78 m/s/s, not by calculation but by how quickly he can stop. That rate of brake performance needs to be reported to the TOC braking engineer. Another driver states his braking entry speeds into platforms; with different length sets. Assuming 23 m carriage length and a 280 m platform with equal spaced stop boards, his intuition / inbuilt accelerometer works out at 6 percent g.

The understanding of friction or rail adhesion is mu, a coefficient with no units of measurement. In general terms with a 3 step brake: 0.03 is step 1 , 0.06 is step 2 , 0.09 is step 3. The industry has this colour code system and numbers sequence to define adhesion. Why don't they just use the same system as engineers. If I saw a notice on wet gusting day in the autumn stating, areas; this, that, and the other have levels of mu 0.3, there is a direct correlation on how to brake in the affected zones.

 

[43066]

The RDG document attached advocates early braking, during leaf fall, as will the professional driving policy, for sure. As you state right on the cusp for step 1 braking from SY29R. I notice in another thread a driver claims a rate of deceleration of 1.78 m/s/s, not by calculation but by how quickly he can stop. That rate of brake performance needs to be reported to the TOC braking engineer. Another driver states his braking entry speeds into platforms; with different length sets. Assuming 23 m carriage length and a 280 m platform with equal spaced stop boards, his intuition / inbuilt accelerometer works out at 6 percent g.

The measurement of friction or rail adhesion is mu, a coefficient with no units of measurement. In general terms with a 3 step brake: 0.03 is step 1 , 0.06 is step 2 , 0.09 is step 3. The industry has this colour code system and numbers sequence to define adhesion. Why don't they just use the same system as engineers. If I saw a notice on wet gusting day in the autumn stating, areas; this, that, and the other have levels of mu 0.3, there is a direct correlation on how to brake in the affected zones.

I notice you’ve made repeated posts along similar lines. Can I ask why obsessing over the minutiae of friction coefficients, deceleration and braking rates is remotely useful? We all know that braking has to be done by feel and can vary by unit, location, season, weather conditions, time of day etc.

As a driver you don’t know (or care) what theoretical m/s/s deceleration you might get per braking step, you just need to know where to put it in to stop in the prevailing conditions.

 

[niggill617@gma]

What I state is directly related to this thread, as part of dialogue with another member. Braking is both theoretical and intuitive.

 

[TheEdge]

Braking is both theory and intuitive.

Not when we are driving though. When I put the PBC in a brake position I couldn't give less of a damn the precise figures going on, I just need to know if the performance today matches the performance I expect and need.

 

[niggill617@gma]

There are numerous cases where the performance was not even close to that selected, yet went unnoticed, during running brake tests.

 

[43066]

There are numerous cases where the performance was not even close to that selected, yet went unnoticed, during running brake tests.

That just highlights the need to do regular running brake tests during leaf fall (and anytime you’re unsure) and drive to the conditions. Knowing the precise braking coefficient you *should* get from a particular step won’t help you if you misjudge it and/or hit a patch of low adhesion. It also won’t help you in the subsequent investigation!

 

[niggill617@gma]

Put the question in the appropriate thread and I will answer. My previous reply goes beyond Salisbury, and so will my answer. I will have to ask the moderators if they want me to elaborate. The investigation will most definitely mention forces at the wheel. If drivers is investigated with such data, they should understand it.

 

[BayPaul]

Put the question in the appropriate thread and I will answer. My previous reply goes beyond Salisbury, and so will my answer. I will have to ask the moderators if they want me to elaborate. The investigation will most definitely mention forces at the wheel. If drivers is investigated with such data, they should understand it.

Incident investigations can cover all kinds of subjects that a driver is very unlikely to understand in scientific detail, things like specific properties of metals, meteorological conditions etc. I see no reason why this is an issue. I'd much rather have a train driver who can feel whether brake performance is acceptable based on experience, than one who can do the calculations to check exactly.

 

[Need2]

Put the question in the appropriate thread and I will answer. My previous reply goes beyond Salisbury, and so will my answer. I will have to ask the moderators if they want me to elaborate. The investigation will most definitely mention forces at the wheel. If drivers is investigated with such data, they should understand it.

Why do you keep peddling the physics and dynamics (or whatever you call it) of braking?
Why should a driver know, or even care about it, it means absolutely nothing to them?
Do you need to know and understand this stuff to drive a car?
NO you don’t so why should a train driver?

 

[niggill617@gma]

Why do you keep peddling the physics and dynamics (or whatever you call it) of braking?
Why should a driver know, or even care about it, it means absolutely nothing to them?
Do you need to know and understand this stuff to drive a car?
NO you don’t so why should a train driver?

This should be in the physics thread, but as you have posted. Car drivers are not subject to Statutory instrument 1798 , the text is clear "understand performance calculation", how many times do I have to state this. The most important thing a driver does is slow down. This understanding need not be some romantic arcane procedure from a bygone era . The whole thing is dimensionless.

The Edinburgh sleeper service incident is a classic example amongst others. Running brake test what a farce; the brakes on 99.999999 % of stock are well maintained and designed by very talented people. The time when the brake test should count failed to yield.

The consist took about 31 seconds to slow by 11 mph with about 50 percent selected, it should of been about 12 seconds simple maths, not "feel the force force the Luke" (inertia). The dynamic brake masking performance; utter folly. I mean 8 carriages of unbraked mass. Could of been the worst disaster this side of Paddington. The driver was let down by non-compliance of Rail Authorities regards continuation training.

Numerous drivers and some competence managers do agree with me. The subject is divisive so I respect your opinion, but that is all it is. I have presented the facts let the readership decide. Remember its knowledge not necessarily a procedure.

 

[ashkeba]

This should be in the physics thread, but as you have posted. Car drivers are not subject to Statutory instrument,

Car drivers are subject to Statutory Instruments including the Construction and Use Regulations and the Highway Code. I expect they are less strict than some railway ones.