ATP-preventable accidents

[edwin_m]

From https://www.railforums.co.uk/thread...r-light-signalling.166778/page-2#post-3538458

Question (which I have asked elsewhere and not got an answer): when was the last UK rail accident resulting in at least one fatality that could only have been prevented by ATP i.e. TPWS and/or AWS would not have prevented it?

Going by the list on Wikipedia, the last one I can see is Colwich in 1986 when the speed of approach and short overrun might have been too much for a TPWS installation (although perhaps not for TPWS+).

The project that eventually led to TPWS looked back (in about 1994) to all accidents since about 1968 and estimated what would have happened had either what became TPWS or an ATP system been available. A simple TPWS (not TPWS+) was predicted to avoid some 70% of ATP-preventable fatalities. This conclusion was bad-mouthed by Uff-Cullen but has pretty much been borne out.

https://en.wikipedia.org/wiki/List_...ited_Kingdom#1995_onwards:_Post-privatisation

 

[MarkyT]

From https://www.railforums.co.uk/thread...r-light-signalling.166778/page-2#post-3538458

Going by the list on Wikipedia, the last one I can see is Colwich in 1986 when the speed of approach and short overrun might have been too much for a TPWS installation (although perhaps not for TPWS+).

TPWS+, which was completed fairly quickly after the initial TPWS project, was created specifically to cover all such higher speed junctions with minimum overruns, cases over about 70mph ISTR. At Colwich the overrun is only about 200m, just enough for a clear overlap so I'm sure it MUST be a TPWS+ site.

The Wootton Bassett steam excursion near miss clearly wasn't prevented. It was only the fortunate relative positions of trains in the area that prevented a major tragedy.

 

[Bromley boy]

The Wootton Bassett steam excursion near miss clearly wasn't prevented. It was only the fortunate relative positions of trains in the area that prevented a major tragedy.

But, in that instance, the AWS/TPWS system had been improperly isolated, had it not?!

So not really a true reflection of the system’s efficacy.

 

[gsnedders]

But, in that instance, the AWS/TPWS system had been improperly isolated, had it not?!

So not really a true reflection of the system’s efficacy.

Correct.

 

[Wilts Wanderer]

Wasn’t there a near miss between an HST and a Turbo at Didcot North Junction a few years ago in which TPWS was a preventative factor? IIRC the HST failed to brake after receiving preliminary caution and caution aspects, partly due to a badly positioned TSR magnet confusing the driver, plus an alleged distraction from the steam museum. I imagine a head-on collision would have had a closing speed of 80+mph so it was quite a big save.

 

[louis97]

TPWS+, which was completed fairly quickly after the initial TPWS project, was created specifically to cover all such higher speed junctions with minimum overruns, cases over about 70mph ISTR. At Colwich the overrun is only about 200m, just enough for a clear overlap so I'm sure it MUST be a TPWS+ site.

Colwich, in the down direction at least, is also protected by conditional double red signalling. Therefore a train isn't able to approach the red signal protecting the junction without approaching another red signal, which then clears upon approach, first.

 

[edwin_m]

Colwich, in the down direction at least, is also protected by conditional double red signalling. Therefore a train isn't able to approach the red signal protecting the junction without approaching another red signal, which then clears upon approach, first.

That probably wasn't the case at the time of the accident, but if it had been in conjunction with TPWS it sounds like it would have prevented it.

 

[MarkyT]

Colwich, in the down direction at least, is also protected by conditional double red signalling. Therefore a train isn't able to approach the red signal protecting the junction without approaching another red signal, which then clears upon approach, first.

That probably wasn't the case at the time of the accident, but if it had been in conjunction with TPWS it sounds like it would have prevented it.

Thanks for the clarification. It certainly seems plausible that the extra red on approach was a mitigation provided after the incident. It was the only practical thing they could do at the time with no ATP or other protection system available I guess. With that control in the interlocking you probably don't need any extra over-speed loops for TPWS+.

 

[edwin_m]

I've just skimmed the Colwich report and while it discusses changes to the flashing yellow arrangements there's no mention of a double red either existing or being recommended. I think they were pretty much unheard of in 1986 so may have been added later.

So if Colwich was TPWS-preventable, when was the last accident that was only ATP-preventable? From the list in the OP I wonder about Seer Green in 1981, where the driver went too fast after being talked past a signal at danger. An ATP system might have enforced a lower maximum speed until the next proceed aspect.

 

[driver_m]

I've just skimmed the Colwich report and while it discusses changes to the flashing yellow arrangements there's no mention of a double red either existing or being recommended. I think they were pretty much unheard of in 1986 so may have been added later.

So if Colwich was TPWS-preventable, when was the last accident that was only ATP-preventable? From the list in the OP I wonder about Seer Green in 1981, where the driver went too fast after being talked past a signal at danger. An ATP system might have enforced a lower maximum speed until the next proceed aspect.

Can ATP do that? Obviously TPWS wouldn't have prevented that crash if the driver was talked past a red and then opened it up, Can any ATP drivers or people competent on it answer that? Curious now (I've never used ATP)

 

[MarkyT]

I've just skimmed the Colwich report and while it discusses changes to the flashing yellow arrangements there's no mention of a double red either existing or being recommended. I think they were pretty much unheard of in 1986 so may have been added later.

So if Colwich was TPWS-preventable, when was the last accident that was only ATP-preventable? From the list in the OP I wonder about Seer Green in 1981, where the driver went too fast after being talked past a signal at danger. An ATP system might have enforced a lower maximum speed until the next proceed aspect.

The lack of any kind of continued supervision leads to this kind of scenario and is what I most worry about concerning TPWS. Bletchley played host to a similar case in 2012 where a light locomotive had slowed down sufficiently to pass an overspeed loop on approach to a red signal on the up slow. That signal already had a route set forward over limited speed crossovers to the up fast immediately south of the station. The signal soon cleared on berth occupancy and the driver opened the controller thinking he had a fast route straight on I can only assume (as also concluded by the RAIB inspectors). The loco achieved sufficient speed in the distance available to derail part way through the tight geometry of the junction, coming to rest foul of both fast lines. Fortunately there was no traffic on the down fast at the time and no injuries occurred. The signalling in the area has been replaced since the incident and the junction moved further south. A speed restriction applied for a distance by a more sophisticated protection system could have prevented the incident. Such a system need not be that much more sophisticated. PZB or 'Indusi' in Germany applies a standard restriction for a fixed distance or time after having passed an overspeed inductor and a forced standard decceleration after a distant inductor. Such functionality could be incorporated in a limited supervision ETCS based replacement for TPWS and AWS in UK.

Bletchley incident: https://www.gov.uk/raib-reports/derailment-at-bletchley-junction-bletchley
Indusi: https://en.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung

 

[MarkyT]

Can ATP do that? Obviously TPWS wouldn't have prevented that crash if the driver was talked past a red and then opened it up, Can any ATP drivers or people competent on it answer that? Curious now (I've never used ATP)

An ATP system could notionally apply a standard speed restriction for a set distance or time after passing a red under such controlled conditions if designed to do that. In my previous post I mentioned PZB in Germany. That system does not apply such a restriction after passing a red, as the driver just presses a button to override the trainstop completely on instruction of the signaller via a substitute signal. Some but not all substitute signals require the driver to proceed at caution until the next signal but there's no technical supervision of that.

 

[driver_m]

Should point out that with the Bletchley incident, I recall that the signal in question had a theatre box indicator, but only one route that used it IIRC, it was poorly lit as well in comparison to the signal. Never understood why it had a route indicator instead, but was there once a route to Oxford available via that signal to connect back to the flyover? It also cleared on approach to the platform which obviously gave time to build up speed, rather than using a much later Track Approach Track Circuit.

 

[MarkyT]

Never understood why it had a route indicator instead, but was there once a route to Oxford available via that signal to connect back to the flyover?

I believe you are correct that there was a route via these crossovers towards Oxford which would have had a separate route indication in the same 'theatre' box. If speed is low enough and sighting satisfactory, they were and still are a standard solution, but the modern ones are much brighter and clearer. I guess the signal for the new faster junction further south has feathers?

 

[Taunton]

Ladbroke Grove?

 

[MarkyT]

Ladbroke Grove?

Ordinary TPWS would have worked at Ladbroke Grove. There was a very long overrun beyond SN109 before the conflict point, 600 or 700m ISTR.

 

[edwin_m]

Can ATP do that? Obviously TPWS wouldn't have prevented that crash if the driver was talked past a red and then opened it up, Can any ATP drivers or people competent on it answer that? Curious now (I've never used ATP)

I don't know about ERTMS or GWATP but train control systems on metros usually have a mode where the system does not supervise operation but limits the train to a low speed. This would be used in the equivalent of a signal failure situation where a fault in the system prevented the ATP letting the train proceed.

Ladbroke Grove?

I've already responded to a post of yours on this subject this weekend, so I won't expand here on MarkyT's response.

 

[43096]

Going by the list on Wikipedia, the last one I can see is Colwich in 1986 when the speed of approach and short overrun might have been too much for a TPWS installation (although perhaps not for TPWS+).

Colwich is certainly an interesting one. Reading the accident report (http://www.railwaysarchive.co.uk/documents/DoT_Colwich1988.pdf) it is certainly debatable if TPWS would have prevented it. Obviously TPWS would have initiated an emergency brake application when 86429 passed the signal at danger, but based on the driver's evidence that would not have made any difference. The question then is if the Manchester train would have triggered the TPWS OSS - that must be debatable. ATP, as I understand it, measures the "braking curve" to stop at the next signal and if it isn't being met, then intervenes. On that basis, ATP would have prevented the accident.

Looks like this might be the answer...

 

[CyrusWuff]

In terms of being authorised to pass a signal at danger, I believe both ATP and TPWS allow the Driver to suppress the Brake demand that would normally occur when doing so but there is no forced restriction of speed.

 

[MarkyT]

Colwich is certainly an interesting one. Reading the accident report (http://www.railwaysarchive.co.uk/documents/DoT_Colwich1988.pdf) it is certainly debatable if TPWS would have prevented it. Obviously TPWS would have initiated an emergency brake application when 86429 passed the signal at danger, but based on the driver's evidence that would not have made any difference. The question then is if the Manchester train would have triggered the TPWS OSS - that must be debatable. ATP, as I understand it, measures the "braking curve" to stop at the next signal and if it isn't being met, then intervenes. On that basis, ATP would have prevented the accident.

The driver of the Manchester train thought he was going to stop short of the diamond. Tests ascertained the final brake application may have been made as close 30yds before the protecting signal CH23 at a speed of 45mph so I'm now thinking TPWS with an additional OSS loop closer to the signal than standard and set at a lower trip speed could have detected that the train crossing over at <50mph had not continued to slow down sufficiently for the red. A 35mph set speed OSS even as close as 100yds from the signal could have prevented the collision if not the SPAD.

I maintain that any junction layout can be fully protected* by TPWS with additional OSS loops as neccesary, either between the standard OSS and the signal or TPWS+ loops further out.

*What TPWS cannot do is to prevent a train actively accelerating again after successfully passing under an OSS speed trap. Sometimes additional OSSs are provided routinely where this is considered a particular risk such as after a station stop where the signal is a significant distance from the platform. Although it is not perfect, the system has definitely saved lives since introduction.

 

[gsnedders]

I don't know about ERTMS or GWATP but train control systems on metros usually have a mode where the system does not supervise operation but limits the train to a low speed. This would be used in the equivalent of a signal failure situation where a fault in the system prevented the ATP letting the train proceed.

Any authority to travel beyond the end-of-authority in ERTMS has an attached speed limit, as far as I'm aware, which is enforced in the normal way.

 

[Dieseldriver]

Southall would have been prevented if ATP had been switched on and the Driver trained in its use.

 

[driver_m]

Given that TPWS OSS typically seems to be typically set at about 42-45mph on the approach to reds, I think it could have prevented Colwich. Having done the same move myself hundreds of times under normal circumstances, i would presume that the driver would have almost certainly triggered the overspeed loops. The Loops at the signal would have likely left the train in the same position, but I can't see how if TPWS had been put in at the time, it wouldn't have had OSS loops . So IMO I dont think Colwich is the answer. I dont actually think there's been an accident that ATP would have prevented that TPWS wouldn't have .

 

[edwin_m]

Southall would have been prevented if ATP had been switched on and the Driver trained in its use.

It would almost certainly also have been prevented if the AWS had been operating on the leading cab, as it would have drawn the driver's attention to the caution signals and applied the brakes if either of them wasn't acknowledged. So it doesn't fit the criteria of being preventable by ATP but not preventable by AWS/TPWS.

 

[Dieseldriver]

It would almost certainly also have been prevented if the AWS had been operating on the leading cab, as it would have drawn the driver's attention to the caution signals and applied the brakes if either of them wasn't acknowledged. So it doesn't fit the criteria of being preventable by ATP but not preventable by AWS/TPWS.

Agree with you however with the exact scenario at Southall with the isolated AWS it would have prevented the collision. Not relevant now due to the rule changes regarding isolated AWS.
Worth noting that I personally think TPWS is a fantastic safety system that has greatly improved safety on our Railway. I am aware of a good number of incidents (SPADs and overspeed) that have stopped short of a collision/derailment due to TPWS interventions.
The only thing is, there are still a number of locations on the network that are still vulnerable due to the lack of TPWS, however in general the protection afforded by TPWS has greatly improved things.

 

[Taunton]

Colwich, Southall and Ladbroke Grove, and others, would indeed have also been prevented if the traditional principles of track layouts with Flank Protection had been in place. Ladbroke Grove in particular, because the points were physically in place there to do it.

 

[43096]

Southall would have been prevented if ATP had been switched on and the Driver trained in its use.

Southall was (in Great Western terms) a pre-1910 accident in 1997 and was AWS preventable. The GWR had ATC in place in the early part of the century that was equivalent to AWS. Southall was really a safety management failure by GWT as much as anything else.

 

[MarkyT]

Colwich, Southall and Ladbroke Grove, and others, would indeed have also been prevented if the traditional principles of track layouts with Flank Protection had been in place. Ladbroke Grove in particular, because the points were physically in place there to do it.

At LG, not entirely. The flank points 8059B, part of a crossover that might have been swung reverse away from the up main, would have diverted the 165 to the parallel down relief. Thus if a train had been passing on the down relief at the time the points would have been normal and flank protection would have been absent. Perhaps an extra point end 8063C, with an overrun leading to a sand drag or friction stop might have been added but it's possible the wreckage of a high speed uncontrolled runaway diverted into such a spur might still have ended up foul of the up main, or the down relief. The real tragedy at LG in my mind was the lack of ATP on the turbo when the infrastructure in the area was already fully equipped, but sighting on approach to SN109 and preceding signals was also a contentious issue, with (arguably) insufficient care taken when new support stanchions were added and wires strung up around the signal gantries erected only a few years earlier.

Colwich was signalled from a lever frame and typical of many traditional junction layouts on paired by direction corridors. The rare feature at the time was the new flashing yellow sequence for the DF>DS crossover move before the geographical junction, about which the SPADing driver appeared genuinely confused when interviewed. BR later introduced refinements to the rules for the application of such flashing sequences.

The correct safe path for the future is to use ALL forms of flank protection as expedient, including on board train protection technology, to bring trains to a stand before collisions or derailments take place.

Ladbroke Grove enquiry diagram:
http://www.railwaysarchive.co.uk/documents/HSE_Lad_Track001.pdf

 

[nom de guerre]

Colwich was signalled from a lever frame and was typical of many traditional junction layouts on paired by direction corridors. The rare feature at the time was the new flashing yellow sequence for the DF>DS crossover move before the geographical junction, about which the SPADing driver appeared genuinely confused.

Perhaps if he'd read the notices he'd signed for...

 

[driver_m]

Perhaps if he'd read the notices he'd signed for...

Even if he'd read them though, who's to say he'd have understood them? It does seem pretty clear reading that stuff in the report, that you were still expected to be prepared to stop at a red when they were introduced back in 1978... When I was taught flashing yellows, it was striking how Colwich was used as the example of it being emphasised that you must not expect anything other than a red after the steady yellow. It is drummed into you when you learn this strand of signalling.