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Croydon Tram Crash

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Scott M

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It wouldn't do any harm in having them and as mentioned previously Manchester Metrolink has them, whether they have avoided any accidents is impossible to say but in all honesty I doubt it. Something that would bring the tram to a halt if it hadn't reduced speed sufficiently would be of far more use, how practical that is on a tram system I don't know.

I don't see why it wouldn't be practical, as if a driver is following the correct speeds then surely they would have no effect?

In terms of cost, perhaps tramways have a lot more fast - slow sections that would require a TPWS, but it isn't really acceptable to use cost as an excuse to not implement safety features.
--- old post above --- --- new post below ---
It wouldn't do any harm in having them and as mentioned previously Manchester Metrolink has them, whether they have avoided any accidents is impossible to say but in all honesty I doubt it. Something that would bring the tram to a halt if it hadn't reduced speed sufficiently would be of far more use, how practical that is on a tram system I don't know.
--- old post above --- --- new post below ---


But you haven't explained how such features would reduce the risk of a crash.

Fatigue is far more likely to occur later in the day but anyway there is little point speculating further about what the driver did or didn't do.

Would have detected overspeed and brought on the track brakes.
 
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Antman

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I don't see why it wouldn't be practical, as if a driver is following the correct speeds then surely they would have no effect?

In terms of cost, perhaps tramways have a lot more fast - slow sections that would require a TPWS, but it isn't really acceptable to use cost as an excuse to not implement safety features.
--- old post above --- --- new post below ---


Would have detected overspeed and brought on the track brakes.

I thought you were talking about chevrons? Yes some sort of TPWS system would be good, perhaps somebody with a bit more knowledge on them could shed some light on the practicalities?
 

mirodo

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Was reading that it's beleievd that there could potentially be more bodies underneath the tram.

Gavin Barwell, the local MP, is quoted in the Croydon Guardian thus:

“Body parts” may still be at the wreckage of the Croydon tram crash, according to the local MP, as the carriage is set to be removed today.

But Gavin Barwell, the Croydon Central MP, said all the bodies of victims have already been discovered by emergency services.

http://www.yourlocalguardian.co.uk/...wreckage_as_crane_arrives_to_remove_carriage/
 

BestWestern

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I'd have thought that a TPWS style system would be catasrophically expensive to develop and retrofit. I wonder if something a little more basic could be an option; perhaps for example a stop signal on approach to the curve. This could be protected by a tripcock as per LUL, requiring just a (relatively) simple modification to the tramcars incorporating an arm fed into the emergency brake system. A simple bit of electronics could register the tram approaching, a timer then releasing the signal and tripcock after a set period sufficient for the car to have reduced speed. Totally self contained, and completely effective. Just a thought of course!
 

Antman

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I'd have thought that a TPWS style system would be catasrophically expensive to develop and retrofit. I wonder if something a little more basic could be an option; perhaps for example a stop signal on approach to the curve. This could be protected by a tripcock as per LUL, requiring just a (relatively) simple modification to the tramcars incorporating an arm fed into the emergency brake system. A simple bit of electronics could register the tram approaching, a timer then releasing the signal and tripcock after a set period sufficient for the car to have reduced speed. Totally self contained, and completely effective. Just a thought of course!

Sounds good to me, there is already a signal there protecting the junction which I think doesn't clear until the tram is very close to it.
 

otomous

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It wouldn't do any harm in having them and as mentioned previously Manchester Metrolink has them, whether they have avoided any accidents is impossible to say but in all honesty I doubt it. Something that would bring the tram to a halt if it hadn't reduced speed sufficiently would be of far more use, how practical that is on a tram system I don't know.
--- old post above --- --- new post below ---


But you haven't explained how such features would reduce the risk of a crash?

Fatigue is far more likely to occur later in the day but anyway there is little point speculating further about what the driver did or didn't do.


Later in the day is a relative concept. If tram shifts are anything like the railwyays you don't know whether you're coming, going or been most of the time. Fatigue is entirely possible that early if you didn't get much sleep before having to rise at 3 to travel for a 4.30 book on or the like, especially if you were not doing the same on the previous day.
 

RobShipway

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Sounds good to me, there is already a signal there protecting the junction which I think doesn't clear until the tram is very close to it.

But a stop symbol would be no different than my idea for a chevron showing the speed that the driver should slow down too, so that they could get round the corner at 12mph safely surely?

Later in the day is a relative concept. If tram shifts are anything like the railwyays you don't know whether you're coming, going or been most of the time. Fatigue is entirely possible that early if you didn't get much sleep before having to rise at 3 to travel for a 4.30 book on or the like, especially if you were not doing the same on the previous day.

I have to agree with the above, especially if as I suspect that we will find out that the driver of the tram the night before did not get a goodnight's sleep which is why they blacked out if they did prior to the corner. Admittedly it is not as dangerous, but in previous roles that I have done in IT one of those was spent being a Computer Operator of mainframe machines, where I would be working 8, 10 or 12 hour shifts either through the day or through the night. Now, I lost my job as a Computer Operator after working doing the job for over 8 years, due to the fact that I fell asleep for an hour at about 2am in the morning during the night, leaving my shift leader on his own with keeping the mainframe computer equipment doing the night batch work and loading tapes/cartridge tapes where needed in doing this work as well as dealing with both reel paper and laser printers that were printing reports.

Now, I fell asleep in the instance above having gone from doing 3 days of 12 hours through the day, to doing 3 days of working 12 hours through the night. The daytime before the night shift that I fell asleep on shift and was caught by the manager of the Ops team coming back to the office in the early hours of the morning, was down to lack of sleep during the day before coming back on shift. In hindsight as I did not get much sleep, I possibly should have called in sick and the same thing is possibly going through the driver's mind if it was the fact that he did not get much sleep the night before which caused him to blackout.
 
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Domh245

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But a stop symbol would be no different than my idea for a chevron showing the speed that the driver should slow down too, so that they could get round the corner at 12mph safely surely?

The difference being that BestWestern's proposed signal (assuming that symbol is a typo) is protected by a tramstop - it will *try* to stop the tram if things have gone wrong. Your chevron doesn't actually add anything to slow the tram down in the event of an overspeed.
 

edwin_m

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I think railway-type systems such as TPWS or trainstops, which rely on timing the approach of the vehicle, would have difficulty coping with the rapid speed changes that a tram is capable of. So there would be a high risk of false positives or even failing to detect a genuine overspeed.
 

ainsworth74

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It is only in the last few years though that the decision was made to move from breakable windows to aid escape, to toughened windows designed to retain pax inside the vehicle. This explains the general removal of the hammers previously always found throughout passenger saloons.

The breakable windows were made from toughened glass which will tend to shatter completely as soon as you break any small part of it, particularly when you break an edge, meaning it then very easy to clear the window of glass and escape (or get thrown out of the vehicle). Rail vehicles now use laminated glass (the same stuff that is in a car windscreen) as this will shatter but is very much harder to achieve a total breakthrough.
 

jon0844

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The BBC reporting has now mentioned it being run by First, which makes me wonder when comments will switch to it being run by a private operator? As if that makes the slightest difference.
 

507 001

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--- old post above --- --- new post below ---


So you'd rather not have safety features that could reduce the risk of a crash?

Some are suggesting the tram sped up - could be that the driver accidentally sped up instead of braking due to fatigue (more likely on an early morning shift such as this). I just feel "I blacked out" is too easy an excuse that is thrown around a lot.

No, that is not what I'm saying.

What I'm saying is that we should be looking at schemes that actually work, not putting time, money and effort into something that would have very little effect, if any.

It wouldn't do any harm in having them and as mentioned previously Manchester Metrolink has them, whether they have avoided any accidents is impossible to say but in all honesty I doubt it. Something that would bring the tram to a halt if it hadn't reduced speed sufficiently would be of far more use, how practical that is on a tram system I don't know.
--- old post above --- --- new post below ---


But you haven't explained how such features would reduce the risk of a crash?

Fatigue is far more likely to occur later in the day but anyway there is little point speculating further about what the driver did or didn't do.

Metrolink only has chevrons in one place, and they're there for a completely different reason. That being to remind drivers that the route had been diverted onto a completely new bit of line.
 

AlterEgo

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I'd have thought that a TPWS style system would be catasrophically expensive to develop and retrofit. I wonder if something a little more basic could be an option; perhaps for example a stop signal on approach to the curve. This could be protected by a tripcock as per LUL, requiring just a (relatively) simple modification to the tramcars incorporating an arm fed into the emergency brake system. A simple bit of electronics could register the tram approaching, a timer then releasing the signal and tripcock after a set period sufficient for the car to have reduced speed. Totally self contained, and completely effective. Just a thought of course!

Alternatively, a simpler "double tripcock" sort of TPWS would be cheap to install.

Two tripcocks a certain distance apart - the speed can be detected by the time difference between both trips.

I am not sure a tripcock can be mounted to a tram, however, thanks to ground clearance issues when street running.
 

westcoaster

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Alternatively, a simpler "double tripcock" sort of TPWS would be cheap to install.

Two tripcocks a certain distance apart - the speed can be detected by the time difference between both trips.

I am not sure a tripcock can be mounted to a tram, however, thanks to ground clearance issues when street running.

What about one of those smiley/sad face speed gun things you see at the side of the road, obviously have it set to the corner speed (doesn't need the smiley face symbol), attached to a stanchion flashing yellow for to high a speed and green for the correct speed.
 

AlterEgo

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What about one of those smiley/sad face speed gun things you see at the side of the road, obviously have it set to the corner speed (doesn't need the smiley face symbol), attached to a stanchion flashing yellow for to high a speed and green for the correct speed.

Again, how does that help if the driver is unconscious? A tripcock will halt the train.
 

neonison

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I am just speculating but good though it was in its day, has the world now not moved on from tripcocks to solid state systems? I do not suggest it would be cheap but rather than full TPWS some form of approach control would only be needed at a limited number of places on the UK's tram networks such as the curves inbound to Sandilands on Tramlink, the curve next to Hartford Mill, Werneth and those occasional terminals which are approached after a period of faster running, such as the bay platform at Shaw on Metrolink. Those more familiar with NET, Midland Metro, Edinburgh and Sheffield will have their own thoughts.
 
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fusionblue

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Again, how does that help if the driver is unconscious? A tripcock will halt the train.

A tripcock plus increasing the delay time from a tram approaching the signal to it changing to a proceed signal.

One prevents the tram from overspeeding and the other forces the tram to come to a complete stop (or as close as possible) to be below the limit (in normal circumstances).
 

Domh245

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IIRC, the trams already have an induction loop system (used for triggering onboard announcements and sending information back to the control centre) - so it shouldn't be impossible for it to also be used for some kind of safety system, although there might be issues with safety systems sharing equipment with non safety systems?
 

MarkyT

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I think railway-type systems such as TPWS or trainstops, which rely on timing the approach of the vehicle, would have difficulty coping with the rapid speed changes that a tram is capable of. So there would be a high risk of false positives or even failing to detect a genuine overspeed.

A weakness of TPWS is that it can only sample trainspeed at a particular instance of that train passing a specific overspeed trap. After that there is nothing it can do to stop a train reapplying power and racing towards a stop signal or restriction after successfully passing under the approach speed trap. In this respect it is little better at enforcing action than AWS's 'acknowledge and carry on regardless' functionality. That's not to criticise TPWS unduly. It was the right system at the right time and was the only concept ready and available that could have been fitted so widely and quickly when the need arose. It has saved many lives since. More sophisticated systems can pass a message to the train however that forces it to enforce a speed reduction or continue to obey a restriction for a given distance or time AFTER passing the transponder, or until cancelled by a subsequent transponder. German Indusi, as used in a simplified form in UK on the T&W, does this, but perhaps better today would be to adopt a modern implementation of similar functionaly using ETCS level 1 Limited Supervision (LS). This could incorporate speed control traps, signal trainstop and distant warning functions similar to TPWS and AWS but with 'Indusi like' state memory on board that could be used to enforce a continuing restriction that prevented re-acceleration, rather than just the momentary speed checks of TPWS, and all without going to the full extent of continuous braking envelope calculations etc as required by main line Level 2 systems, and their radio movement authority. Instead, LS could implement simple functionality using eurobalise control beacons, some passive some active, selectively as necessary in critical places where exceptional risk demands it, such as for speed control on approach to Sandilands. Lack of effective technical speed controls on a tight curve following a long high speed section has been a common theme in a series of major rail disasters around the World in recent years, from Spain to the US. It seems Croydon Tramlink has now joined that tragic list.
--- old post above --- --- new post below ---
I am just speculating but good though it was in its day, has the world now not moved on from tripcocks to solid state systems? I do not suggest it would be cheap but rather than full TPWS some form of approach control would only be needed at a limited number of places on the UK's tram networks such as the curves inbound to Sandilands on Tramlink, the curve next to Hartford Mill, Werneth and those occasional terminals which are approached after a period of faster running, such as the bay platform at Shaw on Metrolink. Those more familiar with NET, Midland Metro, Edinburgh and Sheffield will have their own thoughts.

I agree, that is why I am advocating ETCS L1 LS. Tripcocks can only do momentary speed traps and signal trainstops like TPWS, while a digital system could pass a more sophisticated message such as "slow down to a target speed within a given distance of the warning, then continue without accelerating for a further given distance or until reset by a 'higher code'. Also for a tram how can you incorporate a mechanical arm operated system that doesn't also represent a protrusion hazard when on street? A digital system can have balises below rail level and an on board antenna safely under the bogies behind the skirts.
 
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BestWestern

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Also for a tram how can you incorporate a mechanical arm operated system that doesn't also represent a protrusion hazard when on street? A digital system can have balises below rail level and an on board antenna safely under the bogies behind the skirts.

For the specific purposes of preventing dramatic overspeed incidents, this is unlikely to be an issue, given that a tram will only be running at 'high' speed on a segregated track section anyway, and thus will have passed the required point of speed reduction - and thus the tripcock - before it goes 'on street'.

A digital system would, of course, have increased functionality though as you say.
 

edwin_m

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My concern with TPWS, and also timer-based trainstop systems, is that they can measure the average speed over a certain distance, but that doesn't say anything about whether the tram is accelerating, decelerating or at constant speed. This doesn't matter too much with trains where the deceleration is relatively gentle, but placing it in the zone where a tram should be braking hard (around twice the deceleration of the train) it's just not going to be very accurate. Some calculations would be needed about whether this matters, in the light of the margin of safety that would exist between permitted speed and overturning speed.
 

Scott M

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From reading the discussions, I am starting to favour approach control over TPWS, as it seems simpler and cheaper yet effective. Approach control wouldn't delay things too much here as the trains almost slow to a stop (20 kmh) to take this curve anyway.
 
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507 001

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I am just speculating but good though it was in its day, has the world now not moved on from tripcocks to solid state systems? I do not suggest it would be cheap but rather than full TPWS some form of approach control would only be needed at a limited number of places on the UK's tram networks such as the curves inbound to Sandilands on Tramlink, the curve next to Hartford Mill, Werneth and those occasional terminals which are approached after a period of faster running, such as the bay platform at Shaw on Metrolink. Those more familiar with NET, Midland Metro, Edinburgh and Sheffield will have their own thoughts.

From reading the discussions, I am starting to favour approach control over TPWS, as it seems simpler and cheaper yet effective. Approach control wouldn't delay things too much here as the trains almost slow to a stop (20 kmh) to take this curve anyway.


Approach control is already used in this location. In fact all tram signals work on approach release.

The problem is, there's nothing to stop the vehicle if it passes the signal at stop.
--- old post above --- --- new post below ---
IIRC, the trams already have an induction loop system (used for triggering onboard announcements and sending information back to the control centre) - so it shouldn't be impossible for it to also be used for some kind of safety system, although there might be issues with safety systems sharing equipment with non safety systems?

The induction loop system is used for route setting and triggering of approach release signals.
 

Busaholic

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The BBC reporting has now mentioned it being run by First, which makes me wonder when comments will switch to it being run by a private operator? As if that makes the slightest difference.

Let me state from the start here that I am not aiming this at First or commenting specifically on (Croydon) Tramlink. The few tram systems operating in the UK for fifteen or more years, and LRT systems too, have seen changes of operators on one or even two occasions, and given they do not choose routes, timetables, fares or even the vehicles used the only real criteria are cost and performance, and, as stated, many of the costs are borne by the commissioners. So what we are really talking about are PEOPLE and trying to operate a system with the minimum requisite number at the lowest possible cost. That means what some might consider to be cutting corners (and I do realise that is not a good phrase to use, perhaps) can result, particularly if one of these operators has been told, officially or unofficially, or maybe just is feeling paranoid, that their contract is under threat of non-renewal. Something akin to this situation is certainly a feature of the TfL-contracted bus services where different companies vie with each other week by week and there is plenty of evidence of route controllers under pressure to produce the best service in a cosmetic sense, if maybe not to a great proportion of the users of that route at time i.e. the passengers. Such pressure is then transferred to the individual drivers who, with congestion increasing month by month in most areas of London, can only meet it by driving faster and spending the absolute minimum time at stops when they are able to. Some drivers will (rightly, imo) resist this but many, particularly younger and more inexperienced ones, will heed the call and, perhaps, drive dangerously. I will say this, as someone who has been travelling on London's buses for well over sixty years and made thousands of journeys, that I had only felt on about four or five occasions until about fifteen years ago that I'd travelled on a dangerously driven bus, but now, even though I can unfortunately not get to London very often now, if I spent a day on the buses I would certainly come across two or three badly-driven ones and a very good chance of one I'd place in the dangerous category. Now, if a tram is a 'bus on tracks, basically' as Andrew Braddock of Tram UK said on the 'Today' programme yesterday (he could of course have said trolleybus but he would probably have to explain what that was) I have no doubt that drivers are experiencing the same 'challenges' as those bus drivers. A system operated directly by a transport authority, as still occurs on most trams around the world, may not have quite the same financial pressures: whether that is a good thing is in the eye of the beholder, of course, but I would suggest there could be a subtle difference between how a private or public operator runs a system.
 

jon0844

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Let me state from the start here that I am not aiming this at First or commenting specifically on (Croydon) Tramlink. The few tram systems operating in the UK for fifteen or more years, and LRT systems too, have seen changes of operators on one or even two occasions, and given they do not choose routes, timetables, fares or even the vehicles used the only real criteria are cost and performance, and, as stated, many of the costs are borne by the commissioners. So what we are really talking about are PEOPLE and trying to operate a system with the minimum requisite number at the lowest possible cost. That means what some might consider to be cutting corners (and I do realise that is not a good phrase to use, perhaps) can result, particularly if one of these operators has been told, officially or unofficially, or maybe just is feeling paranoid, that their contract is under threat of non-renewal. Something akin to this situation is certainly a feature of the TfL-contracted bus services where different companies vie with each other week by week and there is plenty of evidence of route controllers under pressure to produce the best service in a cosmetic sense, if maybe not to a great proportion of the users of that route at time i.e. the passengers. Such pressure is then transferred to the individual drivers who, with congestion increasing month by month in most areas of London, can only meet it by driving faster and spending the absolute minimum time at stops when they are able to. Some drivers will (rightly, imo) resist this but many, particularly younger and more inexperienced ones, will heed the call and, perhaps, drive dangerously. I will say this, as someone who has been travelling on London's buses for well over sixty years and made thousands of journeys, that I had only felt on about four or five occasions until about fifteen years ago that I'd travelled on a dangerously driven bus, but now, even though I can unfortunately not get to London very often now, if I spent a day on the buses I would certainly come across two or three badly-driven ones and a very good chance of one I'd place in the dangerous category. Now, if a tram is a 'bus on tracks, basically' as Andrew Braddock of Tram UK said on the 'Today' programme yesterday (he could of course have said trolleybus but he would probably have to explain what that was) I have no doubt that drivers are experiencing the same 'challenges' as those bus drivers. A system operated directly by a transport authority, as still occurs on most trams around the world, may not have quite the same financial pressures: whether that is a good thing is in the eye of the beholder, of course, but I would suggest there could be a subtle difference between how a private or public operator runs a system.
I was thinking more of comments elsewhere than here, with people jumping to conclusions just because they've now been told it's a private company operating it. Of course when conveying information, there's no harm saying but the way I saw it written (it may have been updated, as many BBC stories are) it did sound like the fact it was run privately could in some way have something to do with what happened.
 

SpacePhoenix

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How close is the curve that it derailed on to the absolute minimum radius curve that a tram can negotiate?
 
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