Croydon Tram Accident

[ruggedpeak]

Though it's now 14 years since I retired the standard definition of a road traffic accident included a phrase that ran along these lines "If due to the presence of a motor vehicle on a road injury is caused to any person either in or on the vehicle"  Thus  passenger injury is a road accident and reportable.  I can' remember the rest of the full definition, I did learn it in basic training in 1973 but I've slept since then.   As far as I remember it allows you to exchange details with the other driver either at the scene or within 24 hours after that you have to report it.  IIRC then if there is injury it is always reportable.

 

Jamie

You are absolutely correct. Brain fade on my part.

[jamie92208]

BTP state a man was arrested on suspicion of manslaughter. He has been released on bail until May.

 

http://media.btp.police.uk/r/13403/updated_statement_on_tram_derailment_-_croydon

 

http://media.btp.police.uk/r/13405/updated_statement_on_tram_derailment_-_croydon

 

Clearly manslaughter is one of the most serious criminal offences, so I'll not comment/speculate any further on this aspect of the tragedy.

 

Yes Manslaughter is known as a Serious Arrestable Offence under the Police and Criminal Evidence Act and the act and the various codes of practice give greater powers if one of this class of offences are involved.  However in such cases the decision to charge will I think always be made by the Crown Prosecution Service and they always have the option of going for either a less serious offence or of not prosecuting if the evidence doesn't warrant it.

 

Jamie

 

Jamie

[Budgie]

BTP state a man was arrested on suspicion of manslaughter. He has been released on bail until May.

 

...

 

Clearly manslaughter is one of the most serious criminal offences, so I'll not comment/speculate any further on this aspect of the tragedy.

I suppose they couldn't use "causing death by dangerous driving" as the tram was on reserved track rather than the road. Or could they, as it's a tramway? Perhaps someone on here knows.

 

Off topic: It makes me wonder why people who are charged with causing death by dangerous driving on the roads aren't changed with manslaughter instead.

[edcayton]

I suppose they couldn't use "causing death by dangerous driving" as the tram was on reserved track rather than the road. Or could they, as it's a tramway? Perhaps someone on here knows.

 

Off topic: It makes me wonder why people who are charged with causing death by dangerous driving on the roads aren't changed with manslaughter instead.

 

Sometimes they are.

 

Ed

[jamie92208]

I suppose they couldn't use "causing death by dangerous driving" as the tram was on reserved track rather than the road. Or could they, as it's a tramway? Perhaps someone on here knows.

 

Off topic: It makes me wonder why people who are charged with causing death by dangerous driving on the roads aren't changed with manslaughter instead.

 

I remember being told in a law lecture that Causing death by reckless driving contained all the necessary legal elements of murder, and that causing death by dangerous driving contained the necessary elements of manslaughter  However there were various things that meant that the Road Traffic act offence was the preferred one.  The mina one was that juries are very reluctant to convict of Murder/manslaughter and the other was that t was CPS policy to use the Road Traffic Act offence.  I believe that the person (I use the word advisedly) who ran over and killed a police officer in Liverpool a couple of years ago was charged with and convicted of either murder or manslaughter.   As I mentioned above the actual charge preferred will be decided by the CPS.   However I don't think that a tram counts as a motor vehicle for the Road Traffic Act.

 

Jamie

[Edwin_m]

When I was doing train driver training many years ago we were told that curves had a 100% safety error built in, but as speed increases the lateral forces increase with the square root of the speed if that makes sense, maybe someone more technically minded than me can remember the formula.

 

...

 

I also witnessed a safety exercise on the Croydon system before it opened, featuring a First Capital bus being hit by a tram in central Croydon. I've got some photos somewhere and will download them when I find them. The first thing the fire brigade done was to turn the current off; I pointed out the man in charge that may cause problems. No power=no compressors=no air to keep the air suspension inflated=possibility of further injuries to anyone trapped under the tram.

The lateral force is proportional to the square of the speed and inversely proportional to the radius.  Therefore if the radius is halved the speed has to be reduced by the square root of 2 to keep the lateral force the same. 

 

The Croydon CR4000 trams do not have air suspension, relying like most modern trams on springs. 

[Edwin_m]

I'm afraid it isn't It's the conical shape of the tyre profile that keeps rail vehicles on their track. The flanges are only there for extreme cases (and even then only the most severe due to the actual profile of the tyre) and basically intended to guide the wheel past frogs. On perfectly infinitely straight track, a free rolling wheelset will oscillate with ever decreasing amplitude until it finds the exact spot where both tyres are of equal diameter and then continue in that spot. But track never is infinitely perfectly straight, nor is it free rolling   Similarly, in a curve the wheelset will shift outwards until again it has found the spot where the diameters of each wheel matches the circumference required to make the curve. The smaller the radius of the curve, the more the wheelset will shift outward. Of course there's a limit how much tyre is available, so engineers found that artificially enlarging the wheel diameter will also work. That's why, in a cross-section of the tyre, there's a sharp radius curve between the tyre and flange. I'd be happy to post a link to, or even an image of this, but I'm more then confident you'll find those w/o my assistance, should you want to see that  

For the wheel to run without flange contact, the ratio of the wheel radii at the two contact patches must be the same as the ratio of the distances travelled by those two wheels, which is the ratio of the length of the inner and outer rails round the curve. 

 

By a crude bit of measuring on Bing Maps I estimate the radius of this curve to be around 30 metres.  This means that the ratio of the outer to inner rail distances is about 31.435/30, so the outer radius is about 5% more than the inner one.  I don't know the wheel diameter but let's say 750mm, this means that the conicity would have to give a diameter difference of 37.5mm between the two contact patches.  This is far greater than the sort of conicity found on tram wheels.  So even at normal running speeds the tram will be relying on flange contact to steer it round this curve, and even if it this wasn't the case in normal running, the overspeed here would be pushing it into flange contact. 

Edited November 12, 2016 by Edwin_m

[dhjgreen]

There is always a lot of squealing on the tight curves on Metrolink; flange against rail?

[Budgie]

I don't know the wheel diameter but let's say 75mm, ...

75mm is approx 3 inches. Did you mean something a bit bigger?

[Colin_McLeod]

BTP state a man was arrested on suspicion of manslaughter. He has been released on bail until May.

 

http://media.btp.police.uk/r/13403/updated_statement_on_tram_derailment_-_croydon

 

http://media.btp.police.uk/r/13405/updated_statement_on_tram_derailment_-_croydon

 

Clearly manslaughter is one of the most serious criminal offences, so I'll not comment/speculate any further on this aspect of the tragedy.

You just did so that was a rather pointless post.

[Edwin_m]

75mm is approx 3 inches. Did you mean something a bit bigger?

Thanks for pointing it out - changed to 750mm which is what I meant originally, and doesn't affect the calculation! 

Edited November 12, 2016 by Edwin_m

[The Stationmaster]

Trams stop and start frequently. One extra stop isn't going to make much difference to journey times.

 

Would it be practical to bring a tram to stand before continuing where there is a big reduction in permitted speed? You could even build a tram stop there.

 

It would be a lot cheaper than fitting a full TPWS system.

 

Martin.

 

That sounds like a very simple - and hopefully effective - answer if the situation is identified as a particular problem by the various inquiries currently underway.  I do wonder if there is actually a perception problem for tram drivers when they are running on reserved track as they are not then having to consider any other traffic apart from their 'drive on sight' requirement so there might be a tendency to believe they could increase safely speed.  We thus are looking at something with some similarities to a train Driver's route knowledge - and we know that has at various times proved fallible for numerous reasons which have led to using fixed equipment to reinforce the need to reduce speed.

 

I cannot see any need to go to that sort of technical extreme in the much simpler world of a tramway but a 'stop & proceed' arrangement would make considerable sense as (unlike a railway signal) it would undoubtedly be monitored by regular passengers (and also by by whatever data recorder the vehicles have).  However this does of course assume that the alleged overspeed was not caused by some sort of technical problem.

[roundhouse]

Whilst no loss off life or serious injury is to be accepted, this tram system has been running for many years now with generally no serious injury to passengers (OK cyclists have come unstuck as have motorists) I have no problem using it in future. It's probably saved more lives by reducing car usage and associated accidents.

 

However if there are shortcomings then finding them out and reducing them is also good for everyone concerned

[phil-b259]

I remember being told in a law lecture that Causing death by reckless driving contained all the necessary legal elements of murder, and that causing death by dangerous driving contained the necessary elements of manslaughter  However there were various things that meant that the Road Traffic act offence was the preferred one.  The mina one was that juries are very reluctant to convict of Murder/manslaughter and the other was that t was CPS policy to use the Road Traffic Act offence.  I believe that the person (I use the word advisedly) who ran over and killed a police officer in Liverpool a couple of years ago was charged with and convicted of either murder or manslaughter.   As I mentioned above the actual charge preferred will be decided by the CPS.   However I don't think that a tram counts as a motor vehicle for the Road Traffic Act.

 

Jamie

My understanding is that a tram does count as a "road vehicle" - otherwise it would not be permitted on the public highway.

 

It might seem trivial but modern tram systems still fall under the same regs as those around in the 1950s. The tendency to use reserved alignments or ex railways these days for large chunks of the system makes no difference to the law.

 

Light railway systems such as the Metro in Newcastle and the DLR are however considered as railways by law and from a legal perspective they are no different to the national network / Heritage railways / London Underground

[Pacific231G]

I suppose they couldn't use "causing death by dangerous driving" as the tram was on reserved track rather than the road. Or could they, as it's a tramway? Perhaps someone on here knows.

 

Off topic: It makes me wonder why people who are charged with causing death by dangerous driving on the roads aren't changed with manslaughter instead.

Since an arrest has been made I suspect that publishing speculation about possible charges is on very shaky ground.  Reporting restrictions apply to any publication not just to professional journalists and that includes online.  Good summary here http://www.bbc.co.uk/academy/journalism/article/art20130702112133630

[The Stationmaster]

A "Stop and Proceed" sign is a token solution, IMO. How do you enforce it? Camera's? Who's watching those all day? An Inspector standing at the site the whole day? A technical solution like ZUB (or similar, there are several) is easier and cheaper, as it can also be used elsewhere w/o additional costs (bar the installation of magnets and optional electronics if different speeds need to be enforced for different situations).

 

You miss the point fairly completely - if the regular passengers know the sign is there (which they almost certainly would after this incident) they become the monitoring people; they'll shout quickly enough if tram drivers start to ignore the sign.

 

However as we still don't know the reason for the alleged overspeed it is not clear if such a simple method would be anymore effective than relying on a tram driver to reduce speed for the curve.  However coming to a stand is far more noticeable event than a change of speed.  What you seem to be seeking is to load a relatively simple operation with extra technology which would be of fairly limited application on the Croydon network but would still have to be fitted to its entire fleet at - no doubt - considerable cost plus the training cost for drivers and maintenance staff.  The simple question is does something as simple as a tramway, with very limited need for such an expensive technical solution, actually need something that sophisticated?

 

RAIB might make such a recommendation, the other inquiries might make such a recommendation but until they (and by inference we) know the cause of the alleged overspeed and subsequent derailment we don't know what problem - if any - we are trying to solve so a simpe, approach strikes me asa  realistic starting point.

[royaloak]

I'm afraid it isn't It's the conical shape of the tyre profile that keeps rail vehicles on their track. The flanges are only there for extreme cases (and even then only the most severe due to the actual profile of the tyre) and basically intended to guide the wheel past frogs. On perfectly infinitely straight track, a free rolling wheelset will oscillate with ever decreasing amplitude until it finds the exact spot where both tyres are of equal diameter and then continue in that spot. But track never is infinitely perfectly straight, nor is it free rolling   Similarly, in a curve the wheelset will shift outwards until again it has found the spot where the diameters of each wheel matches the circumference required to make the curve. The smaller the radius of the curve, the more the wheelset will shift outward. Of course there's a limit how much tyre is available, so engineers found that artificially enlarging the wheel diameter will also work. That's why, in a cross-section of the tyre, there's a sharp radius curve between the tyre and flange. I'd be happy to post a link to, or even an image of this, but I'm more then confident you'll find those w/o my assistance, should you want to see that  

On a straight (or nearly straight) you are correct but I am on about going round curves where the flange does indeed keep the wheelset on the rails, hence the squealing or need for flange greasers to stop the squealing, or are you going to tell me the flange greasers serve a different purpose?

 

What polishes the flange then, they are always shiny?

[Derekstuart]

Thank you Jamie. Sorry, I should have thought that it might have been unpleasant for you to dwell on the subject given your personal connection. Apologies if I have been tactless in any way.

 

I have no information on US built coaches, other than to say that the outer skin that you see as it goes past will have nil structural strength in it and I would be surprised if the skeleton between the inner and outer skin is any different to British/ European designs. But that is an opinion on my part without any evidence.

Hi Derek, unfortunately I don't have any data.   The Wakefield coach crash, where I knew many of the passengers, obviously is one I know about.   Perhaps the word common was the wrong one.   I remember at the time there was a lot of talk about how the glass formed a portion of the strength and obviously that disappeared once the glass broke. I have vague memories of another overturning incident with a tour bus in Scotland but can't give any details.  From personal observation US greyhound buses have smaller windows and are basically a big strong steel frame with large pillars that have windows fitted in rather like railway coaches.  There was much talk at the time of the Wakefield crash about how our standards should be the same as the US ones.   However I do not have any comparative data.   I have also see the same mechanism of injury in one or two car crashes though these decreased one seatbelts became compulsory. 

 

Jamie

 

In that era, Plaxton and Duple bodied Leyland Leopards & Tigers and Volvo B58 and B10M. They all had a full chassis from the front bumper to after the rear axle, but it is correct to say that there was very little behind the rear axle of most coaches. Certainly the driver was sitting above a full strength chassis.

 

What might surprise you more is that modern coaches, being mostly rear engine, have no heavy chassis BETWEEN the axles, with a lattice of lighter weight structure holding it all together. However, where the older chassis relied on thickness of metal for strength, newer designs rely upon mathematical calculations by design engineers- much like modern cars.

 

As I have written some 4 or 5 times now, buses and coaches are engineered to go on their side or roof without collapsing- it is R66 approval (now superseded as part of eu whole type approval- soon to be superseded by a new name I would expect post Independence).

If it is of any interest I have a bus up in the air outside my door at the moment if you want some photos of the underneath. It has no chassis at all and all main components- engine, transmission, axles and so on are bolted directly onto the bottom of the body.

Few observations. I travelled to school by coach in the late 80's and used to chat to the drivers. I recall discussing Plaxtons coach bodies as we were in one. The driver advised that certain coach chassis (made by the likes of Volvo etc) that Plaxtons put their bodies on were shorter than others. I forget which, but some only had solid chassis frames between the axles, meaning the front and rear of the coach was just bodywork. This led to cracks and the fact that the driver had no crash protection as he was sitting in a bit of bodywork unsupported by a chassis frame. The body was just sheet metal and glass on the chassis, with only the chassis providing structural strength. Hopefully coach design has improved since then but I don't think road coaches are designed to withstand overturning to any great degree.

 

Again, apologies for the slightly off topic reply. I don't know if that helps anyone or not.

[JDW]

Without wanting to get too bogged town in off-topic matters, there was a Lochs & Glens Jonkheere coach that rolled over a couple of years ago in the Highlands.  When I saw the pictures in the media, I thought it was hype, it was on its wheels in a field, the only real clue it had rolled being soil on the roof/air con, plus a few broken windows.  

 

You can often see the structure behind the side panels, especially on coaches, when the weather is cold, the heat from inside and the dew/moisture outside forms patters on the bodywork that reflect the lattice pattern of the frame behind.  There has to be a reasonably solid chassis on coaches/buses in front of the front axle, otherwise (as delivered) there would be nothing to support the steering wheel etc en route to the bodybuilders!  Moderns coaches have FIPS (Front Impact Protection System) or similar to protect drivers, although any protection is generally lower down, especially on buses where the windscreen can come as low as ankle-level on some, the most solid thing between the driver's torso and the brick wall being the steering wheel.

 

Anyway, back to trams, which I'm told are considerably more solid and generally come off better in any collision...

Edited November 12, 2016 by JDW

[Gwiwer]

Wheel flanges do make contact with rails in the normal course of movement.  That can be whilst negotiating sharp curves or might be the result of "hunting" where the vehicle tends to waddle from side to side within the free play of its suspension or the slack which must exist between wheel flanges and rail gauge.  In extreme cases it is possible to spot fine shavings of metal lying on the road-bed through curves where flange and rail have met.  This severe wear and tear affects tramways as much as any other railed operation.  Flange greasers are used in some instances though it has been argued that the grease then spreads itself along the rail-head and is a cause of lost adhesion where it is required rather than easing friction where that is not required.  It is also undesirable to introduce grease to street running where rubber-tyred vehicles may encounter residual grease and themselves lose traction and control especially in wet conditions.

 

Trams typically have extremely robust frame structures, even more so than buses or coaches, in order to withstand high-energy impacts.  The body panels are basically a sacrificial skin.  Windows are, theoretically, a high-risk inconvenience since they often break in major incidents and can themselves be the cause of passenger injuries which might otherwise not have occurred.  They are also however very necessary as any occupant of the original C&SLR "padded cell" tube cars could have told us.  The use of "Contra-vision" serrated vinyl advertisements over windows is widely loathed as it restricts and affects vision in both directions but it has been flagged as offering a little more protection if a window is broken simply by dint of the adhesive vinyl holding it together.  Laminated glass as required generally holds shape even in extreme impacts but broken glass is still - well - broken glass and causes damage.

 

I mentioned one factor above which no doubt RAIB will take account of but hasn't been picked up elsewhere that I've seen.  The incident took place at around 6am on an Autumn morning meaning it was dark.  The tram had traversed a stretch of former suburban rail line which is in a deep cutting and most recently had come through a tunnel.  Therefore there would be little in the way of "marker" illumination other than the permanent tunnel lighting which I believe is always on.  Whether that had any effect on the driver's judgement is for RAIB to determine.  Whether the minutes in the dark, then the rhythmic passage of tunnel lighting, induced micro-sleep again is for the experts.  Whether the earlier alleged overspeed which is also being investigated was in any way similar, and whether any other related incidents come to light now, again is for the RAIB.  That is one reason they call for witnesses - to speak with the greatest number of people involved and obtain the fullest possible picture.

 

A simple Stop and Proceed board might be a quick fix though there is no more to prevent that being passed at speed than a 20kmh speed limit sign.  Trams are driven more like buses than like trains.  They run on line of sight other than where signalled for specific reasons, they stop and start very frequently and they mix with road traffic for, in Tramlink's case, a modest proportion of the total network mileage.  To have the equivalent of TPWS on a former suburban railway-come-tramway seems excessive given it cannot be applied through the street sections.  And no-one is suggesting bus drivers even have vigilance control let alone external intervention in speed and direction management.  The reports will make interesting reading.  I don't expect, at this stage, too much will change at Croydon.  It has always been and remains a safe system.

Edited November 13, 2016 by Gwiwer

[Dagworth]

For the wheel to run without flange contact, the ratio of the wheel radii at the two contact patches must be the same as the ratio of the distances travelled by those two wheels, which is the ratio of the length of the inner and outer rails round the curve. 

 

By a crude bit of measuring on Bing Maps I estimate the radius of this curve to be around 30 metres.  This means that the ratio of the outer to inner rail distances is about 31.435/30, so the outer radius is about 5% more than the inner one.  I don't know the wheel diameter but let's say 750mm, this means that the conicity would have to give a diameter difference of 37.5mm between the two contact patches.  This is far greater than the sort of conicity found on tram wheels.  So even at normal running speeds the tram will be relying on flange contact to steer it round this curve, and even if it this wasn't the case in normal running, the overspeed here would be pushing it into flange contact. 

 

 

There is always a lot of squealing on the tight curves on Metrolink; flange against rail?

If the coning is not enough to account for the difference in length of the inner and outer rail of the curve then one wheel must be skidding somewhat to take up the extra (or less) distance. Is this also part of the squeal?

 

Andi

[roythebus]

I would agree with Gwiwer's comments in paragraph 4 in post 231. Having driven trains on that line in 1979/1980 I was familiar with the location. We had to be aware of the rail head conditions especially in autumn. My view is that no matter what sort of train protection you put in it will not make one iota of difference in autumn in such conditions.

 

To comment on the construction of road coaches, they've been built chassisless for about 20 years now. The main contender for longevity and strength is the Routemaster bus! Chassisless, it has a front and rear subframe with all the strength in the body. As for glass, it is not permitted to use other than triplex type glass in the side windows of buses and coaches. Front and rear screens can be triplex or laminated; most these days are the latter.

[Budgie]

To have the equivalent of TPWS on a former suburban railway-come-tramway seems excessive given it cannot be applied through the street sections.

What is that gubbins in the four-foot that you can see at 1:44 into this video of the Manchester Metrolink at Oldham, which is also a former suburban railway-come-tramway?

[JDW]

AT around a minute in, there's a sharp left bend - the black and white chevron boards are interesting, something I wouldn't have expected to see on a tram-only section, though an obvious and simple solution to highlighting the left bend where the original alignment went straight ahead.

[dhjgreen]

AT around a minute in, there's a sharp left bend - the black and white chevron boards are interesting, something I wouldn't have expected to see on a tram-only section, though an obvious and simple solution to highlighting the left bend where the original alignment went straight ahead.

There are also 3, 2 ,1 countdown markers leading to the bend. That tram has just climbed the lesser Werneth bank, so easy to slow down. The other direction has a road crossing just before the bend.

 

Edit to add. When it first opened this line went straight on through the tunnel to Mumps station, would enforce the need to remind the drivers about the curve.

Edited November 13, 2016 by dhjgreen