Talltim Posted November 10, 2016 Share Posted November 10, 2016 (edited) Interesting to learn about Eddy Current brakes, that was completely new to me. Obviously an issue with both the electromagnet version of that and the magnetic track brake is that they fail if there is no power. (Not specific to this incident at all, just speaking generally) Edited November 10, 2016 by Talltim Link to post Share on other sites More sharing options...
ejstubbs Posted November 10, 2016 Share Posted November 10, 2016 (edited) Many trams have a block that drops onto the top of the rail. I dont know what the Croydon trams have though. The braking systems on the Croydon trams was described quite well in post #24 in this thread. Edited November 10, 2016 by ejstubbs Link to post Share on other sites More sharing options...
RMweb Premium Richard E Posted November 10, 2016 RMweb Premium Share Posted November 10, 2016 (edited) Aren't those civil offences that are judged on the balance of probabilities as opposed to criminal offences requiring to be proven "beyond reasonable doubt"? I'm not a lawyer but someone reading this must know the law. Speeding is a criminal offence, I'm not certain about the others, probably decriminalised but originally tried as criminal. The reason for decriminalising parking for example was to relieve pressure on the courts. Edited November 10, 2016 by Richard E Link to post Share on other sites More sharing options...
david.hill64 Posted November 10, 2016 Share Posted November 10, 2016 Interesting to learn about Eddy Current brakes, that was completely new to me. Obviously an issue with both the electromagnet version of that and the magnetic track brake is that they fail if there is no power. (Not specific to this incident at all, just speaking generally) Eddy current brakes are also fitted to Japanese Shinkansen trains, specifically on the trailer cars. The difference here is that they act on axle mounted discs. The advantage is that you don't heat the rails: the disadvantage is that you still rely on wheel-rail adhesion to get brake force. Link to post Share on other sites More sharing options...
leopardml2341 Posted November 10, 2016 Share Posted November 10, 2016 (edited) Electromagnetic (friction) track brakes are appropriate and VERY effective for emergency applications but not so for routine vehicle retardation, e.g. service brake applications. I speak from personal experience, practically and technically. Separately, leaf mulch forms a chemical bond with the steel which when exposed to further moisture acts as very effective lubricant and of course if two (in contact) surfaces are coated in this compound, with a water film between them rail/wheel adhesion becomes comparatively very low indeed. Wheel tread brakes have the effect of scrubbing the wheels, but not the rail per se, when they are used as the primary brake and thus the leaf mulch compound is abraded from the contact surface of the wheel and removes 'half'{sic} of the problem. Noting what I said about track brakes and routine use above, it is unlikely that the same scrubbing effect will be realised. Eddy current brakes are also fitted to Japanese Shinkansen trains, specifically on the trailer cars. The difference here is that they act on axle mounted discs. The advantage is that you don't heat the rails: the disadvantage is that you still rely on wheel-rail adhesion to get brake force. Same principle as a road vehicle retarder Edited November 10, 2016 by leopardml2341 Link to post Share on other sites More sharing options...
david.hill64 Posted November 10, 2016 Share Posted November 10, 2016 Separately, leaf mulch forms a chemical bond with the steel which when exposed to further moisture acts as very effective lubricant and of course if two (in contact) surfaces are coated in this compound, with a water film between them rail/wheel adhesion becomes comparatively very low indeed. Wheel tread brakes have the effect of scrubbing the wheels, but not the rail per se, when they are used as the primary brake and thus the leaf mulch compound is abraded from the contact surface of the wheel and removes 'half'{sic} of the problem. Noting what I said about track brakes and routine use above, it is unlikely that the same scrubbing effect will be realised. The main rationale of trying the magnetic track brake on the Merseyrail unit was to see if it would scrape the leaf mulch off the rail head and improve the adhesion for the unit involved and following trains. IIRC the unit had a magnetic track brake on the two end bogies with the control circuitry arranged so that in step one braking, only the track brakes were deployed. In normal conditions these brakes would provide the complete braking force required for the whole unit. However, for the reasons that you state, the low friction between rail and track brake due to the leaf mulch meant that braking was insufficient. The track brakes did reduce the surface leaves but did not remove the film. Actually a modern WSP system is more effective at removing the film from the rail head. By controlling the slip of the wheel so that it is rotating at less than synchronous speed (rather than sliding) adhesion is improved. BR research identified 'wheel conditioning' and 'rail conditioning' parameters. 'Wheel conditioning' described by how much the adhesion was improved for that particular wheelset and 'Rail Conditioning' described by how much the adhesion was improved for following wheelsets. These factors were built into the highly successful WSPER rig. WSPER: the Wheel Slip Protection Evaluation Rig, also known informally as 'Rosser's Organ' after its inventor and the manner of pipework attached - (though the noise it produced might also have had something to do with the name) used these factors together with wheel rail adhesion records taken from the Tribometer train to enable WSP systems to be tuned to best meet the characteristics of the vehicles to which the WSP system was fitted. Link to post Share on other sites More sharing options...
leopardml2341 Posted November 10, 2016 Share Posted November 10, 2016 (edited) The main rationale of trying the magnetic track brake on the Merseyrail unit was to see if it would scrape the leaf mulch off the rail head and improve the adhesion for the unit involved and following trains. IIRC the unit had a magnetic track brake on the two end bogies with the control circuitry arranged so that in step one braking, only the track brakes were deployed. In normal conditions these brakes would provide the complete braking force required for the whole unit. However, for the reasons that you state, the low friction between rail and track brake due to the leaf mulch meant that braking was insufficient. The track brakes did reduce the surface leaves but did not remove the film. Actually a modern WSP system is more effective at removing the film from the rail head. By controlling the slip of the wheel so that it is rotating at less than synchronous speed (rather than sliding) adhesion is improved. BR research identified 'wheel conditioning' and 'rail conditioning' parameters. 'Wheel conditioning' described by how much the adhesion was improved for that particular wheelset and 'Rail Conditioning' described by how much the adhesion was improved for following wheelsets. These factors were built into the highly successful WSPER rig. WSPER: the Wheel Slip Protection Evaluation Rig, also known informally as 'Rosser's Organ' after its inventor and the manner of pipework attached - (though the noise it produced might also have had something to do with the name) used these factors together with wheel rail adhesion records taken from the Tribometer train to enable WSP systems to be tuned to best meet the characteristics of the vehicles to which the WSP system was fitted. A limited experience of the WSPER rig is from where my knowledge stems, but as they say a little knowledge......... The brake fitted to the 507 would be magnetic friction rather than magnetic eddy then? Edited November 10, 2016 by leopardml2341 Link to post Share on other sites More sharing options...
RMweb Gold The Stationmaster Posted November 10, 2016 RMweb Gold Share Posted November 10, 2016 The nightstock (often called 'Nightstar) was fitted with magnetic track brakes as it would run in Germany. There is (was?) a standard DB test for the magnetic brake which involved the vehicle being 'slipped' at 100kph and relying on the magnetic brake to bring it to a stand. The vehicle passed which would indicate the system is effective - at least under service trial conditions. Link to post Share on other sites More sharing options...
Talltim Posted November 10, 2016 Share Posted November 10, 2016 With regards to the efficiency of magnetic track brakes in low railhead adhesion situation, there can be a big difference between good and bad in the same way as wheel brakesThe RAIB report into the tram collision at Shalesmoor on the Sheffield system has some interesting information on it.https://www.gov.uk/raib-reports/collision-between-two-trams-at-shalesmoor 61 In the tests the stopping distance was found to increase from around 12 metres on dry uncontaminated rail to around 35 metres in the simulated low adhesion conditions, when using the full service brake. When the hazard brake was used (and sanding was automatically activated), the braking distance was found to increase from around 8 metres to around 19 metres. Link to post Share on other sites More sharing options...
Pacific231G Posted November 10, 2016 Share Posted November 10, 2016 Without speculating on this particlularly tragic accident, there is always a kneejerk reaction to want "something to be done about it" whenever a bad rail accident occurs. I don't know what the cost would be of developing and fitting to all tramways automatic overspeed sensors responding to local speed limits, as has been widely suggested this week, but suspect it would be prohibiitve and less cost effective in terms of increasing safety than many other measures. Clearly, if the investigation of this acccident reveals an underlying deficiency or that overspeed, whether due to driver error ot otherwise, was causing a significant number of non-fatal derailments then that would need to be dealt with. That is surely how railways generally moved from being a rather dangerous form of transport to the safest. Link to post Share on other sites More sharing options...
RMweb Premium jamie92208 Posted November 10, 2016 RMweb Premium Share Posted November 10, 2016 (edited) Without speculating on this particlularly tragic accident, there is always a kneejerk reaction to want "something to be done about it" whenever a bad rail accident occurs. I don't know what the cost would be of developing and fitting to all tramways automatic overspeed sensors responding to local speed limits, as has been widely suggested this week, but suspect it would be prohibiitve and less cost effective in terms of increasing safety than many other measures. Clearly, if the investigation of this acccident reveals an underlying deficiency or that overspeed, whether due to driver error ot otherwise, was causing a significant number of non-fatal derailments then that would need to be dealt with. That is surely how railways generally moved from being a rather dangerous form of transport to the safest. Having recently ridden the Nottingham system and much of the Manchester system I would agree with this. On both systems there are very sharp curves after quite high speed sections. I hope that there are no knee jerk reactions. I also heard on BBC radio that the driver has now been released on bail pending the results of the full investigation. Not quite what are known as live proceedings yet but even more reason to be circumspect in what is said. Jamie Edited November 10, 2016 by jamie92208 Link to post Share on other sites More sharing options...
edcayton Posted November 10, 2016 Share Posted November 10, 2016 It should be borne in mind that for a very long time this country had no trams (apart fro Blackpool which is pretty flat) and therefore there could be no accidents, let alone fatalities. None the less I hardly think this can be described as a "knee-jerk reaction". Ed Link to post Share on other sites More sharing options...
Dr Gerbil-Fritters Posted November 10, 2016 Share Posted November 10, 2016 I've decided; decided to remove the user's access to this topic so it ceases to exist for him. Problem solved. Can you make that happen for me, regarding Trumpy and Brexit? Thanks so much. Will Sleep-Better-At Night 2 Link to post Share on other sites More sharing options...
david.hill64 Posted November 10, 2016 Share Posted November 10, 2016 A limited experience of the WSPER rig is from where my knowledge stems, but as they say a little knowledge......... The brake fitted to the 507 would be magnetic friction rather than magnetic eddy then? Yes. Link to post Share on other sites More sharing options...
Edwin_m Posted November 10, 2016 Share Posted November 10, 2016 I was involved in a detergent-on-rail test of a Croydon tram in 1998, and it seemed very sure-footed with it being almost impossible to make it slide even with the sanders disabled. Link to post Share on other sites More sharing options...
RMweb Premium Gwiwer Posted November 10, 2016 RMweb Premium Share Posted November 10, 2016 It should be borne in mind that for a very long time this country had no trams (apart fro Blackpool which is pretty flat) and therefore there could be no accidents, let alone fatalities. None the less I hardly think this can be described as a "knee-jerk reaction". Ed Blackpool and Eastbourne. The latter operation moved to Seaton. Yes there has been an interval between having multiple and large systems but nonetheless it has been 57 years since a British tramway passenger was killed abd trams have run for all of those years. However few in number. I have seen some disingenuous comments (possibly from lack of knowkedge) to the effect that the curves at Sandilands are far too tight and have been an "accident waiting to happen". They are normal tramway radius curves with a suitable speed limit. The DLR features similar and is for the most part automatically driven. There is a procedure for dealing with an overspeed - which I have experienced - and which first applies the energency brake abd ends with the staff member on board assuming manual control. I don't know what overspeed protection, if any, Tramlink vehicles are fitted with. RAIB might choose to look at whether this is needed in the light of other recent allegations of excess speeds here and at other locations. Finally since I cannot find where the comment was posted and it could be anywhere on the many discussions across the internet this was an Addington to Wimbledon working which would have emerged from the tunnel to face the curve but trail through the junction points; the tram has not derailed on facing points as it took them heading towards Addington as I saw suggested somewhere. Link to post Share on other sites More sharing options...
RMweb Gold Colin_McLeod Posted November 10, 2016 RMweb Gold Share Posted November 10, 2016 February 1946 a runaway tram crashed into a pub in Belfast. Note I am not speculating that this is what happened at Croydon. Link to post Share on other sites More sharing options...
RMweb Premium jamie92208 Posted November 10, 2016 RMweb Premium Share Posted November 10, 2016 It should be borne in mind that for a very long time this country had no trams (apart fro Blackpool which is pretty flat) and therefore there could be no accidents, let alone fatalities. None the less I hardly think this can be described as a "knee-jerk reaction". Ed I hope I haven't caused confusion. I was meaning that I hope that in the aftermath of the reports and enquiries that at that point there are no reactions that end up making tram systems unaffordable and stop new ones being built. I would hope that any changes are measured and based on proper risk assessment. At the moment there has been no such reaction and for that I am grateful. Jamie Link to post Share on other sites More sharing options...
Edwin_m Posted November 10, 2016 Share Posted November 10, 2016 (edited) Santiago de Compostela and also the crash of the test TGV in France illustrate how small the margin of error is when decelerating from very high to lesser speeds. A few seconds late in braking and the train has travelled hundreds of metres further, and the place where it reaches the necessary lower speed has also moved by the same distance. So it is particularly important that the system provides speed supervision in these sections - in fact far more so than on the high speed line proper where (ignoring the issue of preventing collisions with other trains) derailment is probably unlikely at any speed the trains can reach. In Spain this section was classified as not a high speed route so didn't have the signalling required for high speed routes, and in France the overspeed protection had been disabled to allow a test to take place at higher than the normal permitted speed. This doesn't really copy across into the Croydon situation, where as it runs on line of sight it should be possible to delay decelerating until the curve becomes visible and even then get down to a safe speed without the use of the more powerful track brakes (which are then available as a reserve in the event of a gross misjudgement or severe loss of adhesion). Having spent a lot of the last few years facilitating tramway safety workshops (not in Croydon) I suspect that we will now see some kind of crude automatic speed supervision system for these situations where a fast off-street section leads into a tight curve. However I can't say any more about the nature and reasons for it without making some assumptions about the reasons for the overspeed, which I would not wish to do on an open forum. Edited November 10, 2016 by Edwin_m Link to post Share on other sites More sharing options...
stadman Posted November 10, 2016 Share Posted November 10, 2016 Somewhat dismayed that the editor of a magazine saw fit to comment on the cause last night on BBC radio 2 Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted November 10, 2016 RMweb Premium Share Posted November 10, 2016 I see the BBC are already starting scaremongering about the safety of trams. At least on this occasion their resident 'expert' on all things rail is trying to put things in perspective. http://www.bbc.co.uk/news/uk-37941085 Link to post Share on other sites More sharing options...
JOHNMCDRAGON Posted November 10, 2016 Share Posted November 10, 2016 In relation to the last tramway deaths which were in Glasgow in 1959, I remember hearing of it when I was a child. Apparently it happened in very thick fog when a tram which had stopped in Argyle St was unfortunate enough to be backed into by a lorry reversing out from St. Enoch Square loaded with scaffolding poles. One of the scaffolding poles encroached into the tram and by a fluke pierced the main fuse box near the rear exit and caused a short circuit starting a fire in which several people perished I believe. So that accident was not connected to tram safety in itself, just a tragic turn of events. Link to post Share on other sites More sharing options...
stewartingram Posted November 10, 2016 Share Posted November 10, 2016 I'm not advocating speculation on this, but just commenting on what I saw in one of the pictures published. There is a view from inside the tunnel, looking towards the tram, with the tunnel lights on. Obviously taken with a telephoto lens which does given "distance distortion" but just look at the way the rail is not so smooth, it twists and bends all over the place! As one who is familiar with Blackpool, I am only too aware of the excellent condition of the present new track there, but can compare it with certain sections of the old track just before renewal. It didn't seem to be as bad as that in the photo? Stewart Link to post Share on other sites More sharing options...
JOHNMCDRAGON Posted November 10, 2016 Share Posted November 10, 2016 Sorry, got some details wrong in previous post,(should have looked it up instead of doing it from memory). Was in Shettleston Rd, not Argyle St. and overhead came down causing fire. Regardless , point being trams worldwide still have good safety record. Link to post Share on other sites More sharing options...
BR-Green Posted November 10, 2016 Share Posted November 10, 2016 I have seen it reported on the BBC news that the driver was released from hospital and was arrested for seven counts of manslaughter Link to post Share on other sites More sharing options...
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