Push-Pull

Discussion in 'UK Railway Discussion' started by ikar, 18 Feb 2006.

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  1. ikar

    ikar Member

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  2. RJ

    RJ Established Member

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    It's like saying driving a train or a car isn't safe because accidents occur. It's not a common occurance and in this day and age I think that steps have been taken to increase the safety of propelled trains.
     
  3. AlexS

    AlexS Established Member

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    If you take a look at the DVT in the accident at Selby in the pictures of the accident report, unless you know what you are looking for, you won't spot it. It's a flat sheet of steel lying in a field, the bodywork was completely destroyed, and flattened by a trailing coach.
     
  4. TheSlash

    TheSlash Established Member

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    DVT's etc are now modified to be nearer the same weight as the loco pushing them
    As for that website, i wouldn't take alot of notice, it sounds like sour grapes, especially the broken fishplates part
     
  5. Nick W

    Nick W Established Member

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    If they make the DVTs the same weight they might has well just have 2 half locos at each end but still with space for luggage and bikes like HSTs.
     
  6. metrocammel

    metrocammel Member

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    Ive always though about "How safe actually are DVT's (or push-pull in general)?", as on a very small (and relativley unrealistic scale) when I run a 86 / 87 or 90 with a mk2 / 3 set and a DVT (at the front)), if it derails the whole train will derail and "jack-knife" across the tracks (as the loco keeps pushing for a bit) and causes a general mess. Whereas, if I have a set with a loco at the front that de-rails it will stop very soon, and rarely causes the coaches to de-rail.

    Obviously this is not a "real" situation, but I know (god forbid) that I'd rather derail on a loco at the front rather than a loco at rear (and DVT)
     
  7. O L Leigh

    O L Leigh Established Member

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    Hi Gang!!

    Firstly, every accident is different. Quite often unexpected things happen for the strangest of reasons, so expectations are not always borne out. A loco-hauled set may still jack-knife if the loco is at the front because there is still an awful lot of mass in a loaded set and, hence, momentum to be dissipated.

    As to the particular DVT-related question, I have no problem with them. A DVT is hardly any more robust than an MU, but at least does not contain any passenger accomodation and so provides a crumple zone between the accident and the punters. Selby would still have been a proper mess even if the IC set had been running the other way round.

    Pity the driver, but then it doesn't really matter what you're driving if you're going to have a "big one". At least a DVT/MU offers an escape route along which the driver can beat a hasty retreat if need be.

    one TN
     
  8. ChrisCooper

    ChrisCooper Established Member

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    I don't know, I think if I was driver and was going to have a "big one" I'd much rarther be in a loco than anything else. You only have to look at Southall and Great Heck, both horrific collisions but the HST driver and the second driver on the 66 survived, and of cource that one where the 87 hit a Pacer, with the 87 driver surviving (ok, the pacer took a lot of the impact, but the 87 would still have suffered some serious forces due to the high speed). The only serious collision involving a unit where the driver at the impact end survived I can think of is Purley, and that involved a Mk1 unit, and was tame by the standards of the above crashes. For a start, not only do locos provide an escape route (engine room) but there is a heavy engine to offer protection (this is what saved the Southall driver), wheras in a unit, unless you are planning on running a couple of coaches back (unlikely when you're probably got seconds to do anything), you're not going to get that much extra protection, and if anything, the fact you were standing might make you worse off.
    As one TN said though, accidents involve many factors and are all very different. The fact that the leading vehicle in an accident performs badly can save lives further back due to it acting as a crumple zone. It is just as likely that the crushing of the first 2 coaches of the second train at Clapham Junction saved lives in the leading train and the carriages behind. Afterall, the energy from a collision has to go somewhere, and proper crumple zones can only deal with a small amount, and can lead to deaths or injuries if people are inside them at the time of the accident (I hate to imagine a busy Voyager with people standing in the crumple zone behind the cab being in an accident). A loco will do more damage to the train it hits, or just transfer the energy to the coaches being it, and the extra weight means more energy to loose. Anyway, in most respects it's better to concentrate on preventing the accident in the first place, then take reasonable steps to reduce the consequences of any accidents that do occur.
     
  9. O L Leigh

    O L Leigh Established Member

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    Hi Chris,

    I think it depends very much on the type and design of the MU involved. I have heard that Networkers do have a load-bearing bulkhead to provide protection to the passengers. However, this bulkhead forms the back wall of the driving cab, so the driver really is sitting in the crumple zone. In that respect just nipping through the connecting door into the passenger saloon will afford more protection than staying put. In fact, with any design of MU the further away from the point of impact you can get, the higher your chances of survival ought to be (though it isn't always the case). Besides, once you've put the brake into emergency there's nothing more you can do, so you might as well get out.

    one TN
     
  10. Sprog

    Sprog Established Member

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    Arg :mad:

    To many silly things said in this topic. Im aint got time to reply to them all.....

    Just be carefull about saying things you have no idea about (aka, Selby)

    All im saying is if the 91 had been leading, it might have been alot worse. Although, if it was........the train may not have even derailed in the first place............

    All these factors and 'what if's' just make you go in circles and its not worth it.

    Basically, sh*t happens, and as ive said with Ufton Nervet, so matter how much me 'um' and 'ahh' about it, we can do nothing now, but learn from our mistakes and bring in measures to prevent a siiar incident in future. Selby in particular was a coincidential and freaky set of events that all combined to make a horrific accident. No one could have forseen this.

    Oh, and also, you talk about the DVT as a crumple zone - you are forgetting the driver who was in it :( .............

    .......on that note, Does anyone actually know where they found the GNER drivers body in the Selby wreckage....cus i do aint it aint a nice thought :(
     
  11. O L Leigh

    O L Leigh Established Member

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    You have a PM.

    one TN
     
  12. Sprog

    Sprog Established Member

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    Got it.!

    I wasnt just reffering to you bud.......to yes, we do agree......! :)
     
  13. Bill EWS

    Bill EWS Member

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    Hi everyone,
    This was a good discussion that didn't treat the subject matter lightly. Personally, I have never been a lover of push-pull trains and thankfully never had to work any, albeit I have travelled in many just like yourselves. Prior to the electrification from Basingstoke to Southampton, around 1966, I hadn't given this much thought until they introduced the new high-speed push pull units. Before this (steam days) push-pull was restricted to a maximum speed of 50 mph and suddelnly going up to 95 mph seemed strange indeed. We worked over this line from the steam days and from day one of the electrification and I always felt uneasy when passing a push-pull on the opposite line. If the front ever lifted off the track you didn't stand much chance should that train come charging your way.

    Thankfully, such derailments proved very few but I have never forgotten that the possibility has always been there. Even more so when the Southampton line speed was raised to 100 mph. Then there were the DTV's on the Northwestern lines and working over those lines kept my feelings alive on that issue.

    Increasing the weight of the driving trailers came about after the Scottish accident and mainly to stop the vehicle lifting off the tracks in a similar incident. No-one ever expected that a Cow would create such a disaster when hit by a train. but if these left the track for any reason the extra weight and the fact the train is being pushed woud make no difference to the eventual outcome. It would still be pot-luck. I remember my driver and I relieving a train at Reading once that had hit a heard of cows near Banbury and the train managed to continue it's journey to Southampton, albeit with some delay, and the underside of the coaches looking like a butcher's shop!! The loco, a 47, was sent to the shed for servicing.

    Another thing that came from this incident was pushing in-cab radios to the fore and a flashing light warning on front of locomotive operated by the driver. The sad fact of the Scottish incident was that the Cow on the track was reported to the signalman but was too late to get the approaching train stopped.

    The Glasgow-Edinburgh push-pull Class 26's (or was that 27's) didn't ease my worries. They used radio waves and transmitters and receivers along the lenghth of the train to operate the controls of the rear locomotive and hopefully you didn't loose the signal anwhere on the way!! However, as with HST's, having power at both ends is a lot different and equalises the pressures throughout the train more evenly, but both driving units have to be well serviced so that power starts andcuts off within tight equally specifications. If you ever travelled on the HST + Class 91 formation in the early days of Class 91's between King's Cross and Leeds you may still remember the very rought ride you got and the heavy jolts when the 91 would power faster than the HST, or vice-vera, and you felt as if the sole bar was going to come up through the coach floor, or if it ocurred when taking a curve your shoulder would be slammed against the window edge. I saw many a worried look from fellow passengers at such times.

    Thankfully this was resolved when class 91's and driving trailers came together in greater numbers. But it all proves the inherent difficulties of running high-speed push-pull trains. Personally, I will never be happy about them but perhaps as the law of averages has proved over the years, with so few serious incidents, then this is how we have to live with it.

    In regard to 'crushability' it is interesting that B.R. baulked at passengers travelling up front in high-speed DVT's, or using a DMU type train for long distance travel, but here we are today accepting both!

    Having worked on and travelled all these years on the railway and understanding many of these incidents it still counts that the railway is very much a safe way to travel. Staff in all departments DO see safety as the priority and many of these incidents ocurr in spite of everything possible being done to avoid them and keeping them to the very minimum. However, push-pull still doesn't sit very squarly with me, personally. Unless it is two power cars at each end.

    Regards.

    Bill EWS.
     
  14. O L Leigh

    O L Leigh Established Member

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    Hi Bill,

    Thanks for the interesting and informative post. I've only just joined the driving grade, so it's always good to hear from someone with more experience.

    My own personal view is that there is a difference between trains designed from the outset for push-pull operation (IC225's) and those that were later used as such (WCML and now GEML Mk2/3 sets). My own experience from travelling on each was that the IC225's had a much smoother ride because there seemed to be some clever blending of the Mk4's brakes and Cl91's power when initially starting away. For this reason it was always possible to tell when a Cl90 was deputising because there was always a hard shove as the loco tried to accelerate hard into the back of the coaches while the brakes were still bleeding off. On the other hand, the Mk2/3 push-pull sets with Cl86/87/90 power were dreadful and seemed to require careful driving to prevent snatches (or whatever the passenger equivalent is called).

    However, I was never worried about the leading vehicle taking off for the same reason that I'm not worried about the leading vehicles of MU's taking off. It seems odd that there seems such concern over DVT's when the leading vehicle of a 100mph EMU could weigh the same or less and is full of passengers (incidentally, we agree on the matter of passengers riding up-front in trailer vehicles on high speed services), which is a situation we've had for at least the last 30 years.

    Then again, as you rightly say, there's so much experience now of both push-pull and top-and-tail operation that should inform this discussion. There have been too many accidents involving all manner of different rolling stock, and the outcomes are always far too tragic. I doubt that anyone could conclusively prove that one form of operation was any more or less dangerous than any other. Even HST's don't have a particularly enviable crash record, and they always have a loco at the leading end.

    Good discussion, as you say.

    one TN
     
  15. ChrisCooper

    ChrisCooper Established Member

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    Just a few comments on Bill EWS's post. Firstly, the original sets operated on the Glasgow to Edinburgh run were top and tail using Class 27s. They didn't use radios, but the blue star multiple control system was wired thorugh the train, and infact was very similar to the system on the HSTs. Recently, the same system was used on Wexssex Trains and Arriva Trains Northern services using 31s and 37s respectivly, top and tailing through wired air conditioned Mk2s. In the case of the original Scotrail service, a big problem was jerking and snatching caused by the delay in the control signals getting to the rear loco. With the HSTs experiance with this type of operating allowed the problem to be reduced, but it is still there, and is very noticable if the train is badly driven. Interestingly, the HSTs are set up so that on notch 1, the rear powercar is pushing the train more than the front is pulling, since the engine is running a notch higher. From notch 2 though the engines are at the same speed, and since the rear powercar is providing the train supply, the front is pulling more than the back. With the more recent top and tail trains, further leasons were learned and they supposedly managed to deal with the problem of jerking quite well. When it comes to push-pull, jerking is again quite a problem. It is true that the ECML sets arn't as bad on starting, and I think one TN is right in saying that the 91s are set up to work well with the Mk4s. They still suffer from jerks when power is shut off, in particular when previously accelerating hard. The 91s and 90s seem worst for this, which makes me thing it is the automatic speed control that is to blame often. A particular problem is that the ASC is set to apply the loco's rheostatic brake if the speed is above that set by the driver (to hold speed downhill). If speed is set low, and full power is used, by the time the system reacts the speed can be above the set speed. This then causes the train to go from full power to fairly hard rheostatic braking quickly. Since the train will be buffered up, this causes the train to snatch as the couplings suddenly go from compression to tension. Another problem can be if the driver sets a lower speed whilst power is on. This again causes the rheostatic brakes to apply. Then again, jerking is noticable on many units, most of which work on a sort of push pull system with driving trailers at each end.
     
  16. Nick W

    Nick W Established Member

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    Can having a wall between the two tracks help like they have in some places on the DLR?
     
  17. Bill EWS

    Bill EWS Member

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    Thanks to One TN, ChrisCooper and Nick W for another very nice response. I knew that the earlier Class 27 pairings were via standard cabling but remember reading much later that they were using a transmitting & Receiving system. I appreciate One TN's comments and to learn more about this. I know too that when DTV's were introduced many of the drivers that I met and talked to in messrooms didn't care for them. Not only the lightness but the lack of feeling the weight and power of the rear locomotive. The quietness was appreciated but appeared to take away some personal contact with the loco. No doubt, with time and experience and improvements in newer DVT's this became less and less a concern.

    I never experienced any serious knocking from HST's and indeed they are one of the most successful train sets ever and as proved today, the private companies are having difficulty replacing them with something that will meet the same standards. The 180's may run at 125 and have a better enviornment than the average unit but they still feel very much like a DMU and could never take over from the HST.

    I did handle HST's during route divergences and from drivers I was friendly with and they were very impressive.

    Sorry Nick W a wall is no answer at such speeds. The docklands is quite a different set-up. You have to ask yourself, would you prefer being hit by another train or be on the train that hits the brick wall!!! High speed derailments like this require space and ground contact to participate the pressures and slow down the stopping rate. I remember watching a train split at Didcot east, on its way to Oxford (This was in vaccum brake days) and both halves of the train came to a stand at virtually normal rates and most passengers on both halves of the train didn't realise they had an incident and remained in their seats, looking out of the windows as if it was a normal stop. Only if the train had detailed would they have known about it.

    Whatever, many thanks for your remarks and good luck to One TM in his railway career with EWS.
     
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