Is the berth offset of Wem station wrong?

Discussion in 'Allocations, Diagrams & Timetables' started by Typewind, 4 Dec 2018.

  1. Typewind

    Typewind Member

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    Hopefully there are some rail data guys, or the Wales/West Middleland Train Driver who is familiar with Wem station here.

    I'm doing a data exploration of Manchester Piccadilly - Cardiff Central journey, and surprisingly found the berth offset of Wem stations is 450s/220s, say
    - Berth 8330 to 8316, offset = -450s
    - Berth 8405 to 8447, offset = -200s

    The berth map of wem, http://www.opentraintimes.com/maps/signalling/cre-shr#T_WEMM


    Any reply/discuss will be appreciated, thanks in advance
     
    Last edited: 5 Dec 2018
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  3. Freightmaster

    Freightmaster Established Member

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    Why 'surprisingly'? The resignalling of that line was done on the cheap, resulting in signal spacing being
    barely any better now than the manual block signalling it replaced!



    MARK
     
  4. Typewind

    Typewind Member

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    Awww I see. Because most of the offsets are -120 ~ 120, totally shocked when a 450 jump out
    This situation is not uncommon in Wales, is there any cheap resignalling line in Wales as far as you know?
     
  5. Freightmaster

    Freightmaster Established Member

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    The North Wales Coast (Abergele to Shotton) isn't much better - not as bad at stations,
    but there is a notable lack of intermediate signals, especially in the westbound direction
    for some reason...


    MARK
     
  6. The Planner

    The Planner Established Member

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    The re-signalling of the Shrewsbury to Nantwich section was a shocker, I don't think the bi-di has ever been used in anger.
     
  7. Typewind

    Typewind Member

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    Not just the signals, but also the stations are missing on the west coast (I mean the gap between Aberystwyth and Fishguard Harbour)..is it because few people live in the west coast and NR simply don't care that area?
     
  8. Typewind

    Typewind Member

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    sorry for a very stupid question:frown:...what's the meaning of shocker and bi-di here?
     
  9. Llanigraham

    Llanigraham On Moderation

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    What stations? The nearest and only 2 would have been Cardigan and Aberaeron, both on the end of little used, slow single track branches.
    The lack has got nothing to do with Network Rail as they were closed well before NR or Railtrack were even thought about.
     
  10. Llanigraham

    Llanigraham On Moderation

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    "shocker" - rubbish and not wel planned.
    "bi-di" - bi-directional.
     
  11. Typewind

    Typewind Member

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    sounds like a mysterious historic, thanks for explaining
     
  12. Llanigraham

    Llanigraham On Moderation

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  13. Typewind

    Typewind Member

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  14. craigybagel

    craigybagel Established Member

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    It's been used once or twice to rescue trapped trains and return them to Crewe/Shrewsbury. It doesn't help that it is effectively useless for everyday use as you can't go over the crossover at Nantwich with passengers on, and you can't crossover at Shrewsbury without a MOM getting involved.

    The block sections are basically the same as what they were before the resignalling - and they even recreated the fact that Whitchurch signal box was closed a few years earlier by leaving a long section Press - Wrenbury. We were told at the time that they'd put another signal in that block in the near future but 5 years later and there's still no sign of it.

    And don't get me started on the reliability issues with the level crossings.....
     
  15. Typewind

    Typewind Member

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    What's wrong with the level crossing? I thought it's used to stop pedestrians. And if it's not reliable what will happen?
     
  16. Llanigraham

    Llanigraham On Moderation

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    Plural "level crossings".
    There have been problems with the LIDDAR units making false reports and the barriers not dropping. Result; stopped train!
     
  17. craigybagel

    craigybagel Established Member

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    This. The fail safe works great, people are never put in danger, but I've lost count of how many times I've been delayed by issues with the crossings. If you're lucky, it's just a case of getting cautioned across - if you're unlucky, the whole line is blocked for a time. These issues have not been once off - they happen many times per year (the last time I got cautioned was only 3 days ago!). It's not just Wem, it's all 4 sets of full barrier crossings on the line.

    There have also been issues with the system not recognising trains correctly - adjusting the level crossing timings to suit the all stops local and not a 90mph non stop express. This results in trains getting checked at almost every crossing. To be fair, that issue has mostly been eradicated - even when services get diverted this way they don't normally get held up any more, but when the line was first resignalled it was a recurring issue for several months.
     
  18. Typewind

    Typewind Member

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    Sounds a restrict safety manner...But does the level crossing incident influence the berth offset of the section?
     
  19. craigybagel

    craigybagel Established Member

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    Couldn't tell you - I don't have a clue about how it all works (or doesn't as the case often is) I'm afraid.
     
  20. Llanigraham

    Llanigraham On Moderation

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    I don't even know what "berth offset" is!
     
  21. Typewind

    Typewind Member

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    Nah that's fine, you already explained a lot :D
     
  22. Tomnick

    Tomnick Established Member

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    It doesn’t influence the berth offset, but it’ll affect the accuracy of the berth offset for a given train movement. If the train is delayed between, for example, departing Wem and passing the next signal (which is when the movement report is generated, with the berth offset applied to approximately compensate for the time that’s elapsed since the train actually departed Wem), then the departure time recorded will be later than the actual - unless there’s another check that I’m not aware of.
     
  23. craigybagel

    craigybagel Established Member

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    I wonder if it would explain why the PIS screen at Whitchurch on the down always thinks the service will be about 5 minutes later then it actually is in reality (ie if it's on time the screen shows 5 late, if its 5 late it shows 10).
     
  24. Typewind

    Typewind Member

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    The official explanation of berth offset:
    https://safety.networkrail.co.uk/jargon-buster/berth-offset/

    It's used to calculate timestamp on seconds level (rather than minutes). The actual timestamp is also calculated by berth offset but the seconds part was dropped out...

    And don't expect the accuracy of the result as berth offset is an average of the runtime of all the trains passing that section..no idea why not use GPS data though
     
  25. Muzer

    Muzer Established Member

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    My understanding is that the stopper/non-stopper is something the signallers would usually set manually for each level crossing for each train (do correct me if I'm wrong here; I might be overgeneralising). Maybe this was before the signallers got used to the idea of having to do something different for fast/slow trains?
     
  26. tsr

    tsr Established Member

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    The problem with trains is that they can (or could) generally use GPS to work out where they are, with the exception of tunnels. But there isn’t always a reliable way to transmit GPS position data back to either the signalling system or customer information systems on the stations.

    The berth offset is related to the interpretation of the data recorded by the signalling system. The signalling system, which doesn’t use GPS, is more likely to be able to track trains reliably (although there are quite a few other areas of the country where it would not always know the precise position of trains without human input) so that is what is used to work out where they are for the purposes of customer-facing systems.

    What you see in terms of problems with berth offsets is not something which would necessarily have been widely understood before the last decade or so, during which two things have happened: firstly, demand for customer information has been matched by an ever-greater increase in information systems on station premises and online, meaning flaws and data anomalies with data interpretation have become easier to spot; secondly, “open data” about train running has become much more widely available, meaning many more third-party web developers have used it for public-facing information services like Realtime Trains, but in turn the data shown by these things have become open for a lot of scrutiny by interested parties such as enthusiasts.
     
  27. craigybagel

    craigybagel Established Member

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    I believe the system is meant to automatically recognise the headcodes and set the crossings accordingly - presumably there is a manual over ride for diversions how ever. But then everything I hear is pretty anecdotal so I could be taking nonsense - I'm just traincrew on the line that's all!
     
  28. Typewind

    Typewind Member

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    From your reply I feel the industry seems not care about the accuracy of berth offset haha. So what kind of analysis is the real interests, rather than a "scrutiny by interested parties such as enthusiasts"?
     

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