S Stock Update

Discussion in 'London Underground' started by mainframe444, 1 Sep 2016.

  1. bluegoblin7

    bluegoblin7 Member

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    If only it were that simple. Just because a train is fitted it doesn't necessarily mean that the VOBCs (Vehicle Onboard Computers) are functioning - if they're not both available then a train won't be going into the CBTC area. Even since 21551/2 has been stood down trains that cannot run to Hammersmith have been presented at Edgware Road. This will remain a problem pretty much until there is no tripcock railway left.

    Additionally, the S8s have always been the bigger priority for SMA1/2. All S8s must be VOBC equipped before that section can go live; unfitted trains will not be able to proceed south of Wembley Park, which significantly hampers service options. If a train without a VOBC does get to Finchley Road, you're looking at a significant suspension whilst the train is worked forwards in RM until it is able to reverse (not necessarily at Marlborough Road either...). It has always been possible to operate a fully service in SMA0.5-2 with less than all of the S7s converted (I forget the exact amount) - they'd just be kept to District Main services.
     
  2. philthetube

    philthetube Established Member

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    I am sure you are correct but can I ask why not?
     
  3. rebmcr

    rebmcr Established Member

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    I see! Thanks for the extra detail. :)
     
  4. bluegoblin7

    bluegoblin7 Member

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    Simply due to service conditions. It may be that it is decided to work the train forwards, in RM, to Baker Street and stable it in a bay road until close of traffic, rather than suspend the northbound - not only do you have to find (or create) an appropriate gap (and the northbound will also clog up the City, knocking onto the C&H and District!), the nature of the RM move then delays services behind and takes much of the Signaller’s attention whilst it is in progress. In some circumstances the loss of a bay road is the lesser of two evils. Indeed, such steps are often taken even on the conventional railway if there are train defects, and the risk of moving the train in traffic hours causes further disruption.
     
  5. rebmcr

    rebmcr Established Member

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    Would it be permissible for such a unit, operating in RM, to couple to the rear of a CBTC unit and then be towed (out of service) into City Sidings?
     
  6. Dstock7080

    Dstock7080 Established Member

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    In normal operation it is usually the rear VOBC (VOBController) that is active.
     
  7. bluegoblin7

    bluegoblin7 Member

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    Theoretically yes, but in reality it's a non-starter. Push-outs (/pull-outs, but the terminology is always the former) are generally considered an option of last resort. They're slow speed movements and, in this case, would also have to be done in RM (because as suggested by @Dstock7080, the rear VOBC is active, and if that's in the middle of the train you're going to end up with issues regarding both communication and separation [oversimplified, but you get the idea]). The greater distance involved shuts down the City for longer, including now C&H services, and of course you have the reverse to then get it back out. All the additional time of getting an assisting train into position also adds up, of course.
     
  8. philthetube

    philthetube Established Member

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    Makes perfect sense, probably actually a toss up which would be better as a reversing train would be able to resume normal running a Finchley Rd
     
  9. bramling

    bramling Established Member

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    Yes, but the combined train would remain being limited to RM, which defeats the purpose.

    There's no procedure for two trains to run at line speed coupled together. The trains aren't designed for it, and neither is the signalling (although the system does in theory have the ability to do it if specified - DLR can and do run trains of varying lengths).

    So far any actual need to use assisting trains has been extremely rare under TBTC, although this is partly because Jubilee and Northern line trains are sufficiently reliable and well designed that they simply don't require it very often. The last case on the Northern Line was a good 18 months ago, and that's possibly the only time since TBTC came in AFAICR. Ironically doing a pushout is actually quite straightforward under TBTC, although naturally it will screw up the service simply due to the line being blocked. Generally because of staff non-familiarity with the procedure (even though it's trained very few staff will ever do it for real, and when done for real curved balls will always be thrown up such that the procedure likely won't work as the book says) it's an option of absolute last resort - although this is all to do with the trains not the signaling.
     
    Last edited: 4 Jun 2019

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