Signal Weirdness : Interlocking/route setting ?

Discussion in 'Infrastructure & Stations' started by ComUtoR, 4 Dec 2019.

  1. Sunset route

    Sunset route Member

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    We have in our area replaced a section of SIMBIDs with more conventional fully signalled Bi-Di which comes complete with three aspect (plated) distant signals at certain locations for the Bi-Di working. But under normal directional running the plated distant signals will display a red aspect, (they are listed as “non approachable at red distant signals”. But under certain failure conditions (wrong direction running before you’ve had a chance to implement Bi-Di running as the whole section needs to be clear of trains first) you can in fact have trains approaching them while at red, so we have to be careful not to end up with two trains in a signal section.
     
  2. Tomnick

    Tomnick Established Member

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    That's exactly the one I was thinking of, ta!
     
  3. Tomnick

    Tomnick Established Member

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    Ah, mid platform signals. We have some where you have to be really careful. You get signalled into the platform and, unless the signal at the far end is already off, the mid-platform signal will clear once you’re occupying the track circuit in the first half of the platform. Sometimes, though, it doesn’t, and then you’re left halfway into the busiest part of the platform with the back still hanging off the platform. It’s an awfully constrained layout with various conflicting moves though.

    Generally, though, I thought that the principle was that you’d not be signalled towards a closing-up signal until the train already in the platform was shown to be on the move (perhaps occupying the first track circuit beyond the starter signal). You should get the closing-up signal off by the time you get to it, but it isn’t *guaranteed* because the line has to be clear to the overlap of the platform starter as normal, and there’s the possibility that the departing train might’ve stopped for some reason with its posterior still partly in the platform?
     
  4. philthetube

    philthetube Established Member

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    If you have been told that officially then the union should be seeking an exemption for any spads, if not they you should drive accordingly
     
  5. ComUtoR

    ComUtoR Established Member

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    The core has pretty modern signalling and I assume pretty funky interlocking. If the one in front clears the mid point overlap then it clears the one in the rear and your good to pull away. The core is pretty good in that I don't think its possible to approach the mid point at red because the overlaps are so tight. The one in front pulls out and clears pretty much before you hit the platform so the mid point tends to step up and the red is the platform starter.

    We always have to be prepared for ANY signal not to step up. :)

    For VS5 I think we need a Vic Signaller. It's kind of unique.

    Before we digress too far and whilst I do enjoy the digressions.. How easy would it be to change the interlocking or give a specific aspect ? When some signals have faults we get a notice in the WON To say that signal X has been restricted to show a double yellow (the most typical) because the next one can only show a single.
     
  6. Tomnick

    Tomnick Established Member

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    I'm just doing a bit of digging on this one...

    I've done some digging here too. Simsig is a wonderful resource sometimes ;) . The risk seems to be a read-through from platform 2. VS5 will only clear if platform 2 is empty, or if there's a route set from platform 2, or if there's a route set from platform 3-5 towards VS5 *and* the train is close to the signal. I've tested it in Simsig (which is written with accurate data, usually straight from the real control tables, but obviously isn't absolutely 100% guaranteed!), and it appears that the signals reading towards VS5 from platforms 3-5 won't show a proceed aspect until all other conditions are met for VS5 to clear, but if platform 2 is occupied then VS5 is approach released, and thus it is pretty much guaranteed to come off because the conditions must have already been met for you to be able to proceed towards it. Or something like that.

    It's easier on modern electronic-based interlockings, if I understand correctly. The technician has his own terminal with which he can apply these restrictions. On relay interlockings, it's presumably still possible but a little more involved and possibly involves testing because of the risk of making a mistake and creating a wrong-side failure somewhere else. Perhaps one of our resident S&T bods could elaborate or correct me as necessary!
     
  7. Belperpete

    Belperpete Member

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    With SSI and its more modern derivatives, the technician can apply a control to hold a signal at red, or apply temporary approach control. Applying this control affects all routes from that signal. Anything else requires a full-blown interlocking data change. However, you can restrict a signal to yellow by applying temporary approach control to the signal ahead.

    With a relay interlocking, you should be able to hold a signal at yellow or double-yellow by disconnecting the relevant wire. Disconnecting a wire should not cause a wrong-side failure. However, any wiring change should be properly controlled and recorded. You will want the wire reconnected properly at some time in the future (and getting that wrong could cause a wrong-side failure), and you don't want anyone thinking the wire has been accidentally or wrongly disconnected and putting it back before time.

    Note that if for some reason (such as a fault) a signal cannot clear above yellow, then the signal in rear will automatically be restricted to double-yellow in a 4aspect area, by the standard aspect sequencing controls built-into the interlocking. The tech doesn't need to do anything to achieve this.
     
  8. ComUtoR

    ComUtoR Established Member

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    The technique for driving it is.. At the point in which you panic and want to hit the brake, it steps up. If it doesn't, hit the brakes.

    I didn't know simsig was so accurate. I just had a very brief look and discovered I'd never make a Signaller :lol: If you have VS Simulation, the offending Signal was the one you guessed at (VS178) 10a towards the Up Chatham Main.

    I got sucked into the SimSig forum... wow, mind blown !!
     
  9. Controller1701

    Controller1701 Member

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    I recall from my route learning days that the main 'issue' with VS 5 is if there is a train fairly close to VS 3 could see VS 5 clear and not realize that VS 3 was still at danger owing to being virtually below it.

    Paul
     
  10. ComUtoR

    ComUtoR Established Member

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    Exactly, A read through issue and you only get the approach control if there is a unit in the platform.
     
  11. gingertom

    gingertom Member

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    as a mere mortal it strikes me that there's an awful lot of thought gone into these arrangements to minimise risk. We should be thankful to all those concerned.
     
  12. Class 170101

    Class 170101 Established Member

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    If its a planned change it should be in the WON surely. An unplanned problem that may be around for some time should it not be a late notice case job for drivers to receive and read?
     

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