Flashing Double Yellow Aspect

Discussion in 'Infrastructure & Stations' started by Mordac, 19 Jun 2019.

  1. Mordac

    Mordac Established Member

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    I was walking along the Worcester and Birmingham Canal towpath, which runs alongside the cross city line, and saw something I didn't know existed before: a signal on the line was displaying a flashing double yellow aspect. What does this mean?
     
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  3. Leo1961

    Leo1961 Member

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  4. Darandio

    Darandio Established Member

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  5. dk1

    dk1 Established Member

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    Very common across the network.
     
  6. sprinterguy

    sprinterguy Established Member

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    Common as they may be across the network, this has piqued my interest as I'm quite familiar with the section of the Cross City line alongside the Birmingham and Worcester canal and I've never noticed a flashing double yellow on that stretch before: There's nothing shown on the most recent route map I have to hand, and usually flashing yellows are in advance of a fast diverging junction, which doesn't seem relevant to the section of route between Bournville and New Street?
     
  7. hexagon789

    hexagon789 Established Member

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    Junction set for train to diverge to a line with a lower permissible speed than the mainline. It allows a higher diverging speed than approach release from Red where a train is checked practically to a stand.

    I believe there were introduced about the same time as the HSTs as a result of their superior braking.
     
  8. ForTheLoveOf

    ForTheLoveOf Established Member

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    Exactly my thoughts - the area hasn't been resignalled recently (though signal heads have gradually been made LED over the years). It was all regular 4-aspect colours when I used to frequent the line.
     
  9. sprinterguy

    sprinterguy Established Member

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    Yeah that was my understanding as well, and a quick glance at the route map appears to confirm this. Quite curious as to where a flashing double yellow might have popped up: The only divergence in that neck of the woods is onto the Lifford curve, which as far as I am aware is controlled by the standard feather, as it's only 10mph round the curve.
     
  10. GB

    GB Established Member

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    Flashing yellows are no longer reserved just for high speed junctions. As hexagon789 says, they allow a higher speed approach than what would have been possible under standard approach release. I know of a couple of areas where the diverging speed is 30 or 40 but has flashing yellows. I don't know the area in the OP but there must be a junction somewhere there that the flashing yellows relate.
     
  11. Mag_seven

    Mag_seven Established Member

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    Isn't there a flashing yellow on the approach to Kings Norton from the University direction?
     
  12. edwin_m

    edwin_m Veteran Member

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    Yes, there was a risk of an HST overspeeding a junction if they just obeyed the normal aspects with the system of approach control in use at the time (some "main aspect yellow" routes I think). But it's since become much more widespread, effectively giving the driver a warning of a divergence and allowing them to optimise their speed for the actual conditions rather than to brake towards a red at a particular place.

    Where more exactly is the signal in question? The only diverging junctions I can think of on that section are towards the Lifford curve and the crossovers at Kings Norton. The former is rarely used so I'd expect the signal to be for the more frequent divergence at Kings Norton, as a signal that can display more than one flashing aspect isn't allowed. The sequence would be flashing YY, flashing Y, then steady Y with indicator at the junction signal releasing to less restrictive aspect if line clear ahead, so this signal would be some way from the junction.
     
  13. ForTheLoveOf

    ForTheLoveOf Established Member

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    Yeah, it's a tight radius that one. I don't think there are flashing aspects for diverging at Lifford South Junction either (plus this is well after the section of parallel running the OP talks about) so I'm a bit mystified.

    If cleared for the fast lines it's a straight-ahead run with the speed staying the same 45mph until more or less the start of the King's Norton disused platforms where it's 90mph. It's 30mph onto the (electrified) slow lines, but the Simsig simulation of the area has it as an ordinary approach-controlled turnout. Of course, that may be out of date.
     
  14. Darandio

    Darandio Established Member

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    The 2015 documentation I have here doesn't show any flashing aspects on that section. It's not unknown for official documentation to be wrong or incomplete though.
     
  15. sprinterguy

    sprinterguy Established Member

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    If that proves to be the case then signal SY48 would be the one with a flashing double yellow aspect: That's to the north of Bournville station, which is adjacent to the canal so that would make sense.
     
  16. hexagon789

    hexagon789 Established Member

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    Thanks, I couldn't recall the precise details but knew it was something to do with their better braking.
     
  17. LNW-GW Joint

    LNW-GW Joint Veteran Member

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    Hasn't the Midland line signalling around Birmingham been upgraded recently with the move of control from Saltley PSB to WMSC?
    It included extension down the line for the electrification extension to Bromsgrove, and on to the River Avon bridge approaching Tewskesbury.
    The New St end (western approach) has also been upgraded.
    There are of course flashing single yellows as well.
     
  18. edwin_m

    edwin_m Veteran Member

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    With 6 cross-city trains per hour crossing onto the Slow lines and many of them having faster trains close behind, it would be an excellent candidate for a flashing aspect.
     
  19. Mordac

    Mordac Established Member

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    It was the signal in the attached pic, although that was taken after a train had passed and the signal had reverted to red.

    EDIT: Just saw this post after having posted the picture

    That was indeed the signal in question!
     

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  20. ForTheLoveOf

    ForTheLoveOf Established Member

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    Interesting - so the upgrade allude to by @edwin_m appears to have already been done. Does anyone know when this was done?

    I agree, and I'm slightly perplexed why this wasn't done when the area was electrified and the 6tph service introduced. The service pattern now is remarkably similar to that back then.
     
  21. sprinterguy

    sprinterguy Established Member

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    Ah, excellent, thanks for confirming. A minor mystery solved. :smile:
     
  22. edwin_m

    edwin_m Veteran Member

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    Electrification was back in the 90s when flashing yellows weren't used so liberally (and wasn't it 4TPH at that time?).
     
  23. The Planner

    The Planner Established Member

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    It would have been done as part of the Cross City re-control from Saltley into the WMSCC a couple of years back. You wouldn't mess with it on its own if you knew that was happening as its not cost effective.
     
  24. The Planner

    The Planner Established Member

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    I think you can if the flashing aspect is different on the signal, ie a double flasher for one route and a single for another. I think that is done at Hitchin.
     
  25. JN114

    JN114 Established Member

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    No, Hitchin uses a steady YY as the outer signal. (Presuming we’re referring to the consecutive flashing routes on the DF?)

    There has been a very recent rules change that now allows that configuration, but it was after the Hitchin remodelling - it was previously banned as top yellow aspect of double yellow signals wasn’t proved lit.
     
  26. sw1ller

    sw1ller Established Member

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    I know local route knowledge makes up for 99% of all anomalies. But that’s a bit much right?? That would allow for a serious miss read of the signal. I know it’s been refuted by @JN114 but still. Does this happen anywhere? I’d be very surprised if it was.
     
  27. 142094

    142094 Established Member

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    There is an interesting set up on Network Rail between Sunderland and Pelaw Junction which is shared by Tyne and Wear Metro trains. On the Down Sunderland after Fellgate, the PSR for Metro units is 80kmh and the junction back onto Metro infrastructure is also 80kmh - but the flashers are provided I assume so that any other stock (i.e. non-Metro) has advance warning that a wrong route has been set.
     
  28. lammergeier

    lammergeier Member

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    Just to confirm what has been suggested, the flashing yellows are indeed for the slow lines into Kings Norton and not for Lifford curve, which just has a standard checking down sequence. Never used to be the case but it was introduced during the resignalling works about 18 months ago
    Are we talking about consecutive flashing yellows? If so it happens at Bromsgrove now on the Down, again a result of recent resignalling (and to be fair, remodelling.) it's the only location that I know of where it happens, though if course there may be others.
     
  29. JN114

    JN114 Established Member

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    They wouldn’t have opened up the regulations for no reason - I can’t put my finger on where but I’m sure I’ve seen it in some very recent scheme; I just forget which!

    As for mis-read issues, I don’t think it’s a huge issue. Fancy junction signalling arrangements are given a lot of attention and emphasis in route learning materials and assessments. Also I don’t think you’re allowed to FYY - FYY within the same line of route, just that you have 2 consecutive signals that *can* display FYY.
     

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