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Signal 110 and 120 overlap

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Signal 110 and 120 overlap 24/10/2020 at 02:34 #133290
Hawk777
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Looking at the diagram with overlaps turned on, it looks as if the overlap for signal 110 should be TVG clear for a delayed yellow, or TVG + TVF clear for full overlap. However, in practice, when TVE is occupied, signal 120 still displays delayed yellow behaviour. Any idea why? This happens in both eras.
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Signal 110 and 120 overlap 24/10/2020 at 03:01 #133291
GeoffM
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The marker is indeed in the wrong place - at least for photos dated 2008 and 2014. It is possible the overlap was as far as VF in the early 2000s and before, since the switch diamonds were replaced with fixed diamonds. The conditions for 120 to show proceed are a bit weird - typically this would be a controlled signal because of the conflicting pointwork after 110 but I guess they had their reasons for doing it this way.

https://photos.signalling.org/picture?/21029/category/2219-2008_may

SimSig Boss
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Signal 110 and 120 overlap 24/10/2020 at 09:18 #133293
kbarber
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GeoffM in post 133291 said:
The marker is indeed in the wrong place - at least for photos dated 2008 and 2014. It is possible the overlap was as far as VF in the early 2000s and before, since the switch diamonds were replaced with fixed diamonds. The conditions for 120 to show proceed are a bit weird - typically this would be a controlled signal because of the conflicting pointwork after 110 but I guess they had their reasons for doing it this way.

https://photos.signalling.org/picture?/21029/category/2219-2008_may
I think it was not unusual to have an auto whose normal aspect was R -> delayed Y (warning aspect as default) at that time. A little earlier, St Pancras had one during the stageworks (it must have been about 1980 when I saw it thus, the original Westinghouse indication panel had been replaced by something based on a standard LMR diagram). I'm fairly certain I've seen something similar in other places as well, though I don't recall specifically where.

Regarding the delayed Y with TVE down, it may be relevant that one of those signals on the northern approach to Bethnal Green (I don't recall which one specifically) was identified, after Ladbroke Grove, as one of the most-spadded signals in the country. I'm not so sure it wasn't, even more worrying, on the list that Railtrack kept under wraps of the most-spadded where the spads went beyond the overlap. Whether that led to additions of all sorts of restrictions in the approach I'm not sure, but given the panic at the time it wouldn't surprise me.

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Signal 110 and 120 overlap 24/10/2020 at 09:42 #133294
geswedey
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Regarding the delayed Y with TVE down, it may be relevant that one of those signals on the northern approach to Bethnal Green (I don't recall which one specifically) was identified, after Ladbroke Grove, as one of the most-spadded signals in the country. I'm not so sure it wasn't, even more worrying, on the list that Railtrack kept under wraps of the most-spadded where the spads went beyond the overlap. Whether that led to additions of all sorts of restrictions in the approach I'm not sure, but given the panic at the time it wouldn't surprise me.

Believe it was the signal on the curve protecting the UP SUB platform L100

Glyn

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Signal 110 and 120 overlap 24/10/2020 at 16:52 #133297
Hawk777
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GeoffM in post 133291 said:
The marker is indeed in the wrong place - at least for photos dated 2008 and 2014. It is possible the overlap was as far as VF in the early 2000s and before, since the switch diamonds were replaced with fixed diamonds. The conditions for 120 to show proceed are a bit weird - typically this would be a controlled signal because of the conflicting pointwork after 110 but I guess they had their reasons for doing it this way.

https://photos.signalling.org/picture?/21029/category/2219-2008_may
Ah, if the display looked like that photo then everything would make sense to me. Does that mean there should be a Mantis ticket to move the overlap marker in the sim?

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Signal 110 and 120 overlap 24/10/2020 at 21:13 #133304
Albert
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The overlap marker displays the track that needs to be clear for approach control, right?

Not very different from the 'double red' protected signals on Carlisle in that case.

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Signal 110 and 120 overlap 24/10/2020 at 21:35 #133309
Hawk777
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Albert in post 133304 said:
The overlap marker displays the track that needs to be clear for approach control, right?

Not very different from the 'double red' protected signals on Carlisle in that case.
Well, there are two overlap markers. The first one is at the end of the first TC in both the photo and the sim, and marks the TC that needs to be clear for approach control. The second marker is at the second TC in the sim but the third TC in the photo, and marks, I assume, the TCs that need to be clear for non-approach-controlled clearance; the sim requires the first three TCs to be clear for that to occur, and the photo shows that second marker at the end of the third TC, but the sim shows the marker at the end of the second TC instead of the third.

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Signal 110 and 120 overlap 26/10/2020 at 08:56 #133343
kbarber
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geswedey in post 133294 said:
Regarding the delayed Y with TVE down, it may be relevant that one of those signals on the northern approach to Bethnal Green (I don't recall which one specifically) was identified, after Ladbroke Grove, as one of the most-spadded signals in the country. I'm not so sure it wasn't, even more worrying, on the list that Railtrack kept under wraps of the most-spadded where the spads went beyond the overlap. Whether that led to additions of all sorts of restrictions in the approach I'm not sure, but given the panic at the time it wouldn't surprise me.

Believe it was the signal on the curve protecting the UP SUB platform L100

Glyn
Thanks Glyn. So if there were lots of panics and additional restrictions on signals to mitigate possible SPADs, making the default warning route on 120 apply also if there were a train between 2099s and 100 might have seemed an appropriate (over-)reaction. Even though it wouldn't directly affect whether drivers actually stopped at 100 (it would enforce the slower approach with a preceding train further ahead than necessary). And as is the way with these things, once something has been applied for reasons classed as 'safety related' no-one dares ease the restrictiveness just in case something goes wrong and their signature is on the latest alteration.

I've no idea if that was what happened, but quite honestly it would never surprise me.

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Signal 110 and 120 overlap 26/10/2020 at 11:00 #133344
trolleybus
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There used to be a warning sign saying something like '100m to L100', and then a SPAD indicator was installed just by the crossovers. Don't know if it's still there.
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