Signal Weirdness : Interlocking/route setting ?

[ComUtoR]

Signal A (controlled) (J1+2)
4 Aspect

Signal B
3 Aspect Distant

Signal C (auto)
4 Aspect

Signal A with junction indicator 1 takes you to signal B which is a distant. Typically you wait at Signal A until the fast clears signal C. Signal A then steps up to 2Y.

What has suddenly started to happen is that Signal A now clears to 1Y. Suffice to say it's caused a little bit of confusion. The signal was challenged as it appears as an incorrect sequence and Signal A has never shown a single yellow until now. Clearly it's possible as its happening but wouldn't this need specific intervention from the Signaller to set the correct route and to specifically set it as a single yellow ?

My initial assumption is that because this signal causes delays as it takes a train to clear signal C before it can step up, this is being done to improve performance.

For Signallers and people who know about interlocking etc. This is for Victoria box.

Cheers as always.

 

[headshot119]

It's quite possible that due to a fault of some description that temporary approach control has been applied to signal A which will cause it to show a maximum of a single yellow on a particular route.

It's not an incorrect sequence assuming you are getting one of:

Y > YY > Y
Y > Y > R

If you want to PM me the signal numbers I can investigate further.

 

[Nippy]

It could also be the top yellow out... These weren't always lamp proved.....

 

[headshot119]

It could also be the top yellow out... These weren't always lamp proved.....

Good point, though I'd have expected that to have been sorted out if it's been queried as an incorrect sequence.

 

[ComUtoR]

It was queried. Unfortunately I can't post the Signallers reply but it is not a fault.

It's not an incorrect sequence assuming you are getting one of:

Y > YY > Y
Y > Y > R

If you want to PM me the signal numbers I can investigate further.

'Incorrect' as its a single yellow onto a distant being that you shouldn't get a single yellow as the next one can't show a red. However, I do see that it isn't incorrect as your always checked down to the red safely. Nobody has ever seen this sequence before. The sequence we are getting (Drivers perspective) is Y Y G . Odly, now I think about it further, I don't ever remember seeing 2Y on the distant either. I always thought it was a 2 Aspect but the map shows it as a 3 :/

 

[Nippy]

I quite enjoy investigating unusual signal faults if drivers report them. I like to try and work out what's happened whilst the tech downstairs looks at his equipment.

 

[ComUtoR]

It could also be the top yellow out... These weren't always lamp proved.....

The signal has been challenged and there is another junction indicator that will show 2Y. Unless the interlock/proving is broken in one direction only ?

 

[edwin_m]

Two consecutive single yellows is a valid sequence. There's one south of Leicester where two three-aspect signals are closer than braking distance but they didn't want to introduce a four-aspect (it was discussed somewhere on here a few weeks back as being an operational headache). Are any speeds being increased in the area, that might have made the braking distance insufficient with the original aspect sequence?

The signaler doesn't get to choose the aspect displayed. They just set the route and the interlocking, or separate relays at the trackside, work out what the aspect should be according to the circumstances of that route (eg approach control) and the aspect of the next signal.

 

[ComUtoR]

Two consecutive single yellows is a valid sequence.

I get the validity of getting Y Y but this specific set of signals is a single yellow onto a distant. Surely under normal circumstances it wouldn't do that when it steps up. This isn't somewhere that Y Y is deliberate. The unit in front clears the auto signal (C) and then the sequence should (and does normally read) R Y YY. For the sequence to step up to Y Y R doesn't seem right. It's never happened before :/

Are any speeds being increased in the area, that might have made the braking distance insufficient with the original aspect sequence?

Nothing has changed. 60mph through both junction indications and your only ever held when they send one in front.

The signaler doesn't get to choose the aspect displayed. They just set the route and the interlocking, or separate relays at the trackside, work out what the aspect should be according to the circumstances of that route (eg approach control) and the aspect of the next signal.

Which is why I and others are a little bemused why it has started to step up to the single yellow. The Signaller pulls the road and the aspect of the next signal is, at worse, a single yellow. The junction signal should therefore show YY.

For it to suddenly show a single yellow means something has changed. It's only been doing it the last couple of days. No engineering works that I'm aware of either.

With approach control. The route is normally set and your checked down before the signal clears. This scenario is where a train is being held on a red and then when the unit in front clears the junction it then steps up. For additional clarity, you are following the unit through the junction. They come across you from Up Slow (you're on the Up Fast) and you trundle behind them when it clears. Is there a method of approach control where the route isn't set and your controlled away from a stand ?

Is there any circumstance where you would be given a Y Y(distant) sequence from a standing start ? Could the signal be specifically restricted to a single yellow under normal circumstances; not due to a fault ?

Our current thinking is that instead of waiting for the two yellows it is being stepped up to a single yellow to get us out the platform earlier. Is it possible to allow the signal(s) to step up to Y Y R if the one in front hasn't cleared the overlap ? (I know that sounds crazy) The likelyhood of that is slim to none so Y Y R especially when the one in front is a fast service seems quite restrictive.

Cheers for the reply(s) folks

 

[Llama]

We have a flashing yellow sequence in one place where the signal after the diverging junction (which the flashing yellow sequence effectively brings you down to) is a distant.

The relevant RGS documents are always worth a read, try RIS-0703-CCS

 

[alxndr]

I'm a bit puzzled by what signals are where and what each signal is doing from your description I'm afraid.

I get the validity of getting Y Y but this specific set of signals is a single yellow onto a distant. Surely under normal circumstances it wouldn't do that when it steps up. This isn't somewhere that Y Y is deliberate. The unit in front clears the auto signal (C) and then the sequence should (and does normally read) R Y YY. For the sequence to step up to Y Y R doesn't seem right. It's never happened before :/

This part in particular is confusing. How are you reading R Y YY when you can't pass the red?

 

[pompeyfan]

I understand what question you’re asking but am neither S&T or a bobby. If you’re suggesting you’re getting a single yellow to allow you into the same block that’s already occupied I would 100% hope not, because you’d have no warning if the train in front failed to clear the section. If it’s been challenged and there’s no fault with signal A showing 2Y then I’m stumped but then again that’s not my field.

So to confirm hypothetically,

signal A - TT1
Signal B - TT3R
Signal C - TT3

 

[ComUtoR]

This part in particular is confusing. How are you reading R Y YY when you can't pass the red?

Apologies. "R Y YY" is me calling the sequence backwards. As in when the train in front goes past the Auto signal (C) which reverts it to danger and you get the correct sequence towards it. The signal in question (A) then correctly shows YY. Sorry for the 'backwards thinking' hope that clears it.

So to confirm hypothetically,

signal A - TT1
Signal B - TT3R
Signal C - TT3

Yep. So when TT3 shows Red. TT3R shows a single yellow. TT1 then steps up from Red (as that's where we have been held) to .....

It has always stepped up to two yellows. Just this week it has started to step up to a single yellow for no rhyme or reason.

No changes to anything
60mph in all directions
No approach control used in normal running
Same box for both signals (there is a panel change)
We've been told there is no fault

The relevant RGS documents are always worth a read, try RIS-0703-CCS

All the 'normal stuff™' I'm happy with. Flashy junctions, fixed distants, checking down, keyed signals, reduced overlaps etc etc and the Y Y sequence per se doesn't matter. I've been reading the RGS but couldn't find anything that stood out. Cheers for the doc ref.

The single yellow will reduce performance because Drivers will only pull away in low power due to the more restrictive aspect. Because we drive this multiple times in a day it increases risk factors. Drivers will start to compensate for the sequence and because they know the next one is a distant they will start to ignore it and because the sequence results in the next one being clear pretty much all the time, again they will start to push it a bit further.

 

[pompeyfan]

Single yellow -

• Single yellow – Caution. The driver must be prepared to stop the train at the next signal.

How can a driver be expected to stop the train at the next signal which isn’t physically capable of showing a stop signal?

 

[Belperpete]

When the aspect was challenged, was any reason given as to why it was considered correct to have a Y reading up to a signal that can never show red?

Speaking as an ex-signal engineer, a yellow aspect reading up to a distant doesn't seem right. If someone has discovered that there is inadequate braking from the YY on the junction signal to the red on next-but-one signal ahead, then the sequence may have been amended to that you describe, so you get the YY on the signal in rear of the junction signal. Repeated aspects are non-preferred these days, so nowadays in cases of under-braking the usual solution would be to approach-control the signal in rear of the red, but in this case that wouldn't be possible as it is a distant.

If this is a relay interlocking area, then a circuit fault could prevent a signal from showing YY - such a fault would also prevent the signal from showing Green. In the case of a junction signal, depending on the location of the fault, it might prevent the signal from showing YY/G for just the one route, or for all routes.

As has already been mentioned, the failure of the top-yellow aspect would mean the signal would show Y instead of YY. This would obviously apply for all routes from that signal. The signaller would not be aware of such a fault, as the top-yellows are not lamp-proved. If the signal is LED, then the technician will also probably be unaware of the fault. If it is an old filament-lamp signal, then the technician should have got an alarm when the first of the two filaments in the top-yellow bulb went. However, in a relay-interlocking area a lot of signals are usually grouped into just one alarm, so it may not be easy for the tech to know which signal let alone which bulb has started to fail - particularly if more than one signal has a first-filament blown.

 

[theking]

Why can't you tell us the signallers response?

Also signal A can't be cleared until the fast is clear of the overlap of C so I can't see how a at single or double makes a difference?

 

[Tomnick]

We've had a similar discussion at our place recently. There's one place - far from unique, I'm sure - where you get a flashing yellow sequence with the next signal after the junction being a distant signal. You still get a single yellow in the junction signal as you approach - as you'd expect - which steps up to a green just before you get to the magnet. A colleague reports finding that it didn't step up to a green on one occasion. We could only conclude that it was a (right side!) fault in the interlocking somewhere which stopped it stepping up and thus giving a similar sequence.

I can say with absolute certainty that it isn't a measure to allow the junction signal to clear before the line's clear to the overlap of the next stop signal!

Does it involve 178, 172R and 172 by any chance?

 

[ComUtoR]

When the aspect was challenged, was any reason given as to why it was considered correct to have a Y reading up to a signal that can never show red?

No, and we have been told there is no fault. Just that this sequence is correct.

Speaking as an ex-signal engineer, a yellow aspect reading up to a distant doesn't seem right.

Which is what we are all thinking.

If someone has discovered that there is inadequate braking from the YY on the junction signal to the red on next-but-one signal ahead, then the sequence may have been amended to that you describe...

We have had a lot of resignalling and a lot more to come. If there was a new standard or that someone has discovered that the signals are non compliant then I would happily accept that. Personally I would say there is plenty of braking distance but technically I wouldn't know.

As has already been mentioned, the failure of the top-yellow aspect would mean the signal would show Y instead of YY. This would obviously apply for all routes from that signal. The signaller would not be aware of such a fault, as the top-yellows are not lamp-proved. If the signal is LED, then the technician will also probably be unaware of the fault. If it is an old filament-lamp signal, then the technician should have got an alarm when the first of the two filaments in the top-yellow bulb went. However, in a relay-interlocking area a lot of signals are usually grouped into just one alarm, so it may not be easy for the tech to know which signal let alone which bulb has started to fail - particularly if more than one signal has a first-filament blown.

I can see that. Drivers will tend to compensate for any irregularities as long as they are checked down to any red and once its been know that someone had reported it, we tend to again accept what we are told.

Why can't you tell us the signallers response?

Firstly because it isn't relevant and secondly as a professional courtesy; especially as this is a public forum. Suffice to say the Driver was told it wasn't a fault.

Also signal A can't be cleared until the fast is clear of the overlap of C so I can't see how a at single or double makes a difference?

On a single, you would pull away expecting a red on the next signal. The next signal can't show a red. Also, there is no need for it. There is no apparent reason why it shows a single yellow. As its a 4 aspect signal and the entire area is 4 aspect you would always expect G YY Y R as your sequence. In general terms anything else would be incorrect and you would report it as an incorrect sequence because there may be a fault (as described by the top bulb posts) braking distance would also be a factor because you could potentially be checked down suddenly with a single yellow. We had one the other day where a Driver got G Y R in a 4 aspect area. This resulted in the Driver passing the signal. Hope that helps.

A colleague reports finding that it didn't step up to a green on one occasion. We could only conclude that it was a (right side!) fault in the interlocking somewhere which stopped it stepping up and thus giving a similar sequence.

Similar our side. As TBROC consumes more of the London End of the network we have had some weird sequences. Places where you previously got checked now give an approach on greens or junctions we rarely go across and you suddenly see an indicator when your at linespeed resulting in a change of trousers at the next station.

Does it involve 178, 172R and 172 by any chance?

Ding ding ding !! Yes it does. Vic 10a

 

[GreenSignal]

The Signaller gave you a response as to the reasoning behind it, yet you won't share it out of professional courtesy?
However, all the people contributing their reasoning to the post would be better informed if they knew what the signallers response was.

 

[Esker-pades]

The Signaller gave you a response as to the reasoning behind it, yet you won't share it out of professional courtesy?
However, all the people contributing their reasoning to the post would be better informed if they knew what the signallers response was.

As was explained, this is a public forum. Whether the information would be helpful or not is not relevant. It is internal industry information that the OP does not feel comfortable (or simply cannot) unilaterally putting out in public.

 

[GreenSignal]

'Internal Industy Information' much like the information the OP was requesting from their initial post?
Unfortunately it seems somewhat disingenuous to post a thread relating to a specific area, which has been identified by another member and confirmed by the OP, to then state that the OFFICIAL REASONING behind it, can't be shared.
Are we just expected to speculate and hope that an explanation given matches the signallers response, or is the OP looking for information to prove the Signaller wrong?

 

[Esker-pades]

'Internal Industy Information' much like the information the OP was requesting from their initial post?

Possibly. I don't know.

Unfortunately it seems somewhat disingenuous to post a thread relating to a specific area, which has been identified by another member and confirmed by the OP, to then state that the OFFICIAL REASONING behind it, can't be shared.
Are we just expected to speculate and hope that an explanation given matches the signallers response, or is the OP looking for information to prove the Signaller wrong?

We don't know what the person's information is.
To me, it seems like a reasonable question. People can choose to respond or not. They could even do so in private.

I don't understand your objections.

 

[Belperpete]

We've had a similar discussion at our place recently. There's one place - far from unique, I'm sure - where you get a flashing yellow sequence with the next signal after the junction being a distant signal. You still get a single yellow in the junction signal as you approach - as you'd expect - which steps up to a green just before you get to the magnet. A colleague reports finding that it didn't step up to a green on one occasion. We could only conclude that it was a (right side!) fault in the interlocking somewhere which stopped it stepping up and thus giving a similar sequence.

Clearing up just before you get to the magnet doesn't seem right. The old principle for flashing yellow junction sequences required that the junction signal should be held at yellow until the train has passed the AWS magnet (so the train gets an AWS horn for the diverging route). This requirement was removed awhile back as being too restrictive (if you have seen the flashing yellows then you know you are taking the diverging route), but there are a lot of places that still work that way.

 

[Tomnick]

Clearing up just before you get to the magnet doesn't seem right. The old principle for flashing yellow junction sequences required that the junction signal should be held at yellow until the train has passed the AWS magnet (so the train gets an AWS horn for the diverging route). This requirement was removed awhile back as being too restrictive (if you have seen the flashing yellows then you know you are taking the diverging route), but there are a lot of places that still work that way.

That's definitely what happens though, in every case on my routes if I've not forgotten any. My understanding, possibly wide of the mark, is that the requirement is for the junction indicator to be clearly visible to the driver before the signal steps up. There are certainly a couple of examples where the junction indicator is initially obscured.

 

[sw1ller]

Same thing happens to us here in the northwest. You leave Runcorn under double flashing yellows, next signal single flashing, next is a yellow with route 4 for the Halton curve...... as you get closer it goes green.
I don’t understand this as the next signal is FJ12 which is a 1 aspect distant signal. What’s with the yellow at WE3820?

 

[sw1ller]

Is there any circumstance where you would be given a Y Y(distant) sequence from a standing start ? Could the signal be specifically restricted to a single yellow under normal circumstances; not due to a fault

kind of.

in my example the second yellow is also a stop signal, but I think it counts.

leaving P6 at Crewe heading to Chester having stopped behind the mid platform signal, you will see a single yellow at the mid platform and a single yellow at the end with a C in the theatre box. always found that strange.

 

[ComUtoR]

We have a platform starter that gives us the most freaky approach control. It has been alleged that it is 'Guaranteed' to come off. There is a unique situation where its Y R purely because of a risk of reading through so its held right to the last second.

We also have a couple that we aren't 'supposed' to ever see at red because of how the signalling has been designed.

I can count the number of distants I drive past on one hand. Getting a single yellow on to it has totally thrown my brain out of whack

 

[Tomnick]

We have a platform starter that gives us the most freaky approach control. It has been alleged that it is 'Guaranteed' to come off. There is a unique situation where its Y R purely because of a risk of reading through so its held right to the last second.

Guaranteed? I can only think that it's one where the signal in rear won't clear until there's a route set from that signal, but then it's subject to approach release itself.

We also have a couple that we aren't 'supposed' to ever see at red because of how the signalling has been designed.

I can think of a couple (on a reversibly-signalled line) where at least one stop signal in the wrong direction is plated as a distant for a similar reasons. You'd presumably still come up to a red during some forms of degraded working though.

 

[ComUtoR]

Guaranteed? I can only think that it's one where the signal in rear won't clear until there's a route set from that signal, but then it's subject to approach release itself.

Hence the quotes. We both know how dangerous it is to say silly things However, the setup is just because there is a risk someone will read through and there is a huge risk of a collision. (VS5 at Vic) You only get signalled onto it if there is a unit in platform 2.

You'd presumably still come up to a red during some forms of degraded working though.

I'd always expect the unexpected when things go bad.

In degraded working you still don't really get the midpoint ones at Red (in the core) as they are there to step up as the one in front is departing. Stopping at one would be as rare as unicorn poo.

The other ones I'm thinking of is setup in such a way that there should be a train in the overlap so you have the additional red protecting the back of you and you need to clear that before anything steps up. So you 'shouldn't' really get one of those at red either.

 

[TheEdge]

I can count the number of distants I drive past on one hand. Getting a single yellow on to it has totally thrown my brain out of whack

And I need several hands and feed of a small orchestra to count the amount of distants I drive past and this doesn't quite seem right to me either. I cannot understand how getting a single yellow before a distant is a correct sequence.

Even back to very basics in AB semaphore your last stop signal is always a green, it has to be, as your next signal is the distant of the next box, which can never show red. I drive several routes with basic 2 and 3 aspect signalling and again, you never see anything but a green leading onto the next distant, in fact most of those section signals (not sure if that the technical correct term in their case) are 2 aspect red green for this exact reason.