Signal Weirdness : Interlocking/route setting ?

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.

 

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.

 

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.

 

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.

 

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

 

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

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

 

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

 

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?

 

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.

 

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?

 

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?

 

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.

 

'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?

 

Possibly. I don't know.

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.

 

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.

 

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?

 

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.

 

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.

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.

 

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.