A few, simple questions about signals

[A-driver]

I've seen several occasions at Sheffield where an late running southbound XC train has left platform 7 at the same time as an on time EMT train from platform 5. The EMT train then stops at the next signal, with the rear of the train in the platform to wait for the XC train clear the signal. I'm pretty certain that this is done so the EMT train has left on time (even if it is then late at Chesterfield) as it has only gained about a train length.

I don't know Sheffield stations layout but in some cases a longer train would take up 2 platforms when they are 'halved'. Therefore moving the longer train forward can free up the platform enough for a short train to use it.

 

[rdeez]

2-I hilly doubt he was passing numerous red signals. At a guess the lines into BNS are bi directional or there are multiple approach lines. In that case I would say its likely you were viewing the signals for the adjacent line. Your line may have had signals on gantries above the train so out of view. Either that or as 455driver said, the signals were returning to danger straight away. Failing that you may have witnessed the train being signalled into an occupied platform so the red light had the cats eyes lit up next to it authorising it to be passed under caution. The train wouldn't need to stop first for that.

I'm not 100% sure, but I recall reading that the signals around New Street have no overlap because there isn't a safe margin for it. That would account for them being red by the time they came into view. Also if my memory is correct, the signal(s) in question aren't mounted on overhead gantries, they're lineside.

The one thing I do know is that the platforms at New Street have mid-platform signals that split them into 'A' and 'B'. Would I be right in thinking the signals on approach wouldn't need the 'cats eyes' in this case?

 

[A-driver]

I'm not 100% sure, but I recall reading that the signals around New Street have no overlap because there isn't a safe margin for it. That would account for them being red by the time they came into view. Also if my memory is correct, the signal(s) in question aren't mounted on overhead gantries, they're lineside.



The one thing I do know is that the platforms at New Street have mid-platform signals that split them into 'A' and 'B'. Would I be right in thinking the signals on approach wouldn't need the 'cats eyes' in this case?

Cats eyes are a different thing to splitting platforms. Cambridge platform 1 and 4 is the same as it's also split into 2. If they want you in the far platform then you get signalled down with a proceed aspect mid platform. If they want you to only go as far as the platform split then there will be a red half way down.

Cats eyes are for permissive working so would only be used if you are going into an occupied platform. So if they wanted you to go to the platform on top of another train you would get a red with 2 white lights. Unless Birmingham is done differently, and as I say I don't know the location, then the cats eyes won't be used to indicate which platform to use.

But the overlap stuff makes sense.

 

[rdeez]

Cats eyes are for permissive working so would only be used if you are going into an occupied platform. So if they wanted you to go to the platform on top of another train you would get a red with 2 white lights. Unless Birmingham is done differently, and as I say I don't know the location, then the cats eyes won't be used to indicate which platform to use.

But the overlap stuff makes sense.

Thanks. Always interesting to hear from someone in the know about these things.

 

[455driver]

ermmm... Very true, except under degraded signalling conditions (formerly known as ticket working) where a driver is stopped at a controlled signal.

So the driver has stopped at the (first) red signal then, just like I said! :roll:

I refer you to the thread title, specifically the "simple" part of it, the OP wasnt asking about every variation but just the basics!

 

[Tomnick]

Now that we've moved on to talk about signals at terminal stations, I remain puzzled by the signalling on the low numbered platforms at Kings Cross.
It's possible for a train to depart on a yellow from platforms 0, 1 or 2 for it then to be held at a red at the next signal (before Belle Isle crossovers) so that the rear of the train is still occupying the platform and also occupying the crossovers between those platforms.

I can't see why signallers would put a train in this position - but they do. No doubt it can also happen at other stations with complex junctions but elsewhere I see trains being held on the platform until their route is set and clear.

It makes sense to me - given that the dispatch process (in most cases) shouldn't nowadays be started until the signal's cleared, it takes rather longer to get a train on the move from a platform once the signal clears than it does a train that's been allowed to drop down to the next signal. Not at KX, but in other cases it might also free up a platform. I doubt it's solely to get a 'right-time' departure - it'll only pick up the delay in the next reporting section instead!

 

[Railsigns]

But the overlap stuff makes sense.

Not to me.

Whether there is or isn't an overlap beyond the signal, it is unrelated to whether the signal aspect has first or last wheel replacement.

 

[edwin_m]

I'm unfamiliar with Kings Cross, but is that not just a headway thing? If the bobby can pinch five or ten minutes an hour by doing that then train planning can timetable one or two more trains an hour in and out of the station. I could be horribly wrong on this of course but it is the first assumption I would make.

I was looking today at St Pancras Thameslink which has a signal half way along the platform. Since I very much doubt that two trains are ever expected to stop at the platform, and there is no evidence of "a" and "b" platform ends etc to facilitate this, I believe this is simply a "closing up" signal for headway purposes. It would allow a following train to enter the platform as the previous one was just clearing the far end (depending on the length of the overlap) and no doubt the driver of the following train would crawl in at minimum speed to maximise the chance that it will clear before having to stop half way down the platform with the tail of the train probably in the tunnel.

 

[MarkyT]

Not to me.
Whether there is or isn't an overlap beyond the signal, it is unrelated to whether the signal aspect has first or last wheel replacement.

Agreed. I don't know specific details but I would expect that at BNS routes to the mid platform signals don't have CLEAR overlaps proved in their aspects, which is allowed by group standards where needed operationally if the route class is 'warning', that forcing an appropriate approach release condition to allow clearance from red to yellow at the entrance. This relaxation applies to track circuit clearance only and an overlap is still required to be route locked beyond the mid-platform exit signal. That prevents two simultaneous arrivals from opposite ends of the station, but once the first has arrived and 'timed out' (thus assumed to be entirely at rest) the second can be allowed to enter the other half of the platform even though the first is still occupying what would otherwise be the overlap track circuit for the second arrival.

 

[A-driver]

I was looking today at St Pancras Thameslink which has a signal half way along the platform. Since I very much doubt that two trains are ever expected to stop at the platform, and there is no evidence of "a" and "b" platform ends etc to facilitate this, I believe this is simply a "closing up" signal for headway purposes. It would allow a following train to enter the platform as the previous one was just clearing the far end (depending on the length of the overlap) and no doubt the driver of the following train would crawl in at minimum speed to maximise the chance that it will clear before having to stop half way down the platform with the tail of the train probably in the tunnel.

The extra signals in the core stations are not to allow 2 trains in the platform at once but as you suggest, just to bunch signals up to improve capacity. I believe an 8 car train occupies both sections when stopped at st pancras on the up.

 

[A-driver]

Agreed. I don't know specific details but I would expect that at BNS routes to the mid platform signals don't have CLEAR overlaps proved in their aspects, which is allowed by group standards where needed operationally if the route class is 'warning', that forcing an appropriate approach release condition to allow clearance from red to yellow at the entrance. This relaxation applies to track circuit clearance only and an overlap is still required to be route locked beyond the mid-platform exit signal. That prevents two simultaneous arrivals from opposite ends of the station, but once the first has arrived and 'timed out' (thus assumed to be entirely at rest) the second can be allowed to enter the other half of the platform even though the first is still occupying what would otherwise be the overlap track circuit for the second arrival.

It was relating to the approach signals, not to the platform signals themselves.

 

[MarkyT]

I was looking today at St Pancras Thameslink which has a signal half way along the platform. Since I very much doubt that two trains are ever expected to stop at the platform, and there is no evidence of "a" and "b" platform ends etc to facilitate this, I believe this is simply a "closing up" signal for headway purposes. It would allow a following train to enter the platform as the previous one was just clearing the far end (depending on the length of the overlap) and no doubt the driver of the following train would crawl in at minimum speed to maximise the chance that it will clear before having to stop half way down the platform with the tail of the train probably in the tunnel.

You are absolutely correct. The additional signals were provided specifically for closing up and the aspect sequences don't need to be complex either because braking distances are fairly short through the core tunnels with low speed and trains all compliant with the superior passenger braking performance curves.

 

[Bald Rick]

The extra signals in the core stations are not to allow 2 trains in the platform at once but as you suggest, just to bunch signals up to improve capacity. I believe an 8 car train occupies both sections when stopped at st pancras on the up.

A four car train occupies both sections, in that it is still within the overlap of the signal in rear. If you look at the rails in the platform you can see the block joints for the overlaps quite clearly. Although the platform staff may well ask you what you're doing.

 

[6Gman]

You can see them at lots of places at signals will either stop at or pass by at a low speed. They are as common in stations as they are out on the running line, often you will see them at big stations with multiple lines running into them and they will display things like S (slow) or U (up) or M (main) or one of numerous other letters which indicate to local names for lines.

The lettering is sometimes ... er ... interesting, and not what you would expect. Am I right in thinking that if you're heading south out of Crewe you are offered - F Fast Line Stafford; S Slow Line Stafford; W Shrewsbury Line - Whitchurch? West?; and I can't recall what indicates the Stoke Line - D for Derby?

 

[MarkyT]

It was relating to the approach signals, not to the platform signals themselves.

OK, I think I WAS trying to describe the behaviour of those 'home' signals controlling entry to the station! The Original Poster was concerned about APPARENTLY passing a red there. He is certainly mistaken but the impression may be due to entering on a permissive route with cats eyes displayed together with the red, or alternatively with a main or warner route into the station approach released from red, from the train he may have missed the yellow or better actually only displayed for a very short time before being replaced back to red immediately by the front of the train passing the signal.

 

[Railsigns]

The lettering is sometimes ... er ... interesting, and not what you would expect. Am I right in thinking that if you're heading south out of Crewe you are offered - F Fast Line Stafford; S Slow Line Stafford; W Shrewsbury Line - Whitchurch? West?; and I can't recall what indicates the Stoke Line - D for Derby?

P for Potteries.

 

[6Gman]

P for Potteries.

Thanks. I did wonder if it might be that.

 

[Cherry_Picker]

You will get D for Derby at the east end of Birmingham New Street though.

 

[broadgage]

To add to the points made by others, it should be noted that signals are usually placed such that if the signal is at danger, that the train may enter the platform but not leave it.

It would be rare for a signal to be placed just before a platform, except of course at a terminus.

That's not true at all!

Are you certain ?
It seems to me that at most stations, other than terminals, that the signals are placed as I describe.
Certainly at Nunhead, New Malden, Surbiton, London Blackfriars (through platforms),and Taunton, the signal is at the far end of the platform in the usual direction of travel. A train may then enter the platform if the signal is at danger, but cant leave until the signal clears.

The stations I list do not seem exceptional or unusual in any way but are a random selection of those that I use regularly.

 

[Tomnick]

Most major stations will have a signal a short distance in rear too, necessary to protect conflicting moves across the station throat. Through stations are no different to termini in that respect - indeed, I think the through platforms at London Bridge have signals very close to the platform ends to shorten the platform reoccupation times.

 

[The Planner]

I think there may have been a bit of confusion with what Broadgage was explaining, I have to admit as first reading it as that a train can pass a red signal that is prior to the station platform, not the end of it which is meant.

 

[plastictaffy]

2-I hilly doubt he was passing numerous red signals. At a guess the lines into BNS are bi directional or there are multiple approach lines. In that case I would say its likely you were viewing the signals for the adjacent line. Your line may have had signals on gantries above the train so out of view. Either that or as 455driver said, the signals were returning to danger straight away. Failing that you may have witnessed the train being signalled into an occupied platform so the red light had the cats eyes lit up next to it authorising it to be passed under caution. The train wouldn't need to stop first for that.

New Street platforms have both "A", and "B", and platform 4 has a "C". On arrival into that station, the driver is using the position lights to determine where he is going on the platform. Next time you're there, if you look on the roof about halfway down the platform, you'll see a signal. If you are approaching NS from the Derby/Stour tunnels, you should get a platform indicator just after Proof House, before the tunnels - which you have to be quick to see as a guard!! Then the driver is relying on a position light to actually call him into the platform. As he crawls down the platform, and the signal on the roof is NOT red, then the signaller wants him on the B end. If it's red, he wants him on the A end - and in an 8 car, the driver may well buzz you up to check he's clear of the starting signal, as there's not a huge amount of room.
Also, as a little aside, trains MUST NOT be despatched from NS on anything but a green. That doesn't stop NS despatchers trying to get you to leave on a yellow, mind.

 

[A-driver]

Are you certain ?

It seems to me that at most stations, other than terminals, that the signals are placed as I describe.

Certainly at Nunhead, New Malden, Surbiton, London Blackfriars (through platforms),and Taunton, the signal is at the far end of the platform in the usual direction of travel. A train may then enter the platform if the signal is at danger, but cant leave until the signal clears.



The stations I list do not seem exceptional or unusual in any way but are a random selection of those that I use regularly.

I am definately certain! You have named 5 stations there which have starter signals. How about st Neots, sandy, shepreth, harringa, arlsey, cuffley, Bayford, crewes hill, welham green, oakleigh park, baldock, new southgate... There is 12 stations which all have a platform with no signal visible from the platform.

As I say, with the exception of junction stations and major stations, any starter signals are generally a coincidence rather than deliberate. Many stations have a signal visible but which is a long way out of the platform so not a starter signal.

 

[455driver]

Signals get put where they need to be taking into account braking distances etc (if the drivers can see them its a bonus , Havant jn cough) and if that happens to be on the end of the platform fair enough, if it happens to be before the platform then that is where it goes.
We have many stations where the 'starter' is further away from the station than the 'home' signal.

Before all the pedantic monkeys wet themselves, the signals are still called these names despite being colour lights and track circuited!

 

[Tomnick]

Unofficially, and a useful way of describing their position relative to a station, perhaps...but certainly not official terms, on TCB lines at least!

 

[455driver]

Not official of course but if the signalman or drivers says <the station> home signal then the other person will know what is being talked about!

 

[edwin_m]

Usually there will be a platform starter signal if there is pointwork within a short distance beyond that end of the platform. Subject to complying with the various rules regarding overlaps, this allows a stopping train to run in to the station on a red while a conflicting move is taking place ahead, which will often have finished allowing the signal to be cleared before the train is ready to leave the station.

At other stations it is mainly down to whether the platform position coincides with the natural spacing of the signals as suggested. It's unusual, but not unheard of, to find a signal immediately on the approach side of a platform, as this would have a capacity disbenefit because a train in the platform will be in the overlap so any following train will have to wait two signals back. Before anyone jumps on me, yes the new Reading layout has signals immediately before the platform but the combination of low speed and high capacity means the signals have to be really close here anyway.

 

[DaveNewcastle]

There is a starter so far beyond the north end of Blair Atholl station and slightly round a curve to the right, that I'm not convinced that a guard on the platform could see round the curve far enough to see the signal. I've never remembered to ask a guard there if it really is a starter, or a section just happens to start near the station. (It may protect the crossover a mile ahead). Anyone here know the area?

But that reminds me, Blair Atholl is at the south end of a section of the HML over the summit at Drumochter which is twin-track for about 20 miles and composed of 'double intermediate block sections'. What is a 'double intermediate block' ? Does it create one long signalling section out of two shorter elements?

 

[Cherry_Picker]

Are you certain ?
It seems to me that at most stations, other than terminals, that the signals are placed as I describe.
Certainly at Nunhead, New Malden, Surbiton, London Blackfriars (through platforms),and Taunton, the signal is at the far end of the platform in the usual direction of travel. A train may then enter the platform if the signal is at danger, but cant leave until the signal clears.

The stations I list do not seem exceptional or unusual in any way but are a random selection of those that I use regularly.

It's certainly not true where I work (London Midland region) and in the time I've been driving trains I have have been held outside stations at a red signal during times of disruption and not allowed to enter the platform, even if the platform has been clear.

 

[edwin_m]

But that reminds me, Blair Atholl is at the south end of a section of the HML over the summit at Drumochter which is twin-track for about 20 miles and composed of 'double intermediate block sections'. What is a 'double intermediate block' ? Does it create one long signalling section out of two shorter elements?

An "intermediate block" signal (usually two signals in fact, a distant and a stop signal) divides a long block section between widely-space signal boxes into two shorter sections.

"Double Blocking" is the practice of spacing the trains more widely so there is only ever one per two block sections instead of potentially one in each section. It used to be applied in poor visibility if fogsignalmen were not on duty, and for the royal train, but I'm not sure if it is used at all these days.

So logically "Double Intermediate Block" should mean half of double blocking which is back to the normal arrangement of one train per block section!

In fact I think it probably means there are two intermediate block stop signals between successive signal boxes. Another example of sloppy use of railway jargon.