Signalling question

[CosherB]

I was at Alderley Edge station this morning (Manchester - Crewe line, with modern 4-aspect bi-directional signalling). There is a signal array at either end of both platforms.

Not surprisingly, the 'reverse direction' signals (down end of the up platform and up end of the down platform) were at 'red'. The signal at the up end of the up platform was showing single yellow when I arrived, and soon cycled through double yellow to green (so an up train must have passed through before I arrived).

However, the signal at the down end of the down platform was at red, as was the next signal down the line in that direction towards Wilmslow - with no train in sight that might have recently passed.

A 323 unit was waiting in the down siding on the Chelford (up) side of the station.

A train passed in the up direction, and the signal at the up end of the up platform changed to 'red' behind it, as expected, and then cycled through yellow, double yellow, and finally green as the train sped on out of sight towards Crewe.

Question: Since no down train had passed while I was there, why were two the down signals I could see (the one at the down platform end, and the one half a mile further on) all 'red'? If the one half a mile away was held at Red because of a down train out of sight (maybe stopped in Wilmslow station) why wasn't the platform end signal at single yellow?

Suddenly, both of those down signals went to green, and a few minutes later a Pendelino sped through. Of course, behind it the signals turned red again, and the 323 came out of the siding into the down platform where it stopped to pick up, and the platform end signal cycled through the sequences to green in the usual manner. When the 323 departed, once again the down signals went red, then cycled through to green as one would expect.

So why, as I ask above, were those two down signals, prior to the Pendo's passage, held at red? There is a crossover (down to up) between those two red signals so that up trains from Wilmslow can enter Alderley's down platform, but that took no part in the train movements described and would have been set to 'straight on'.

 

[Donny Dave]

Sounds as though those signals are semi-automatic, but are manually controlled or ARS is being used to regulate traffic through the station.

 

[O L Leigh]

There could be any number of reasons why those two signals were held at red. However, I suspect the simple answer is that they are both "controlled" signals rather than "automatics". The fact that there are shunt moves and crossovers in the vicinity of the station that makes me believe this.

It is often the case at locations where there are lots of controlled signals that consecutive signals are held at red even though the line in between is clear. I can't really say much more than that as it would just be speculation because I don't know the area or the normal sequence of signal aspects along that route.

O L Leigh

 

[driver9000]

The signal could be an approach controlled signal, the signal could be showing 1 yellow until the approaching train gets within a certain distance of it before clearing to a less restrictive aspect. This is purposly designed to slow trains down especially if approaching a converging junction with a reduction in speed (see also Euxton Balshaw Lane in the Up direction on the slow line). Im not familiar with the Alderley Edge area though so couldnt say for sure.

The signalling at Balshaw Lane on the Up Slow will have the signal just off the end of the platform showing one yellow until the train gets to approx. 300yds in rear of it then it will change to green (usually) despite the one on the Up Main WCML being at green already. The linespeed on the Up Slow is 75mph with the junction being 50mph converging onto the WCML.

 

[Tomnick]

I think the best way to approach this one is to explain the three different 'types' of signal found in MAS areas, and then have a dig around - without particularly knowing the signalling, only a very vague appreciation of the track layout, at Alderley Edge - to try and answer the original question. O L Leigh seems to be closest to hitting the nail on the head though!

So then, automatic signals (identified by the two horizontal white lines above the signal ID plate) are just that - they cycle through the normal sequence based on the occupancy of the track circuit(s) as far as the overlap of the signal in advance to allow them to clear to 1Y, and then based on the aspect of that next signal (be it automatic or controlled) to clear to 2Y and G. The signalman's generally got no control over them (and would have no reason to, as they'd only ever be found with plain line beyond them), but can sometimes replace them to danger by means of an emergency replacement switch.

Semi-automatic signals work in a similar manner, but can also be replaced to danger to protect a ground frame, level crossing or similar. Again, the signalman generally plays no part in this. The ID plate is similar to that of an auto signal, but also bearing the word 'SEMI' on the top white stripe. In both cases, the driver can pass the signal at danger under his own authority if he can't contact the signalman.

Finally then, controlled signals - found protecting areas of pointwork, level crossings controlled by the signalman, and a whole load of other things...in very simple terms, anywhere that a signalman might need to stop a train to protect a conflicting move or other obstruction. Contrary to popular belief (and also to LUL practice, I believe?), a semi-automatic signal is not a controlled signal that has the facility to be worked automatically - that'd still be a controlled signal, but (when the 'auto' button is operated) the inner workings don't release the route after the passage of the train and instead allow the signal to clear again once the relevant TCs are clear (as seen in Simsig). In this case, the driver can't pass at danger under his own authority (unless he's established that the controlling signalbox is closed, which is unlikely unless he's at a stand outside a small mechanical box!).

So I'd suggest that the signals on the up road are either automatic (identified as above), and cycling through the aspects as the previous train clears track circuits in advance, or controlled but working in auto, with similar results. Is there any pointwork beyond the station on the up line in that direction? On the down, given the crossover between running lines, the signals will almost certainly be controlled signals and would have had to have been taken out of auto (if the facility exists!) to allow the EMU to cross over to the down - in that case, the signalman might not have set the route and put it back into auto until he needed to pull off for the Pendolino (after which the signal would continue to clear after the passage of each train). The other possibility, as hinted at by David, is that ARS is in use in the area in question (no idea, I'm afraid), which generally won't set routes from a controlled signal until it needs to.

Approach control is another definite possibility, but I'd say that it would be unlikely here given the 'straight through' nature of the route (and the high speeds involved).

 

[CosherB]

Thanks, guys. I suspect the Up signals are semi-autos working in auto (there is a siding betond the staion on the up side, and at least one crossover, but these were not involved in any of the movements I describe).

It makes sense that the down signals which were at red are 'controlled', becuase beyond the first is the crossover that the 323 must have used to get to the Alderley down siding (it would have come from manchester on the up line, crossed to the down, set-down at the down platform before taking refuge in the down siding to allow the pendo to pass before re-positioning back to the down platform to pick up - it would be a service from Manchester to Alderley and back to Manchester).

Beyond the second up signal, about a mile along the line, is Wilmslow where there is quite a complex junction (numerous sidings, crossovers, and the divergence of the 'Styal line' (via Manchester airport) from the direct Manchester via Stockport line. No doubt that signal was protecting the approach to all of that.

I don't think Approach Control comes into it. Both reds cleared to green several minutes before the Pendo came into view round a bend, so its driver would only have seen those signals at green.

Many thansk for the comprehensive replys!

CS

 

[Tomnick]

Thanks, guys. I suspect the Up signals are semi-autos working in auto (there is a siding betond the staion on the up side, and at least one crossover, but these were not involved in any of the movements I describe).

Have a look at the ID plate on the signals at the up end - if it's just a black square, then it's a controlled signal, and if it's got the two white stripe, it's automatic. Given the presence of sidings and a crossover at that end too, I'd suggest that they are indeed controlled signals working in auto (distinct from semi-automatic signals - see my previous post!), but perhaps you could confirm that next time you're there?

It makes sense for the next signal on the down to be controlled - if it's not the signal protecting the junction, then the distances involved make it sound as if it'll be the one in rear of that. There's a good chance that'll be controlled, either because there's signalled shunt moves onto the down in the up direction, or because some of the pointwork falls within the overlap of the junction signal.

 

[Metroland]

Yep, I would say the signal on the down beyond the platform signal is a controlled signal, there is a loop at Wimslow about a mile ahead. So I would guess that the signal protecting that has the points within the overlap, therefore the signal in rear needs to be controlled too. It could also be controlled for shunting moves.

Of course some controlled signals can be set to work automatically, so without looking at the plates, it can be confusing - although this is less common in IECC areas with ARS. I'm not sure whether Manchester South (Which replaced the 1950s OCR Wimslow box) has ARS off hand.

http://supersignaller.fotopic.net/p45387152.html

 

[Muttley]

Have a look at the ID plate on the signals at the up end - if it's just a black square, then it's a controlled signal, and if it's got the two white stripe, it's automatic.

NO NO NO

A plate on a signal DOES NOT tell you how it is worked. That information is totally irrelevent. A plate on a signal tells the driver if/how to get past it if its at danger.

As there is pointwork after the said signal, the protecting signal WILL be controlled.

 

[Tomnick]

Ok, there's the odd exception, such as where an automatic signal will be plated as controlled, to prevent a driver passing it under his own authority when it protects something like a long tunnel or viaduct - but generally, the ID plate 'on the ground' reflects the reality of whether it's controlled, semi-automatic or automatic, even though it is there primarily to tell the driver what to do should he be unable to contact the signalman.

 

[Voltage]

NO NO NO

A plate on a signal DOES NOT tell you how it is worked. That information is totally irrelevent. A plate on a signal tells the driver if/how to get past it if its at danger.

As there is pointwork after the said signal, the protecting signal WILL be controlled.

As far as I know, when I did my training, I was told that auto-signals are controlled by passing trains, while controlled signals are controlled by the signaller. (Im not including semi-auto signals for sake of simplicity)

I was also told that a driver may only pass an auto-signal at danger on own authority if there are no means to contact the signaller (faulty CSR radio, no mobile phone to hand etc) while a controlled signal may ONLY be passed at danger if the driver can confirm the controlling signalbox is closed (which Im guessing is extremely unlikely)

I would be too afraid to pass a controlled signal at danger anyway, because for all I know any facing points could be set that; if crossed would put the train in a dangerous position, such as going down on an up line.

 

[driver9000]

I would be too afraid to pass a controlled signal at danger anyway, because for all I know any facing points could be set that; if crossed would put the train in a dangerous position, such as going down on an up line.

you would have a very short driving career if you did!! NEVER pass a controlled signal in TCB on your own authority, its a different rule regarding AB areas where the signalbox is closed. Section S5 details all you need to know on passing signals at danger.

Ive never heard of Autos being marked up as controlled signals to prevent a driver passing it on his own authority either. The signalbox does have the ability to throw back certain Autos in emergency (every 5th one if I remember rightly) to stop a train if need be.

 

[Metroland]

You can pass auto signals and intermediate block signals without authority if the signal doesn't clear for some time and there is no communication available - in the days of mobile phones and the forthcoming in-cab radio system this would be in exceptional circumstances.

On older installations it tends to be 1 signal every 4-5 miles (or other circumstances) must be replaceable to danger in an auto section, and, unless stated these must be considered to not have guaranteed to go back!

On newer installations, every auto signal is capable of being replaced.

 

[TDK]

On the bi directional signalling between Sandbach and Alderley edge all the signals on the down (or up) depending on the direction of travel are keyed to red if a train is travelling in that direction. I can only surmise this is done to prevent any read across by the drivers. This is all done with risk assessments and signal sighting. The only time you will see the signals clear on the bi-directional lines is when a train is travelling on that line, this must have been a safety feature installed on the outset of the swim project.
--- old post above --- --- new post below ---

As far as I know, when I did my training, I was told that auto-signals are controlled by passing trains, while controlled signals are controlled by the signaller. (Im not including semi-auto signals for sake of simplicity)

I was also told that a driver may only pass an auto-signal at danger on own authority if there are no means to contact the signaller (faulty CSR radio, no mobile phone to hand etc) while a controlled signal may ONLY be passed at danger if the driver can confirm the controlling signalbox is closed (which Im guessing is extremely unlikely)

I would be too afraid to pass a controlled signal at danger anyway, because for all I know any facing points could be set that; if crossed would put the train in a dangerous position, such as going down on an up line.

I remember manchester picadilly signal box having a security alert with 40odd trains under their control. The box was vacated for 25 minutes and in that time no trains passed any signals with the driver's authority so it is a very rare occurance these days and to be honest I would call Gordon Brown as a last resort before passing a red.

 

[dave55uk]

Reading this thread raises an interesting question. I see some people describe the signal-plate on an automatic signal as having two horizontal white lines. I always thought it was a white plate with a single black horizontal line. So, is it a white plate or a black plate...?

 

[GB]

Black plate with white writing indicates a Controlled signal,
White plate with horizontal black stripe indicates an automatic signal,
White plate with horizontal black stripe and "SEMI" written on top indicates a semi-auto signal,
White plate with a black vertical stripe indicates an IBS.

 

[dave55uk]

Thanks GB. That's cleared that up nicely.