Can permissive working permit two moving trains in a block?

[MarkyT]

Exactly the same at my place.

(Although the interlocking will let you and if you’re not careful ARS will kindly do it for you as well)

Must be a fairly old installation then. Some IECCs are getting on a bit now.

 

[contrad!ction]

Some IECCs are getting on a bit now.

Your words not mine

Do the newer interlockings implement full Huddersfield locking as standard then? It’s something we have to watch at a few of our locations - mainly due to the ARS and some very tight timetabling.

 

[ComUtoR]

I'd be interested to hear a little more detail from ComUtoR

I read the title and according to the rulebook (as you posted) I wouldn't see anything wrong with it. There is no distinction made between platform or not. Ergo my reply as a yes.

Also the OP posted a second part to their question regarding other circumstances where two trains are allowed to move. I stated yes as again, that is allowed and would be one of those places as per the rule book and your TCB instructions for 'where permitted'

Finally I can attest to it from personal experience. One of the more common times where this would occur is during an attachment on a platform and your being brought in on top and the attachment is still taking place. This may not involve another signal as it can be into a terminal platform.

I can cite other specifics that would certainly appear to break your 3.3.4 rule.

I'm not a Signaller so I have no idea about their specific rules and regulations but if the Sig pulled the road I would't question it and take that as their authority (as in being permitted) I would also absolutely travel at caution.

Hope that helps

 

[MarkyT]

Your words not mine

Do the newer interlockings implement full Huddersfield locking as standard then? It’s something we have to watch at a few of our locations - mainly due to the ARS and some very tight timetabling.

I believe it continues to be a standard requirement for new installations today. It certainly was on control table work I was involved with directly over two decades ago, including Paddington, Swindon B, Marylebone (Evergreen enhancements).

 

[edwin_m]

Are you describing position light/shunt signals?

And are these always available on approach at stations which allow platform permissive working?

In an area with colour light signalling, two white lights will be used to signal a train into an occupied platform. For an approaching passenger train this will be two white lights underneath or alongside a red on the main signal controlling entry to the platform, known as a subsidiary aspect. Non-passenger trains coming out of sidings or depots may get the same displayed on a shunt signal.

 

[Tomnick]

”When it is permitted" - which, according to TS2/3.3.4, does not include on platform lines.

...

I certainly don't know it all rulebook-wise and am always happy to be educated, but TS2/3.3.4 seems clear with regards to platform lines.

Thanks - I’d completely overlooked 3.3.4! I don’t think there’s an equivalent clause in the AB regs, but perhaps it’s prohibited in the SBSIs at the few remaining locations where it’d be applicable. Other than that, I can only think that it’d apply on permissive goods lines nowadays, or an engine following its train out of a terminal platform towards the platform starter?

 

[MarkyT]

Other than that, I can only think that it’d apply on permissive goods lines nowadays, or an engine following its train out of a terminal platform towards the platform starter?

And depot reception and departure roads etc. Generally never allowed for passenger trains except at platforms where shown in sectional appendix as PP (permissive passenger), which includes attaching, run-round etc with a loaded passenger train involved. PF means permissive freight and can apply at platforms or other cases such as freight or depot lines. many platforms are marked as PP/PF to cover shunting and attachments of parcels vans and empty stock where no passengers involved. Application of permissve working, especially where it involves passengers on board either the attacher or attachee portion must be properly risk assessed for new installations taking account visibility or rear of train, clear understanding of purpose etc. Ops managers are supposed to review older existing installations for risk and implement any special measures considered necessary.

 

[Taunton]

One of the less common signal installations was that put in on the LMS DC Line from Watford to Camden, installed in the 1930s and replaced in the 1970s. This had non-standard very frequent signals, generally at each the next one ahead was visible, and Underground-style trainstops. If the berth track circuit at a signal at red was occupied, after just 1 minute a calling on light appeared automatically, the train stop lowered, and it was permissive working on ahead. This was principally meant to overcome signal failures on a frequent service.

However, if a train was stopped with a fault there could quite quickly be a string build up stopped behind. The usual rules about ready to stop clear applied, and equally usually there were a few collisions over time through not doing so, which as alternate trains were main line size and Bakerloo tube trains with different, lower buffing heights would lead to more damage than normal. It does appear that working on sight with passenger trains is just not reliable enough.

Which makes it all the more surprising to read about recent reports of collisions continuing to happen, I can think of at least three recent ones, at Norwich, Kings Cross and Plymouth, none because of attachments. It appears there is an increasing trend to regard the terminal platforms as surrogate stabling sidings full of stock, possibly because NR charge by the movement out to sidings, and also to then squeeze in further trains that, I believe in all three cases, only just fit or even don't quite fit at all and passengers were expected to get out through the front door only. Surely any meaningful risk assessment would have stamped this out by now.

 

[MarkyT]

One of the less common signal installations was that put in on the LMS DC Line from Watford to Camden, installed in the 1930s and replaced in the 1970s. This had non-standard very frequent signals, generally at each the next one ahead was visible, and Underground-style trainstops. If the berth track circuit at a signal at red was occupied, after just 1 minute a calling on light appeared automatically, the train stop lowered, and it was permissive working on ahead. This was principally meant to overcome signal failures on a frequent service.

However, if a train was stopped with a fault there could quite quickly be a string build up stopped behind. The usual rules about ready to stop clear applied, and equally usually there were a few collisions over time through not doing so, which as alternate trains were main line size and Bakerloo tube trains with different, lower buffing heights would lead to more damage than normal. It does appear that working on sight with passenger trains is just not reliable enough.

Which makes it all the more surprising to read about recent reports of collisions continuing to happen, I can think of at least three recent ones, at Norwich, Kings Cross and Plymouth, none because of attachments. It appears there is an increasing trend to regard the terminal platforms as surrogate stabling sidings full of stock, possibly because NR charge by the movement out to sidings, and also to then squeeze in further trains that, I believe in all three cases, only just fit or even don't quite fit at all and passengers were expected to get out through the front door only. Surely any meaningful risk assessment would have stamped this out by now.

The Watford set up was in some respects a precursor the modern PoSA aspect, but the 1 minute automatic clear to permissive was a step too far. AFAIK this was never used elsewhere, even on LU owned routes which seems odd seeing as many of the trains were Bakerloo tubes.

I think there was some criticism of local ops management, the driver, and the signaller concerned following the Plymouth incident, as it was an unexpected out of course rerouting. Perhaps the driver ought to have been called to confirm understanding before clearing the signal. Also Plymouth station area is a fairly elderly colour light signalling installation and I believe the long platforms on the panel are not split into multiple, separately indicated train detection sections to help the signaller estimate how much space is available for a second move. As it happened the HST almost completely occupied the platform, but even if there had been 2 car single car 153 at the London end starter it's possible the indication could have looked exactly the same on the panel. Where regular permissive working is planned in modern installation for various purposes, much thought is given to splitting track indications through platforms as part of a safe system for planned permissive moves. At terminal platforms, Lime Street controls have been applied as standard for much longer than Huddersfield controls. The technique employs
separate measuring track circuits in the platform and on approach to the protecting home signal to determine whether there really is sufficient space available to accommodate a second or third move. This is particularly important at terminals as otherwise an overhanging train could snake out over the throat blocking all other moves in or out with no means of signalling a route back out again for the offending train. Complete deadlock! Where permissive working is newly proposed for a particular timetable, then it is also supposed to be risk assessed, but often it is felt that as long as movements are planned there's little chance of a misunderstanding. Other causes could be driver misjudgment, unexpected lack of rail adhesion, or technical failure of brakes to apply sufficiently as demanded, but generally the number of movements on the railway is growing faster than infrastructure capacity is expanding so it's unsurprising that some permissive movements continue to be necessary beyond those required specifically for joining.

 

[Taunton]

. Where regular permissive working is planned in modern installation for various purposes, much thought is given to splitting track indications through platforms as part of a safe system for planned permissive moves.

The arrangements for Up trains at Taunton in semaphore days were typical of previous working. The Up Relief platform was normally used for main line services, and also local terminating arrivals from Exeter/Barnstaple/Minehead. These latter were then drawn back over crossovers across the layout. If an Up express was not too long, and a local followed it then it was stopped at the platform entry signal and then brought in behind with the calling on arm. This helped the connecting passengers, and was a regular event. If the express was too long for this then the stopper would be put into the Up Bay alongside, but this was a nuisance as the crossovers did not allow access from there back across to the down side, so a cumbersome double shunt was required later. This all happened right under the noses of the signalmen in the box, who could judge the length and stopping positions of it all. With the non-gangwayed WR suburban DMUs used, and back before this with steam non-corridor stock, there was no question of passengers being able to walk forwards.

 

[Tomnick]

And depot reception and departure roads etc. Generally never allowed for passenger trains except at platforms where shown in sectional appendix as PP (permissive passenger), which includes attaching, run-round etc with a loaded passenger train involved. PF means permissive freight and can apply at platforms or other cases such as freight or depot lines. many platforms are marked as PP/PF to cover shunting and attachments of parcels vans and empty stock where no passengers involved. Application of permissve working, especially where it involves passengers on board either the attacher or attachee portion must be properly risk assessed for new installations taking account visibility or rear of train, clear understanding of purpose etc. Ops managers are supposed to review older existing installations for risk and implement any special measures considered necessary.

I’ve never come across anywhere authorised for both PP and PF - do you have any examples? Indeed, I’ve not seen anywhere with PF on a platform line. Light engines and ECS moves are permitted to work permissively on PP lines, although any shunt movement to attach or detach vehicles is authorised generally in its own right anyway.

 

[Belperpete]

At terminal platforms, Lime Street controls have been applied as standard for much longer than Huddersfield controls. The technique employs separate measuring track circuits in the platform and on approach to the protecting home signal to determine whether there really is sufficient space available to accommodate a second or third move.

It is a long time since I have seen Lime Street controls implemented on any new scheme I have been involved with. The problem is that the variety of rolling stock in use, and hence the variety of train lengths, make a system based on a small number of fixed-length track-circuits almost unworkable.

Much more common nowadays are mid-platform signals, to permit two trains to share a platform, as at Birmingham NS, Nottingham, Leeds, Bristol TM, etc. The second train then comes in on a main aspect, not a permissive aspect. I was surprised that they weren't provided at Derby, where trains regularly share platforms 3 and 4. One day we might even get a signalling principle to tell us how they should work!

 

[Ken H]

The Stafford 1990 accident is relevant here. A driver went into a partially occupied platform and hit the train standing there.
The starter for the platform was off for the front train. The driver of the following train (4 car 310) stopped at sig 139 on the up fast. The signalman cleared the calling on position light for the permissive move, which also lit the junction indicator.
Its thought the driver of the rear train thought that the starter signal was for him and the report (para 122) says the starter should not be cleared while a permissive move is being made to the rear. He failed to see the flashing tail lamp on the front train.
There were other factors, like was the driver was fit to work and whether the fact the position light signal was dimmer than the junction indicator was a factor.
http://www.railwaysarchive.co.uk/documents/HSE_Stafford1990.pdf

 

[MarkyT]

It is a long time since I have seen Lime Street controls implemented on any new scheme I have been involved with. The problem is that the variety of rolling stock in use, and hence the variety of train lengths, make a system based on a small number of fixed-length track-circuits almost unworkable.

Much more common nowadays are mid-platform signals, to permit two trains to share a platform, as at Birmingham NS, Nottingham, Leeds, Bristol TM, etc. The second train then comes in on a main aspect, not a permissive aspect. I was surprised that they weren't provided at Derby, where trains regularly share platforms 3 and 4. One day we might even get a signalling principle to tell us how they should work!

I wonder what they did for the terminal platforms at London Bridge. At least south of the Thames unit types and lengths are more standardised. An idea I had years ago was if axle counters are used in a terminal platform it ought to be possible to provide the signaller with a readout of the current axle count from which an estimate of the remaining space might be made.

Reading didn't get mid platform signals in the remodelling. That would probably have been difficult for aspect sequences with the high through line speeds involved, but the layout does have closing up signals at the running in end from which any position light permissive move would be signalled, and the platforms being fairly straight means the rear of a train ahead should be clearly visible from the authorising signal. There are 'rear clear' markers for various length trains placed at strategic positions along the platforms to indicate where to stop if the forward section needs to be kept clear for a subsequent arrival.

 

[Ken H]

I wonder what they did for the terminal platforms at London Bridge. At least south of the Thames unit types and lengths are more standardised. An idea I had years ago was if axle counters are used in a terminal platform it ought to be possible to provide the signaller with a readout of the current axle count from which an estimate of the remaining space might be made.

Reading didn't get mid platform signals in the remodelling. That would probably have been difficult for aspect sequences with the high through line speeds involved, but the layout does have closing up signals at the running in end from which any position light permissive move would be signalled, and the platforms being fairly straight means the rear of a train ahead should be clearly visible from the authorising signal. There are 'rear clear' markers for various length trains placed at strategic positions along the platforms to indicate where to stop if the forward section needs to be kept clear for a subsequent arrival.

but can the starter for the 'front' train be cleared while the permissive move is carried out?

 

[MarkyT]

I’ve never come across anywhere authorised for both PP and PF - do you have any examples? Indeed, I’ve not seen anywhere with PF on a platform line. Light engines and ECS moves are permitted to work permissively on PP lines, although any shunt movement to attach or detach vehicles is authorised generally in its own right anyway.

I think it's historic, maybe a Western Region peculiarity?
Here's Plymouth (1960):

Gloucester (early 1970s)

Some platforms at Exeter (mid 1980s) are also shown as PP/PF but more recently resignalled areas such as Reading, Cardiff, Bristol are now PP only, although I seem to remember from my time on the Western in the 1980s and early 1990s it was common at most big stations.

 

[MarkyT]

but can the starter for the 'front' train be cleared while the permissive move is carried out?

I don't know for sure, but I'd expect full Huddersfield controls to have been applied.

 

[Tomnick]

I think it's historic, maybe a Western Region peculiarity?
Here's Plymouth (1960):
View attachment 56055
Gloucester (early 1970s)
View attachment 56056
Some platforms at Exeter (mid 1980s) are also shown as PP/PF but more recently resignalled areas such as Reading, Cardiff, Bristol are now PP only, although I seem to remember from my time on the Western in the 1980s and early 1990s it was common at most big stations.

Interesting, thanks! I wonder whether only one of PP and PF are permitted at a time, though - presumably dropping a heavy stone train in on top of a passenger train would be frowned upon?!

 

[Ken H]

Interesting, thanks! I wonder whether only one of PP and PF are permitted at a time, though - presumably dropping a heavy stone train in on top of a passenger train would be frowned upon?!

surely a freight train is unlikely to fit in a partially occupied platform.

 

[MarkyT]

Interesting, thanks! I wonder whether only one of PP and PF are permitted at a time, though - presumably dropping a heavy stone train in on top of a passenger train would be frowned upon?!

Yes one or the other is used at any time, but there's considerable 'overlap' in the case of empty stock, parcels vans, attaching locos etc. I believe the PP/PF designation was conceived to allow many different types of non passenger trains to be handled flexibly in platforms at a time when there was much parcels, mail and newspaper traffic. If any train involved has passengers on board then PP rules must be used for a permissive movement, but a passenger train that had terminated and become empty stock could theoretically then have a subsequent PF movement brought in, say a short departmental train placed out the way behind such an ECS awaiting a movement to a depot. PP alone doesn't allow that I believe.

 

[MarkyT]

surely a freight train is unlikely to fit in a partially occupied platform.

True in most cases on the modern railway, but there are some short formations that also count as freight such as certain engineering workings.

 

[Ken H]

True in most cases on the modern railway, but there are some short formations that also count as freight such as certain engineering workings.

Ah, OK. spose a tamper is a 'freight train'

 

[Belperpete]

Reading didn't get mid platform signals in the remodelling. That would probably have been difficult for aspect sequences with the high through line speeds involved, but the layout does have closing up signals at the running in end from which any position light permissive move would be signalled, and the platforms being fairly straight means the rear of a train ahead should be clearly visible from the authorising signal. There are 'rear clear' markers for various length trains placed at strategic positions along the platforms to indicate where to stop if the forward section needs to be kept clear for a subsequent arrival.

None of the bay platforms at Leeds have Lime Street controls, for example. There are plenty of places (including Leeds) where the platform track is split for indication purposes, but very few that I can think of with the measuring tracks on the approach signals.

Back in the 1960s a signaller could be sitting in a panel box with no view of the trains, and little idea of their make-up or position in the platform. Nowadays it is a lot easier for signallers to find out train consists, communications with platform staff have become a lot easier with fairly wide-spread use of radios, and I understand at some places even have CCTV available.

I thought that there had been an agreement that, for new schemes, call-ons would usually only be used where trains are genuinely joining, and so routine platform sharing would only be permitted where the platform was properly signalled for it, i.e. with mid-platform signals.

 

[edwin_m]

Much more common nowadays are mid-platform signals, to permit two trains to share a platform, as at Birmingham NS, Nottingham, Leeds, Bristol TM, etc. The second train then comes in on a main aspect, not a permissive aspect. I was surprised that they weren't provided at Derby, where trains regularly share platforms 3 and 4.

Nottingham doesn't have them either, nor did it prior to the remodelling.

 

[MarkyT]

I thought that there had been an agreement that, for new schemes, call-ons would usually only be used where trains are genuinely joining, and so routine platform sharing would only be permitted where the platform was properly signalled for it, i.e. with mid-platform signals.

I think that's generally the ideal scenario, but in many places it's practically impossible. At Reading for instance with the high through line speeds (compared to Bristol, Birmingham Leeds), mid-platform signals MIGHT have been possible with repeated yellows in the sequence or special approach release controls, but such odd (albeit 'legal') sequences are thought to introduce risks of misunderstanding so those risks must be balanced against the permissive risks. These problems will largely disappear once ETCS is introduced widely as the link between braking distance and block lengths is removed with the train equipment working out its own braking curve within the movement authority. Thus there can be as many block markers as desired along a platform.

 

[MarkyT]

Nottingham doesn't have them either, nor did it prior to the remodelling.

And the platforms there contain the only track circuits within the resignalled area which is otherwise entirely equipped with axle counters for train detection. The platform tracks are split into a number of separately indicated sections to help signallers understand space available for permissive moves. A problem using axle counters for such an application is that it is highly likely that sometimes an axle will stop directly over a counter head sensor at a boundary. When this happens the evaluator can sometimes register a miscount when the train moves off again, safely occupied when actually clear (so 'right side') but very operationally inconvenient. There is a new (for UK) axle counter technique, known as 'supervisory sections' that can overcome this problem and is planned to be introduced at Birmingham New Street in the forthcoming resignalling, after a successful test installation at Coventry. In this, an overlaid supervisory section A-C, using the same sensors at the extremities, monitors three separate sections A, B and C and if there is a disturbance at any of the intermediate sensors, the system will do an automatic reset of any affected sections once the overall supervisory section goes clear. The technique is in common use in Germany, home of axle counter technology.

 

[Llama]

Ironically, Lime Street now no longer has Lime Street Control.