• Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!

Permanent 10 mph through Bristol TM platforms

Status
Not open for further replies.
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R

RailUK Forums

Signal Head

Member
Joined
26 May 2013
Messages
398
Re: Westpac at al:

A former guru of these things suggested that a few relays were a necessary part of any geographic installation, as there would always be something there wasn't a pack for ...
There are always additional relays and associated wiring with any geographical interlocking, even when the basic interlocking requirements are satisfied by the internally wired circuits. This 'free-wiring', eg to insert additional controls, can be quite complex on a complicated layout.
 

MichaelAMW

Member
Joined
18 Jun 2010
Messages
1,011
I suspect the 10 mph will be permanent, as from talking to industry insiders the St Andrews Crosses were considered an anachronism which was viewed has a high collision risk, even though I can't remember an accident which was attributed to them. The only means of getting the station to meet current standards while still handling the current level of traffic was to adopt the intermediate back to back signals and a 10 mph restriction, with no AWS within the station limits. I can envisage more missed connections in the future, especially if from platform 15 to platform 1, as sometimes happens.
You make it sound very similar to Birmingham New Street, which I believe also has zero-distance overlaps beyond the signals, and that has a 10 mph speed limit.
 

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
10mph versus 25mph for any more than a few metres is likely to have some impact. Even if the boards are on the entry to the platforms travelling 200m at 10mph loses about 20s. Couldn't something have been done with delayed yellows approaching the platforms if a suitable overlap beyond the mid-platform signal wasn't available?

I suspect the 10 mph will be permanent, as from talking to industry insiders the St Andrews Crosses were considered an anachronism which was viewed has a high collision risk, even though I can't remember an accident which was attributed to them. The only means of getting the station to meet current standards while still handling the current level of traffic was to adopt the intermediate back to back signals and a 10 mph restriction, with no AWS within the station limits. I can envisage more missed connections in the future, especially if from platform 15 to platform 1, as sometimes happens.

You make it sound very similar to Birmingham New Street, which I believe also has zero-distance overlaps beyond the signals, and that has a 10 mph speed limit.

I've seen a picture of the new Bristol screens at TVSC and the split platform arrangement includes restricted overlaps, butting up to each other, in a space between the new mid-platform signals. This suggested to me initially that simultaneous warning routes might be set into the same platform from both ends, but actually there is no appreciable distance between the signals, mounted on the same structure. so a route can only be set towards one at any time and a train following the first route set in must time out to a stand at the appropriate end before the second can be set in at the other end - see my later post some other details.
 
Last edited:

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
Re: Westpac at al:

A former guru of these things suggested that a few relays were a necessary part of any geographic installation, as there would always be something there wasn't a pack for ...

There are always additional relays and associated wiring with any geographical interlocking, even when the basic interlocking requirements are satisfied by the internally wired circuits. This 'free-wiring', eg to insert additional controls, can be quite complex on a complicated layout.

The later versions of geographical technology required progressively fewer additional free wired modifications than the earliest models, as manufacturers gradually incorporated more of the sophisticated behaviour BR required (swinging overlaps, automatic warning route step up to main route when available, for examples) but they never quite managed to eliminate the necessity entirely.
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
I've seen a picture of the new Bristol screens at TVSC and the split platform arrangement includes restricted overlaps, clear of each other, between the new mid-platform signals. This can permit simultaneous warning routes to be set into the same platform from both ends, not possible withe the previous St Andrews Cross srrangement. Main routes are also provided from the two gantries to the mid platfrom signals with full overlaps ocked and proved clear to the far end of the platform in question.

Here is a diagram to illustrate a typical case:
View attachment 44850
I'm not sure what that diagram refers to, but it bears no relationship whatever to what has been done over the Easter holiday. The intermediate signals are literally back to back, there is certainly no overlap between them. Also the ones on platform 4 are further west than the position of the St Andrews crosses, possibly to get a 10 car IET in clear in platform 3.
 

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
I'm not sure what that diagram refers to, but it bears no relationship whatever to what has been done over the Easter holiday. The intermediate signals are literally back to back, there is certainly no overlap between them. Also the ones on platform 4 are further west than the position of the St Andrews crosses, possibly to get a 10 car IET in clear in platform 3.

I was trying to replicate what is actually shown on the new control screen at TVSC. That shows restricted overlaps from each direction butting up to each other between the signals and as depicted this implies that delayed yellow warning routes can be set towards the mid platform signals simultaneously. I've only just found a picture of an actual example of the signalls on platfrom #5/6, where the signals are indeed back-to-back mounted on the same post.

Here's a small extract from the original photo of the TVSC screen I saw, zoomed right in. Note the ROLs between the back to back signals.
bristol2.jpg
 
Last edited:

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
I've received some insider info. My original assumption that simultaneous warning class routes can be set towards the same pair of mid-platform signals from opposite directions was wrong. The first train entering on a main class must time out to a stand at the appropriate end of the platforms before the second enters the other end, on a warner. That's not significantly different to functionality with the St Andrew's Crosses except in that case the second move came in on a call-on class route with a position light aspect. The safety problem with the old arrangement was that the position light itself didn't tell you whether the obstruction was before or after the Cross, although there was a difference in route indication given. Drivers could become habituated to entering boldly with a train at the far end (beyond the cross) then be surprised by an obstruction at the near end if they had missed the difference in route indication.
 

Jan

Member
Joined
22 Dec 2008
Messages
69
Can anybody confirm how the speed limit is actually implemented - is it done similar to Leeds, i.e. 10 mph from the start of the platform up to the mid-platform signal and then back to 25 mph?

Minor point, but London Bridge was not resignalled on the old layout prior to works; most stageworks were done on the old system (Westpac Mk1), with the resignalling done in sequence when the final layout was achieved for individual stages.
London Bridge is/was Westpac MkIV actually.
 

WelshBluebird

Established Member
Joined
14 Jan 2010
Messages
4,923
So had a couple of journeys through Temple Meads over this weekend, my first since the resignalling. You can certainly notice the speed restriction. it really does feel like you are crawling through there. Certainly confused a few people when we were going that slow but not stopping where they expected! Also not a fan of the fact platform 12 and 10 are as far away as they are now. Not looking forward to short connection times with those platforms as they now are.
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
Can anybody confirm how the speed limit is actually implemented - is it done similar to Leeds, i.e. 10 mph from the start of the platform up to the mid-platform signal and then back to 25 mph?
No, the 10 applies from one end of the platforms to the other, but not the pointwork, so it takes a while before a departing 10 car IET for example can accelerate. It looks as though platform 15 is still 15 mph going west at least, and the through roads remain at 25.
 

Johncleesefan

Member
Joined
4 Sep 2013
Messages
729
Actually it’s 10 in and 25 out. At least that’s the instruction gwr have given me. This does lead to slight confusion for say freight or ecs signalled directly through a platform and if such happened to me I’d be inclined to do 10 the whole way in that case.

However, on departing after station duties I’m straight to 25.

Just another piece of confusion to go with the “upgrade”
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
Actually it’s 10 in and 25 out. At least that’s the instruction gwr have given me. This does lead to slight confusion for say freight or ecs signalled directly through a platform and if such happened to me I’d be inclined to do 10 the whole way in that case.

However, on departing after station duties I’m straight to 25.

Just another piece of confusion to go with the “upgrade”
I've seen the 25 PSR boards at the ends of the platforms, are you telling me you can accelerate before the whole of your train has passed them?
 

vikingdriver

Member
Joined
11 Mar 2010
Messages
307
When I was last in at work, there was a late notice in the case saying 10mph in and out. Think it came out at 0300 (if I recall correctly) the morning it reopened. Not sure if it's still there as I'm on A/L. Before that out our brief said 10mph in, 25mph out.
 
Last edited:

plymothian

Member
Joined
26 Sep 2010
Messages
735
Location
Plymouth
When I was last in at work, there was a late notice in the case saying 10mph in and out. Think it came out at 0300 (if I recall correctly) the morning it reopened. Not sure if it's still there as I'm on A/L. Before that out our brief said 10mph in, 25mph out.

Briefings have changed like the wind over this that everyone is so confused.
It is 10mph in and out due to a cock-up with the placings of the speed limits. As D1009 says the 25s are at the platform ends, not at the platform sharing signals, which means the 10 covers the whole length of the platform.
 

Johncleesefan

Member
Joined
4 Sep 2013
Messages
729
Hmm, well as you have stated, what with the multiple last minute brief changes and all I can see the confusion, our latest brief does definitely state 25 out though as in as soon as you take power
 

Crossover

Established Member
Joined
4 Jun 2009
Messages
9,247
Location
Yorkshire
Not the best picture in the world but here is a photo of the signals ‘dark’ but not covered on the main platform (i.e. the one nearest the main barriers under the shed) taken about a month go. I had it explained then that the St George’s Crosses were going and being replaced by these as the Crosses were not a common thing now
 

Attachments

  • D56ED42F-5439-4518-8035-9CE8047DB5F7.jpeg
    D56ED42F-5439-4518-8035-9CE8047DB5F7.jpeg
    2.2 MB · Views: 101

MarkyT

Established Member
Joined
20 May 2012
Messages
6,232
Location
Torbay
Not the best picture in the world but here is a photo of the signals ‘dark’ but not covered on the main platform (i.e. the one nearest the main barriers under the shed) taken about a month go. I had it explained then that the St George’s Crosses were going and being replaced by these as the Crosses were not a common thing now

Not just uncommon. They were unique I believe. Anyone know of any other example?
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
Hmm, well as you have stated, what with the multiple last minute brief changes and all I can see the confusion, our latest brief does definitely state 25 out though as in as soon as you take power
Presumably the amendments to Table A of the Sectional Appendix should show the correct position. Does anyone know how other TOC's drivers have been briefed?
 

pompeyfan

Established Member
Joined
24 Jan 2012
Messages
4,181
Presumably the amendments to Table A of the Sectional Appendix should show the correct position. Does anyone know how other TOC's drivers have been briefed?

I’ve not seen any briefs put out by SW, but saying that only Salisbury sign Bristol so there’s a chance it’s not gone to every depot.
 

Quickthorn

Member
Joined
21 Dec 2012
Messages
137
I wonder why this could not have been dealt with using a sectional appendix instruction to the effect that drivers must enter platforms at 10 mph on single yellow or position light at the east/west gantry. This would be backed up with TPWS OSS at the end of each platform for the approach to each platform sharing signal, with grids set at 10 mph and energised if the relevant platform sharing signal is at danger.

Earlier today, I was on a service coming in from the East and terminating in platform 12. From the ramp of platform 11, it took 90 seconds before we were at a stand. When you get dwell times of a minute on some services (eg Cardiff-Taunton and Parkway-Weston), during which crews often change, this bound to have an impact.
 

Wilts Wanderer

Established Member
Joined
21 Nov 2016
Messages
2,463
I have an inside source about this. The 10mph restriction was only imposed very late in the day (far too late to incorporate the impact into timetables for example) and was to mitigate an issue which only came to light very late into the installation.

Failure to mitigate this issue would have meant BASRE could not have been commissioned, or at least require severe loss of functionality at Bristol TM.

Basically, with back-to-back mid platform signals, the block joints are positioned directly underneath the signals. The block joint for one direction is the signal replacement joint for the other. So a train arriving across the mid-signal releases the track circuit in rear once the last axle has passed the replacement joint. Problem is, modern rolling stock have increasingly long nose cones, and it was realised that the last axle could clear the replacement joint and stop with the rear nose / couplers still occupying the section behind. The signalling system would not be able to detect this and could then release the East Gantry / West Gantry junction signal to a single yellow without the near-end platform actually being clear. This could be interpreted as a wrong-side failure.

The mitigation is therefore to impose the 10mph and warn drivers to approach the mid-platform signal at extreme caution as there is a slight possibility that another train could be standing foul without occupying the track circuit. Unfortunately speed signage can’t be made signal-aspect specific so it will apply to all trains regardless of movement. Interesting the comments about whether it applies for the whole length of the platform or not - I had heard it would be to the mid-platform signals only. Either way, this restriction is going to be exceptionally difficult to remove, without redesigning the interlocking or moving the mid-platform signals about 8m apart, which would allow the block joints to be positioned in a more appropriate position.

I must admit, I can’t help looking at this situation and just seeing engineering incompetence and loss of knowledge, although I’m sure this isn’t an entirely fair reflection on the people involved.
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
I have an inside source about this. The 10mph restriction was only imposed very late in the day (far too late to incorporate the impact into timetables for example) and was to mitigate an issue which only came to light very late into the installation.

Failure to mitigate this issue would have meant BASRE could not have been commissioned, or at least require severe loss of functionality at Bristol TM.

Basically, with back-to-back mid platform signals, the block joints are positioned directly underneath the signals. The block joint for one direction is the signal replacement joint for the other. So a train arriving across the mid-signal releases the track circuit in rear once the last axle has passed the replacement joint. Problem is, modern rolling stock have increasingly long nose cones, and it was realised that the last axle could clear the replacement joint and stop with the rear nose / couplers still occupying the section behind. The signalling system would not be able to detect this and could then release the East Gantry / West Gantry junction signal to a single yellow without the near-end platform actually being clear. This could be interpreted as a wrong-side failure.

The mitigation is therefore to impose the 10mph and warn drivers to approach the mid-platform signal at extreme caution as there is a slight possibility that another train could be standing foul without occupying the track circuit. Unfortunately speed signage can’t be made signal-aspect specific so it will apply to all trains regardless of movement. Interesting the comments about whether it applies for the whole length of the platform or not - I had heard it would be to the mid-platform signals only. Either way, this restriction is going to be exceptionally difficult to remove, without redesigning the interlocking or moving the mid-platform signals about 8m apart, which would allow the block joints to be positioned in a more appropriate position.

I must admit, I can’t help looking at this situation and just seeing engineering incompetence and loss of knowledge, although I’m sure this isn’t an entirely fair reflection on the people involved.
I take the point about long nose cones, but surely that applies to any train, the wheels are some way back from the ends. Are there any other locations where there are back to back signals where the same situation could occur? Someone mentioned New Street earlier, but as I recall there is some distance between the signals.
 
Last edited:

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
24,793
Location
Nottingham
Could they not provide a block joint a nosecone-worth of distance on the approach to each of the mid-platform signals, with the intervening section being its own track circuit that, when occupied, forced the interlocking to treat both main platform track circuits as also being occupied? They could have a car stop board to ensure that units without nosecones stoppe a bit further back to prevent them putting a wheel over the block joint and locking the signal.
 

Wilts Wanderer

Established Member
Joined
21 Nov 2016
Messages
2,463
There are probably some technical solutions, hopefully one will be viable for the current less than ideal arrangement.

It would be interesting to know whether there are any restrictions currently in place on ARS to prevent through freight trains from being routed via a 10mph platform. I shudder to think how long it would take a freightliner to crawl through the station throat at that sort of speed, particularly if it applies right through the platforms.
 

Wilts Wanderer

Established Member
Joined
21 Nov 2016
Messages
2,463
Could they not provide a block joint a nosecone-worth of distance on the approach to each of the mid-platform signals, with the intervening section being its own track circuit that, when occupied, forced the interlocking to treat both main platform track circuits as also being occupied? They could have a car stop board to ensure that units without nosecones stoppe a bit further back to prevent them putting a wheel over the block joint and locking the signal.

I am informed there is a signalling standard which requires approximately 4.5m stand back between a stop signal and it’s replacement joint, to mitigate the nosecone effect. But this was written with junctions in mind, not platforms, so I guess there may have been some ambiguity as to what was relevant to Bristol TM or not.

Another interesting side effect of block joints directly under signals is that the signal returns to red very soon after the front of the train passes. Whilst for modern units this is no problem, as the driver sits right at the front, what happens for locomotives where the driving position is some way back? For instance a steam locomotive, or Class 20 running bonnet-first. The driver will see the signal return to red before he passes it - doesn’t this risk misinterpretation? I wonder when the next steam charter is running to Bristol.
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
24,793
Location
Nottingham
Another interesting side effect of block joints directly under signals is that the signal returns to red very soon after the front of the train passes. Whilst for modern units this is no problem, as the driver sits right at the front, what happens for locomotives where the driving position is some way back? For instance a steam locomotive, or Class 20 running bonnet-first. The driver will see the signal return to red before he passes it - doesn’t this risk misinterpretation? I wonder when the next steam charter is running to Bristol.
Last wheel replacement would address that one.
 
Status
Not open for further replies.

Top