Signal Sighting (not Siting)

[iands]

May be of interest- Signal sighting distance chart from NR SMS part Z

 

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Thanks for the info. The last time I was involved with "setting" a signal head was back in the late 70s. Obviously things have moved on a bit since then.

 

Regards, Ian.

[TheSignalEngineer]

Hi Big Jim,

 

Very interesting to hear the "end users" views regarding the LED signals. Although I work in the railway industry, I'm not a (train) driver. I find it difficult sometimes driving at night to judge the distance of on-coming vehicles when all you can see are the headlights, I imagine this is similar to what you experience. I'm not suggesting the "lamp lit" signals were easy to judge the distances at night, but what you seem to be saying is it was at least a bit easier to judge the distance (relatively speaking).

 

Regards, Ian.

I'm no longer involved in the industry but my impression of modern signals is that there is a wide variation in what is acceptable under the current regime. From just after the inception of colour light signals up to the widespread adoption of LEDs there was a clearly defined and very tight specification of how the signal should look, light intensity, colour temperatures, beam spread angle etc. This meant that wherever you saw a signal the perspective you got was the same throughout the system, other than a small number of low speed instances fitted with 'Spreadlite' 20 degree beam lenses. Today it seems that anything goes as long as it is approximately red, yellow and green, doesn't show up very well from a distance in daylight and dazzles at night when close up.

[big jim]

i had a high up bod from network rail with me on a test train last year on the chase line, i invited him into the cab for a look at the signals at night, one i highlighted in particular was just before a foot crossing (50m or so), it was so bright that you couldn't see the crossing until you had passed the signal and your eyes had adjusted back to the darkness, he agreed it was far too bright, had there been something or someone on the crossing there was no way of knowing, with normal signals you could at least make out "shapes" beyond the signal 

 

one of the biggest "curses" of led signals is if you stop as per the defensive driving policythe correct distance back from one you cant see the signal number plate 99% of the time 

Edited November 23, 2017 by big jim

[royaloak]

How far away do you need to see the signal, as against how far away would you like to see it?

 

The braking distance is, after all, calculated from the signal, not some distance before you reach it.

 

Jim

The braking distance is okay, but as with most things, more is better especially this time of year where the railhead conditions might not correspond with the specification. 

[The Stationmaster]

IIRC modern rules dictate that drivers must be able to see the signal aspect for 10 seconds at a minimum when traveling at line speed (reduced to 7seconds for older pre 2000 installations). For the last 5 seconds that view must NOT be interrupted by structures (e.g. OLE masts, platform canopies, bridges, etc.)

 

Where sighting times cannot be met then banner repeaters MUST be used or the line speed reduced so as to bring the time the driver has to observe the signal to within the guidelines.

 

There's quite amusing one in the Thames Valley where a signal obviously failed to meet the modern distant view requirement and therefore acquired a banner repeater.  I have often wondered if it would have been simpler and cheaper to cut down the lineside foliage and growth (wholly within the NR boundary) than erect a banner repeater?

[keefer]

i've read previously on RMWeb that the older filament lamp signals can be better in low-visibilty situations e.g. mist and fog.

i can't remember exactly the reason but it may have been because the light from filament lamps is focussed through a glass lens, giving a strong 'beam'.

whereas the LEDs, although very bright, have an overall more diffuse spread of light.

 

Maybe someone can confirm if i'm talking out me 'arris or not?

[big jim]

There's quite amusing one in the Thames Valley where a signal obviously failed to meet the modern distant view requirement and therefore acquired a banner repeater.  I have often wondered if it would have been simpler and cheaper to cut down the lineside foliage and growth (wholly within the NR boundary) than erect a banner repeater?

there is someing similar just south of banbury but the opposite way round, they have cut back the foliage and smoothed off the bank to get a view of the signal on a left hand bend, all fine and dandy straight after the new installation was completed but now its startign to grow again, not to an extent to effect the signal but give it another year

 

the daft thing with that particular signal is had they sighted it 200m futher back it would have been on the end of a straight with 1/4 mile of visibility

[TheSignalEngineer]

there is someing similar just south of banbury but the opposite way round, they have cut back the foliage and smoothed off the bank to get a view of the signal on a left hand bend, all fine and dandy straight after the new installation was completed but now its startign to grow again, not to an extent to effect the signal but give it another year

 

the daft thing with that particular signal is had they sighted it 200m futher back it would have been on the end of a straight with 1/4 mile of visibility

Before submitting any signalling plan for approval I would walk the line with one of the local S&T Inspectors and we checked what the available sighting was at the proposed signal positions and the likely type of structure required. I liked to get a quarter of a mile first sight if possible and an uninterrupted view before reaching the AWS. There were often a few tweaks to get off a tight bend or further beyond a bridge. Sometimes in the case of a left-hand bend it was a matter of using a 13' post instead of 11' and using a 2' offset to get the head at minimum clearance from the track. Sadly some signal positioning makes it look as if that sort of thing isn't done these days.

[SM42]

there is someing similar just south of banbury but the opposite way round, they have cut back the foliage and smoothed off the bank to get a view of the signal on a left hand bend, all fine and dandy straight after the new installation was completed but now its startign to grow again, not to an extent to effect the signal but give it another year

 

the daft thing with that particular signal is had they sighted it 200m futher back it would have been on the end of a straight with 1/4 mile of visibility

 

Jim

 

It may be worth highlighting this if you haven't already so a pre-emptive strike can be arranged. 

 

PM me if you want

 

Andy

[jim.snowdon]

There's quite amusing one in the Thames Valley where a signal obviously failed to meet the modern distant view requirement and therefore acquired a banner repeater.  I have often wondered if it would have been simpler and cheaper to cut down the lineside foliage and growth (wholly within the NR boundary) than erect a banner repeater?

There's quite an amusing one at West Drayton, for Down movements on the Up Goods Loop, where a banner repeater has now been provided on a line that is heavily speed restricted and the signal aspect is unlikely to be better than a yellow. Whilst the curve through the platform and the presence of the station buildings (those that haven't yet been demolished for Crossrail) obstruct the view of the signal, as they always did, the driver is expected to have his train under control with an expectation of the approaching signal aspect. Given that a banner repeater is not a signal but an aid for drivers, I am not at all certain what this one really achieves, other than blind compliance with a standard that is overly prescriptive.

 

As for minimum sighting times, even 7 seconds is a long time, 10 seconds even more so. If the Underground was signalled that way, it would never work, and it is a 2-aspect system, where there is no pre-warning of a red aspect unless the sighting distance is less than the braking distance.

 

Jim

[The Stationmaster]

There's quite an amusing one at West Drayton, for Down movements on the Up Goods Loop, where a banner repeater has now been provided on a line that is heavily speed restricted and the signal aspect is unlikely to be better than a yellow. Whilst the curve through the platform and the presence of the station buildings (those that haven't yet been demolished for Crossrail) obstruct the view of the signal, as they always did, the driver is expected to have his train under control with an expectation of the approaching signal aspect. Given that a banner repeater is not a signal but an aid for drivers, I am not at all certain what this one really achieves, other than blind compliance with a standard that is overly prescriptive.

 

As for minimum sighting times, even 7 seconds is a long time, 10 seconds even more so. If the Underground was signalled that way, it would never work, and it is a 2-aspect system, where there is no pre-warning of a red aspect unless the sighting distance is less than the braking distance.

 

Jim

 

I am left with the impression that quite a number of banner repeaters which have appeared in recent years are only about 'blind compliance' with a standard which often appears to be downright ridiculous.  Talking about these things a while back with the former BRB Signalling Officer we were both of the view that whoever ordained the standard was not exactly familiar with the reason for providing a banner repeater - which is really to indicate if a signal is 'off'.  This of course part of the very sensible reason for providing green banner indications as they can give a far more exact indication of the proceed aspect being shown by the signal to which they refer.

 

The only potential advantage I can see at West Drayton is that the banner might give a Driver a chance to keep his train rolling when he/she might otherwise be preparing to stop at the signal - but the obvious question is just how often a train is likely to be approaching that signal when it is showing a proceed aspect? If the answer to that is a very small number (be it in either real or percentage terms that I, for one, would be questioning the value for money afforded by the banner repeater as well as asking just what advantage it might confer for train handling?

 

Incidentally I noticed recently that yet another one has now sprouted between Didcot and Reading - for a signal which hasn't moved an inch in over 40 years. and which (and on a lineside which has had ohle masts for the better part of two years).  I reckon for a train slowing to stop at said signal the banner will give the Driver probably an extra 3-4 seconds to release the brake and open the controller, on signalling which has a designed 3 minute headway at line speed.  I'm still waiting for one to appear at a signal west of Twyford which had an offset head from 1961 until it was replaced by a Dorman head about 18 months ago - that would be the ultimate (but line curvature suggests that won't happen, I hope).

[iands]

I am left with the impression that quite a number of banner repeaters which have appeared in recent years are only about 'blind compliance' with a standard which often appears to be downright ridiculous.  Talking about these things a while back with the former BRB Signalling Officer we were both of the view that whoever ordained the standard was not exactly familiar with the reason for providing a banner repeater - which is really to indicate if a signal is 'off'.  This of course part of the very sensible reason for providing green banner indications as they can give a far more exact indication of the proceed aspect being shown by the signal to which they refer.

 

The only potential advantage I can see at West Drayton is that the banner might give a Driver a chance to keep his train rolling when he/she might otherwise be preparing to stop at the signal - but the obvious question is just how often a train is likely to be approaching that signal when it is showing a proceed aspect? If the answer to that is a very small number (be it in either real or percentage terms that I, for one, would be questioning the value for money afforded by the banner repeater as well as asking just what advantage it might confer for train handling?

 

Incidentally I noticed recently that yet another one has now sprouted between Didcot and Reading - for a signal which hasn't moved an inch in over 40 years. and which (and on a lineside which has had ohle masts for the better part of two years).  I reckon for a train slowing to stop at said signal the banner will give the Driver probably an extra 3-4 seconds to release the brake and open the controller, on signalling which has a designed 3 minute headway at line speed.  I'm still waiting for one to appear at a signal west of Twyford which had an offset head from 1961 until it was replaced by a Dorman head about 18 months ago - that would be the ultimate (but line curvature suggests that won't happen, I hope).

These days a "Signal Sighting Committee" is usually convened (with a chairman and reps from the signalling designers, Operations and TOC/FOC and possibly others) at the behest of a Project or a report from a TOC/FOC, to review the sighting requirements for particular signals. I can only assume that in the cases quoted above that the banner repeaters have been provided to satisfy a particular issue with a signal. As the process of providing a banner repeater will cost a substantial amount of money, I can't imagine that Network Rail would go to the trouble of providing one on a "whim" if one wasn't really necessary. With their budgets so tight, NR would need proper justification for doing so.

 

Regards, Ian.

[jim.snowdon]

My experience of Signal Sighting Committees is that they are led by the TOCs, is the drivers (which is sensible) but have no accountability for the costs of any decisions they take, hence the usual principle of "reasonably practicable" ceases to apply, and no one from the project, ie NR, will challenge them, usually for fear that doing something will lead to delay, and incurring delay is less preferable to accepting the cost overrun.

 

Jim

[The Stationmaster]

These days a "Signal Sighting Committee" is usually convened (with a chairman and reps from the signalling designers, Operations and TOC/FOC and possibly others) at the behest of a Project or a report from a TOC/FOC, to review the sighting requirements for particular signals. I can only assume that in the cases quoted above that the banner repeaters have been provided to satisfy a particular issue with a signal. As the process of providing a banner repeater will cost a substantial amount of money, I can't imagine that Network Rail would go to the trouble of providing one on a "whim" if one wasn't really necessary. With their budgets so tight, NR would need proper justification for doing so.

 

Regards, Ian.

 

It's my understanding (might well be wrong of course) that nowadays a banner repeater has to be provided if a signal does not comply with minimum sighting time at line speed.  Which is not quite the same as a Signal Sighting Committee looking at the sighting and saying one is needed (one does of course then have to presume that the members of such a committee understand the proper purpose of a banner repeater, i.e. to give a Driver slightly earlier notice of the fact that a signal is showing a proceed aspect).  

 

Interesting point is that back in the days when I was involved in SPAD mitigation work and meetings we very rarely thought about banner repeaters in the  SPAD mitigation context.

[jim.snowdon]

It's my understanding (might well be wrong of course) that nowadays a banner repeater has to be provided if a signal does not comply with minimum sighting time at line speed.  Which is not quite the same as a Signal Sighting Committee looking at the sighting and saying one is needed (one does of course then have to presume that the members of such a committee understand the proper purpose of a banner repeater, i.e. to give a Driver slightly earlier notice of the fact that a signal is showing a proceed aspect).  

 

Interesting point is that back in the days when I was involved in SPAD mitigation work and meetings we very rarely thought about banner repeaters in the  SPAD mitigation context.

Or, more correctly, giving the driver earlier notice that the signal he is approaching is no longer showing a stop aspect.

 

Jim

[royaloak]

Incidentally I noticed recently that yet another one has now sprouted between Didcot and Reading - for a signal which hasn't moved an inch in over 40 years. and which (and on a lineside which has had ohle masts for the better part of two years).  I reckon for a train slowing to stop at said signal the banner will give the Driver probably an extra 3-4 seconds to release the brake and open the controller, on signalling which has a designed 3 minute headway at line speed.  I'm still waiting for one to appear at a signal west of Twyford which had an offset head from 1961 until it was replaced by a Dorman head about 18 months ago - that would be the ultimate (but line curvature suggests that won't happen, I hope).

Only if the ATP steps up, a lot of the time the signal steps up as we approach it but we still have to brake to get below the release speed as the beacon for the ATP is after the release point, and some signals on plain line have a release speed of 5mph, it is bloody annoying when the signal instantly clears to green but we cant power up for 30 seconds and it just wastes time.

Edited December 5, 2017 by royaloak

[w124bob]

IIRC modern rules dictate that drivers must be able to see the signal aspect for 10 seconds at a minimum when traveling at line speed (reduced to 7seconds for older pre 2000 installations). For the last 5 seconds that view must NOT be interrupted by structures (e.g. OLE masts, platform canopies, bridges, etc.)

 

Where sighting times cannot be met then banner repeaters MUST be used or the line speed reduced so as to bring the time the driver has to observe the signal to within the guidelines.

Macclesfield has a signal on the up main platform which is obscured by the canopy, a 50mph temp speed restriction has been in place for the best part of a decade whilst we wait for a banner repeater to be erected. Since the route up from Cheadle junc is due to be resignalled (by directional) I guess we'll be waiting a bit longer(not holding breath) as it's not seen(pun intended) as a priority due to the 45mph approach through the tunnel.

[big jim]

As a slight aside to the above you wouldn’t believe how many TSRs are now in place due to lack of sighting time for pedestrians on foot crossings, mainly since they have erected palisade fencing at various crossing locations

[The Stationmaster]

As a slight aside to the above you wouldn’t believe how many TSRs are now in place due to lack of sighting time for pedestrians on foot crossings, mainly since they have erected palisade fencing at various crossing locations

 

If they are using temporary restrictions of speed for that purpose somebody in NR is working a fiddle. (explanation available for anyone who may be interested but i sincerely hope that in the meanwhile NR is paying money to any affected TOCs - although I bet they aren't)