Signals - Present-Day Semaphore, Lights and Repeaters

[The Stationmaster]

8 hours ago, david.hill64 said:

Mike, Are you sure that was the conclusion? The issue with 14X and 15X not activating track circuits is usually ascribed to the superior wheel-rail interaction characteristics of these vehicles compared to the DMU's they replaced. The later designs lost much less energy at the wheel-rail interface than the older designs: hence lower wheel wear/ lower rail wear and better ride. The downside is that if you are not scrubbing the muck off the rail head you run the risk of not shunting the track circuits as the resistance is too high.

David

That was what the report they sent to Swindon said as I took the opportunity to read it.   I can't remember the numbers but the percentage of ime that contact was not being maintained was considerable.   The tests were carried out well our tside the leaf fall season but the Exmouth branch was wholly converted to 142 operation so what you say might well be a factor.  Whether or not the 142s had a habit of disappearing from track circuits elsewhere I don't know and I can't recall if there was anything unusual about the track circuits on the Exmouth branch,  But there was also quite a catalogue of trains 'disappearing on track circuits elsewhere in the West of England - not just on lines solely used by the 142s

 

Apparently it was something to do with the springing and damping rate in the springing.   But without asking if something could be done  the WR had already made up its mind they wanted shot of the trains anyway and this turned out to be a convenient  'reason'.

 

 

[melmerby]

6 hours ago, Rugd1022 said:

Banbury when it was a nice mix...

 

 

 

Is it normal to remove the green spectacle, when a distant is converted to fixed as this one obviously is ?(no pull off wire)

[iands]

4 minutes ago, melmerby said:

Is it normal to remove the green spectacle, when a distant is converted to fixed as this one obviously is ?(no pull off wire)

Yes, is the simple answer. 

[Michael Hodgson]

6 hours ago, Rugd1022 said:

Banbury when it was a nice mix...

 

 

Whilst by no means unknown, that combination of a colour light and a semaphore side by side is relatively unusual, and is usually the result of piecemeal replacement of life-expired or damaged signals, although that practice is now out of favour.  If a locality needs resignalling, colour lights would be used throughout of course, but these days if a single semaphore needs replacement, in recent years has generally been replaced with a brand new semaphore,

 

When semaphores were still it by oil lamps, there could be a risk of "reading through", that is taking the next (colour light) signal in advance showing a proceed aspect overpowering the intervening dimly lit semaphore which might be at Danger for good reason.  The engineers had to take care to avoid the risk by not replacing certain home or starting signals with colour lights; it became less of an issue if intensified lamps were fitted to surviving semaphores.  Like for like replacement is easier as a change in technology involves more design and planning effort and can necessitate locking changes.

[The Stationmaster]

6 hours ago, Wickham Green too said:

Since the invention of Token or Staff working of single lines it has always been a requirement to be in possession of the Token or Staff ( or Ticket ) before entering the section - so how does this differ ?

 

5 hours ago, Mike_Walker said:

We had Stop signs like that at BE when the points were simply worked by a manual lever frame.  That was replaced by powered points worked from a Ground Switch Panel and the signals, sorery, points indicators were installed as part of that.  As they are not technically signals it's the wording on the Stop board that takes priority.

Technically it's not exactly like that becauses you can't have two signals which give conflicting instructions to a Driver.  The history of providing STOP boards in this sort of situation goes back partially into some NSKT problems where Drivers were forgetting to obtain the token    Plus what happened with NST(R) where there was a need to create a sort of fake Station Limits/Clearing Point at. crossing places.

 

Thus the history of this type of STOp board is actually not necessarily so much as an instructions but in some situations very much as a reminder.  This no doubt is what is really meant at Bourne End because without knowing the latest details there I presume that the signal can give a proceed aspect independently of the token or train staff working.  So in reality the board is more of a 'stop and think again' (have you got the token or staff?) board rather than the absolute Instruction not to proceed (which is conveyed by the red signal aspect).

 

It is unusual in effectively having two things which say STOP when only one is necessary to indicate to a Driver that he has no authority to proceed.  Hence it is only  'reminder' element provided by the board.  The SPAD comment is interesting because if a Driver has a  proceed aspect from the colour light signal he has not committed a SPAD but if the Driver proceeds into the section without the relevant token or train staff that is a different safety of the line matter on its own account.  

 

The confusion really arises from the provision of two signals which say 'stop' and the fact that they can give conflicting indications.  That would be avoided by using a points indicator serving no other function or retaining the main aspect signal and altering the board to read 'Obtain Token or Train Staff Before Proceeding'.

 

Coming back to Wickham Green's question the simplistic answer is 'no'. There were (and might still be without checking the latest Regulations) certain situation in everyday working (i.e. not an emergency) where a movement could proceed into a single line section with the visible authority of a train staff or token etc (sse personal example below).  And of course there were various emergency situations where smething similar could happen under certain circumstances.  

 

Example - On one occasion I instructed the Driver of a 10 coach passenger train to pass a signal at danger to propel his train into an 11 mile long token worked single line section a few minutes after a passenger had set off into the same section (that train of course had the token).  He refused to move so I had to go the signal box, borrow its copy of the General Appendix and take it back to the Driver and read to him the relevant Instructions ('never heard of that.before').  But he was an Old Oak Common man so token worked single lines were a bit off his regular stamping ground although he signed the road.  So he duly set back and, for a few minutes, we quite legitimately had two loaded  passenger trains in a token worked single line section at the same time.

 

But in normal working for train running in the right direction completely througfh a single line section the Driver was required to be in possession of the token, tablet, train staff or train staff ticlet, etc when such a system of signalling was in use.

Edited May 15, 2023 by The Stationmaster

[melmerby]

43 minutes ago, Michael Hodgson said:

Whilst by no means unknown, that combination of a colour light and a semaphore side by side is relatively unusual, and is usually the result of piecemeal replacement of life-expired or damaged signals,

An already replaced signal. It is an UQ from the days of the LMR, having presumably replaced a GWR style LQ.

[The Stationmaster]

One of my many photos of Reading.  This one was taken in 2012 during the transitional stage of Reading rebuilding and resignalling but at this time - March that year - the original 1965 resignalling signals in this part of the station were mostly where they had been erected 47 years preb viously.  Even numbers so Down direction signals but numbered in this case in the 3XX series to distinguish them from Mian Line and Relief Line signals.  Also note they had been renumbered with control te transferred to TVSC at Didcot but basically at this stage on the original layout.

 

The signal at extrenme right - on the smaller span version of the two Reading designs of colour light signal gantry - is what was R38, now TR38.  The blue faced SPAD Indicator signal just in advance of it carries the same number.  The next three signals reading towards the left are TR338 - removed some years earlier to its ground mounted position to allow longer trains to use Platform 3 .  Then what the WR did when it had run out of using the same final part of the number three or four times (with different prefix numbers) was to step up to the next number - so we have on the bracket structure TR340 (for Platform 2), then at extreme left TR342 for Platform 1.  

 

The bracket structure ss the standard Reading design gradually refined in detail between c.the mid 1950s and the early 1960s but it extends an un unusually longer distance than normal either side of the upright in order to (originally) cater for all three of the bay lines.  It repaced a rather nice semaphore three doll bracket and I have got a photo of that as well -stashed awaty with my older signal photos from the 1960s.

 

 

 

 

[The Stationmaster]

16 minutes ago, melmerby said:

An already replaced signal. It is an UQ from the days of the LMR, having presumably replaced a GWR style LQ.

Not an exact replacement by any means as that line was originally the Up Goods with a substantial number of connections from the yard plus a facing connection. to the Up Main.  The nearest signal to that site was probably an ordinary straight post signal with a 3ft arm and maybe at one time had a Goods 'ring' on the arm - and no lower arm distant for Banbury South.

[The Stationmaster]

A rather distant view of TR114 (at that time on its 3rd number in almost 51 years reflecting two lots of signalling alterations which it sailed through almost unmolested losing only its original Position 4 JI and a change of 'phone cabinet).  The bracket structure is an example of the smallest version in Readings range of designs and examples were fairly few in number - note there is no ladder.  Alas this signal went teh way of all good things following the platform extension to cater for Crossrail trains and one of the fold-down 'lollipop' things was erected at the end of the platform - slightly reducing the braking distance to the next signal in advance (the signal in rear of it is, presumably, still 4 aspect ).

 

But what the photo does show is the Dorman head equivalent of a 'hot strip' in the lens with the upper left quadrant much brighter at this angle than the rest of the LEDS

 

 

 

 

 

 

 

 

 

[Coach bogie]

7 hours ago, Michael Hodgson said:

Whilst by no means unknown, that combination of a colour light and a semaphore side by side is relatively unusual

 How about on the same post. Belasis Lane outer home with Billingham colour light distant below. Distant only illuminates when home is off. Originally a combined semaphore home and distant, the home was moved down to the distant mounting when the light distant was installed. Eventually replaced with a lower post, it was recently swept away when the Tees to Sunderland line was upgraded. Though there is little evidence left, there was a station platform on both sides of the line, between both signals served by workmen only trains until 1961.

 

Mike Wiltshire

 

Edited May 16, 2023 by Coach bogie

[Northmoor]

I hope as much of this recently-replaced equipment as possible, has been saved for preservation

[phil-b259]

On 14/05/2023 at 10:54, Michael Hodgson said:

 

The platform on that bracket doesn't look ideal for anybody working on the signal - you'd have to squat at floor level to fiddle with the innards as its position is by your boots.  Not that I imagine it needs much maintenance.  Excellent photo, but it's plated TLW 10 & 12, not 1o & 11 as per the caption by the way.

 

The LED units are sealed boxes which require no maintenance plus cannot be repaired outside of a factory setting and are connected with plug coupled cables. If one requires replacement then its a quick wip the old one out put the new one in type job.

 

In fact many of these sort of signals now only require basic maintenance checks every 5 or 6 years - with NR no doubt wanting to push it out further if they can.

 

 

NB At present there is a yearly check to make sure the structure is secure as a result of an incident a few years ago at Newbury where a corroded post (with the corrosion hidden by ballast) failed and dropped the entire signal across the down line in the early hours of the morning. Fortunately a passing up train called it in because otherwise nobody would have known anything was wrong till a down train collided with the now horizontal post. https://www.gov.uk/raib-reports/collision-with-a-collapsed-signal-post-at-newbury

 

 

[Michael Hodgson]

20 minutes ago, Northmoor said:

I hope as much of this recently-replaced equipment as possible, has been saved for preservation

Very little of the traditional colour light stuff I suspect, although the remaining semaphores are more likely to found good homes. 

 

It depends on the preservation S&T people having contacts with their opposite numbers on the big railway and knowing what's going to happen when - and being able to turn up with suitable transport on the right day  (which is always subject to the goalposts being moved).  Fortunately the day job of some S&T people in the preservation movement often happens to be something similar on the big railway, so their work on preserved lines is something of a busman's holday.

[phil-b259]

13 hours ago, Michael Hodgson said:

 

This delay between the feather lighting and the aspect clearing seems to be of the order of half a second to a second - but note that this applies to relay based interlocking and traditonal filament lamps.  LED signals and electronic locking operate a lot faster and I have not noticed any delay.

 

 

Actually SSI is usually SLOWER than a Relay based interlocking!

 

Thats because:-

 

(1) BR SSI was designed in the late 1980s and computers / data transmission of that data and age were SLOW. Though computers may have increased in speed since then, the need (until relatively recently*) to make sure modern signalling kit was 'backwards compatible with stuff from previous decades meant in practice there was no performance increase from more modern computers.

 

(2) With an SSI installation the data that the route indicator is lit has to be passed all the way back to the signalling centre then back again which can easily be hundreds of miles. By contrast a relay interlocking will have all the signals it controls within a couple of miles of it (because voltage drop on the 50V used for signalling circuits becomes to great).

 

Typically where relay interlockings are used, then what you get is a bunch of individual relay rooms at places where there are 'islands' of  pointwork and controlled signals - with many miles of plain line 'automatic working) in between (which has no interlocking running it and which the signaller does not control!)

 

With SSI or its modern equivalents then the interlockings are all in one place (usually the signal centre) and there are no relay rooms scattered along the track and no 'automatic' sections

 

 

* The introduction of advanced trackside modules by Siemens and Alstom has meant significant improvements in speed are now possible when combined with their latest computer based interlocking - though it should be noted that said modern interlockings can still made to interface with trackside stuff designed to late 1980s BR SSI standards if required - albut with rather pedestrian performance as a result.

 

[melmerby]

55 minutes ago, Coach bogie said:

 How about on the same post. Belasis Lane outer home with Billingham colour light distant below. Distant only illuminates when home is off. Originally a combined semaphore home and distant, the home was moved down to the distant mounting when the light distant was installed. Eventually replaced with a lower post, it was recently swept away when the Tess to Sunderland line was upgraded. Though there is little evidence left, there was a station platform on both sides of the line, between both signals served by workmen only trains until 1961.

 

Mike Wiltshire

 

Why leave the distant dark when the UQ is on?

Surely if it is a distant it would be logical to just duplicate what the equivalent semaphore would show?

[Dagworth]

6 minutes ago, melmerby said:

Why leave the distant dark when the UQ is on?

Surely if it is a distant it would be logical to just duplicate what the equivalent semaphore would show?

Because at night the yellow aspect would wash out the red of the semaphore giving a false impression of a proceed aspect.

 

Andi

[melmerby]

6 minutes ago, Dagworth said:

Because at night the yellow aspect would wash out the red of the semaphore giving a false impression of a proceed aspect.

 

Andi

Was it always like that or was that based on experience?

[Grovenor]

When that arrangement was introduced there was already many years experience with both types of signal so the likely effect was pretty obvious. 🙂

[david.hill64]

7 hours ago, phil-b259 said:

 

With SSI or its modern equivalents then the interlockings are all in one place (usually the signal centre) and there are no relay rooms scattered along the track and no 'automatic' sections

 

I am not disputing this as I don't have recent experience on main line signalling, but on metros it is usual to have a single central control centre (usually with a separately located back-up which may or may not be a hot standby). The interlockings though are distributed, mostly because there is a practical limit to the length of cabling between a switch machine and its object controller, which is part of the interlocking. If the cable is too long the voltage drop is such that the current needed to throw the switch is likely to fry the controller. I would be interested to understand how this problem is overcome on main lines especially as we move to fewer larger control centres.

 

On the systems I dealt with the cycle time of an interlocking controller was just over half a second, so it would take over a second from receiving a command to acting on it and then sending proof back that the command had been successfully implemented.

[phil-b259]

14 minutes ago, david.hill64 said:

I am not disputing this as I don't have recent experience on main line signalling, but on metros it is usual to have a single central control centre (usually with a separately located back-up which may or may not be a hot standby). The interlockings though are distributed, mostly because there is a practical limit to the length of cabling between a switch machine and its object controller, which is part of the interlocking. If the cable is too long the voltage drop is such that the current needed to throw the switch is likely to fry the controller. I would be interested to understand how this problem is overcome on main lines especially as we move to fewer larger control centres.

 

On the systems I dealt with the cycle time of an interlocking controller was just over half a second, so it would take over a second from receiving a command to acting on it and then sending proof back that the command had been successfully implemented.

 

A computer based interlocking (be it old school BR SSI or one of the more modern equivalents works) by a central computer interlocking accessing remote modules over secure telecoms links with each trackside module being given its own address and suitable locally provided power supplies to drive whatever is connected to it.

 

Because the information being exchanged between the two is in the form of secure digital codes rather than mere voltages there is no physical or practical need to have remote interlockings so current practices tends to have them concentrated in one place (which has the advantage that you can then justify having a dedicated technician to look after them all - particularly in this day and age when additional protection with techs applying controls like occupying track circuits to prevent routes being set etc is increasingly being mandated by the safety authorities).

 

Relay based interlockings are, as you say, limited by the issue of voltage drops - which can only be alleviated with repeater relays every mile or so. This is both expensive and uses more cabling plus introduces more points of failure so what you get with these is lots of individual interlockings housed in their own relay rooms at strategic intervals along the scheme. 

 

 

 

 

[david.hill64]

16 minutes ago, phil-b259 said:

 

A computer based interlocking (be it old school BR SSI or one of the more modern equivalents works) by a central computer interlocking accessing remote modules over secure telecoms links with each trackside module being given its own address and suitable locally provided power supplies to drive whatever is connected to it.

 

Because the information being exchanged between the two is in the form of secure digital codes rather than mere voltages there is no physical or practical need to have remote interlockings so current practices tends to have them concentrated in one place (which has the advantage that you can then justify having a dedicated technician to look after them all - particularly in this day and age when additional protection with techs applying controls like occupying track circuits to prevent routes being set etc is increasingly being mandated by the safety authorities).

 

Relay based interlockings are, as you say, limited by the issue of voltage drops - which can only be alleviated with repeater relays every mile or so. This is both expensive and uses more cabling plus introduces more points of failure so what you get with these is lots of individual interlockings housed in their own relay rooms at strategic intervals along the scheme. 

 

 

 

 

Thank you. So essentially the object controller is divorced from the interlocking module. I think I probably knew that at one time but it's over 20 years since I was involved with main line practice. But I do remember now reference to track side modules. More recently on all of the MRT signalling projects that I have been involved with, there are a number of solid state interlocking centres spread around the system, located within 1km of the objects they control. Because MRT stations are close together it is convenient to do it this way.

 

Edit to make clear that the interlockings are modern!

Edited May 16, 2023 by david.hill64

[phil-b259]

1 hour ago, david.hill64 said:

Thank you. So essentially the object controller is divorced from the interlocking module.

Correct - and it remains true*, from BR SSI through to latest Siemens and Alstom products.

 

For example all the old relay interlockings scattered in their own buildings throughout south London (installed as part of the 1980s Victoria Area resignalling scheme) are being replaced with computer based interlockings all sites within Three Bridges ROC building many miles from the trackside modules they talk to..

 

 

* There might be a few exceptions - but these will either be experimental installations (like the first SSI which went in at Lemington Spa) or temporary / partial jobs.
 

Examples of the latter would include Kings Cross BEFORE the latest remodelling where the origional 1970s relay based interlocking was renewed with a computer based type in the 2000s but none of the external signaling was touched and all the signal modules were simply mounted in the same relay room as the interlocking so as to feed the multicore cables going out of building to operate trackside relays. All done away with under the latest remodelling - the interlocking sits at York ROC now and it feeds trackside modules directly from there

[Rugd1022]

More from Banbury...

 

 

 

 

 

[iands]

A bit later than planned, but here are a few photos of semaphores that disappeared from Sleaford within the last few years.

 

Sleaford West SW20 Up Main towards Rauceby.

 

Sleaford West SW25 Shunt Spur to Siding/Up & Down Local

 

Sleaford West SW16 Siding to Shunt Spur

 

Signal on left (Down/Up Joint from Sleaford North): Top arm SW5; Middle arm SE2; Bottom arm SW9. Signal on right (Down Main from Rauceby): Top arm SW3; Middle arm SE2; Bottom arm SW7. Both signals also have Theatre type route indicators.

 

Same two signals seen from the rear.

 

 

[Rugd1022]

Another view of the old GWR gantry at the south end of Oxford station, taken at silly o'clock on 17th February 2017...

 

 

An example of the 1967 installed colour lights at Padd, taken in March '1989, now long gone...

 

 

 The up end of Truro station in August 1989...