Returning semaphores to danger

[AberdeenBill]

Hi all,

 

Was there ever a rule/protocol(?) for how long to wait after a train passed semaphore signals before the signalman/person returned them to danger?

 

Thanks,

Bill

[The Stationmaster]

Hi all,

 

Was there ever a rule/protocol(?) for how long to wait after a train passed semaphore signals before the signalman/person returned them to danger?

 

Thanks,

Bill

 

Yes - several in fact! In very simple terms if it is on a passenger running line a stop signal must only be returned to danger after the entire train has passed it. The reason for this is help ensure that there is no risk of points being moved underneath a passing train (there is also something else which would also stop that but we are looking at all kinds of points, both facing and trailing when we consider signal protection).

 

The opposite extreme is on a line worked under Goods Permissive Block Regulations where the signal has to be returned to danger immediately the loco has passed it. In this case the aim is to avoid the risk of a second train taking the signal at 'off' as applying to it - no doubt resolved long ago as being a much greater risk than anything associated with wagons passing over points.

[PaulRhB]

This is the modern rule book which is derived from the older ones in this respect, see section 4.3 onwards on page 31

http://www.rgsonline.co.uk/Rule_Book/Rule%20Book%20Modules/TS%20-%20Train%20Signalling/GERT8000-TS1%20Iss%205.pdf

[BR60103]

One ex-BR (Sc) signalman told me that their ideal movement was to "chop the tail lamp off the rear".

[Gwiwer]

The guard of a passenger train will also need to be certain that the complete train has passed a signal in a clear position; if not they are required to apply the brakes as the signal may have been reset in response to an emergency or signalling error.

 

Freight guards would be aware of those locations where resetting the signal as the loco passes applies but otherwise the same consideration would apply.

 

A signalman was required to set all signals to danger as soon as they received six bells ("Obstruction Danger") and this might therefore have occurred with a train part-way past the signal in question which could then be stopped by the guard before it reached any obstruction.

[DavidB-AU]

Hull Paragon in 1927 is an example of what can go wrong if you return a signal to danger too early, although it wasn't the only factor involved. The chances of accidentally pulling the only lever that could cause a disaster in the couple of seconds the points were unlocked had to be astronomical.

 

Cheers

David

[beast66606]

The guard of a passenger train will also need to be certain that the complete train has passed a signal in a clear position; if not they are required to apply the brakes as the signal may have been reset in response to an emergency or signalling error.

 

Freight guards would be aware of those locations where resetting the signal as the loco passes applies but otherwise the same consideration would apply.

 

A signalman was required to set all signals to danger as soon as they received six bells ("Obstruction Danger") and this might therefore have occurred with a train part-way past the signal in question which could then be stopped by the guard before it reached any obstruction.

 

A lot of emergency brake applications would have been made if that was the case, certainly around the Wirral from the late 1970s it was not uncommon for the signal to be replaced before the train had completely passed it and the guards didn't panic, although the bobbies tended to adhere to the rule if any facing points were in the route.

 

I believe the "do not replace until the complete train has passed it" rule excluded distant signals.

[Gwiwer]

Custom and local practice may have varied there as much as it did in other locations, Rule Book notwithstanding. What actually happens and is known by the local staff to happen can and does vary from official versions. As is usual with the railway so long as it didn't break a rule it was probably let go.

 

I believe the "do not replace until the complete train has passed it" rule excluded distant signals.

 

Correct. Because a distant signal is not a stop signal and has no indication at which a train may be brought to a halt. They were very often out of sight of the bobby in the 'box or at best at such a distance that precise sighting of the moment a train passed was impossible to determine.

[The Stationmaster]

A lot of emergency brake applications would have been made if that was the case, certainly around the Wirral from the late 1970s it was not uncommon for the signal to be replaced before the train had completely passed it and the guards didn't panic, although the bobbies tended to adhere to the rule if any facing points were in the route.

 

 

 

The explicit requirement for Guards to observe signals has long gone out of the Rule Book and was definitely no longer there by the mid 1970s - for a variety of reasons including removal of lookout facilities from passenger brake vans and Guards having to deal with other duties such as ticket examination.

 

The only subsequent - and more recent change - is for Guards to observe the aspect displayed by any platform end etc signal where they are responsible for giving the driver the right-away (introduced to mitigate against the possibility of a 'ding-ding-and away' SPAD).

[Gwiwer]

Although there were lots of semaphores still around in the mid 70's there was also a significant shift to what was usually then called MAS (Multiple Aspect Signalling, aka Traffic Lights) which of course eliminated many manual boxes, a not insignificant number of jobs and did away with the need to lower the arm as the train passed.

 

(introduced to mitigate against the possibility of a 'ding-ding-and away' SPAD

The same logic was applied to justify a need for the not inconsiderable cost of fitting DRA's and the slightly lesser cost of installing what seems to the average passenger to be faintly ridiculous instruction signs to "Observe Signal Aspect". One would hope that anyone qualified to drive a train would know they are required to do this!

[beast66606]

I've never seen a railway signal show Amber or Red and Amber together (aside from when the aspect changes) so I don't think the traffic light comparison holds water.

 

The major power box schemes were in the 1960s and early 1970s, through the later 1970s the old order, somewhat decrepit at times, was still holding sway, then more power/simplification schemes came along and swept another lot away.

 

The WCML North of Nuneaton retained a lot of manual boxes to work the colour lights - although a lot of these have now gone - so not all MAS were/are worked from power boxes.

[Edwin_m]

The same logic was applied to justify a need for the not inconsiderable cost of fitting DRA's and the slightly lesser cost of installing what seems to the average passenger to be faintly ridiculous instruction signs to "Observe Signal Aspect". One would hope that anyone qualified to drive a train would know they are required to do this!

 

According to the cost benefit analysis at the time, if used properly the DRA would pay for itself in savings from accident damage never mind the safety benefit. When it was first thought about then Bellgrove and other ding-ding-and-away accidents were fairly recent memories. While train drivers have historically had an excellent record in obeying signals - how many road drivers have never gone through a red traffic light? - the consequences of the occasional error can be severe.

 

Since DRA, TPWS and other SPAD reduction and mitigation measures were introduced in the 90s, rates of serious SPADs and SPAD-related accidents have reduced significantly while the number of trains has increased, so something must have been done right...

[LNERGE]

At one time colourlights were arranged to 'last wheel replace' so the guard didn't see the signal change aspect. In my set up here all the colourlights between Cambridge and March were last last wheel replacement. Later the rules were changed and this left us with an unusual signal at Ely North Junction. No40 (down March Starter) was controlled from red to yellow by ENJ. Yellow to green was controlled by Chettisham as the down main distant (14 lever) The ENJ circuits were arranged for last wheel replacement and the Chettisham circuit were arranged for first wheel... If the signal was showing green when a train passed it went from green to yellow and as the last vehicle cleared the approach track the signal reverted to red.

[The Stationmaster]

According to the cost benefit analysis at the time, if used properly the DRA would pay for itself in savings from accident damage never mind the safety benefit. When it was first thought about then Bellgrove and other ding-ding-and-away accidents were fairly recent memories. While train drivers have historically had an excellent record in obeying signals - how many road drivers have never gone through a red traffic light? - the consequences of the occasional error can be severe.

 

Since DRA, TPWS and other SPAD reduction and mitigation measures were introduced in the 90s, rates of serious SPADs and SPAD-related accidents have reduced significantly while the number of trains has increased, so something must have been done right...

 

Exactly so although in retrospect some of the mitigation measures did seem a bit OTT at the time - but a lot of effort was put into SPAD reduction (and still is so I understand) and they seem to have worked.

 

Mind you having said only a week ago I was a passenger in a train which was involved in Category 1 SPAD which even with TPWS (which I suspect was the thing that did the effective part of the braking?) might have resulted in a near head-on collision if the timing had been somewhat different. Thus the onus has in some respects been placed on the S&T engineer and SPAD mitigation process to ensure that any potential over-run avoids potential collision risk.

[The Stationmaster]

At one time colourlights were arranged to 'last wheel replace' so the guard didn't see the signal change aspect. In my set up here all the colourlights between Cambridge and March were last last wheel replacement. Later the rules were changed and this left us with an unusual signal at Ely North Junction. No40 (down March Starter) was controlled from red to yellow by ENJ. Yellow to green was controlled by Chettisham as the down main distant (14 lever) The ENJ circuits were arranged for last wheel replacement and the Chettisham circuit were arranged for first wheel... If the signal was showing green when a train passed it went from green to yellow and as the last vehicle cleared the approach track the signal reverted to red.

 

I suspect practice is not always like that - for instance on the Western comparatively few signals are shown on Locking Charts as 'LWR' (Last Wheel Replacement)and its use is more for locking reasons than than the Guard watching the signal (although I could understand that on much older schemes).

 

However the contrary problem is that on many WR 1960s autos the signal does not return to danger until the track circuit in advance of the overlap tc is occupied. In some places this results in the rather worrying situation of a short train having passed out of sight and the signal still displaying a proceed aspect

[LNERGE]

I found myself on a callout after our staff had disconnected the signalling gear on an auto section ready for relaying work. When i turned up there was no track next to a signal and it was showing green. Just about everybody and his dog were demanding to know why... The section for relaying stopped short of the overlap and all the signalling gear was intact beyond the block joint. I'm not sure i had convinced everybody it was actually working ok but i keyed it to danger to ensure a quieter night..

[phil-b259]

However the contrary problem is that on many WR 1960s autos the signal does not return to danger until the track circuit in advance of the overlap tc is occupied. In some places this results in the rather worrying situation of a short train having passed out of sight and the signal still displaying a proceed aspect [/i]

 

This is common practice now with auto sections and as you say, will result in a signal not returning to red untill the leading vhicle is 200 yards beyond it (i.e. hits the next track circuit). Controlled signals however (i.e. where the signalman has to set a route for the signal to clear) usually have a additional short track circuit that starts 10 yards beyond the signal and runs up to the 200 yard point which will replace it to red as soon as the leading vhicle passes the signal.

[beast66606]

However the contrary problem is that on many WR 1960s autos the signal does not return to danger until the track circuit in advance of the overlap tc is occupied. In some places this results in the rather worrying situation of a short train having passed out of sight and the signal still displaying a proceed aspect [/i]

 

Not just 1960s WR

[Edwin_m]

Having a single track circuit per signal in auto sections simplifies the logic and importantly halves the number of track circuits and therefore of track circuit failures. First wheel replacement is pretty much standard for colour lights, the only exceptions I can think of are where propelling is common (eg south end of Derby) and I believe in the tunnels under Glasgow, though I can't remember why.

 

TPWS was never intended to prevent all SPADs, rather to prevent or mitigate a good proportion of serious SPADs consistent with remaining a relatively simple system. I was involved in a small way in a SPADRAM study in the mid-90s which examined accident reports from the previous few decades to determine whether TPWS would have prevented or mitigated the accident, concluding that it would have prevented some 69% of "ATP-preventable" fatalities. This figure was sneered at by Uff and Cullen but the declining casualty rate since then suggested it was pretty much spot on!

[beast66606]

First wheel replacement is pretty much standard for colour lights, the only exceptions I can think of are where propelling is common (eg south end of Derby) and I believe in the tunnels under Glasgow, though I can't remember why.

 

Some appear to be last wheel because its of a combined berth and overlap, a train passes a signal and then the signal is returned when the wheel strikes the berth for the next signal, which starts at the overlap for the one it's just passed - i.e it's 200yds past the signal, this can give the appearance of last wheel.... Liverpool approaches from Allerton work this way.

[flyingsignalman]

The signals in the Sandhills station to Bootle Junction and to Kirkdale South Junction on the Merseyrail Northern lines are last wheel replacement as propelling moves used to be authorised for stock to and from Horwich Works from Kirkdale depot. Everywhere else is first wheel replacement.

 

The sectional appendix used to have a local instruction for Manchester Victoria advising drivers of banking engines to be aware of the fact that the signals would revert to danger before the banking engine would pass them.

[Pacific231G]

I live fairly near the junctions controlled by Greenford East box- the last WR box controlling lower quadrant signals in London apparently- and until the two nortbound junction semaphore brackets (GE52/63 & GE22/51) were replaced with a single three way junction CLS it was quite interesting to see the variation in operation. With some signallers the two signals would remain clear, after the northbound Greenford train had passed until the signals were pulled off for its southbound return. Some signallers though seemed to return them to danger fairly soon after the train had passed. It's much harder to see what's going on northbound with the new CLS unless you're actually on the platform at S. Greenford but there still seems to be a fair variation in the time before clearing the south bound semaphores. Obviously nothing else could enter the junction from the south until the next route was set so it wouldn't matter particularly when they were returned to danger but I did wonder if there was any good practice about this.

Greenford East is a mechanical box but some of its signals are CLS and there's more on it on http://www.roscalen.com/signals/Greenford/index.htm

though that page hasn't been updated since before the new CLS was activated. The CLS was installed because of subsidence problems on the embankment and the GE52 arm was prone to showing a rather vague half way indication when it was pulled off.

[Edwin_m]

First wheel replacement is pretty much standard for colour lights, the only exceptions I can think of are ... and I believe in the tunnels under Glasgow, though I can't remember why.

 

Thinking back I now believe I was wrong on Glasgow. They are either replaced as the cab passes the signal (with separate overlap track circuits) or approach lit and therefore extinguished as the train passes them. The reason quoted to me many years ago was to do with the green glow from the signals reflecting down the train side and tunnel walls and possibly confusing the driver of a following train.