125mph with 3-aspect colour light signalling

[The Planner]

Most of it south of Crewe could do that now, but wouldnt give you 20% you could utilise.

 

[LNW-GW Joint]

True, but I believe it was designed for 140mph. Signals spaced closer for 125mph might allow 2 1/2 minute headways, nearly a 20% increase in capacity.

Not 140mph surely, that was the Railtrack moving block idea that died along with Railtrack.
140mph would now be with ETCS (which will also supersede GW ATP eventually), and might give you better headways too.
Although we still have Virgin's desire for 125+mph with 390s, probably too late now with HS2 in prospect.

 

[pt_mad]

Get the feeling that was part of the arguement for HS2. Only part. That speeds on the WCML couldn't realistically exceed 125mph now. That seems to be broadly accepted .

 

[Taunton]

When the HSTs were introduced in the GWML, wern't two drivers required at all times up until the early 1990s?

Required over 110mph if I'm correct?

Correct. When the HSTs started, 125mph had two drivers and AWS, and subsequently ATP was installed as well as a pioneer installation on the eastern end of the line.

Eventually the two drivers requirement was indeed removed in the early 1990s, as you describe. But there were still the other measures, which had been used in justification of going down to single driver.

Then the ATP installation fell into disuse, as the first privatisation TOC contract had not stipulated it, so the training etc was not continued, although train and track were still fitted. But there was still AWS.

Then the compulsory AWS 125mph requirements were relaxed. I'm not sure, but I think it was justified on the basis that there were two drivers . If failed, the "signalman was to be advised", to take extra precautions. And, if possible, the set was to be turned on a triangle so the failed unit was trailing.

Railtrack saw turning on a triangle, eg at Landore if leaving Swansea with a failed AWS, as an "extra movement". For which they made an extra charge. So it was thus seen as not possible.

The procedure for "advising the signalman" was very casual, the driver just informed control, who had no formal procedure for passing this on, or what the signalman should then do.

So. 19 September 1997. Train leaves South Wales with known failed AWS, not turned at Landore to run good cab forward, one driver, not trained in ATP operation, so switched off. Message sent to control about the AWS was just scribbled on a Post-It and nothing more was done with it. Running at full 125mph approaching Southall in 4-aspect territory. No second driver looking out. No working ATP. No working AWS. No message to signalman to take extra precautions if making a crossing movement in front. You know the rest.

 

[MichaelAMW]

...so are these things red railway signals that can actually be passed at danger without a calling on aspect? Just a note that it is a repeater - which must be unique to LU! I believe BR introduced banner repeaters precisely so that there would never be a situation where a conventional signal was passed at danger without a special authorisation.

No, they are yellow green, sometime with "F" superimposed on the yellow, so they are distant signals in the usual language, but also repeaters as they exactly repeat the stop signal to which they apply, albeit with different colours. As implied, they use to switch them on only in poor visibility, when driving on sight was prevented, but now they are appparently on all the time. On the higher-speed sections, e.g. the Met main line and that non-stop Piccadilly bit, there are also proper repeater signals that are distant signals in the usual sense, used when the stop signal is not visible from far enough away - occasionally also in slow-speed sections in tunnels were sighting is poor, e.g. sharp curves. The fog repeaters are of a different design, most obvious they don't have a lens hood as weren't intended to be used in the sunshine. (I'm partly repeating bionic and Taunton here.)

 

[MichaelAMW]

Correct. When the HSTs started, 125mph had two drivers and AWS, and subsequently ATP was installed as well as a pioneer installation on the eastern end of the line.

Eventually the two drivers requirement was indeed removed in the early 1990s, as you describe. But there were still the other measures, which had been used in justification of going down to single driver.

Then the ATP installation fell into disuse, as the first privatisation TOC contract had not stipulated it, so the training etc was not continued, although train and track were still fitted. But there was still AWS.

Then the compulsory AWS 125mph requirements were relaxed. I'm not sure, but I think it was justified on the basis that there were two drivers . If failed, the "signalman was to be advised", to take extra precautions. And, if possible, the set was to be turned on a triangle so the failed unit was trailing.

Railtrack saw turning on a triangle, eg at Landore if leaving Swansea with a failed AWS, as an "extra movement". For which they made an extra charge. So it was thus seen as not possible.

The procedure for "advising the signalman" was very casual, the driver just informed control, who had no formal procedure for passing this on, or what the signalman should then do.

So. 19 September 1997. Train leaves South Wales with known failed AWS, not turned at Landore to run good cab forward, one driver, not trained in ATP operation, so switched off. Message sent to control about the AWS was just scribbled on a Post-It and nothing more was done with it. Running at full 125mph approaching Southall in 4-aspect territory. No second driver looking out. No working ATP. No working AWS. No message to signalman to take extra precautions if making a crossing movement in front. You know the rest.

Sounds like a classic example to illustrate what the Swiss Cheese model is all about - does the railway interest itself in this?

https://en.wikipedia.org/wiki/Swiss_cheese_model

 

[ComUtoR]

From an investigation perspective. CAT A (I'm aware of the current rating system) SPADs all have the correct sequence leading up to the Red. Drivers reset the AWS so regularly that they are often ignored and often simply forgotten about. Even having the sunflower doesn't mean the Driver notices or acts upon the warning. For whatever reason the AWS/Sunflower is pushed to low priority due to the various human factors. Even when I pass a Red due to other reasons, the first thing I check is the sunflower, even though I am fully aware of what happened and even being aware that I just had the AWS for the Red I'm flying past at linespeed.

There is a phenomenon (I forget what its called atm) but it highlights what I'm saying.

(for old school watch wearers)
Have you ever noticed that you will almost always check your watch when someone asks you the time ? Even when you have just checked it ?

That's what happens with the AWS. You get the horn, use the press and call technique, and then it can be instantly dismissed and put to the back of your attention. Thankfully the AWS is backed up with TPWS. For the more technical forumites amongst us. Would their be a greater use of TPWS overspeeds in 3 aspect, high(er) speed lines ?

 

[Mugby]

What determined 3 aspect or 4 aspect signalling when it was originally installed wasn't linespeed, it was density of traffic.

 

[Taunton]

Drivers reset the AWS so regularly that they are often ignored and often simply forgotten about. Even having the sunflower doesn't mean the Driver notices or acts upon the warning.

Some may not be aware of the Signal Repeating AWS (SRAWS) experiment of the 1970s, on the Bournemouth-Southampton Up line, which the east end cabs of the 4-REP units (which always led REP/TC combinations eastbound) were fitted with, as well as trackside. An extra panel for the driver showed the last of the four aspects, and there were three acknowledgement buttons alongside the restrictive aspect lights which had to be acknowledged appropriately, instead of the normal AWS single button. I think there were different warning tones for the different aspects as well. It was an excellent advance on traditional AWS, which is nothing more than the original GWR 1910 concept, and unfortunately fell to one side just because of personalities; it was a Southern Region instead of BR Headquarters idea.

Even the GWR on steam locomotives managed differentiated AWS warnings between single and double yellow by the 1940s, with the track ramp fed positive current for clear, negative current for double yellow, and no current for single yellow, which gave either the bell, double hoot or single hoot on the locomotive as appropriate.

 

[driver_m]

The 140mph was meant to be for moving block signalling though. Not conventional 4 aspects.

 

[WrongRoad]

90mph past some single yellows on the Portsmouth via Guildford line.

 

[Dieseldriver]

Except if they had sneezed past a yellow aspect they would have acknowledged an AWS warning. If they had a green the signal previously then they know they have just passed a yellow and brake accordingly. If they are still somehow unsure (unlikely) then i'd expect them to act as though they had a cautionary aspect.

Regardless of this it's extremely unlikely anyway given the vast majority of signals are sighted for a few seconds beforehand, it would need to be a lengthy sneeze.

Could have been checking timings/diagram, could have been distracted by Pway or something unusual catching his eye. Could have been fatigued and had a lapse in concentration. The end result would still have been the same.
Let's make this clear, we are talking about a lone Driver driving a train at 125mph with no working AWS. That is the concerning part.
Believe me, until you have driven trains day in day out, you will never fully understand just how easy it can be to cause an incident of varying levels of severity, no matter how alert or professional you are.

 

[AndrewE]

I don't think anyone has actually said

driving a train at 125mph with no working AWS.

It's just a yellow with little sighting time before a potential red.

 

[edwin_m]

...but perhaps not so aware of the AWS horn (or its modern equivalent) and the visual indicator/reminder that you have just passed a signal with a restrictive aspect. The horns used to be deafening, especially if you were an extra person stood up in the cab with your back to the engine-room bulkhead!

If the horn is missed and the button not pressed the brakes would go on. I'm sure if the horn was inaudible then drivers would complain and something would be done.

If the ATP reactivation had been done fully Ladbroke Grove would not have happened.

Only if "reactivation" had included fitting ATP to the Thames Train that SPADded, which was never intended to be so fitted. The GW train was under clear signals and going too fast to stop whatever the ATP might have done in the short time available. In fact TPWS would have prevented Ladbroke Grove, but the request for funding was still sitting on Prescott's desk.

Another capacity disbenefit of three-aspect on high speed routes is that if the driver sees a single yellow they have to assume the next signal is red and approach it accordingly. If they are just catching up a train in front the signal will probably have cleared by the time it comes into view, but if its sighting is a bit short the train might be down to 20mph or so. With four-aspect it's quite possible that the initial slowing at the double yellow will be enough that the signal where the driver expects a single yellow will have cleared to green by the time they see it, so the loss of speed is that much less.

 

[43096]

Question (which I have asked elsewhere and not got an answer): when was the last UK rail accident resulting in at least one fatality that could only have been prevented by ATP i.e. TPWS and/or AWS would not have prevented it?

 

[edwin_m]

Question (which I have asked elsewhere and not got an answer): when was the last UK rail accident resulting in at least one fatality that could only have been prevented by ATP i.e. TPWS and/or AWS would not have prevented it?

Such an interesting question that it deserves its own thread.

https://www.railforums.co.uk/threads/atp-preventable-accidents.166812/

 

[louis97]

I believe 3-aspect signalling is in place on everything west of Tilehurst, including such complex layouts as Didcot and Swindon.

Worth noting that it isn't entirely 3 aspect signalling West of Tilehurst. There are pockets of 4 aspect signalling approaching various locations, such as Didcot, Swindon and Chippenham.

 

[driver_m]

Here's a possible headscratcher for you with a fairly tenuous connection to the OP's question. North Wales only has one 4 aspect signal in its entirety. Is this true or false? Bonus point if you can place it/them!

 

[MarkyT]

Worth noting that it isn't entirely 3 aspect signalling West of Tilehurst. There are pockets of 4 aspect signalling approaching various locations, such as Didcot, Swindon and Chippenham.

It is very common for a nominally 3-aspect signalled line to have some closer spaced 4-aspects approaching stations. This is to provide some 'closing up' functionality so if there is a train in a platform the next one following behind can get closer to the platform to wait clearance.

 

[Mintona]

No... I am fully aware of the AWS horn as well!

It’s off the end of the 125 stretch, but a single yellow on the 100mph at Bathford approaching Bathampton Jcn usually produces a brake application sufficient to knock a cup of coffee over. The poor sighting of the signals and very short (approx 1.5 mile) section has long been hated by drivers.

The issue with this specific signal sequence is that it’s downhill, approaching a junction and prone to being slippery due to the close proximity of many trees. Drivers are encouraged to knock most of the speed off as quickly as possible to try and prevent any incidents as the train approaches the stop signal.

On a more general note, much of the line between Didcot and Swindon is 4 aspect, it only becomes 3 aspect close to Didcot. The signal after the A34 at Milton on the up main can show either a single yellow or a double yellow (the previous signal being green), a double yellow meaning the train is signalled into Platform 2 at Didcot Parkway and a single yellow meaning the train is to be halted at Foxhall Junction. If it is single yellow the driver must get hold of the train fairly quickly as at 125 you don’t have too much time to react and slow the train down.

 

[mmh]

Here's a possible headscratcher for you with a fairly tenuous connection to the OP's question. North Wales only has one 4 aspect signal in its entirety. Is this true or false? Bonus point if you can place it/them!

Ooh, interesting! Being from Llandudno / Deganwy / Junction my "it's the centre of the universe" ridiculous bias wants it to be there, but I'm not that daft!

I've been wondering about where you might want it if there's a difference between line speed and what the trains used can do, but thought these days every planned train can do 90.

Then I thought about stopping patterns, and the only stretch that came to mind was Rhyl to Colwyn Bay, which until recently had the down platform on a loop. But it feels more likely that would be handled by timetabling?

Then I thought about the Conwy bridge, but seemed unlikely.

My random guess is going to be there is one, on one side of the bridge between Bangor and Anglesey. I guess the Anglesey side.

I know my guesses will completely wrong!

 

[Wilts Wanderer]

This has turned into an interesting discussion, thank you to all who have posted. I wasn’t aware of the 4-aspect signals between Didcot and Swindon, I will make a point of looking out for them next time I travel that way.

 

[philthetube]

London underground signalling is two aspect with repeaters (distants) only provided for badly sighted signals. I know line speeds are far lower but at certain locations the driver has very little reaction time indeed. They also have no AWS, TPWS or DRA and the train stop system only intervenes when it's too late. A very different world from the one upstairs.

The Met has three and four aspect signalling between Harrow and Amersham on a 60mph railway.

 

[bionic]

The Met has three and four aspect signalling between Harrow and Amersham on a 60mph railway.

Good point. I was thinking more along the lines of the conventional "tube" rather than the Metropolitan "Railway". Either way I don't suppose it'll matter soon anyway after they eventually sort the signalling upgrade out.

 

[krus_aragon]

Here's a possible headscratcher for you with a fairly tenuous connection to the OP's question. North Wales only has one 4 aspect signal in its entirety. Is this true or false? Bonus point if you can place it/them!

True: on the approach up to Llandudno Junction from the Bangor direction. I've seen it wink at me occasionally when playing SimSig.

(I can't recall seeing another one, but there might have been a new one installed during the recent resignalling.)

 

[driver_m]

Ooh, interesting! Being from Llandudno / Deganwy / Junction my "it's the centre of the universe" ridiculous bias wants it to be there, but I'm not that daft!

I've been wondering about where you might want it if there's a difference between line speed and what the trains used can do, but thought these days every planned train can do 90.

Then I thought about stopping patterns, and the only stretch that came to mind was Rhyl to Colwyn Bay, which until recently had the down platform on a loop. But it feels more likely that would be handled by timetabling?

Then I thought about the Conwy bridge, but seemed unlikely.

My random guess is going to be there is one, on one side of the bridge between Bangor and Anglesey. I guess the Anglesey side.

I know my guesses will completely wrong!

You're right actually! It's Bangor controlled and it's on the up between Gaerwen and Llanfair PG.

 

[Darandio]

The reply wasn't just to you, it also quoted someone who was being quite, I think deliberately, offensive about the Southall crash, who latched onto your post about potentially missing a signal by sneezing and AWS. I half wish I'd not replied here, because he's presumably just a disrespectful arse looking for attention.

Understood, and yes the post does like that was the intention.

 

[Taunton]

The Met has three and four aspect signalling between Harrow and Amersham on a 60mph railway.

This was installed in 1960, when the line here, although owned/signalled by LT, was still shared with BR express steam-hauled, vacuum braked trains from Marylebone to Nottingham etc via Aylesbury, and even heavy unbraked freights. It's the only part of joint BR/LT running that was signalled by LT. All the rest were BR signalled.

 

[MarkyT]

I think it should be pointed out that while trainstops cannot prevent SPADs, LU's practice of providing a fully braked overlap beyond each signal prevents any such SPAD leading to a junction collision. That is why underground driving style approaching reds is so much more aggressive than we're used to on today's main line network. It takes ATO as employed on Thameslink to match this and exploit the headway advantages of cutting platform reoccupation time.

 

[pt_mad]

Has anyone else ever noticed a coloured light signal 'winking' once as though the signaller might have re-set the signal but to the same aspect it was already showing? LED type. Like the colour disappears for about .2 of a second but is then seen again? Or could this be a faulty signal? Note not seen this when a train has been anything within 3 mins of a signal.