TPWS for Permanent Speed Restrictions

[notadriver]

Humans make mistakes and everyone has an off day now and then.

Fair enough. In any case it's just my opinion and TPWS over speed loops are fitted for most permanent speed restrictions but there are many places that don't have them.

 

[Railsigns]

Don't forget that temporary and emergency speeds don't have TPWS overspend loops either.

Some TSRs do.

 

[notadriver]

Where is your proof ?

 

[Railsigns]

Where is your proof ?

Network Rail standard NR/SP/SIG/10137 "Train Protection & Warning System - Selection of Signals and Other Locations for Provision of Track Sub-System", section 8.1.1.

 

[notadriver]

But have you actually encountered one set up that way and where as I haven't ...

 

[Railsigns]

But have you actually encountered one set up that way and where as I haven't ...

No, not personally, but then I have no involvement with TSRs and few would meet the criteria for TPWS fitment.

 

[A-driver]

Where is there a speed change from 125 mph straight down to 30 not controlled by signals ? Don't forget that temporary and emergency speeds don't have TPWS overspeed loops either. They rely on the professionalism of the driver and that's enough for me.

Well you do have the curve up north on the ECML, no idea on speeds but think its something like 125 down to 50. How about 70-30 at bounds green on the up Hertford, 85-40 on the up cambs at Cambridge junction, 90-40 at shepreth branch junction on the down cambs etc... High risk of derailment, certainly dewirement if hit too fast. And none of those are protected by approach controlled signals - just TPWS. whilst I see your point with TSR and ESR generally the risk is less as a rough ride is more likely than an actual derailment.

 

[Ploughman]

Would you be referring to Morpeth?
Would TPWS have prevented that derailment back in the 80s (I think)?

 

[notadriver]

Well you do have the curve up north on the ECML, no idea on speeds but think its something like 125 down to 50. How about 70-30 at bounds green on the up Hertford, 85-40 on the up cambs at Cambridge junction, 90-40 at shepreth branch junction on the down cambs etc... High risk of derailment, certainly dewirement if hit too fast. And none of those are protected by approach controlled signals - just TPWS. whilst I see your point with TSR and ESR generally the risk is less as a rough ride is more likely than an actual derailment.

Fair enough but flashing signal aspects for diverging junctions are not fitted with TPWS. I can think of one where the line speed is 100 and the turnout is 40 mph.

 

[Railsigns]

But have you actually encountered one set up that way and where as I haven't ...

I found this TPWS-fitted TSR mentioned in an old WON:

 

[A-driver]

Fair enough but flashing signal aspects for diverging junctions are not fitted with TPWS. I can think of one where the line speed is 100 and the turnout is 40 mph.

The flashing junction will be adequate protection without TPWS-a flashing junction brings you down to a red so you are not just driving to the speeds but also to the approach to the red. At a flashing junction the turnout signal is single yellow. If you approach that at a speed that will make it impossible to slow down enough for the junction then you are also liable to spad the next signal anyway.

A single AWS on approach to a speed restriction is far less protective than an AWS for the double flashing yellow, AWS for a single flashing yellow, AWS for the steady yellow and an approach to a red at the next signal. You obviously don't assume that the steady single yellow will clear to a less restrictive aspect so are reducing your speed anyway.

 

[notadriver]

I understand what you are saying A driver but that flashing aspects rely on the driver slowing down. The speed reduction is not enforced. @railsigns fair enough. It's the first I've seen in any wons Ive read and you I congratulate you on being resourceful enough to find one.

 

[A-driver]

I understand what you are saying A driver but that flashing aspects rely on the driver slowing down. The speed reduction is not enforced. @railsigns fair enough. It's the first I've seen in any wons Ive read and you I congratulate you on being resourceful enough to find one.

I'm not sure you do-all red signals and speed restrictions rely on the driver slowing down! TPWS obviously isn't a type of automatic operation, its a last resort safety system.

If you can pass 2 flashing signals AND a steady yellow signal and are therefore approaching a red signal and still havnt slowed down then there is setting seriously wrong. People make mistakes but ignoring 3 restrictive aspects and approaching a red, which you are on a flashing junction, without slowing down is not a mistake, it means something has gone very seriously wrong!

Flashing junctions work like any other approach control junction-they slow the train to a red signal. That is protection enough. TPWS combined with AWS on approach to a speed restriction isn't incase the driver forgets so much as if the driver underestimates the approach speed.

 

[TDK]

Network Rail standard NR/SP/SIG/10137 "Train Protection & Warning System - Selection of Signals and Other Locations for Provision of Track Sub-System", section 8.1.1.

ATP is frequently implimented on the Chilterns also for TSR's

 

[notadriver]

@Adriver No there is a difference. As I said the TPWS overspeed loops (where fitted) will be armed on approach to the red signal before the junction. So there is no way the turnout can be taken at too high a speed.

Not so with flashing aspects. It's down to the driver.

 

[A-driver]

@Adriver No there is a difference. As I said the TPWS overspeed loops (where fitted) will be armed on approach to the red signal before the junction. So there is no way the turnout can be taken at too high a speed.

Not so with flashing aspects. It's down to the driver.

You seem to be missing the whole point of flashing junctions and arguing that there is no protection from a driver ignoring or deliberately not reducing speed for a flashing junction. What if a driver approached a tight bend/junction and reduced speed enough to get past the grids and then looses concentration and takes full power?

There is no absolute 100% safety system, it relies on the driver doing their job properly and TPWS is nothing more than a back up,

Flashing junctions are low risk junctions. If there was a serious risk of them being taken too quickly then they would be standard approach controlled junctions. The risk of overspeed at the junction is minimal which is why they are there.

If there was a real possibility of drivers forgetting to brake and hitting a 40mph set of points at 100mph then it would be given additional protection but flashing junctions provide enough protection, as I say no driver will accidentally miss 2 flashing caution aspects and a single yellow. As soon as you get a flashing aspect you know that you are being turned out at the next junction and your route knowledge tells you the speeds of the junction. There will also be advanced speed warning boards incase you do forget. And if you arnt sure of the speed what do you do? Any driver should come up with exactly the same answer-kill off your speed to a crawl until you know for sure what the speed is. If I am driving of unfamiliar points etc then I just poodle along at 15mph until I see a speed board indicating otherwise.

Sorry, but I can't see your argument here. Trains and their safety systems are in no way automatic and they are controlled (as you obviously know) 100% by humans. Technology provides a last resort at high risk locations to reduce the impact of human error. Flashing junctions by their nature a safe as they force the driver to slow down for a red signal. If your argument was true then they wouldn't be allowed to exist.

 

[TDK]

Flashing junctions are low risk junctions. If there was a serious risk of them being taken too quickly then they would be standard approach controlled junctions. The risk of overspeed at the junction is minimal which is why they are there.

Not all of them - I know of junctions with flashing yellows 125mph - 60mph, 60 - 25mph & 90mph - 30mph. These have TPWS+ & TPWS OSS for the junctions and the signals. In my opinion flashing yellow aspect are put in place to save time and give a better frequency more than anything else. However you are correct in saying it is the drivers responsibility to obey signals.

 

[A-driver]

Not all of them - I know of junctions with flashing yellows 125mph - 60mph, 60 - 25mph & 90mph - 30mph. These have TPWS+ & TPWS OSS for the junctions and the signals. In my opinion flashing yellow aspect are put in place to save time and give a better frequency more than anything else. However you are correct in saying it is the drivers responsibility to obey signals.

By low risk I don't mean you can run them too fast, I mean there is enough warning-as I say 2 flashing restrictive aspects with AWS and then a steady yellow with AWS bringing you down to a red- I can't see a major risk in a driver managing to miss all those warnings. I could accept a drivers may miss/forget about one restrictive signal for whatever reason, possibly resulting in a spad but I think 2-3 restrictive aspects in a row combined with route knowledge is almost impossible.

 

[Bill EWS]

"So when you have a 30mph curve on a 125mph running line you think no TPWS is needed?! So if the driver cancels the AWS but fails to bring the trains speed down in time and runs the train into a field killing dozens that is acceptable?! "

In my 42 years of train driving I don't recall ever forgetting a permannt speed restriction, nor cancelling the AWS then forgetting a permanant speed restriction. These are part of your route knowledge and one of the first things you take note of when learning a new route. They stick in your mind, period just as a red signal does.

While it has happened it is not something that ocurrs on a regular basis but usually where something else has taken the driver's attention away from his driving at that moment. However, having said that having an aws warning for any speed restriction is a worthwhile addition to safety.

When I started on the railway many routes had no aws of any kind and drivers didn't miss speed restrictions in potentially dangerous ways. Many steam locos didn't even have a speedometer and still drivers maaged to bring their trains dow to close to the stated speed. It was serious errors such as happened at Morpeth that encouraged the need for a physical pre-warning that the driver couldn't ignore. Likewise as speeds got higher pre-warnings became more neccessary. But on the main train drivers do not forget permanant speed restrictions and it would be insluting to suggest that they do.

 

[MrC]

but I think 2-3 restrictive aspects in a row combined with route knowledge is almost impossible.

Not wanting to sound argumentative but it's not impossible which is why we have things like TPWS to reduce (but not remove) the risk. Any experienced driver will know there's been plenty of times when people have cancelled the AWS and taken no other action due to tiredness or other distractions.

To back this up there's been one incident I can think of with 4-aspect flashing yellows and a low speed turnout where, if TPWS hadn't triggered (thank god), the train would have derailed at high speed. As it was it entered the turnout quite a bit over the PSR but stayed on the rails.

 

[GB]

but on the main train drivers do not forget permanant speed restrictions and it would be insluting to suggest that they do.

I do not see what is insulting about it. All railway staff are professional, but even professionals make mistakes sometimes...what ever the reason, which is why we have the safety technology/equipment we have.

In reference to TPWS at speed restrictions in general...

There was a TPWS incident a month or so a go and while I do not wan't to go into detail on a public forum, the train tripped the OSS at near line speed which was quite a lot higher than the speed restriction for which it applied. Now whether the driver was distracted, forgot or just mis judged the breaking I do not know, but TPWS in this case was obviously a good thing.

No doubt there are many TPWS OSS that are either set incorrectly, too sensitive or just not needed but that doesn't mean we should do away with all of them.

 

[TDK]

By low risk I don't mean you can run them too fast, I mean there is enough warning-as I say 2 flashing restrictive aspects with AWS and then a steady yellow with AWS bringing you down to a red- I can't see a major risk in a driver managing to miss all those warnings. I could accept a drivers may miss/forget about one restrictive signal for whatever reason, possibly resulting in a spad but I think 2-3 restrictive aspects in a row combined with route knowledge is almost impossible.

To be honest the main risk at flashing yellow/track approch is the driver anticipating the red will pull off, this has happened before and I remember an incident at Wever Junction a few years back, when you do a risk assessment on a route 2 flashing yellows does hold a risk and is marked accordingly. As for ignoring or being distracted this has happened before as we all know resulting in a very serious incident at Ladbrook Grove and it was this incident that was one of the main reasons why TPWS was implimented. Look on the Network Rail/RSSB website and look at the SPADs (accessable by all I believe) and look at the reasons for the SPADS, there are many where the root cause was "driver failing to react to cautionary aspect" so it can happen.

 

[A-driver]

To be honest the main risk at flashing yellow/track approch is the driver anticipating the red will pull off, this has happened before and I remember an incident at Wever Junction a few years back, when you do a risk assessment on a route 2 flashing yellows does hold a risk and is marked accordingly. As for ignoring or being distracted this has happened before as we all know resulting in a very serious incident at Ladbrook Grove and it was this incident that was one of the main reasons why TPWS was implimented. Look on the Network Rail/RSSB website and look at the SPADs (accessable by all I believe) and look at the reasons for the SPADS, there are many where the root cause was "driver failing to react to cautionary aspect" so it can happen.

But that's a different risk to hitting the points too fast, and any approach control setup has a spad risk.

As for overrunning speed restrictions, I'm not suggesting a driver would forget about them, more underestimate the braking needed etc.

I agree that forgetting a large drop in speed is unlikely as its such a big part of your route knowledge. More likely is a distraction, disorientation in poor weather etc making the driver think they have more space than they do. That is when TPWS is useful. The Morpeth curve has had a few incidents, I believe historically there have been overspeed incidents at hitchin coming from Cambridge which resulted in derailment, whilst derailment is rare there are certainly other problems with hitting them too fast-loosing the pan out the side of the wires which has happened before due to extreme swaying, passenger discomfort, damage to infrastructure or trains etc.