A question I have asked before.... what was the last fatal accident that could only have been prevented by ATP i.e. AWS/TPWS would have been ineffective?
That depends on how you categorise AWS/TPWS as being ineffective. And thank goodness, we don’t have many crashes with fatalities. So we don’t actually have much data.
The problem with AWS is threefold:
* the on train equipment is not fail safe, it’s not designed to bring the train to a halt in the event of the system failing, or detect when an input from the track side equipment has not been received.
* there is no distinction between a unlit (black) signal, a signal showing red, a signal showing yellow, a signal showing double yellow or a ESR/TSR speed restriction or advance warning board.
* the driver is able to cancel the warning, which is not normally a problem, but if the driver is not paying enough attention, it has been occasionally known for a driver to not respond to a yellow aspect, then when the next signal comes into view (which is showing a red aspect), find that they can’t stop the train before running past the red signal (one possible reason for a SPAD).
* we know that a faulty signal AWS (track mounted equipment) can go for days before a driver actually reports it, once one AWS was found to have been faulty for over ten years before the problem was discovered.
* we also know that in the past (I don’t have the data for the current situation) the train equipment has been unreliable
* not all signals are provided with AWS.
Nobody knows how many times a fully working AWS has prevented any incidents becoming accidents or crashes. AWS and it’s GWR version (ATC, but no relation to the modern meaning/system) has been in existence for a long, long time now.
TPWS also has problems:
* it’s not fitted to every signal, normally it’s only fitted to signals where there is a possible point of conflict ahead, such as on signals protecting junctions or level crossings.
* the standard installation only is officially effective for speeds up to 75MPH.
* for higher line speeds, to provide better protection, an additional installation is required, called TPWS+. This is just another TPWS installation, but fitted further away from the signal. This extends the effective protection up to speeds of 100MPH.
* not all signals with TPWS have TPWS+ fitted.
* TPWS (and TPWS+) are also not fail safe systems, the on train equipment is not designed to bring the train to a halt in the event of the system failing, or detect when an input from the track side equipment has not been received.
* the track mounted equipment and the control equipment in the lineside equipment cupboard is not fully fail safe, it can detect some failure modes and this results in the signal in rear (the previous signal) being returned and held at red, but it is a ‘dumb’ system in that it has no way of knowing if the trains are receiving its radio signal
* the on train equipment offers no protection if there is a fault with the track mounted equipment or the signal is not fitted.
* the track mounted equipment and the control equipment in the lineside equipment cupboard is less reliable than what you would expect for equipment of its age.
* it can restrict how a driver can drive their train, there are still plenty of nuisance trips where the train is travelling at less than the line speed, at a safe speed, but above the TPWS trip speed, causing it to activate and bring the train to a halt.
The Southall crash could have been prevented if any of these had been working: AWS, TPWS, ATP. The train was fitted with ATP but the TOC had many HSTs running with it isolated, including the HST that SPAD the signal.
However, AWS has not stopped the large number of SPADs that have occurred over the years. We have no idea how close to disaster the railway has come or how many near misses there have been.
The Ladbroke Grove crash illustrates what happens when AWS is not effective. Either TPWS or ATP would have prevented this crash.
But there are some important differences between TPWS and ATP. The very basic TPWS system is designed to apply the brakes
AFTER the train has passed the red signal. Where the distance to the point of conflict (normally the points at the junction ahead) is too short for the brakes of a typical train to bring it to a halt just prior to the point of conflict, an extra item of TPWS equipment is fitted. This activates the train brakes on the approach to the red signal {not to be confused with TPWS+} so that there is just enough distance to stop the train just short of the point of conflict, but
AFTER the red signal.
ATP does things rather differently. The objective with ATP is to
prevent a train from ever (*)
passing a signal at red. * apart from at a very slow speed or if the system is isolated, also ATP sometimes gets the distance travelled by the train wrong due to wheel slip/slide, so may get the actual location of the signal slightly wrong.
ATP monitors the speed of the train and continuously monitors the distance to the target. The target being the limit of the trains authority to proceed. So if you are approaching a signal showing a yellow aspect, the target is the red signal after the the yellow signal. If the driver does not control the speed of the train so that it is within the braking curve calculated by the ATP computers (so as to stop before the red signal), it will apply the brakes and bring the train to a halt.
ATP also enforces all permanent speed restrictions, all junction speed restrictions, all temporary speed restrictions and after it has been updated (*), any emergency speed restrictions. * - for an emergency speed, we have to wait for the restriction details to be supplied before the ATP can be adjusted, more details than just the speed are needed, as distance information is also required.
Because the intention is for all main signals to be fitted on a line, ATP provides protection throughout the trains journey while on a ATP fitted line, not just at where a point of conflict has been identified ar some time in the past.
ATP was proved to be very effective at every test thrown at it during the BR trials. The Great Western Main Line (GWML) system surprised many when a test train (a ECS HST) was found to stop from 125MPH in a distance a lot shorter that they expected during the tests to see what would happen if a signal went to red in front of a ATP fitted train.
So, there is no easy answer, but...
ATP would have prevented nearly all (if not all) of the crashes caused by drivers failing to control their trains where they either ended up passing a signal at red, or were travelling too fast for the speed of the line or junction.
TPWS is the next best, it would have prevented some crashes caused by a driver passing a red signal, and reduced the speed at the point of impact at some others where a driver passed a red signal. But it’s not as effective on high speed lines, and is totally ineffective if the signal is not fitted with TPWS. It is spot fitted to the infrastructure at some advance speed restriction signs, but does not continuously enforce any speed restriction or limit.
AWS is only effective if the driver takes full notice of it and it’s working.
Note that in the book Red for Danger, there is I think a couple of crashes due to drivers failing to stop at a signal at danger on plain line, and hence crashing into the back of a earlier train that has stopped. Of course, now we have much better colour light signals, and there has not been a crash like this in recent history. But this is the type of crash that could be nasty, which TPWS would not prevent (as currently fitted), but ATP definitely would prevent (if fitted).
A bit of speculation on my part, but at Ladbroke Grove it would have in theory stopped the Turbo within the signal overlap after it Spadded SN109.
At Southall (much higher speed approach), TPWS would have at least reduced the severity of the accident by intervening on the speed sooner than the driver did (I think - happy to be shot down by an actual TPWS expert on this)
ATP would have stopped both crashes, the trains would have been stopped before the red signal or well within the overlap.
TPWS most likely would have stopped the Turbo short of the points. For Southall, I would need to reread the accident details. TPWS+ would have done better than standard TPWS though.
At Ladbroke Grove the distance from SN109 to the convergence of the tracks was enough for a TPWS brake application to stop the train safely if both had been TPWS-fitted, as they would have been under the later programme.
Southall would have been prevented by a working AWS (very likely) or a working ATP (certainly) or a working TPWS (almost certainly if fitted). I suppose you can argue that if TPWS had been fitted it might not have been working either, given the attitude to train protection systems at the time. But it would be a stretch to say that Southall was ATP-preventable without also agreeing that it would have been prevented by AWS or TPWS under the same assumptions.
If, and it’s a big if, the ATP was no longer classed as a pilot/trial system, but as a essential safety system, then the TOC should have been maintaining it properly (the track and lineside equipment was being maintained properly) and for it to be in use rather than many HSTs having it isolated.
It was shocking learning that the train AWS equipment was often not operational, or often had faults and defects. Again, the track and lineside equipment was being maintained properly.
The closest "near-miss" I believe we've had (in terms of a SPAD that could have been a very serious accident has circumstances been slightly different) was the Wootton Basset SPAD - which only happened as severely as it did because the AWS (and as a consequence TPWS) had been isolated.
One thing to note though, is that there are rather too many incidents that are not in the public domain. For example, two trains ending up in a signal section because a driver saw the points ahead of him move shortly after a train passed over them. Said driver then moved his train forward and proceeded on to the main line. The signaller was about to report a wrong side failure of the track circuit (because it had gone clear) before realising what was actually happening. Later on the driver when asked, said he had a yellow at the signal. But that signal had no lamp in the yellow aspect, and had a black painted blanking plate instead of a glass lens, because it was not in use. The signal only needing to be a two aspect red/green.
AWS will stop the train in time in the vast majority of cases. There will always be edge cases.
AWS is useless if the signal is not fitted, the AWS on the train is faulty or isolated, or the train has already traveled over the AWS track mounted magnets (platform starter signals, or any other starting from having been stopped at a signal situation), or if the driver fails to react to the signal aspect.
At a junction near Bath, a driver had another two drivers in the cab because they were route learning. Because the driver in control got distracted discussing the speed restrictions, he missed the signal that was showing a yellow aspect. The AWS was working, it was acknowledged. The sighting of the signal protecting the junction is not very good, so by the time he saw it, it was far too late to stop his train. Hence it was passed at danger. Lucky for everyone, this did not result in a crash. But it could have been a lot worse as the junction ahead is a high speed junction.
How many other ‘near-misses’ happen?
Southall was all about the culture of the railway in running with safety systems isolated or staff not trained on them. Both track and train were ATP fitted.
Yes, but why just concentrate on the TOC. The whole system fails to remember the reasons why if it’s inconvenient to the powers that be or individuals at the time.
We appear to go though cycles. An accident happens. Everyone takes notice. Over time the memory fades, then a different accident happens. Years later an accident that should have been prevented because lessons were learnt, happens. Because the why got forgotten and hence system/procedures were not maintained because they were not perceived to be important enough or were inconvenient for some reason/excuse.
ATP significantly reduces the element of human error more than AWS or TPWS does.
It’s like comparing the safety of a 747 passenger jet with one from the 1940s.
Of course technology has moved on, and it would be foolish to fit an obsolete ATP system now. ERTMS (level 1, or level 2) should be widespread on the Network Rail Infrastructure, but it’s not.
At the very least, ERTMS should have been fitted as Network Rail was busy replacing conventional signal boxes and power signal boxes/Panels with ROCs. But no.
BR and the nascent Railtrack did consider what should be installed in the early to mid 1990s - I was the humble minute-taker for one of the committees involved.
It was clear a full ATP system was unaffordable and unjustifiable on safety grounds, and TPWS was developed as a way to get most of the benefits of ATP at far less cost and also much quicker and easier installation. Knowledgeable people from both the rolling stock and the signalling sides were involved in this process - though at the time it was not intended to detect TPWS operation via the lamp proving circuit, which would have made it much simpler to install. The same committee came up with the Drive Reminder Appliance, which was predicted to pay for itself financially in reduced rolling stock damage, as long as everybody used it properly.
And I repeat my point that if ATP had been widely fitted in the 90s, we would now have had the headache of supporting an obsolescent system across the whole network, not just on two routes.
I’m not saying that every single signal should have been fitted with ATP. And I am not saying that ATP fitment should have been a big expensive program on it’s own. I’m saying that provision should have been made for all new rolling stock to either have been fitted with ATP equipment or be designed with provision for retro fitment of ATP (or an equivalent system, such as ERTMS) to be easy to install.
And that for new signalling schemes, ATP to be provided as part of the scheme or provision to be made to enable ATP (or equivalent) to be fitted easily as soon as the rolling stock was available with ATP (or equivalent).
TPWS is a bespoke system where the U.K. railway is tied to a single supplier. Please name which other countries use it.
I agree that the existing ATP systems are old, and will become increasingly difficult to keep operational. But if it had been fitted across the network rather than two different systems on two different areas, demand for replacement equipment and parts may have made it worthwhile for companies to continue to manufacture spares.
As I said above, now, today, ATP is no longer the answer. But TPWS is not really suitable for a modern high speed railway either. TPWS is in my humble opinion, a not very cheap stop-gap.