I'm sorry but I'm probably being a bit thick here. Is the implication that the driver thought that the signal would change from red to amber, but that the train was going too fast (not speeding) for the track circuit to react and step up the signal to amber?
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Double SPAD near Crofton West Junction
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I'm sorry but I'm probably being a bit thick here. Is the implication that the driver thought that the signal would change from red to amber, but that the train was going too fast (not speeding) for the track circuit to react and step up the signal to amber?
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Elecman
Established Member
Yes in a nutshell, until professional driving techniques were introduced used to cause many SPADS and quite a few collisions. As inferred above TOCs DMs advise drivers there no such thing as approach control to avoid the driver setting himself up
Dieseldriver
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I think in this particular incident there were more factors at play. In general though, there are SPADs (and on a lesser level, TPWS activations) that occur when the Driver is approaching the signal too quickly in anticipation that the signal will clear and finds themselves unable to stop when it doesn't. A stark example of why it's best practice (easier said than done) to never make assumptions based on previous trips and to always expect the unexpected. As a Driver, I personally have the mindset that every single red I approach has a train in the section ahead (or a conflicting move set in the case of junction signals) so in my mind, no signal will ever step up to a less restrictive aspect.
I don't believe there is any implication of the Drivers actions or thinking. Just that the signal is setup for Approach control.
*"Typically", approach control signals step up to green.
The problem with that approach.. has been that the non exist 'approach control' is treated as a 'joke' because everyone knows it does. It has also produced a lack of understanding how the signalling system actually works. Because 'approach control' exists and is seen regularly and is part and parcel of a Drivers route knowledge, the issue of human factors takes over. The brain will notice patterns and start to act accordingly. Granted that is also part of the reasons why they were regularly passed but a larger part of the reason was because people were told that the signal 'will' come off.
Far better to teach people the reasons why it exists and what is actually happening so that people can defend against it.
*yes, I know.
It is an issue for drivers to be aware of generally, where they approach signals at danger that routinely clear once they reach a certain point, to then be caught out when the signal doesn't clear because they're to be held there for some reason. I don't think there's been any suggestion that that was the case here - indeed, it's been stated that the route was set anyway but would've required the track circuit on approach to be occupied for a pre-determined period of time (to ensure that the train was under control and slowing down sufficiently to observe the speed restriction through the diverging junction) before the signal could clear.
(it's yellow, not amber!!)
A lot of dodgy misconceptions about signalling in this thread!
A significant proportion of signals have both TPWS TSS and TPWS OSS (some have several sets of OSS, and then there is TPWS+) and some signals (although rare) even have more than one set of TPWS TSS.
Approach control does clearly exist, and an argument for including the concept when training drivers is that it can potentially help them realise sooner that they are being wrongly routed ahead.
Approach control isn't necessarily normally to a clear (green) aspect. Plenty of examples otherwise, and no doubt someone better versed in signalling standards can explain delayed yellows etc.
And it's of course yellow, not amber.
A significant proportion of signals have both TPWS TSS and TPWS OSS (some have several sets of OSS, and then there is TPWS+) and some signals (although rare) even have more than one set of TPWS TSS.
Approach control does clearly exist, and an argument for including the concept when training drivers is that it can potentially help them realise sooner that they are being wrongly routed ahead.
Approach control isn't necessarily normally to a clear (green) aspect. Plenty of examples otherwise, and no doubt someone better versed in signalling standards can explain delayed yellows etc.
And it's of course yellow, not amber.
Clarence Yard
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Ah! So, I strongly suspect the "problem" occurred in the yard before departure and in due course we will find out from the RAIB the reason why it had little or no train braking. Must be quite obvious for them to say that they are issuing a digest.
As I understand, the party(s) implicated held their hands up immediately - certainly reading the control log entry it was clear very early on exactly what happened and why it happened. Digest I imagine because while it is a serious occurrence, there isn’t any learning for the industry to undertake per se, or at least isn’t already the subject of another ongoing RAIB investigation.
Iskra
Established Member
As per forum rules; please can you explain what all these mean, so that your post can be commonly understood.
I think most of us will understand what TPWS means as it is fairly common, the rest however...
TPWS - Train Protection and Warning System
OSS - Over Speed Sensor
TSS - Train Stop Sensor
As for how OSS / TSS is integrated into TPWS, someone with greater knowledge than I shall have to explain.
Iskra
Established Member
Thank you, and what's the difference between TPWS and TPWS+ does anyone know?
Oh, sorry.
TPWS+ is simply an extention of TPWS. As in, it incorporates an additional OSS set prior to the 'usual' OSS set, further back (in advance) of the signal.
It allows for a greater speed to be used, on approach to signal - I believe it may be upto 100 mph.
I am more than happy to be corrected on that point though.
So TPWS has a set of OSS grids + a set of TSS grids.
TPWS+ has two sets of OSS grids + a set of TSS grids.
Found the below diagram, online.
Iskra
Established Member
Excellent, thank you.
alxndr
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TPWS consists of OSSs and TSSs, or just one or the other.
OSSs have two loops/grids/toast racks (depending on preferred name) spaced a calculated distance apart on the approach to a signal. The loops transmit at their respective frequencies when the signal is at red. If a train detects the frequency transmitted by the trigger loop within a set time of detecting the frequency for the arming loop the brakes will be applied. If the train is going slow enough to correctly come to a stop at the signal enough time will have elapsed after passing the arming loop before passing the trigger loop to not receive a brake application.
TSS works the same way, except the two loops are positioned adjacent to the signal and next to each other. They are again only energised when the signal is at danger. This means that any train attempting to pass the signal at red will receive a brake application as it will pass over the trigger loop immediately after the arming loop.
If the signal is showing yellow/double yellow/green the loops will not be active or transmitting.
OSS loops can also be provided for permenant speed restrictions where they are not associated with a signal and will always be active when a train passes over them. TSS and OSS loops may also be provided for buffer stops, again these are not associated with a signal. Special half sized loops are provided for buffer stops due to the slow speed and proximity.
It should be noted that not all cases where there is more than one set of TPWS OSS loops for a signal is deemed 'TPWS+', indeed the term TPWS+ itself is out of favour these days.
TPWS+ loops were usually in the region of 750m+ from the signal they related to.
The concept stems from the fact that when TPWS was rolled out nearly 20 years ago we were all told that it was only deemed effective (to stop a train proceeding without authority before the conflict point after passing a signal at danger) at speeds up to 75mph. Above this speed variations in train behaviour weren't able to guarantee effectiveness presumably because the range in certain variables became larger.
TPWS+ loops were usually in the region of 750m+ from the signal they related to.
The concept stems from the fact that when TPWS was rolled out nearly 20 years ago we were all told that it was only deemed effective (to stop a train proceeding without authority before the conflict point after passing a signal at danger) at speeds up to 75mph. Above this speed variations in train behaviour weren't able to guarantee effectiveness presumably because the range in certain variables became larger.
There is one rather bizarre exception in that when the signal is showing a subsidiary aspect the OSS will still be energised. Normally this wouldn’t be an issue because the train would’ve already been brought to a stand at the red. However if you’re performing a shunting movement on a long bi directional platform it is possible ( depending on the speed the grids are set at ) to have a brake demand at a proceed aspect.
How bizarre....
SN. 201 being the Down Main signal at Acton West. The protecting signal for the Dn Relief to Dn Main point work prior to the London End of Ealing Broadway station.
And SN. 191 being the preceeding signal to SN. 201.
What's the speed trigger setting on the first TPWS OSS++, just out of interest?
Just the OSS and OSS+ on our drawings - the OSS+ being before reaching SN191
SN203 on the Down Relief has OSS-, OSS and OSS+, but they’re all between 199 and 203.
52mph
but approach control doesn’t exist, just ask any driving manager or ops trainer
Haha that really grinds my gears. Why do they have to have to be so patronising?
Someone who is capable of driving trains for a living should be capable of knowing that approach control exists, but still never assuming that a red will step up on approach.
EDIT: I remember during my rules course one of the other trainees (who is now a good mate) took great delight in correcting the instructor when he lied about approach control not existing: “It doesn’t exist, you say. That’s funny, because my signaller friend says it does!”.
He wasn’t too popular with the instructors after that!
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edwin_m
Veteran Member
Indeed. Though TPWS will of course reduce the severity of many of those collisions it doesn't prevent completely, because the brakes will have gone on at the first OSS if the driver hasn't applied them first.
Probably an example of the "range in certain variables" becoming larger. It becomes increasingly difficult to set a speed that applies the brakes in time for a train with relatively poor deceleration to stop in time, without also unnecessarily stopping a train with better brakes that is approaching at a speed that is perfectly safe for it to stop normally at the signal. The difference in the timer between passenger and freight trains corrects for this partially but not fully.
Thanks, JN114.
(i am genuinely intrigued now), if the OSS+ on SN. 201 is preceeding SN. 191, one can presumably sight 201, accurately, prior to passing SN. 191 and apply the breaks if nessessary? Permissible Line speed at that point being 85 / (MU)100 at Acton East / 125 at Acton West.
But I fear we are firmly off topic now, for which I apologise.
Scratch that.... How silly of me!
If SN. 191 shows a single yellow, the OSS+ will be energised, as SN. 201 is showing Red.
Please ignore me!
Safety Digest published
Precis, Train was stabled at Doncaster, used for training and brake pipe cock shut off on loco, driver took train and didn't notice brakes on wagon weren't operative
Precis, Train was stabled at Doncaster, used for training and brake pipe cock shut off on loco, driver took train and didn't notice brakes on wagon weren't operative
pdeaves
Established Member
Slightly less precis, if reading through it you think 'that sounds like the Edinburgh sleeper incident', RAIB points that out at the end.Safety Digest published
Precis, Train was stabled at Doncaster, used for training and brake pipe cock shut off on loco, driver took train and didn't notice brakes on wagon weren't operative
Because the cocks obviously work in both orientations I imagine you'd just end up with a system where both indications are 'normal'.
The two things I think are wrong in this case are people interfering with trains and a prep procedure not taking that into account.
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