SPAD Indicators

[Trainfan344]

I noticed that on the Bittern Line between Norwich and Sheringham, at several locations have the signal as normal, but then have a SPAD indicator which has 3 possible lights on it, so question is what do they do in the event of a spad.

 

[Tomnick]

Three red lights - top and bottom flash, middle one steady (with the word 'STOP' displayed?).

 

[AndyPJG]

I noticed that on the Bittern Line between Norwich and Sheringham, at several locations have the signal as normal, but then have a SPAD indicator which has 3 possible lights on it, so question is what do they do in the event of a spad.

Have a look-see at http://www.railsigns.co.uk/sect8page2/sect8page2.html

 

[a good off]

Most of them were fitted to high risk signals before the wholesale roll out of TPWS.

 

[Crossover]

There are a few in West Yorkshire, specifically just outside Leeds station and on the Shipley triangle. I watched a video linked from here I think in their use and it was filmed on the Bradford - Leeds platform of the Shipley triangle

 

[seawolf]

A YouTube video on the subject: http://www.youtube.com/watch?v=xje3coP9-IM

 

[swt_passenger]

Most of them were fitted to high risk signals before the wholesale roll out of TPWS.

I believe the SPAD indicators at the London end of Southampton were removed during the renewal of the interlocking a couple of years back.

They won't put any effort into removing them as a stand alone job, but as you imply they probably aren't needed with a TPWS installation.

 

[transportphoto]

Here we are, old but relevant:

[youtube]xje3coP9-IM[/youtube]

 

[swt_passenger]

Here we are, old but relevant...

and linked to just a couple of posts ago, 0731?

 

[transportphoto]

and linked to just a couple of posts ago, 0731?

Oh yes... that will teach me for very quickly skim reading and finding the video

 

[craigwilson]

If I recall correctly there's also one at the London end of Gillingham (Kent) station. I'm not sure if there any others in Kent - that's the only one I've seen.

 

[High Dyke]

A couple are fitted to protect the Flat Xing at Newark. Also seen them on the Uckfield line to protect single line section.

 

[scotraildriver]

I believe they were introduced after the fatal crash at Bellgrove which involved a SPAD at a single lead junction.

http://www.railwaysarchive.co.uk/docsummary.php?docID=263

 

[O L Leigh]

I believe the SPAD indicators at the London end of Southampton were removed during the renewal of the interlocking a couple of years back.

They won't put any effort into removing them as a stand alone job, but as you imply they probably aren't needed with a TPWS installation.

Yes they are, because they also show on converging lines where installed. This will alert the driver of any train heading towards a converging point that a train on another line has SPAD-ed the protecting signal and will ensure that the train is stopped as well. TPWS cannot do this.

O L Leigh

 

[edwin_m]

The SPAD indicator could indeed still make a difference but only if ALL the following were true:
- When train A SPADs, train B has already passed its protecting signal showing a proceed aspect.
- When train A SPADs, driver B can still see the SPAD indicator and has enough braking distance to stop short of the junction.
- The TPWS intervention on train A does NOT stop it short of the junction.

Needing all three together means that the chances of the SPAD indicator making a difference are that much less than before TPWS. Therefore it is less likely that one would be provided.

 

[O L Leigh]

Granted, I am not aware of any new SPAD-I installations. However, where these things are still in use the rules stand.

Mind you, your assumptions cannot be, um, assumed. This is especially the case on lines over which heavy freight trains operate. Even where TPWS intervenes, it is not necessarily the case that the train won't come to a stand foul of another line on which another train might be passing.

O L Leigh

 

[edwin_m]

They are not assumptions, they are a chain of events each of which has to happen for the SPAD indicator to be of any use and each of which can (in principle) have a probability attached to it. Risk assessment ought to be taking account of this sort of issue when deciding whether to keep the SPAD indicators.

 

[455driver]

A lot of SPAD indicators are being removed/ disconnected, the ones at Wimbledon are certainly disconnected because they fu um messed up the wiring so the magnet associated with it sounded as you passed the signal regardless of aspect displayed.

In the scenario above mine, I have to agree with Edwin M, unless the train is between the protecting signal and SPAD indicators when the other train SPADs then the SPAD indicators wont help, they would only offer additional protection over and above the TPWS in that one situation.

 

[Railsigns]

Granted, I am not aware of any new SPAD-I installations.

The last new one I can think of was at Margam East Junction in the 2007 resignalling.

 

[MarkyT]

Granted, I am not aware of any new SPAD-I installations. However, where these things are still in use the rules stand.
. . . Even where TPWS intervenes, it is not necessarily the case that the train won't come to a stand foul of another line on which another train might be passing.

TPWS arrests a SPADDING train immediately on passing the red and is designed to stop the train within the locked overlap, which interlocking ensures is clear of any other signalled movements. The only exception is a start-away SPAD where a train has stopped a while and the overlap has timed out and released or was never there in the first place in the case of a bay or terminal platform. These cases are analysed nevertheless in layout risk assessment and appropriate measures such as a trap spur can be implemented. If the starting point is very close to the signal the maximum overrun speed will be fairly low anyway and an errant movement can be arrested in only a few yards. There really is no need for SPAD indicators in the post TPWS world and although they're not being actively removed, they do no harm left in place until they can be abolished under broader renewals or enhancements.

 

[Railsigns]

TPWS arrests a SPADDING train immediately on passing the red and is designed to stop the train within the locked overlap, which interlocking ensures is clear of any other signalled movements.

TPWS is designed to stop a SPADing train before the first possible conflict point (ignoring a rear-end collision), which may be some distance (possibly hundreds of metres) beyond the end of the overlap. This is called the "Safe Overrun Distance".

 

[MarkyT]

TPWS is designed to stop a SPADing train before the first possible conflict point (ignoring a rear-end collision), which may be some distance (possibly hundreds of metres) beyond the end of the overlap. This is called the "Safe Overrun Distance".

Yes indeed, thanks for the correction. Nevertheless the important factor is that no other conflicting signalled movement can be already or subsequently cleared through this 'SOD' path. This has been immensely significant in railway safety, practically eliminating junction collisions and saving lives and injuries for both passengers and rail staff in the years since TPWS implementation.

 

[Railsigns]

This has been immensely significant in railway safety, practically eliminating junction collisions and saving lives and injuries for both passengers and rail staff in the years since TPWS implementation.

Oh yes, although astonishingly a former prolific contributor on this forum once wrote this:

Taken over the lifetime of TPWS, it is calculated that statistically it will kill more people than it will save, but then I suppose the TPWS-ophiles feel that maintenance and installation staff's fatalities are an acceptable outcome.

 

[Pumbaa]

Ha! A rather jaded view.

 

[GB]

I never really understood OT's views on TPWS

 

[NSEFAN]

For reference, here is the full "transcript" of what OT had to say on the matter:

I think it needs to be remembered that only a very tiny percentage of SPADs ever run outside of the overlap, and that in the very vast majority of those cases, the Driver already has control of the train anyway.

Without wishing to be too controversial, as far as I am concerned TPWS has been a massive waste of money.

TPWS-ophiles would have us believe that the equipment is intervening and bring trains running at high speed through signals at Red to a stand before they hit another train. In fact for the reasons stated above, SPADs very very rarely involve trains running at high speed.

Taken over the lifetime of TPWS, it is calculated that statistically it will kill more people than it will save, but then I suppose the TPWS-ophiles feel that maintenance and installation staff's fatalities are an acceptable outcome.

The last time I did some work related to this, no-one could actually point to a situation where TPWS could be shown of itself to have prevented any fatalities as an outcome of a collision.

TPWS was just a recent manifestation of safety by proxy in which the Media, the public and various other uninformed people have brought about an interference with Railway safety without any real long term benefit.

The money that has been wasted om TPWS can only be justified by people making tenuous claims about lives saved. The fact is that statistically Ladbroke Grove HAD to happen, and having happened is unlikely to occur again for some considerable time.

Meanwhile, whilst we spent £ms on TPWS, other far more worthy and productive options were denied through lack of funding. Like for example replacing a variety of Interlockings where the wiring insulation is so bad that every efort is made to avoid going near it, and if a problem occurs, even a simple repair can and does damage other wires with a dominoe-style effect.

When we take into account the various equipment failures caused by TPWS, and the need for rolling stock to be faulted as well, the costs mount up.

Unfortunately whilst ever safety becomes emotionalised by Media commentators, avaricious ambulance chasing lawyers, prehensile relatives, and Politicians with an eye for personal publicity and a quick soundbite, REAL safety improvements will never be able to occur.

Sometimes the best solution to a problem is to do nothing at all. Unfortunately we have lost the ability to manage our Railways now and simply just knee-jerk to the "demands" of an ignorant public/press/media who are unable or unwilling to understand the bigger picture.

The argument appears to be that TPWS = Added complexity = Greater cost = Money distracted from elsewhere = Greater chance for wrong-side failure = Added risk, but he never actually backs up this claim. I can sympathise with his frustration at media outlets, who rarely paint the railway in a good light, but I can't agree that TPWS is a waste of money.

I wonder what he would have said about ATP...

 

[edwin_m]

Having been involved in a small way I can vouch that TPWS was very thoroughly thought through by "proper" railway people in the mid-90s, both BR and the embryonic Railtrack when it only had a few people but they knew what they were doing.

There was an analysis of all accidents back to around 1968 which worked out what would have happened differently in each case had the train and infrastructure in question been fitted with either a full ATP system or a simpler system with the functionality of what later bacame TPWS. It was concluded that TPWS would be about 70% as effective as ATP but be far quicker to fit as well as being cheaper. Thus it would start bringing benefits sooner.

Uff and Cullen duly rubbished this exercise in their report after Ladbroke Grove, which incidentally would have been prevented by TPWS had it been installed but the funding request was still sitting on John Prescott's desk. However a few years later Stanley Hall published an analysis which demonstrated that the prediction was backed up by the reduction in accident fatalities since it was introduced.

I wasn't involved in the detail design and implementation but I believe it did take on some extra compliation and cost at that stage.

As to staff fatalities, even if it doubled the number of track workers killed during the period of installation (which is likely to be a very high-side estimate) the total would only have been a handful, plus the occasional one during maintenance. The reduction of SPAD accidents is reckoned to be worth around two lives saved per year on average.

It is possible that more lives could have been saved by spending the same amount of money on improving the NHS or installing a national network of road speed cameras (tin hat on!). However compared to some spending the railway has got agreed on safety grounds, it was pretty good value.

 

[MarkyT]

For reference, here is the full "transcript" of what OT had to say on the matter: . . . . The argument appears to be that TPWS = Added complexity = Greater cost = Money distracted from elsewhere = Greater chance for wrong-side failure = Added risk, but he never actually backs up this claim. I can sympathise with his frustration at media outlets, who rarely paint the railway in a good light, but I can't agree that TPWS is a waste of money. I wonder what he would have said about ATP...

I think he failed to benchmark UK against other European rail systems. Whilst it is true some countries already had sophisticated modern ATP systems over large track mileages, it is also a fact that many networks also had various combinations of 'forced caution', 'overspeed' and 'trainstop' functionality built into earlier protection systems rolled out widely around the time we were implementing AWS, sometimes even earlier. UK remained with only AWS, a very important advance then and remaining so now in conjunction with TPWS, but an incomplete safety system compared to most of the European systems of the time, and one that can all too easily be cancelled and then completely ignored. Collisions increased because the railway was getting busier. Something had to be done and I think TPWS, whilst being in no way perfect, was a triumph of pragmatic engineering in the circumstances.
--- old post above --- --- new post below ---

It is possible that more lives could have been saved by spending the same amount of money on improving the NHS or installing a national network of road speed cameras (tin hat on!). However compared to some spending the railway has got agreed on safety grounds, it was pretty good value.

Its interesting that the initial expenditure on TPWS *continues* to provide that safety benefit year on year, for what is presumably now only a small increment on overall maintenance, and renewal schemes. I wonder if a similar amount 'invested' in the black hole of general expenditure in government bodies such as the NHS could possibly have maintained such long term 'bang for buck'.

 

[W230]

I think he failed to benchmark UK against other European rail systems. Whilst it is true some countries already had sophisticated modern ATP systems over large track mileages, it is also a fact that many networks also had various combinations of 'forced caution', 'overspeed' and 'trainstop' functionality built into earlier protection systems rolled out widely around the time we were implementing AWS, sometimes even earlier. UK remained with only AWS, a very important advance then and remaining so now in conjunction with TPWS, but an incomplete safety system compared to most of the European systems of the time, and one that can all too easily be cancelled and then completely ignored.

OOI, why do we have much less sophisticated safety systems than some other european countires? I'd assumed maybe our large track mileage would have somthing to do with it but notice that both France & Germany have more track and presume they have more complex safety systems than AWS/TPWS.

While I don't know much about the safety systems in other european countires, i'm assuming that in cab signalling/ATP/ERTMS is more prevalent than it is here.

Is the simple reason just down to good old fashioned ca$h?

 

[MarkyT]

OOI, why do we have much less sophisticated safety systems than some other european countries? . . . . Is the simple reason just down to good old fashioned ca$h?

Things are not quite as cut and dried as that. Sweden in particular is well known for having rolled out a sophisticated computer based ATP system across most of their network starting in the 1970s. On the other hand Germany still largely relies on a system developed prewar but only rolled out widely after WW2 from 1954, around the same time as our AWS was being fitted. The German system is officially called PZB or informally 'Indusi'. See -

http://en.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung

That older system incorporated the full overspeed and trainstop functionality provided later by our TPWS right from the start and it also includes a form of AWS that forces a train to slow down at a caution rather than just requiring the driver to acknowledge the warning. However the Germans, rather like our long drawn out AWS programme took decades to cover the majority of the network with PZB, starting out with the fastest and busiest lines. The project continues even now, with many lines in the former east being fitted since reunification. More sophisticated computer based national systems have been developed in Germany since then and have been fitted on some main lines, but these, along with similar technologies in other European countries are being superseded by ERTMS. Interestingly there is a movement underway (led by swiss SBB) to incorporate the simple PZB type functionality as a standard operating mode in ERTMS (trainstop /overspeed/ enforced caution). This is much simpler to fit to both legacy infrastructure and, importantly, older rolling stock.