ASharpe
Member
On the idea of speeding out of Leeds, I have noticed a few rather aggressive brake tests after leaving Leeds the last couple of weeks. I'm sure they are not speeding but definitely felt stronger than usual.
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Train delayed due to excessive speeding
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Nottingham59
Established Member
Welcome to the forum. I'm sorry this discussion has been diverted away from your original question.
It is not a regular occurance. The overspeed detection system (TPWS) is designed not to engage in normal operations. If TPWS makes an emergency brake application, it means that a driver has passed a signal at danger (serious and potentially fatal); or that he had passed a sensor in advance of a red signal (or tight curve) at a speed judged to be too fast to be able to stop in time; or there is a TPWS fault. Luckily for your driver's career, it seems this last one was the case. I rather imagine is was laughs of relief that you heard from the cab.
Signals are just lamps on posts. They don't stop trains. The separate TPWS system has track components that are activated when signals are red, and train circuitry that detects an overspeed situation when passing over these components and applies the brakes automatically.
Hope this helps
To be fair to them this is a very easy mistake to have made given they said the train arrived at their destination half an hour late. The link you posted appears to have corroborated this subsequently...
It would be easy to have thought that the train was stopped for an extra 10 minutes, rather than having lost that time en route after restarting. Most people wouldn't think to check the times of a train at a station they're not actually going to.
What, exactly, are you hoping to achieve by pointing this out?
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niggill617@gma
Member
TPWS plus is 75 mph to 100 mph, or has that fact been amended?
Yes, a bit silly pointing out facts or correcting information isn't it.
If anyone is still unclear, this video explains things well:
Initially it talks about signals passed at danger. TPWS overspeed sensors associated with a signal are discussed about 2 minutes 50 in. It should be added the same system can be present for a speed restriction. For example, if line speed changes from 75 mph to 40 mph, there will likely be TPWS before you get to the 40 mph. These could likely be set in the ball park of 60 mph, and trigger an emergency brake application should the train travel over them above this speed. In other words, the train could be within the current speed limit (75 mph) but still have an emergency brake application. This is because the calculations based on given maximum brake performance suggest the train would be speeding by the time it reached the 40 mph - not that it is currently speeding.
The issue presently, is modern units have such good brakes that TPWS installations are sometimes a little too keen - where, say on a 195, normal braking will bring the train down safely where this would not have been the case on, say, a 142.
Initially it talks about signals passed at danger. TPWS overspeed sensors associated with a signal are discussed about 2 minutes 50 in. It should be added the same system can be present for a speed restriction. For example, if line speed changes from 75 mph to 40 mph, there will likely be TPWS before you get to the 40 mph. These could likely be set in the ball park of 60 mph, and trigger an emergency brake application should the train travel over them above this speed. In other words, the train could be within the current speed limit (75 mph) but still have an emergency brake application. This is because the calculations based on given maximum brake performance suggest the train would be speeding by the time it reached the 40 mph - not that it is currently speeding.
The issue presently, is modern units have such good brakes that TPWS installations are sometimes a little too keen - where, say on a 195, normal braking will bring the train down safely where this would not have been the case on, say, a 142.
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Wow, way to dob your colleague in…….!
As Lionel Hutz once said in The Simpsons, “there’s ‘the truth’ *smiles brightly* and ‘the truth’ *frowns, shakes head*”
It's definitely very revealing when people create a huge fuss about a very small point which wouldn't be apparent to ordinary travellers, and has no overall effect on anything yes.
Generally, anyone who offers a correction in a case where there was no possibility of misunderstanding is doing it to make themselves sound knowledgeable rather than to actually assist finding the truth.
True, but in layman’s terms the signal does stop trains, but it’s all tied in with the “signalling system”. E.g. An AWS fail to acknowledge or TPWS activation due to the associated red signal.
Ahhh I think I understand now, thank you!
If you don't pay much attention to the time the train stopped, and then get to your destination 30 minutes late, it's not entirely unlikely that you will perceive most of the delay to have been when stopped. Time seems to passed very slowly on a packed train stopped outside a station, as an ex-South London commuter I have plenty of experience of this phenomenon
niggill617@gma
Member
Normal braking should be 6 percent g in good adhesion conditions; this rate within the perturbation curve will not activate TPWS, as stated in the Rail Industry Standard. All passenger trains can easily achieve this rate on clean wet rails/wheels.
Yes the calculations are based on trains with enhanced braking capability. Note annex 3 and 4 of the attachment.
I wonder if this was an attempt at humour that fell flat on it's face, rather than the snarky comment most are taking it as? Just trying to be ironic about speeding when you're sat stationary (the opposite to how everyone calls the M25 a car park), especially if a fault meant the train got stopped when everything was fine.
The common one at Leeds is leaving platform 11 or 12 on a yellow and being routed onto the through road. Then reading across to one of the adjacent signals.
You’d have a job tripping the tpws though as the linespeed is only 15.
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I’d guess that it’s a fault with the train rather than an incident. The delay was probably trying to reset the aws/tpws a few have struggled.
Even if it was, it’s just not appropriate to make jokes like that in this day and age, where everything ends up on social media, without context.
I'm not entirely sure what point you're making here? The annex essentially demonstrates what I was explaining.
As for the 6%g comment, I think you've misunderstood my point (perhaps I didnt explain it thoroughly) - predominantly as, as a driver, you haven't the foggiest idea how much brake force equates to 6%g - you just have your normal brake points and your normal brake %/step used, along with check speeds on the way in. No traction unit displays this information and you're not given graphs/tables to calculate it (as it's far beyond what's necessary to safely operate a train - its good background and base knowledge but theres nothing to be gained from calculating your %g on a given station stop). The problem I'm alluding to, especially when going from an older unit with a much gentler "normal" brake application, is the temptation for drivers to brake later than they would in older units, utilising their "normal", more effective brake/braking technique of the newer units, thus bringing them far closer to the TPWS at a higher speed (far more relevant for PSRs than signals). Its an acknowledged risk across various operators.
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Leave it, it’s his baby and somehow he manages to wrangle it in to any thread!
Can you explain the perturbation curve please. I have never heard of the phrase. Graphs would be nice too.
I am unsure, but why would 6%g not activate the TPWS ? Are there TPWS grids that measure braking forces ? If I was going too fast over the grids but was braking in say, 12%g would the TPWS not fire ?
Precisely this. It has been pointed out on several occasions that we aren’t taught anything like this in training. Not sure if this was previously the case though? We drive to our professional route and traction knowledge and experience.
That one always causes a little bit of confusion among passengers if there's no announcement made about it too, for the train to almost immediately come to stand again, after moving just a few metres out of the platform, and still within the overall station area. Some conductors do specifically say that there's a short wait but the train will be moving again shortly though. Obviously that's with normal operation and not a spad!
rheingold103
Member
Running brake test after train reversal or driver change?
PG
Established Member
With the huge proviso that I'm not in the industry, this document (pages 20-21) may assist with answering that question. As other posters have mentioned it doesn't seem like something that the occupant in the hot seat needs to get het up over. Give me someone who knows what they're doing any day of the week
I’m sure you know that TPWS will intervene whenever the speed of the train is above the trip speed, irrespective of whether the brake is in or not (albeit whether the driver applied the brake will be relevant to how their performance is viewed in any subsequent investigation).
I’m afraid not. Unless I’m missing something, this is related to ERTMS rather than TPWS. These are completely different systems so this document has no relevance to the current situation.
I’d be worried if any person “in the hot seat” didn’t get “het up” over a TPWS event which could end their career (yes, it’s taken that seriously). Would you feel confident travelling on a train being driven by someone who doesn’t brake for speed restrictions to the point where an emergency system (which isn’t present everywhere) has to intervene?
PG
Established Member
Fair point and you're better placed to know than me. Hopefully the poster whom @ComUtoR question was aimed at will reply in due course.
I think we're at crossed purposes here, my 'het up' comment was in relation to the perturbation curve discussion. I totally agree with you. I was more angling at the emphasis a minority of posters were placing on theory over practice. I think @LCC106 put it far better than I have
I think we're at crossed purposes here, my 'het up' comment was in relation to the perturbation curve discussion. I totally agree with you. I was more angling at the emphasis a minority of posters were placing on theory over practice. I think @LCC106 put it far better than I have
Yes apologies I perhaps misread you there. You (and @LCC106) are right in that analysis.
Don’t go there with how that poster thinks we all need to memorise a list of braking curves, calculate E=MC2 to safely drive trains…
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MichaelTrains
Member
Thank you for the above information.
I'm glad that nothing serious happened and that the driver wasn't at fault.
I wasn't criticising them for laughing. I was only reporting what I heard.
It sounds to me that, more than anything, something has been lost in translation slightly, enough to cause a minor misunderstanding.
ASharpe
Member
Yes, (almost) always out of the bay platforms. Just a few have been far more noticeable now for some reason.
eman_resu
Member
I had exactly that problem on a TPWS OSS design project a couple of years ago. The new DMU had far superior braking curve compared to the loco hauled stock also utilised. If we set speed for the DMU, the LHS overran substantially at line speed, if we set for the LHS then the DMU would either trigger every time based on drivers typical braking, or create delay as they had to slow down too early.
The solution was to set the OSS for the DMU, and lower the line speed for the LHS, we eventually had three separate OSS set to just above the typical braking curve for the DMU, which also managed the LHS as the curves closed up as the speed under braking reduced.
It was an interesting project.
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