Could trains be fitted with an Anti-lock braking system?

[Teaboy1]

Moderator note: Split from

Incident at Talerddig, Wales - 21/10/2024

Two trains have collided at Talerddig, Wales. Both trains are reported to be Class 158s running in 2 car sets. (Source, Realtime trains) At this time this is a developing situation and not all details are out in the open. The trains involved are believed to be: 1S71 Machynlleth to Shrewsbury...

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If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop.

Surely modern stuff could be retro fitted with an ABS system.

Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

 

[skyhigh]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

Trains have WSP, not ABS. And yes, 158s are fitted with it.

 

[Bletchleyite]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

The purpose of ABS in a road vehicle is to allow steering control to remain without the driver having to modulate the brake pedal themselves. It doesn't make a significant difference to the effectiveness of the actual braking. Trains have systems more geared towards improvement of braking performance.

 

[bramling]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

Yes they do, albeit more primitive than more recent trains, but there comes a point where WSP cannot overcome slide. WSPs offer an improvement over having no protection at all, but can’t resolve extreme situations. An example is the 375 that slid for a considerable distance at Stonegate, though IIRC the situation there wasn’t helped by the train having no sand.

 

[Spartacus]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

ABS normally works well in motor vehicles because there's a lot of friction between the tyre and tarmac. Take away or massively reduce that friction, say on ice or when aquaplaning, and it's next to useless. Those are the sort of conditions experienced when a train's sliding on a contaminated rail.

 

[millemille]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

Trains have Wheel Slide Protection (WSP) equipment which, when an axle's rotational speed differs from the train's speed over ground by more than a set amount (typically 20%), attempts to control the slide by reducing brake effort on that axle until the slide is under control because the wheel's rotational speed is within the allowed difference. Different WSP systems attempt to control the slide in different ways; some simply release all brake effort until the wheel is no longer sliding uncontrollably and then apply full brake effort again, other release brake effort in a controlled manner until the slide stops and then hold the pressure that the slide stopped at.

The purpose of the WSP system is primarily to prevent damage to the tread of the train wheel that occurs when the wheel is sliding. There is some improvement in stopping performance when comparing an axle being controlled by WSP against a locked axle that is sliding. But you have to remember that as soon as WSP activity occurs the train is no longer going to stop as well as on clean dry rail because, putting it crudely, the brakes are being released to control the slide.

Once WSP activity is occurring the train's ability to stop is limited by the co-efficient of friction in the wheel/rail interface.

Sanders work by improving the co-efficient of friction, the sand is delivered into the wheel/rail interface and is crushed which raises the coefficient of friction.

 

[Lurcheroo]

Trains have Wheel Slide Protection (WSP) equipment which, when an axle's rotational speed differs from the train's speed over ground by more than a set amount (typically 20%), attempts to control the slide by reducing brake effort on that axle until the slide is under control because the wheel's rotational speed is within the allowed difference. Different WSP systems attempt to control the slide in different ways; some simply release all brake effort until the wheel is no longer sliding uncontrollably and then apply full brake effort again, other release brake effort in a controlled manner until the slide stops and then hold the pressure that the slide stopped at.

The purpose of the WSP system is primarily to prevent damage to the tread of the train wheel that occurs when the wheel is sliding. There is some improvement in stopping performance when comparing an axle being controlled by WSP against a locked axle that is sliding. But you have to remember that as soon as WSP activity occurs the train is no longer going to stop as well as on clean dry rail because, putting it crudely, the brakes are being released to control the slide.

Once WSP activity is occurring the train's ability to stop is limited by the co-efficient of friction in the wheel/rail interface.

Sanders work by improving the co-efficient of friction, the sand is delivered into the wheel/rail interface and is crushed which raises the coefficient of friction.

To add to that, I believe (on the 158’s atleast) the leading axle will be locked in a ‘controlled slide’ to help attempt to clean the rail head so other wheel sets May grip better.

TFW’s 158’s (I think they’re the only ones left to have it, but someone may correct me) have an Emergency one-shot sander that the driver can deploy which fires a gluey sand compound under the leading wheels to try and help get the train stopped.

 

[millemille]

To add to that, I believe (on the 158’s atleast) the leading axle will be locked in a ‘controlled slide’ to help attempt to clean the rail head so other wheel sets May grip better.

Pretty sure that isn't the case.

 

[edwin_m]

To add to that, I believe (on the 158’s atleast) the leading axle will be locked in a ‘controlled slide’ to help attempt to clean the rail head so other wheel sets May grip better.

TFW’s 158’s (I think they’re the only ones left to have it, but someone may correct me) have an Emergency one-shot sander that the driver can deploy which fires a gluey sand compound under the leading wheels to try and help get the train stopped.

Pretty sure that isn't the case.

I believe some WSPs release the brakes on the leading axle deliberately to get an accurate measure of train speed, but I very much doubt any lock an axle intentionally, as this would cause the exact thing they are trying to prevent. Perhaps this refers to the tread brakes that are fitted to leading wheelsets on some (maybe now all?) 158s.

I was involved in the trials of the one-shot sander, including stopping with and without it in poor adhesion on the worst part of the Salisbury-Exeter lines on the first ECS on a foggy morning, and it is certainly effective if it is used and functions as intended. Note it sprays pure sand from a pressurised cylinder similar to a fire extinguisher - the gluey compound is Sandite, dispensed from the rail head treatment trains. However, this was the best part of 30 years ago and pretty much all MUs now have far more sophisticated sander systems which can dispense smaller quantities of sand on multiple occasions, whenever the WSP detects poor adhesion while a certain braking level is demanded.

 

[Lurcheroo]

Pretty sure that isn't the case.

Well I have just checked my 158 traction user guide and I will quote from it.
“Remember the audible WSP activity and erratic speedometer movement is being caused by the leading wheel sets operating in a controlled slide condition. This is beneficial because it cleans the rails for other wheels on the train giving them better grip so they are able to exert their full braking effect”

Now, our speedos are no longer erratic under WSP as it is a digits ERTMS Speedo that doesn’t just use a wheel speed sensor to provide the information.

I was involved in the trials of the one-shot sander, including stopping with and without it in poor adhesion on the worst part of the Salisbury-Exeter lines on the first ECS on a foggy morning, and it is certainly effective if it is used and functions as intended. Note it sprays pure sand from a pressurised cylinder similar to a fire extinguisher - the gluey compound is Sandite, dispensed from the rail head treatment trains.

ahh that’s good to know! Must have gotten confused, essentially thought it was a sandite type compound in it.

 

[357]

but I very much doubt any lock an axle intentionally, as this would cause the exact thing they are trying to prevent.

345s and 720s at the very least do exactly this in order to try and clean the rail for the following wheelsets/bogies.

 

[millemille]

Well I have just checked my 158 traction user guide and I will quote from it.
“Remember the audible WSP activity and erratic speedometer movement is being caused by the leading wheel sets operating in a controlled slide condition. This is beneficial because it cleans the rails for other wheels on the train giving them better grip so they are able to exert their full braking effect”

Now, our speedos are no longer erratic under WSP as it is a digits ERTMS Speedo that doesn’t just use a wheel speed sensor to provide the information.

That's the WSP working normally, it isn't "locked" in a controlled slide.

The WSP on the 158's isn't capable of holding a controlled slide, it can only release or apply the brakes, not hold. That's why the speedo was erratic, as the brake effort releases the wheel speed recovers so the brake effort then applies and the wheel goes back into slide and the brake effort then releases and so on. Although I have it in my mind, having been involved on the periphery of the Salisbury investigation and looking at certain aspects of the class 158 brake, WSP and sanding system, that the speed signal didn't come from a single axle but from the WSP rack and it deriving a speed signal from all 4 axles and their behavior because we were looking at the potential risk, with speed dependent variable rate sanding in the future on the 158/159's, that a deep slide could give an artificially low speed signal which meant the sand delivery rate was too low for the train speed over ground. But I've slept since Salisbury and I'm getting old....

More modern WSP system have a 3 function WSP dump valve which can release brake cylinder pressure (vent), apply full brake cylinder pressure and hold at a pressure less than full brake cylinder pressure. The latter being the controlled slide you describe.

 

[anthony263]

If leaf mulch can be so lethal, one question that springs to my mind is are the 158's fitted with ABS? I assume not as I believe they are Disc brake only and once the wheel is slipping on a layer of mulch, it is not likely to stop. Surely modern stuff could be retro fitted with an ABS system. Cars, vans and big HGV's are fitted with ABS and they work brilliantly so why not passenger trains?

Try stopping a. Bus on leaves not easy

 

[Lurcheroo]

That's the WSP working normally, it isn't "locked" in a controlled slide.

The WSP on the 158's isn't capable of holding a controlled slide, it can only release or apply the brakes, not hold. That's why the speedo was erratic, as the brake effort releases the wheel speed recovers so the brake effort then applies and the wheel goes back into slide and the brake effort then releases and so on. Although I have it in my mind, having been involved on the periphery of the Salisbury investigation and looking at certain aspects of the class 158 brake, WSP and sanding system, that the speed signal didn't come from a single axle but from the WSP rack and it deriving a speed signal from all 4 axles and their behavior because we were looking at the potential risk, with speed dependent variable rate sanding in the future on the 158/159's, that a deep slide could give an artificially low speed signal which meant the sand delivery rate was too low for the train speed over ground. But I've slept since Salisbury and I'm getting old....

More modern WSP system have a 3 function WSP dump valve which can release brake cylinder pressure (vent), apply full brake cylinder pressure and hold at a pressure less than full brake cylinder pressure. The latter being the controlled slide you describe.

Ahh right that’s very interesting!
Well I wonder with ERTMS getting it’s speeding readings from other sources too (during a slide or speedos still show the correct speed) if variable rate sanders would have negated that issue. With them due to disappear and lose their ERTMS kit I can’t see why changes being made now!

Perhaps I have confused the front axle getting locked with 197’s which are what I primarily trained on. I’ll have to check the TUG for them and see what it says. I’m also curious as to whether or not they have variable rate sanders.

It would also be interesting if the RAIB report makes any investigation as to if it expects a 197 May have been able to prevent the collision due to better sanding and WSP systems.

 

[amarshe]

Thoughts to all involved. I've aquaplaned and hit black ice several times driving/riding motorbikes/bikes/cars - all you can do is hold tight and ease off the accelerator/brake and resist steering. Can only imagine a train on slippery track - massive credit to all train drivers in this season, steel/steel is a totally different ballgame to rubber/tarmac. ABS I guess not applicable to trains and in any case useless when you're sliding.

 

[Lurcheroo]

ABS I guess not applicable to trains and in any case useless when you're sliding.

As stated above, ABS is designed to allow the driver to still have functional
Steering to avoid an obstacle whereas trains have WSP which has a good explanation in post #180

 

[bahnause]

Ahh right that’s very interesting!
Well I wonder with ERTMS getting it’s speeding readings from other sources too (during a slide or speedos still show the correct speed) if variable rate sanders would have negated that issue. With them due to disappear and lose their ERTMS kit I can’t see why changes being made now!

It usually has at least two sources for the speed readings (doppler radar, accelerometers, LED scanners, rotation counters). However, it does not give an accurate reading, because the algorithm detects wheel slip or differences between sensors and puts a safety margin on top of the actual speed. The speed/distance measured by the ERTMS is safety critical. Even long after releasing the brakes or coming to a stop, the speedo will show a higher speed than the actual speed.

 

[bahnause]

As stated above, ABS is designed to allow the driver to still have functional
Steering to avoid an obstacle whereas trains have WSP which has a good explanation in post #180

In 99% of cases, WSP manages to prevent damage without impairing braking performance. However, there are exceptional cases in which WSP can lead to a massive increase in braking distance. However, this only occurs with certain combinations of WSP systems and specific rail conditions.

 

[Lurcheroo]

It usually has at least two sources for the speed readings (doppler radar, accelerometers, LED scanners, rotation counters). However, it does not give an accurate reading, because the algorithm detects wheel slip or differences between sensors and puts a safety margin on top of the actual speed. The speed/distance measured by the ERTMS is safety critical. Even long after releasing the brakes or coming to a stop, the speedo will show a higher speed than the actual speed.

Yeah I know the 158’s have certainly have at least odometery sensors, Doppler radar and then there are positioning balises that tell the system it’s exact location every so often.

It does explain something that happens sometimes, if a unit is a bit out it will be governing you down to a speed reduction then right as it says you have to be at that speed, the ‘allowable speed’ jumps up a bit and continues reducing again from there.

 

[D365]

However, it does not give an accurate reading, because the algorithm detects wheel slip or differences between sensors and puts a safety margin on top of the actual speed.

Why would that safety margin not be incorporated into the braking curve instead of being presented as a degree of error in the vehicle speed readout?

 

[bahnause]

Why would that safety margin not be incorporated into the braking curve instead of being presented as a degree of error in the vehicle speed readout?

Braking curves have their own safety margins built in depending on the implemented correction factors to determine the confidence level. The additional safety margin is is added for a detected loss of the exact distance measurement. This is one of the reasons why ETCS can noticeably reduce capacity compared to conventional, highly optimised signalling systems.

 

[Re 4/4]

Some trains on the continent have an extra magnetic brake that is for emergency use only and might require the train or the track to be repaired after use. I think the English term is Eddy current braking system.

They are independent of friction and the axles, so they ignore any leaf mulch.

I wonder if something like that could help in theory? In practice, it's probably too expensive to fit everywhere and I believe the braking force is proportional to velocity, so they may be of little use for low-speed SPADs/MA overruns in the first place.

 

[hexagon789]

Some trains on the continent have an extra magnetic brake that is for emergency use only and might require the train or the track to be repaired after use. I think the English term is Eddy current braking system.

An Eddy Current brake is quite different to a traditional electro-magnetic track brake - the former is only found on a limited number of high-speed trains such as the ICE3. The latter is very common in Europe on most curremt trains and has been seen on coaching stock passed for 200km/h or more built since the 1960s (it is a legal requirement in Germany for 200km/h running). It is also standard on Trams, including all modern types used used in Britain and also found on some light rail vehicles such as the Tyne & Wear Metrocars.

Some discussion on emergency track brakes is taking place in this thread:

Could an anchor system help stop trains in an emergency?

Moderator note: Split from https://www.railforums.co.uk/threads/incident-at-talerddig-wales-21-10-2024.275845/ I have plenty of questions about incidents such as this, and how to consider them holistically. I don’t know much about the signalling in operation here, but I’d caution against any...

www.railforums.co.uk

 

[bahnause]

I was involved in the trials of the one-shot sander, including stopping with and without it in poor adhesion on the worst part of the Salisbury-Exeter lines on the first ECS on a foggy morning, and it is certainly effective if it is used and functions as intended.

I found an example for the use of sand in real life on youtube. A single yellow (next signal shows a red) at a speed of 150km/h. Wet conditions, but not a lot of leafs on the track. Some thoughts:

• Stock involved is an ICE 1. Seems to be a long one with 12 or 13 coaches.
• The motor bogies on the ICE 1 tend to be prone of wheelslip.
• Magnetic brakes not used.
• Proprotional brake mode used, so the dynamic brake didn't max out. In normal mode, the dynamic brake is maxed out before applying the dis brakes.
• No sanding over the points, they don't like sand.

All in all not very dramatic, just a "surprise signal". The action begins at around minute 6:55

ICE 1 / Sand