Train delayed due to excessive speeding

[Efini92]

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.

Interesting solution, I wish they had done that on the up fylde approaching Preston.
There was a lot of TPWS activations approaching the 35/55 when it was new.

 

[niggill617@gma]

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 ?

When a train decelerates the retarding force may not be uniform throughout the braking distance, even with a constant brake step selection, and gradient. The reasons for this maybe perturbations; for example the coefficient of kinetic friction will increase with cast iron brake blocks, as the consist slows down. Even a sustained strong gust of wind will have some insignificant effect.

Does the attachment graph satisfy your query? Passenger train TPWS timers are set to 0.974 millisecond. Therefore if the grids are 18.4 m apart, the trip speed will be just over 42 mph ( 18.4 m divided by 0.974 milliseconds = 18.89 m/s ). The illustration graph shows 41.5 mph, I guess this is just within tolerance. If a train is speeding at 45 mph over the grids, but braking at 12 percent g, of course the TPWS will trip.

The attachment also defines defensive driving braking distances, this equates to an established 6 percent g rate of deceleration. That should be 50 percent braking power of modern traction. During a running brake test this would yield 7.6 seconds to slow by 10 mph with an established retarding force.

 

[the sniper]

He sure told you...

 

[ComUtoR]

He sure told you...

Yep, a month later and after I got the answer in post #82

The graph was pretty though.

== Doublepost prevention - post automatically merged: 1 Jan 2023 ==

Does the attachment graph satisfy your query?

Yes, and thank you.

If a train is speeding at 45 mph over the grids, but braking at 12 percent g, of course the TPWS will trip.

This confirms my suspicion that brake rate will not affect the TPWS. It's purely a speed thing. The braking is just to determine the physics.

That should be 50 percent braking power of modern traction. During a running brake test this would yield 7.6 seconds to slow by 10 mph with an established retarding force.

What if I was doing a running brake test at 10mph and only used step 1 ? Does a running brake test always have to be 50% and for 10mph ?

What if I didn't do a running brake test ?

 

[43066]

During a running brake test this would yield 7.6 seconds to slow by 10 mph with an established retarding force.

Nobody times their running brake tests, it’s all done by feel.

 

[niggill617@gma]

Nobody times their running brake tests, it’s all done by feel.

Do you think feel and theory would be better, than feel alone? It clearly would have helped regards the Edinburgh Sleeper near disaster, and other incidents of similar magnitude.

 

[zwk500]

Do you think feel and theory would be better, than feel alone? It clearly would have helped regards the Edinburgh Sleeper near disaster, and other incidents of similar magnitude.

The theory would have made no difference to the Edinburgh incident. The driver performed a running brake test and it was satisfactory. Better physics knowledge would not have opened the cocks when it came to apply the brakes.
Please get off your high horse about this braking figure obsession.

 

[LAX54]

I'm sorry, I don't quite understand this. Why would the linespeed be any higher than the speed at which a train can "safely stop/slow for the associated risk"?

Does this not indicate that the public that think Drivers just sit in the cab and simply start and stop, and follow green lights, is so, so far wide of the mark !

 

[driverd]

Do you think feel and theory would be better, than feel alone? It clearly would have helped regards the Edinburgh Sleeper....

My opinion would be that the theory is useful, but it's too complex to work out what speed reduction should be seen for a certain speed in a certain time. At our TOC we have 3 different types of brake in use (tread/disk/regen). Especially with tread but to a lesser extent with the other two types, speed is going to massively influence you're brake curve. Eg: if you performed the RBT at 40 mph you'd lose 10 mph way quicker than at 70 mph. You'd then need drivers to know how long it should take to lose 10 mph - at 40/50/60/70 heck, even 61/62/63/64 mph etc. Its just too much information to retain. To reference some kind of handbook would present too much distraction - and this is even before we've taken gradient into account.

The RBT is surprisingly accurate as it stands. You can very quickly get a feel for a unit and how it's brakes handle - again, speaking as someone who signs various types of brake system on units of widely varying age, I've had all different types of brake performance and haven't yet missed a station etc (I'm sure plenty of other drivers will vouch for this too). You quickly get a feel for a unit because, on a given route, you tend to do the RBT in the same location, so can quickly detect if you're still braking beyond the point that you've usually lost 10 mph.

Again, as per other posts, the RAIB report into the sleeper problem shows that the brake performance at high speed was satisfactory, so having done a timed RBT, the driver might have thought the set had brakes that were a bit weaker than usual but that'd be about it.

 

[43066]

Do you think feel and theory would be better, than feel alone? It clearly would have helped regards the Edinburgh Sleeper near disaster, and other incidents of similar magnitude.

Nope.

It wouldn’t have helped in the Edinburgh sleeper incident as explained above, and such incidents are (thankfully) vanishingly rare, anyway. Better to focus on more relevant training such as non technical skills.

 

[66701GBRF]

Do you think feel and theory would be better, than feel alone? It clearly would have helped regards the Edinburgh Sleeper near disaster, and other incidents of similar magnitude.

I am curious to know why you seem so hell bent on teaching or mandating that drivers know such physics? The running brake test is a dynamic assessment of the brakes of that particular unit/loco/train and incurs variables such as (not limited to) trailing weight, type of brakes and age of brake equipment. All the driver needs to know and be concerned of is does the control inputs match what is happening there and then in the real world, not whether it matches some equation or theory.

 

[Napier]

What happened anyway? Class 195 speeding? not like Northern to be doing that. Oh well, as long as there are no major delays, i'm sure it would be fine. To be honest, i wonder if trains get tickets for speeding?

Used to get a class 4 self regulating in section so he didn't arrive at a holding point to early, 22 mins in an 11 minute secton, with a possible Pee stop and diver change at a convenient station location.

== Doublepost prevention - post automatically merged: 13 Jan 2023 ==

Sounds serious too, as there was a 30 minute delay. Seen them done at similar sized stations. I can’t think why a TPWS would trip if the train LEAVES a station too quickly other than for a spad though. Hence my first question being, how far from the station were they. But I haven’t got a clue so I won’t argue.

Once had a guard ring me from the rear of a 142 telling me that in his opinion there should be a ESR impossed because he felt a slight jolt, I am still waiting of the driver ringing me and that was in 2012!

 

[TreacleMiller]

I am curious to know why you seem so hell bent on teaching or mandating that drivers know such physics? The running brake test is a dynamic assessment of the brakes of that particular unit/loco/train and incurs variables such as (not limited to) trailing weight, type of brakes and age of brake equipment. All the driver needs to know and be concerned of is does the control inputs match what is happening there and then in the real world, not whether it matches some equation or theory.

Deceleration calculations that use an ideal circumstance for the purpose of an academic exercise only are of no use to a driver in the moment. They never have been and never will be.

Rail adhesion varies considerably so any ideal value is of little use.

That sort of "effort" for calculation is calculated on our traction within the trains control units. Most modern traction can dynamically adjust braking force depending on various factors including demand, carriage weight, adhesion and so on.


Someone who knows something desperately trying to build themselves up on the Internet comes to mind.