Oil Train

[MidlandMike]

I could see letting the railroad opt out of a crude haul, as long as in that case they grant open access for the crude haul to the nearest competing RR.  No one really believes that he railrads don't want the CBR business.

[Euclid]

About 12 days ago, I sent an inquiry to the FRA which was confined to asking why ECP is widely reported to offer a stopping distance of up to 70% less than conventional air brakes, and yet many people claim that the difference in stopping distance is only a few percent.  I asked this question of the FRA just prior to my learning that the difference is explained by the fact that the “Service” application of ECP offers far more reduction in stopping distance than does the “Emergency” application, so I did not mention this in my question.

I just got a reply from the FRA in which they respond to my question about stopping distance as follows: 

They said nothing about the stopping distance difference between a “Service” application and an “Emergency” application.  They said that the stopping distance for ECP will depend on many variables, and conclude with this comment: 

“It is not really possible to come up with a single number (or percentage) that quantifies the benefits of ECP in terms of stopping distance as the benefit will depend on the scenario.”

I do not understand the basis for that conclusion.  I asked about the comparison of ECP to conventional braking, and not about the variation of braking of ECP according to variation in stopping conditions.  For my question, you would pick one variety of stopping condition, and apply it to a stopping test of both brake systems.  So basically, they did not answer my question about stopping distance by saying that the question has no answer.

Then surprisingly, the FRA reply continued and covered other benefits of ECP, some of which have nothing to do with unit trains, and thus go beyond the issue of oil train safety.  That suggests to me that the ECP mandate is partly focused on making railroads generally safer in addition to making oil trains safer.  And even going beyond that, the FRA reply cites several operational advantages of ECP that have nothing to do with safety, but rather, are related to adding operating efficiency to the railroads. 

Immediately after the mandate, the FRA highlighted the ability of ECP to mitigate damage in a derailment.  The AAR countered that they want to prevent derailments rather than mitigate damage after derailments begin.  In the FRA email response to my ECP question, the sender goes into detail about how sequential application of conventional air brakes produces a variety of effects (notably slack run-in) that can cause derailments, whereas, these effects are eliminated by ECP.  So with that, they are now on the same page as the AAR in saying that the objective is to prevent derailments by de-emphasizing ECP-improved stopping and highlighting the reduction of slack run-in.  However, the FRA explanation of this raises many questions about what they mean.

Continuing, the FRA response seems to be referring to load/empty sensors as being a fundamental part of ECP when they say this:

“Additionally, ECP brake systems allow for all cars in the train to brake at the same braking (or deceleration) rate even if they had varying physical brake configurations; which is something that cannot be achieved on conventional pneumatic systems. This ability of ECP cars to adjust their effective net braking ratio (NBR) further adds to ECP’s ability to keep run-in forces to a minimum and thus allow the railroad to potentially operate with a higher train-average NBR.”

 

Again this raises questions.  How do ECP cars adjust their effective net braking ratio, and why is this not achievable with conventional pneumatic systems?    

[Euclid]

In the FRA reply to my inquiry, they said this:

“Under conventional braking, pneumatic brake signal propagation through the length of the train results in notable run-in forces on cars at the head end of the train, which may result in sliding (and potentially a derailment) of heavily braked and/or lightly loaded wheels. Under ECP operation, the simultaneous brake application results in uniform braking and minimal run-in forces, resulting in no additional sliding propensity of the braked wheels. These reduced run-in forces between cars may result in less wear-and-tear on the cars over time and may reduce the potential of a derailment, especially in the case where the train is poorly assembled (for example, if too many empty cars are placed adjacent to each other).”

 

This is the first time that I have ever heard that slack run-in can cause wheel-slide.  I don’t understand the connection.

[Norm48327]

Assume empties at the front of the train and loads toward the rear. If the brakes on the empties are slowing the wheels the weight of the loads would push them before their brakes take hold.

[daveklepper]

i thought ECP mandates load sensing or at least a load-empty switch.    Modern light rail and rapid transit cars have it.

[Euclid]

Norm48327

Assume empties at the front of the train and loads toward the rear. If the brakes on the empties are slowing the wheels the weight of the loads would push them before their brakes take hold.

 

I can understand the point about slack running in.  Even if all cars are loaded or all empty, or any mix of loads and empties, if an emergency application is initiated from the head end, the brakes will apply in sequence from front to rear.  So slack will run in as the forward cars set up before the rearward cars.

 

But why would this cause wheel slide?

 

[schlimm]

Euclid

But why would this cause wheel slide?

The greater mass of the loaded cars still rolling will push the brake-locked empties.  Try it with a large truck pushing a car with locked wheels in front.

 

[Euclid]

Well, there is always a possibility that wheels can lock and slide during braking, and it is the empties that are most likely to slide wheels if that happens. 

 

I just don’t see what slack run-in has to do with it.  Whether slack is running in or not, the whole train is rolling.  So all cars, whether empty or loaded, are contributing the rolling force, and that total rolling force  is far greater than the force needed to slide a car’s wheels; if the actual condition for wheel slide exists.  

 

The actual condition that causes a car’s wheels to slide is when its brake-shoe-to-wheel friction exceeds the wheel-to-rail adhesion.  If that condition is met, there will be more than enough force to move the car with its wheels locked regardless of what the slack is doing.          

 

Also, the premise stated by the FRA reply does not say that empties are near the front and loads are behind them.  They make no distinction about that.

[schlimm]

The process seems clear enough to me and probably most others.

"sliding (and potentially a derailment) of heavily braked and/or lightly loaded wheels. Under ECP operation, the simultaneous brake application results in uniform braking and minimal run-in forces, resulting in no additional sliding propensity of the braked wheels. These reduced run-in forces between cars  may reduce the potential of a derailment, especially in the case where the train is poorly assembled (for example, if too many empty cars are placed adjacent to each other).”

Obviously slack run-in isn't a factor towards the rear of the train.  The empties would be subjected to more pushing on locked wheels towards the front because their brakes were set earlier.

[Euclid]

Slack run-in can definitely cause derailments because it is a surge of compressive or buff force that can buckle the train and jackknife cars.  And slack run-in definitely grows in force as it moves forward.  It is also true that the empty cars subjected to hard slack run-in are most vulnerable to being jackknifed by the surge of buff force because the empties have less weight to hold them down.  It is also true that loads will produce more run-in force than empties.  And it is true that ECP definitely reduces slack run-in.

 

The writer of the FRA reply includes all of these elements in his explanation, but he comes to a different conclusion.  He says nothing about slack run-in buckling the train and causing a derailment.  Instead, he concludes that the surge of buff force causes wheels to slide.  And the wheel slide either directly causes a derailment; or it damages the wheel and that damage later causes a derailment.      

 

Yet, the surge of buff force has nothing to do with causing wheel slide.  Wheel slide is caused by too much braking force in relation to a car’s weight.  The instant, simultaneous application of ECP brakes, and the resulting minimization of slack action helps prevent derailments, but not by preventing wheel slide.   These attributes of ECP brakes have nothing to do with preventing wheel slide. 

 

However, there is the possibility of ECP brakes being equipped to prevent wheel slide by sensing the load of the car and limiting brake force to what that car can stand without reaching the point of wheel slide.  This can also be done with conventional air brakes by adding similar sensing and control equipment.  So wheel slide is definitely related to brake force, but it has nothing to do with slack action. 

 

And even at that, while wheel slide alone could lead to a derailment, the bigger issue is simply the accumulative wheel damage that occurs with multiple brake applications.  The greater objective of the equipment that prevents wheel slide is the ability to raise the brake force on the loads.  Without it, the load brake force has to be limited to what the empties can handle because loads will eventually run as empties.  A system that can discriminate loads from empties can apply the maximum force for both, and thus achieve a much higher brake force for the loads.  Therefore the train stops faster to the extent that it contains loaded cars. 

 

In the FRA reply, the author has woven all of these elements and factors together, but without the proper cause and effect.     

[Paul of Covington]

   Euclid:

     "So wheel slide is definitely related to brake force, but it has nothing to do with slack action."

     I agree.   If the brakes are not locked up, which they shouldn't be with load-empty sensing on any type of brake system, it shouldn't matter how much they are pushed by slack action.  I think they have decided to mandate ECP and don't want to be confused by the facts.

[daveklepper]

I presume that load-empty controls are not generally applied to freightcars today.  Unit trains in truth don't need them, because they are normally all full or all empty.  (And thus the buckling argument against ECP does not apply to unit trains.)  And it is unit trains that generate the revenue that would make ECP a wise investment in addition to whatever safety improvements it makes.

[Euclid]

In the FRA reply to my inquiry, they said this:

“Additionally, ECP brake systems allow for all cars in the train to brake at the same braking (or deceleration) rate even if they had varying physical brake configurations; which is something that cannot be achieved on conventional pneumatic systems. This ability of ECP cars to adjust their effective net braking ratio (NBR) further adds to ECP’s ability to keep run-in forces to a minimum and thus allow the railroad to potentially operate with a higher train-average NBR.”

 

How does EPC do this?  It sounds like he is describing empty/loaded sensing.  He makes it sound like that is a fundamental attribute with ECP, as opposed to an add-on option.  He says it can’t be achieved on conventional pneumatic braking. 

Yet, if he is referring to empty/loaded sensing, it can in fact be achieved on conventional air brake systems as an add-on option.  So he is either wrong, or he is referring to empty/loaded sensing as being a fundamental attribute of ECP rather than an add-on option.

I have never understood empty/loaded sensing to be a fundamental attribute of ECP, but if it is, it would further reduce stopping distance beyond the reduction of stopping distance offered by the instantaneous application of ECP brakes.  

But the reduced stopping distance of ECP is always explained by the instant application.  Other than in the above quote, I have never seen ECP stopping performance explained by optimizing the net braking ratio of each car in the train.  If the NBR were factored in, I would think the stopping distance reduction of ECP would be way higher than 7% for emergency applications, as reported earlier in Wabtec charts.       

[Euclid]

daveklepper

I presume that load-empty controls are not generally applied to freightcars today.  Unit trains in truth don't need them, because they are normally all full or all empty.  (And thus the buckling argument against ECP does not apply to unit trains.)  And it is unit trains that generate the revenue that would make ECP a wise investment in addition to whatever safety improvements it makes.

Unit trains need empty/loaded brake force adjustment as much as any train, but they don’t need sensors to determine whether a car is loaded or empty.  Sensors could be used for that purpose on unit trains, but as you say, all cars in unit trains are either loaded or empty; so the loading of each car is known by the load/empty status of the whole train.  As discussed earlier, I believe the entire train could be switched to set the brake force on all cars simultaneously from low brake force for an empty train to high brake force for a loaded train.   

 

I am not sure what you mean when you say, “And thus the buckling argument against ECP does not apply to unit trains.”

 

What buckling argument is there against ECP?  ECP reduces the buckling tendency. 

[dehusman]

Euclid

Sensors could be used for that purpose on unit trains, but as you say, all cars in unit trains are either loaded or empty; so the loading of each car is known by the load/empty status of the whole train.

Incorrect in the case of hazmat trains (what we are discussing) and there will be exceptions on other types of trains.

[Euclid]

Do hazmat trains consist of loads and empties?

[BaltACD]

Do hazmat trains consist of loads and empties?

 

Both

[Euclid]

Can you elaborate?

[jeffhergert]

We really don't distinguish trains as being hazmat or non-hazmat for operating restrictions.  We use the term, "key train."  A key train is one that meets certain thresholds of hazmat loads. 

An empty ethanol train is not a key train, although it is considered to have hazmat residue.  A mixed manifest with 20 loads of certain types of hazmat, or lesser number of certain hazmat loads is a key train.  If the mixed manifest only has 19 loads of the lesser nasty stuff, but 10 cars of empty-residue cars, it is not a key train.  Even though it has 29 cars of hazmat/residue hazmat. 

That's the basics, without going into more detail about the certain types of hazmat. 

Jeff  

 

[dehusman]

Every "empty" train will have one or two loads (the cover cars).  There is also no guarantee that there won't be loads on an empty train or empties on a loaded train.  If there was a shop at the refinery for the cars, then there might be B/O empties on the loaded train to go to the home shop.  Every once in a while a railroad will move a block of cars on a unit train (such as loads of diesel fuel to an on line fueling location).  You may also have a car that was not loaded but not switched out. 99.99% of the time you are right.   But this whole discussion on oil trains is about exceptions, dealing with the small fraction that has a problem.  If you are dealing with small numbers then small exceptions matter. 

[Euclid]

Well, for what I am talking about regarding the load/empty unit train brake force selector switch, they will have to stop making small exceptions to uniform load/empty consists.  That would just be the price to pay for the greater good of being able to stop faster.  In the big picture, there has to be exceptions made to accommodate system changes.  Otherwise there will be some detail standing in the way of any significant change in anything.

 

Although there is another way around the problem.  You could develop the control system to have the master switch for the whole train, and then be able to set exclusions to the whole train setting.  The system would have to know where the loads and empties were in the train in order to execute the command to exclude individual cars from the whole train setting.  However, this would leave more room for error.      

[dehusman]

Euclid

Well, for what I am talking about regarding the load/empty unit train brake force selector switch, they will have to stop making small exceptions to uniform load/empty consists.

The cover cars aren't "small exceptions".

There are lots of ways to to have load/empty sensing.  You aren't really trying to find the best solution, you are trying to justify the solution you have chosen.

[Euclid]

So just set the cover cars for permanent brake force for a loaded car.  Then when you switch the whole train from loaded to empty, the cover cars remain set for loaded.  Why should that be a big problem?  Or you could just leave the cover cars set for empty, which I assume is where they are set by default.  Maybe they are set to loaded by default.  If so, just leave them set there.

 

My suggestions are based entirely on what I think is the best solution.  I have no stake or agenda that is influencing my suggestions.  Earlier in this thread, I was told that the mechanical-pneumatic load sensors are a maintenance headache, and the can therefore fail.  When they fail, they can flatten wheels or worse.  I presume this is why they are not commonly used. 

 

So, now that the FRA has mandated ECP, you have a communication cable that can be used for other things such as sensor data.  That cable also opens the door to switching brake force for loaded or empty trains to accomplish what those pesky load sensors do without needing them.  It seems like a win-win to me.     

 

But you say there are many solutions, and I am not seeking the best one.  What would be the best one?

[diningcar]

Way too much ?"?

Let's  just allow the soloist to continue communicating with him/herself

[Wizlish]

Euclid

But you say there are many solutions, and I am not seeking the best one. What would be the best one?

As we agreed ... and agreed ... and agreed, one which provides proportional braking force based on actual weight, on a car-by-car basis, which provides quick and positive response to wheelslide (again on a car-by-car basis), and which can provide effective differential braking using cars that may have disparate weights.

The two-position system accomplishes none of these, yet requires much of the expensive componentry of an ECP system.  Now it makes sense to use expensive equipment to compress transmission  bandwidth in DTV because you're using the modulation effectively.  With 'two-speed' proportioning, you're just being cheap.

So, now that the FRA has mandated ECP, you have a communication cable that can be used for other things such as sensor data. That cable also opens the door to switching brake force for loaded or empty trains to accomplish what those pesky load sensors do without needing them. It seems like a win-win to me.

I had never quite appreciated the jokes about carbon-fiber buggy-whip shafts or titanium hypersonic yaw strings before now.  You're going to use a 230V line, modulated as a communication bus, to turn your brake response (properly ignoring that for the locomotives and buffer cars) to one of two positions, regardless of actual car weight or car/brake condition?  Once you have the power and data buses, you can use load cells at the center bearings or in the sideframes and get both the average and instantaneous loadings very simply.  For only a slight increase in complexity you can get the load and force data multiplexed with individual car (or truck) ID, so there is no confusion even about which end of a car is experiencing particular forms of vibration.

Meanwhile of course you haven't described how the engineer knows that all the cars have gone to the desired 'loaded' or 'light' state.  Lights on the car frames won't assure this, and do NOT even assume someone is going to check indicators as part of walking the train for a brake test.  You also can't do an on/off light, since you're essentially having to discriminate three states, as with some 'binary' modulation schemes: high, low, and off/disconnected/broken. 

[daveklepper]

Gee Wiz!   Who needs all this Buuck Rogers stuff for a modern, purpose-built UNIT OIL TRAIN!

All oil cars in the train are loaded or empty, and when loaded are identacle with identacle loads.

So one switch for the whole train should be sufficient, controlled from the head end or manually set on each car when loading or unloading.   In the latter case the position of the switch must be obvious on the walk-by inspection before the train rolls.

Loose car railroading is a problem, but implementation for unit trains shoulo be easy, if the equipment is dedicated.

 

[BaltACD]

daveklepper

Gee Wiz!   Who needs all this Buuck Rogers stuff for a modern, purpose-built UNIT OIL TRAIN!

All oil cars in the train are loaded or empty, and when loaded are identacle with identacle loads.

So one switch for the whole train should be sufficient, controlled from the head end or manually set on each car when loading or unloading.   In the latter case the position of the switch must be obvious on the walk-by inspection before the train rolls.

Loose car railroading is a problem, but implementation for unit trains shoulo be easy, if the equipment is dedicated.

Even in 'unit train' operations, for a variety of reasons, not all loads actually contain full loads of product and not all empties are actually empty.  Any load/empty braking determination must be done on a car by car basis, not by a switch on the locomotive.

[Paul of Covington]

   I'm not trying to sound snarky, but why do we need a switch to select empty or loaded for the whole train?    Wouldn't an engineer know whether he has an empty or loaded unit train and apply the brakes at an appropriate level?   He or she is not a dumb robot who can't figure things out.

   Sorry, but I'm a bit touchy on this kind of thing, having worked (not railroad related) under management who treated us as if we were incapable of figuring things out for ourselves.

[Wizlish]

Paul of Covington

I'm not trying to sound snarky, but why do we need a switch to select empty or loaded for the whole train? Wouldn't an engineer know whether he has an empty or loaded unit train and apply the brakes at an appropriate level?

The whole discussion is predicated on the understanding that 'appropriate level' is emergency braking, 'big-holing the Westinghouse', applying the control in the cab as hard as it will go.  If we were talking about modulating the service brake for minimum controlled/safe stopping distance (which is precisely where I thought the control application ought to be made) it would make some sense to keep the engineer's 'hand' in the loop.  Even there, I'd prefer (as with antilock braking of the usual kinds) to have automatics determine the best modulation moment-to-moment until the train has come to a stop.

In emergency, the situation is de facto out of the engineer's hands when he has moved the lever to emergency position (or the trainline has parted and done the same to the brakeline, or the repeater valves in the EOTD or MTDs have dumped the trainline pressure, etc)  Any further adjustments of the brake apparatus will have to be done automatically, and that very particularly applies to sensing and, if necessary, adjusting the braking ratio.  It is also true that any adjustments made to vary braking ratio prior to an emergency application -- which is what Euclid's little two-position switch would do -- can't be modulated further once the train is in an emergency application.

[Euclid]

Quote by Dave Klepper:

 

Gee Wiz! Who needs all this Buuck Rogers stuff for a modern, purpose-built UNIT OIL TRAIN!

 

All oil cars in the train are loaded or empty, and when loaded are identacle with identacle loads.

 

So one switch for the whole train should be sufficient, controlled from the head end or manually set on each car when loading or unloading. In the latter case the position of the switch must be obvious on the walk-by inspection before the train rolls.

 

Loose car railroading is a problem, but implementation for unit trains shoulo be easy, if the equipment is dedicated.

 

 

Dave,

 

That is the way I look at it.  Apparently load sensors are not preferred on a widespread basis due to their first cost, maintenance expense, and possible failure that may damage wheels.  It may be that ECP offers improved load sensor systems, but the railroads do not prefer ECP either, so better load sensing though ECP has been a non-starter.  But now, oil trains pose a problem that load sensing could remedy, and the ECP brakes are mandated.  So it might be the perfect convergence for oil trains, ECP, and ECP-based load sensing.  ECP brakes reduce stopping distance in emergency applications by 7%.  How much would ECP reduce stopping distance when combined with load sensors?