Western Railroad Discussion > Stalled Trains

Yesterday, at approximately 4:40 PM while standing at Walong siding in Tehachapi Loop, I saw the longest train that I had ever seen there. It was a combination UP mixed manifest being shoved by a BNSF TOFC train. The UP train had a three unit combination of SD70M and C40-8 on the point and a two unit DPU set of same as pushers. Coupled to that was a five unit set of C44-9s from BNSF. I could not see if the BNSF units were MU'd to the UP DPU units, however it most certainly was one single train as it passed me. The spirit of cooperation, espesially at Thanksgiving, lasts on.

My question is: What actually occurs when an under-powered train, for whatever reason this happens, stalls on a grade? We all know that when an automobile stalls the engine lugs down and stops running. Does a similar thing happen on a locomotive? Does it become a wheel slip situation? How does a locomotive, or a trainset, bog down under load? What are the symptoms of a stall? This past Saturday (11/23) a train was stalled in Cliff Siding, but this was caused by too much grease on the rails (as stated by the engineer and overheard on the radio). I won't even guess why there was too much grease in the rails in a siding as normally the greasers are on the main track on this hill.

I do not recall if this question has ever been asked in the five years that I have monitored the Discussion Group so it's nice to have a stumper.

Lane.

Can't speak to why the two trains were coupled together -- you're probably right that the UP train stalled -- but I can offer some thoughts about stalling and about grease on the rail.

No, railroad diesels do not "lug down and stop". The nature of a diesel-electric transmission is that tractive effort is at maximum at 0 MPH. Thus, as the train slows on the grade, tractive effort steadily increases. However, if the tractive effort is insufficient to overcome train and grade resistance, the train just gradually comes to a stop -- with the diesels in Notch 8. On a DC unit, this will push the ammeters into the red zone, and if the engineman does not reduce the throttle he'll burn up the traction motors. On an AC unit, there are no commutators, so the units will just stop and sit, still running in Notch 8. They can stay this way indefinately.

The cause of a stall is simply insufficient tractive effort on the train. This is the result either of assigning too few locos (maybe due to lack of availability) or to an en-route failure.

Grease on *top* of the rail is due to over-active curve lubricators. If too much grease is dispensed, it can migrate to the head of the rail. This causes a loss of traction (obviously) and can result in stalls.

Hope this all helps.

IT could be LOTS of things an engine shots it self down when it gets low on water, starts to over heat, or any problem it detects. The engines sometimes go to half power also! TOO much grease can cause it also, it has happend to me up on Donner Pass! Once you lose your momentum the train just starts to bog down then comes to a stop and you can not get going again.
But as you can see it can be lots of different things.


uprrman156

My experience has been, in non-helper districts, when a train stalls you have the following options:

1) have a following train cut their power away from their train and shove the stalled train

2) have an opposing train leave their train in a siding (or at a meeting point), cut their power off, and pull the stalled train up the hill

3) if the stalled train is stopped between siding switches or on a stretch of multiple main tracks, an opposing train can cut away from their train and may be able to get to the rear of the stalled train to shove them.

4) double the stalled train to the next siding (taking roughly half the cars each time) This is often the only option if no other trains are nearby to assist the stalled train.

I've occasionally been a part of other variations on the above, such as the stalled train securing their train, taking just their power ahead to the next siding and picking up an engine from another train, then returning to their own train and making the hill... and once or twice I've seen a train get a shove from a following train that did not cut their power away from their own train but instead kept it with them... but usually the following train will leave their own train behind, when shoving a train ahead.

WSC

One thing I've noticed on trains that have stalled with me is how the engines lunge forward, and jump around. Major jumping till it finally comes to a stop and come out of the throttle. Had an engineer on an overtonnage coal train that told me. "I'll show you how to get this coal train over the road.....just put it in number 8 and start BS'ing."

GP40X wrote:
Yesterday, I saw the longest train that I had
> ever seen there.
. The UP train had a three unit
> combination of SD70M and C40-8 on the point and a two unit DPU
> set of same as pushers...Coupled to that was a five unit set of
> C44-9s from BNSF.

feel priviledged to see that,they usually do it in the dark,if you follow that rear UP loco around for 9 months a little baby hyrail truck will pop out ...seriously though... it sounds like they were just nostalgic for the SP drags of the 80's.....dave

Los Angeles Area Timetable #2, Effective 4-11-02, Mojave Subdivision, page 20, Misc. Instructions reads:

GRADE SECUREMENT RESTRICTIONS

Do not tie up and leave a train unattended between Slover and Hiland; and between Tehachapi and Ilmon unless:

1. The track the train is tied down on has derail protection; or

2. One of the rails on the descending direction in advance of the trains is separated by M of W which will create a temporary derail.

--------------------------------------------------
So you can see why the BNSF was shoving the UP up the hill with his train behind him. I'd like to know how they got around the HELPER PLACEMENT RULE.

steamjocky....over

A train stalls because you have run out of Tractive Effort. In other words, moving the train up the hill requires more tractive effort than your locos are capable of producing at the moment.

The most common reason they cannot produce enough TE is because they have run out of traction or adhesion thus they are slipping.

The most common reasons for slipping are bad rail (greasey, wet, icy, snowy, etc) or the train is too heavy for the power and thus the speed decreases below that at which maximum throttle can be maintained without slipping.

You CANNOT in most cases just leave the throttle in #8 right down to a stall stop. If you do that the locos will develop more TE than the available adhesion and they will slip. Often violently which can break trains in two. The only exceptions to this rule that I have found in my 30+ years of being an engineer were the Century ALCOs which had a special type of load control. Modern ACs come close to being able to do it but they too will slip at full throttle and very low speeds. So I repeat, you cannot leave the throttle in #8 right to a stop or advance it to #8 while stopped trying to start a train moving. It ain't gonna work. Our BN very heavy SD40-2s (420,000lbs+) could come close to doing it on dry, sanded rail but even they won't quite do it in #8 without slipping.

Note that I am talking about a unit, stopped, in number 8 AT FULL LOAD. Modern locos load slowly to full HP, a minute or more. Therefore you can sometimes just put it in 8, the train will move before the units reach full HP. So in these cases you are not really "stopped in number 8". Modern locos will also reduce their HP output to prevent/control slipping at high loads. In these cases you can also "be in number 8" while stopped. But again you are not really developing full HP so it is the same as if you were in number 4-6 or so.

Normal procedure when you are stalling is to keep reducing throttle when the locos begin to slip hoping that a lower speed will reduce the required TE enough (by reducing rolling resistance) that you can drag it over the hill without excessive slipping. It is a fine line between going over the top or stalling.

Sometimes if you are close to the top this reduction in power will allow the locos to produce enough TE that the inevitable stall is postponed until you've topped over so you win.

If reducing power does not get you over the hill and speed drops even further to an inevitable stall then you must set the train air before you stop and reduce the throttle to number 4 or lower at the stop to prevent slipping and jerking or rail burning.

Another trick is to apply 12-25 psi of independent brakes to help control slipping and to dress the wheels. Since your problem is lack of traction not lack of HP this trick will not CAUSE you to stall.

And remember this too: Tractive Effort will tell you how much you can pull up a grade and Horsepower will tell you how fast you will go up that grade.

Example: GP-40 vs, SD-40....Both are 3000 HP. The GP-40 is a 4 axle. The SD-40 is a 6 axle. The SD-40 will pull more tonnage at the same speed as a GP-40. That's because the SD out weighs the GP. Roughly 400,000 pounds on the drivers for an SD-40 vs a GP-40 which is about 277,000 pounds on the drivers. More tractive effort for the SD-40 or, you might say adhesion.

It's almost like a 350 Chevy with a 4-wheel drive vs a 350 Chevy with a 2-wheel drive. Who can out pull the other? I think that might be a good way to compare TE vs HP.

This is one of the reasons why you don't see too many 4-axle units on heavy grade territory. Of course the newer units (GP-60, B-40, and others) are the exception to the rule.

What do you think guys? Agree?

steanjocky....over, and awaiting your reply

>This is one of the reasons why you don't see too many 4-axle units on heavy grade territory. Of course the newer units (GP-60, B-40, and others) are the exception to the rule.

Yes and they are also the reason for the stall everytime I've stalled in the past 10 years :-(
I don't recall stalling in the past 10 years with all 6 axle power. Not even when I brought a 7600 ton ballast train up the 1.3% at 6 mph with just two old beat up SD40-2s last year. Got sick later from all the traction motor smoke though on that one so I won't do it again.

rresor wrote:

> Grease on *top* of the rail is due to over-active curve
> lubricators. If too much grease is dispensed, it can migrate
> to the head of the rail. This causes a loss of traction
> (obviously) and can result in stalls.
>

This is correct for traditional flange lubricators. But now a new trend has developed--applying grease directly to the top of the rail. This is done with high-rail vehicles (track inspectors) and I believe by track mounted lubricators. As unbelievable as this is, it is done to greatly decrease wheel and rail wear. I guess that is more important than actually running trains.

AAK wrote:

> >This is one of the reasons why you don't see too many 4-axle
> units on heavy grade territory. Of course the newer units
> (GP-60, B-40, and others) are the exception to the rule.
>
> Yes and they are also the reason for the stall everytime I've
> stalled in the past 10 years :-(
> I don't recall stalling in the past 10 years with all 6 axle
> power. Not even when I brought a 7600 ton ballast train up the
> 1.3% at 6 mph with just two old beat up SD40-2s last year. Got
> sick later from all the traction motor smoke though on that one
> so I won't do it again.
>
> [%sig%]

I hear you Al. Same thing happened to me in the late '70's (1978 I think) with a brand new rebuilt GP-20 (4120) fresh out of the Sacramento Shops. I was helping a westbound train up Cajon Pass at the time. I can still smell the odor of the burning wiring and those traction motors. YUCK!

steamjocky....over, and I'll never do that again either!

I Have a Tape Of a Engineer/Dispatcher Conversation About him Stalling at Woodford.

He Had a Set Of SP GP40s (Lead unit was the 7240/That dates the tape Back a Bit)
Said He "Had The Horsepower,But Not the Tractive Effort With "All these 4 Axle Units"

Intersting Tape on The "How are we gonna do this" as He Also Stated He Had a "Shiftable Load" And Helpers Could Not Be Placed On the Rear of the train.

That`s Mountain railroading At Its best
Phil

Our track guys also have gone to grease applicators on their high-rail rigs. At first they'd apply grease on the inside of the rail (not the top of the ball) to every curve. Their applications were too heavy initially and those trips up the hill on the Toledo line were real interesting, stalling out and reducing tonnage by half to get up the hill.

Now our guys apply to the inside of of the rail on the outside of the curve on one left and one right curve per mile (we have an average of 5 curves per mile on this line). The grease will carry to the rest of the curves in either direction and has greatly reduced wheel slip problems when they apply it.

Roustabout out

>allblack wrote:
>
> This is correct for traditional flange lubricators. But now
> a new trend has developed--applying grease directly to the top
> of the rail. This is done with high-rail vehicles (track
> inspectors) and I believe by track mounted lubricators. As
> unbelievable as this is, it is done to greatly decrease wheel
> and rail wear. I guess that is more important than actually
> running trains.

steamjocky wrote:

>
> And remember this too: Tractive Effort will tell you how
> much you can pull up a grade and Horsepower will tell you how
> fast you will go up that grade.
>
> Example: GP-40 vs, SD-40....Both are 3000 HP. The GP-40 is
> a 4 axle. The SD-40 is a 6 axle. The SD-40 will pull more
> tonnage at the same speed as a GP-40. That's because the SD
> out weighs the GP. Roughly 400,000 pounds on the drivers for
> an SD-40 vs a GP-40 which is about 277,000 pounds on the
> drivers. More tractive effort for the SD-40 or, you might say
> adhesion.

The result is correct, but the reasons are bit mixed up.

Horsepower is directly related to tractive effort. The only other variable in the equation is speed. So the SD40 and GP40 produce the same tractive effort at a given speed.

Where the SD has the advantage is it's weight and thus adhesion. Given a 25% adhesion, the SD40 in the example hits an adhesion limit at 11 MPH and 101,250 pounds of TE. The GP40 hits an adhesion limit at 16 MPH and 69,250 pounds of TE.

When you calculate in the train resistance due to a grade, you quickly find that it takes lots of HP to move uphill with any speed. At 11 MPH, two SD40's (TE max = 202,500) can haul 4719 tons up a 2% grade. Two GP40's (TE max = 138,500) can only haul 3219 tons on the same grade, but at 16 MPH. However, the SD's could also take the same 3219 tons up the hill at 16 MPH.

If the train can make more than 16 MPH on a given grade, then 4 axle units are little different from 6 axle units. .

This, of course, is simplified and ignores things like locomotive weights (actually the two GP's can pull 133 more tons of train than the SD's at a given speed because they weigh 133 tons less), and the real world things like wheel wear, rail conditions, weather, and such.

Al Krug (AAK) has an excellent program that you can download from his website that does these kinds of calculations. It can be accessed at:

http://www.vcn.com/~alkrug/rrfacts/traincalc.htm

Interesting and informative thread!

A couple of questions from someone that doesn't understand a lot of this…

1) What is the relationship between torque and tractive effort? It sounds like they are almost synonymous

2) What is the relationship between the number of axles a unit has and its adhesion. One of the previous posts stated that the reason for the performance differences between and SD and GP 40 was its weight, but it would seem that a six axle unit would have more adhesion that an equivalently powered and weighted four axle unit.

3) Way back when, Southern Pacific ordered SD39's to serve as helpers over Tehachapi. These units were effectively SD40's without turbo chargers, and therefore had significantly less horsepower. Based upon what the previous posts have said, would these units have the same ability to push a train up the hill as an SD40, with the only drawback being it could do it with the same speed (which is based on horsepower) as an SD40?

Thanks in advance!

1) What is the relationship between torque and tractive effort? It sounds like they are almost synonymous

You are correct, they would be directly proportional.

2) What is the relationship between the number of axles a unit has and its adhesion. One of the previous posts stated that the reason for the performance differences between and SD and GP 40 was its weight,

That is correct. It is the extra weight that the extra two axles permit a loco to carry without crushing rails that increases the traction.

> but it would seem that a six axle unit would have more adhesion that an equivalently powered and weighted four axle unit.

No. This is a common misconseption. Extra wheels even with extra traction motors does NOT increase the maximimum tractive effort of a loco if there is no weight increase between the two locos. Extra wheels/axles/traction motors on locos of the same weight only spreads that weight out so the loco can operate on lighter rail. The extra traction motors will reduce the minimum continuous speed the loco can operate at without TM overheating. But the extra axles alone do not increase maximum tractive effort.

3) Way back when, Southern Pacific ordered SD39's to serve as helpers over Tehachapi. These units were effectively SD40's without turbo chargers, and therefore had significantly less horsepower.

I am not familiar with SD39s but they SHOULD be a 12 cylinder turbocharged 6 axle 2300 Hp loco??

>would these units have the same ability to push a train up the hill as an SD40, with the only drawback being it could do it with the same speed (which is based on horsepower) as an SD40?

Assuming you meant to say that "it could NOT do it with the same speed" (you left out the not), then yes you are correct. Assuming the SD39s weighed the same as the SD40s they could push/pull just as much as the SD40s but at a lower speed. Similarly my little SW1 (600 hp switcher) that I worked on for 4 years while going to college could pull as much as the SW1500 (1500 Hp switcher) that I currently use occasionally on the Sheridan yard job. The SW1 would just accelerate the same size cuts slower and its top speed with equal cuts would be lower.

Definitions:

Drawbar pull - The amount of HORIZONTAL force a lococomotive (or consist) can exert. This is measured by a dynamometer car, and is effectively the Tractive Effort less the amount of effort it takes to move the engine. This is the force available to start moving a train.

Tractive Effort - The limiting factor to the force that a locomotive can exert upon the rail to move itself and its train. It really has two meanings. (1) The theoretical limit to what force can be delivered by a locomotive to the rail. This is effectively the weight on drivers of the locomotive (sheer weight only - number of wheels doesn't matter) times the factor of adhesion. Normally, this factor is approximately 0.25 for steam and DC drive traction motors, though a bit less for steam due to irregular piston thrust. Up to about 0.33 for AC motors because of the improved computer controlled wheel slip control. Can be improved a few % by adding sand to the rail, and dramatically decreased by adding oil, rust, or wet leaves. (2) The calculated force the designer of the locomotive intended the locomotive to deliver. Whenever the actual tractive effort delivered by (2) exceeds the figure of (1), wheels will slip.

Torque - A force moved through a distance, usually expressed in foot-pounds. Has no meaning to a railroads operating department.

Horsepower - A force moving a distance through time. Starting out, this is a meaningless figure to a railroad, since at 0 mph, there is no movement, thus horsepower delivered to the rail is 0. Only tractive effort matters. Once the load is moving, however, horsepower determines how fast it can be moved on any specific grade.

In 1964, I put together a 10,000 ton iron ore train in a flat yard with an NW2 (120,000 lbs, 1000 hp, 30,000 lbs TE) that stalled 5 miles out of the yard with 4 F3 units on a 0.5% grade (480,000 lbs, 3000 hp, 120,000 lbs TE) because it couldn't maintain the minimum speed to achieve maximum horsepower to keep the train moving.

The advantages of 6 axle locomotives is that they can carry more weight on the same track than a 4 axle engine can, and that due to their electrical characteristics they can deliver their maximum horsepower at a lower speed. Four axle engines max out at about 18 mph, 6 axle engines at about 11. Look at it this way - if a given train on a given grade is going to require 3000 hp to keep it moving at 15 mph, a four axle engine will stall out before achieving maximum horsepower, while a 6 axle engine will still be on the upside of the curve.

It is also interesting that in the 1940's, steam locomotives were being built that could deliver up to 7,000 horsepower at 40 mph. To my knowledge, a diesel still hasn't achieved that. That's why it took 4 diesels to replace each steam engine. It's also why EMD demonstrators first made their sales on the mountain divisions of railroads, where trains were already running less than 20 mph!

We're getting pretty technical here, but a couple of points are worth making.

1) Nobody deliberately lubricates the top of the rail. They *do* use "friction modifiers" that may look like grease, but which actually increase the factor of adhesion (think Super Glue). These are applied either by a hi-rail or by loco-mounted lubricators.

2) The point about steam locos delivering 7,000 HP is worth expanding. Diesels develop maximum tractive effort at 0 mph, and it declines from that point. The 16 mph and 11 mph figures cited are minimum *continuous* tractive effort; below those speeds, amperage is so high it fries the commutators on DC motors.

A steam locomotive, by contrast, has a tractive effort curve that looks like a camel's hump. There is a point well above 0 mph at which the loco is working at maximum output. It used to be said, "A steam loco can move anything it can start; a diesel can start anything it can move". The second is more useful in railroad practice. Starting with a steam loco was a tricky business. That's why slack was designed into the cars, and why a yard engine often shoved a starting train until it got into its maximum tractive effort range.

3) As to SD39s and SD40s, at 11 mph they produce the same tractive effort. But the SD39 "runs out of gas" above about 15 mph. This is interesting because the new AC locos feature a lot more tractive effort for a given horsepower (example: 143,000 lbs. for a 4000 HP SD70 vs. about 85,000 for a 3000 HP SD40). However, while they're good at starting trains, the lower HP means those trains run slower. When BNSF replaced five SD40s (15,000 HP) with three SD70s (12,000 HP), loaded trains took about 10% longer to get over the road, despite roughly equal total tractive effort. "You can't fool Mother Nature".

As a heavy train's speed decreases and tractive effort increases, the engineer will usually reduce the throttle setting. If the tractive effort of the locomotive consist is greater than the tensile strength of the knuckles, a train separation is likely.