Engines pushing

[fredswain]

I guess they're also known as distributed power units. This comes up from time to time I'm sure and I know many reasons for it but I have been seeing more and more of them lately. Typically 2 engines at the front and 1 rear. I live on the north side of Houston. The coal trains that regularly have dpu's go through the south side but up here it's general freight and autoracks. I never saw an engine at the rear of a train coming through here ever until about 2 weeks ago. Now all of a sudden almost all of the general freights have an engine at the rear. What has changed that has warranted this? There are no mountains or long grades anywhere near here.

In a time of high gas prices, the only thing I can think of is that it's a money saving tactic from a maintenance point of view. Would a working engine at the rear of the train save couplers and hence maintenance costs by fatiguing them less? That's all that seems to make sense to me. Thoughts? Insights?

[diningcar]

Are the trains longer? Perhaps heavier? There are reports the RR's are building longer trains to fully utilize the power available and minimize fuel usage.

If there is a pattern I suspect it has to do with minimizing fuel consumotion; and this cannot be analyzed from a few observations by we fans. It would be a systemwide plan that each individual RR operations group creates. 

 

[fredswain]

I understand there's far more to it than what outsiders can tell just by looking at a train going down the tracks. I'm just looking for insight. I'm hoping someone that does know could shed some light on it. The trains don't "seem" longer but I don't know for sure. Most freights coming through here have 3 engines. They still do but now most of the time one of them is pushing. That doesn't imply heavier to me but again I don't know everything.

[dehusman]

Its more fuel efficient to have a DP configuration than having all the power on the head end.

Diesel is $4 a gallon.

Dave H.

[CSXDixieLine]

CSX recently started using DPUs instead of pushers on their coal trains coming down the old Clinchfield line from the Appalachian coal fields to power plans in NC, SC, AL, GA and FL. The DPUs remain with the train even after the trains have left the mountainous grades that require extra power. CSX says one of the main reasons for doing this is because it allows the heavy trains to maintain track speed in hilly areas that otherwise would not warrant extra power, thereby reducing travel times. Jamie

[kolechovski]

The NS trains out at my place used to always have pushers on the rear (2 SD80MACs each on front and rear).  When the new line opened up, and the trains didn't have to tackle the great hill they once did, they now run 3 on the front, no pushers.  I'm sure the costs of extra employees is something to consider when running with rear units, so I guess out on your line, it's efficient enough to be worth having extra employees running it.

Start counting the cars the next few times and see if the length has increased any.  On the old line here, they were usually running 100 cars per train.  With the new line open, they run around 120.  Even a small increase in size will be worth it and not easily just from watching.  And if your trains ever get really huge, they may start putting some units in the middle, too. 

[edblysard]

Fred,

UP has a fuel conservation program in place that prohibits engineers from running above notch 5 unless accelerating the train...having a DPU makes getting up to track speed easier, uses less fuel because both ends of the train start moving at the same time, one pushing the rear, two up front pulling instead of just using the head end to pull the train up to track speed.

Saves fuel.

[fredswain]

It's really interesting that distributing power differently saves fuel. It wouldn't seem to matter but apparently it does. If it does save fuel, why hasn't this always been standard practice? It would seem that you'd always want to run a company as efficiently as possible at all times regardless of gas prices.

To the person who made the comment of an extra crew, I've never seen a trailing engine going by that was manned. I'm sure they are out there but the engines I've seen must be controlled from the front somehow.

[cacole]

Practically all modern locomotives have remote control capability and the DPU units do not require any extra crew members -- still only one engineer and one conductor.  A computer in the lead unit controls the DPUs by radio.

[zardoz]

Sorry guys, but I do not see how a DPU saves fuel.  It is more efficient to pull the train rather than push it, because pushed cars will zigzag slightly, one to the left, the next to the right, pushing the wheel flanges against the inside of the rails and thereby increasing frictional forces. Therefore, it takes slightly more power to push a train rather than to pull it.

However, in regards to train handling, slack control, dynamic use, etc., having a DPU is very useful. 

 

Of course, one might be able to say that trains DO push their loads.  Consider the design of the knuckle: if you look closely, you will notice that the movable part of the knuckle (the part that swings open when the pin is pulled) is configured such that it curves back slightly towards the car to which it is attached. So as the train is being pulled, the 'tip' of each knuckle actually pushes against the 'tip' of the knuckle to which it is coupled as it is being pulled. So each car is being pushed as it is being pulled.

 

[Valleyline]

It has been my impression that the primary advantage of distributed power is its ability to improve train handling. Controlling "pushers" from the head end allows the engineer to better control slack action in his train by differentiating the power between the front and rear units as the train proceeds over rolling terrain. This leads to less damage (broken coupler knuckles and drawbars) as well as the costly delays and service interuptions that result when these problems have to be repaired on an active main line.

[route_rock]

  BNSF loves the whole DP thing. But I didnt know CSX was getting into the DP craze. We have to UN DP coal trains in Galesburg ( Or Eola now for some but we will see how long that lasts)for NS and CSX.

 

  But yeah I dont understand it.We complain we dont have power for trains so lets add a DP to a train.Somedays I think the power desk is high.

[jeffhergert]

Fred,

UP has a fuel conservation program in place that prohibits engineers from running above notch 5 unless accelerating the train...having a DPU makes getting up to track speed easier, uses less fuel because both ends of the train start moving at the same time, one pushing the rear, two up front pulling instead of just using the head end to pull the train up to track speed.

Saves fuel.

The UP's program is not to exceed notch 5 over 50 MPH for most trains.  In some places, loaded and empty coal trains aren't allowed to exceed notch 5 over 40 MPH.  It's given to us in the form of a track bulletin.  Every now and then when a Z train is late, most likely the crew is getting close to their hours of service, the bulletin will be voided to them.  

Jeff 

    

[Modelcar]

....Having just read the different opinions of why DP can be more efficient with fuel usage.  I'm certainly no expert on the subject, just trying to digest all the thoughts on how that does so....

The same power whether it's up front and a certain distance back in the train or....all up front....Can't see where the advantage {on fuel economy}, would be coming from.  Not talking about train handling, slack control, and all the rest....just fuel economy.

As suggested in a post above.....when pushing, cars might be "dragging" against the rails this way and that way with using DP, but if all the power is up front 100% of the cars will be "dragging" on one side of the rails pulling around curves....At least I'd think so in theory.

[selector]

I would expect the chief advantage to be coupler management over rolling terrain.  I do know for a fact that the long unit trains taking coal from Kaiser Resources in eastern British Columbia across the various passes to Vancouver had to manage the strain on the couplers when the train was evenly split across the apex.  So, they had at least one slug/robot mid-consist and often had a couple more pushing at the rear.  Loooooooong trains.

[dehusman]

Can't see where the advantage {on fuel economy}, would be coming from.  Not talking about train handling, slack control, and all the rest....just fuel economy.

O ye of little faith.

The train handling IS the fuel economy.  Better handling means using less fuel.  Quicker starts, quicker stops, better able to maintain an efficient speed.

You may doubt it all you want, but when the two largest railroads in the country, who have research departments, labratory cars, and between the two of them several decades of DP experience are willing to bet literally millions of dollars on increased DP for fuel savings, I'll go with their opinion.

Dave H.

[Murphy Siding]

........................

O ye of little faith.

The train handling IS the fuel economy.  Better handling means using less fuel.  Quicker starts, quicker stops, better able to maintain an efficient speed....................

 

Dave H.

     OK, I guess that make me *semi-doubtful*.  Or is it *quasi-doubtful*?

     How would having DP units save fuel by quicker starts?  Doesn't it take the same amount of expended energy to get the tonnage up to speed to begin with?

[Modelcar]

.....I have plenty of faith......

Trying to use various suggestions in posts above to understand, it is not clear what is making the increased fuel economy.  Suggestions all over the place.

If it really does make such a measurable difference, why has it just been started.....?  Railroads have been trying to cut costs for decades.   

[AgentKid]

Train handling issues, one way or another, come down to overcoming friction and when you can do that you save fuel.

And to further comment on what Selector brought up, as regular forum members will recall last week when I stepped into the deep doo-doo as it were on The Longest Train thread, I read up on CPR Robot units (DPU). In the days of SD-40's the 2 mid train units were positioned at the end point of the A-Rating for the 3 lead units. This produced what they call negative slack and prevented knuckle and drawbar pullouts. In those days if there were units on the rear, they were manned. Now with the AC power they only use 3 units. Apparently the bean counters have determined that it is cheaper to place the third unit on the rear of the train and haul slighly less tonnage than to take the time to insert the DPU unit mid-train. If extra pushers are required they are still manned.

AgentKid

[Ted Marshall]

It's really interesting that distributing power differently saves fuel. It wouldn't seem to matter but apparently it does. If it does save fuel, why hasn't this always been standard practice? It would seem that you'd always want to run a company as efficiently as possible at all times regardless of gas prices.

To the person who made the comment of an extra crew, I've never seen a trailing engine going by that was manned. I'm sure they are out there but the engines I've seen must be controlled from the front somehow.

My belief is that there is a distinct difference between pushers and DPUs. Pushers cut away from the train at some point, usually at the summit of a mountain pass, and are manned whereas  DPUs stays with the train for the duration of the journey and are remotely controlled from the lead engine.

I believe there are savings associated with using DPUs, but the fuel economy theory doesn't seem logical to me. Tonnage is tonnage whether you're pushing or pulling, right? It would make more sense to me that the savings would be due to other factors like:

• Less unscheduled maintenance for equipment
• Less lost time from changing out broken knuckles or setting out bad orders and waiting for the dog catchers. 
• fewer damage claims. 

All the examples given are the result of slack run-in and run-out. As trains get larger, longer and heavier... better train control becomes even more important that ever before. DPUs allow for better train control.

Bottom line... Better train control= lower operating costs= savings. 

My

[CSXDixieLine]

.....I have plenty of faith......

Trying to use various suggestions in posts above to understand, it is not clear what is making the increased fuel economy.  Suggestions all over the place.

If it really does make such a measurable difference, why has it just been started.....?  Railroads have been trying to cut costs for decades.   

The high price of fuel (specifically, so much higher than it was just a few years ago) have the railroads (and airlines, truckers, you, me, etc.) thinking differently about strategies that really never took fuel burn seriously into consideration. Right off the top of my head I can think of the following things that are no longer true due to this:

-- CSX will always use pushers and will never use DPUs
-- Norfolk Southern will never order new AC road power
-- I will drive 200+ miles just to take photos and videos of trains

Jamie

[timz]

Better handling means using less fuel.  Quicker starts, quicker stops, better able to maintain an efficient speed.

What's "an efficient speed"?

[Modelcar]

.....Quicker starts and some of the other thoughts may have possiblities....I don't have the expertise or facts in railroading to know such.  But I do know one thing...Jack rabbit starts in our motor vehicles wastes fuel.

[wabash1]

Remeber when you was a kid and you had to pull your wagon loaded with ( what ever ) but it was heavy so you had a friend or brother to help pull but it was still hard you could do it but it was hard so someone got behind to push while the other pulled it was easier and you got done faster.  same principal applies. even if it was mid train instead of all power in same place you devided and helped it to move the tonnage.

[chicagorails]

 a. more capacity on line,faster starts n stops, easier to maintain speeds,better braking.        

 b.less broken trains, knuckles.   

 c.more interesting trains for us to see.

  has anyone seen rear power on a pure piggybacker yet? not enough tonnage?

  are there minimum tonnage ratings on trains before a dpu can be used?

  any ethynol unit trains that use em? 

  what about a mid train engine and pusher on end,would this be a good combonation?

[Modelcar]

....Wabash 1:  I appreciate taking us back to our "wagon days" but not sure I agree pulling and pushing such, did any better than 2 pulling....Why would it.

Wish I had the wagon I had as a kid....it was a heavy duty one {wood}, and had dual wheels in the back and of course the side boards were  removable.  And I remember it was rated to hold a 1000 lb of weight.  Another fact I remember: It cost $7.50....brand new for Christmas in a box semi assembled.  Would be worth hundreds restored now.

[Murphy Siding]

 a. more capacity on line,faster starts n stops, easier to maintain speeds,better braking.        

  I still don't comprehend how the train will start faster.  Can you explain please?

[fredswain]

I saw an SD-40T-2 being used as a rear dpu last week. It's rare to see them at all and yet I saw that one and there is one being used as a switch engine near me. I saw a BNSF freight with 2 engines at the rear today. They're everywhere!

[Thechief66]

Hey Murphy, nice picture!!

In my area (the UP/BNSF joint line between Denver & Pueblo) it seems like BNSF usualy has helpers on the rear and UP has them in the middle. Why? I don't know. I used to see BNSF engines cut off of southbound loaded coal trains at Palmer Lake ( the high piont between Denver & Colo.Springs) and run light back to Denver, but it seems like they've been leaving them on more lately.

[dehusman]

For all the people asking about why they didn'do this sooner, just read the thread and note the skepticism, even though it has been tested and is a done deal.    Part of the reason it wasn't done sooner is that it took years of data from acutally running trains to prove the point.

Other reasons it took a while:

- Availability of equipment.  It took years for the railroads to amass enough engines to be able to power more than just bulk trains.

- Availability of crews.   It takes years to train the crews so that you can run DP trains over long distances.  There may be hundreds of crews on each crew district and it may take 4-8 crews district to get across a route.  That's a lot of people to train.

A DP train can start sooner because the brakes release from both ends and they stop sooner because the brakes apply from both ends.  When a DP train starts the rear of the train starts moving at the same time the head end starts moving, so the train starts sooner. People will say it doesn't make sense but a DP train handles different from a non-DP train.  A train with all three engines on the point, some trains will stall on hills, but the exact same train with the exact same engines in DP mode will make it up the hill every time.

Each throttle position on a diesel engine burns a different amount of
fuel.  Higher throttle positions burn more fuel than lower throttle
positions.  It takes more energy to accelerate a train than it does to
maintain a train at cruising speed.  Among other things, how much fuel an
engine burns is a function of how long an engine is in each throttle
position.

Disclaimer : The following is all hypothetical and just an illustration,
it is very simplified and does not reflect actual train handling
procedures.
Lets say a train will be placed in run 8 to accelerate from a stop and
once at cruising speed only needs to be in run 5 to maintain its speed.
Lets say it uses 200 gallons an hour in run 8 and 150 gallons an hour in
run 5.
The non-DP train accelerates for 15 minutes (.25 hrs) before reaching
cruising speed.  So in the first 15 minutes from a stop it uses 200 gal/hr
x .25 hrs = 50 gals.
The DP train accelerates for 10 minutes (.17 hrs) before reaching cruising
speed and then cruises for 5 minutes (.08 hrs).  So in the first 15
minutes from a stop it uses 200 gal/hr x .17 hr. + 150 gal/hr x .08 hrs =
34 gal + 12 gal = 46 gal.

The DP train saved 4 gals of fuel by getting to cruising speed sooner.  If there are 3 engines on the train that's 12 gals per stop, lets say the train makes 5 stops on each crew district and runs across 4 crew districts.  So that would be 12 gal/eng X 3 eng x 5 stops x 4 crew districts X $4 a gallon.  Our hypothetical train saved $2880 on its run compared to a hypothetical non DP train.  Do that for 50 trains a day for a year and it adds up.

Once again, the numbers are purely for explanitory purposes.

Dave H.