why are engines put into middle or at end of a freight train?

If I remember correctly this was explained to me years ago, so I will try and answer for you. Sometimes a engine is put in the middle to break the load up per say it's like two trains just back to back. They may have a destination down the line where they will split and go different routes. One on the back is basically a pusher to help get over some high grades or long grades where it would put to much of a strain on the train cars especially if there is curves in the grade. 

Well, engines at the end are usually helpers.  I used to take coal trains over the mountain around Horseshoe Curve and down into Altoona Pa.  Coal trains are normally 130 cars at 140 tons each for NS.  That's a train weighing roughly 18,200 tons (pretty heavy train).  We had engines on the front end and sometimes on the back end.  Sometimes, the engines on the leading end weren't powerful enough to drag the train over the mountain so we had helpers on the rear to not only push but also to help hold the train going down the hill.  Sorry, I have no experience with engines in the middle of a train although I have seen such trains.

Rick

I think the mid-consist helpers are distributed power units (DPU's) that assist in pulling a heavy train. I haven't seen many where I live (western PA) but have seen videos of trains out West (BNSF and UP) with them when moving long stack trains.

Reduces cumulative loads on the couplers and drawbars, and also allows for better distribution of power and dynamic braking on grades.

It seems much more common out west.  I've seen it implemented on the UP for everything from coal drags to intermodal to manifest freight.  Mountain railroading,, or across Nebraska.

I believe I read at one time (I think Trains had an article discussing DPU's several years ago) UP felt it offered improved performance in many situations including flat land running.  The same article I believe suggested that NS wasn't interested.  Maybe look back for that article for firsthand insight.

Jim

I have read that some of the Class 1 RRs have been experimenting with trains 12,000 feet long and more. My guess would be that the mid train engines help take stress off the couplers. They are trying to reduce traffic (by reducing number of trains running), make deliveries faster and reduce fuel costs. I haven't seen anything about this lately, what I did read was in Trains magazine several months ago. I know little about the real trains, so this is just what I have read. Memory is not what it used to be either, but I think I am close here.

Reduce drawbar forces. Trains have limitations for tonnage, especially on mountain grade territory. The mid or rear end helpers prevents the train from breaking in two. Usually 

UP has been running trains that are really a 2 in 1 train. Reduces crew starts at the originating terminal, and then when they get to a midway point, they split the train and it becomes 2 separate trains to their final destinations.

Traditionally), helper engines would assist trains over designated helper districts where heavy grades required additional power. A helper with a separate crew usually would be added at the end of the train (either behind or ahead of caboose, depending upon construction of the caboose) and then cut off at the end of the helper district. It would then either return light to the bottom of the grade, or be turned at the facility where it was cut off so that it could assist a train running in the other direction, if the grades were heavy both ways. Sometimes an additional engine would be cut into the middle of the train as well. Rio Grande sometimes ran trains over Tennessee Pass using three L-131 2-8-8-2s -- one at the front, one in the middle, one at the rear end. 

With distributed power, remotely controlled diesel units are added at the end of train (sometimes also in the middle) in order to reduce loads on draft gear and to improve train handling (by reducing slack action) and to improve air brake application. These additional units typically remain in the train from origin to destination. On the old Sunset route through Tucson, UP trains typically run through with two units up front and one at the rear. I haven't seen any mid-train units so far.

I once saw a video of a Western Maryland hopper train with 2 Consolidations at the front, 3 Consolidations in the middle and then 2 more at the rear.  All for a 70 car train.  They had some wicked grades.

Merry Christmas

Ed

I believe it also  extends the life of the  rail by a few years. (a big savings)   

I can remember when Detroit Edison coal trains destined for the Monroe, Mich. poser plant, would have three engines on the front and two more about 80 cars back bringing up another 60 cars, for a total of 140 cars.  The mid train engines were referred to as slaves, they were radio controlled from the head end.  All their engines were painted in the EMD demo colors of blue and white...

Marty

Reduces cumulative loads on the couplers and drawbars Changing a broken knuckle is not fun and takes a long time.  Railroads and crews don't like to have broken knuckles.  Mid train and rear end helpers help to DISTRIBUTE the load off of all the couplers. 

If the train is a mixed commodity train it becomes even more important as you may have a few light cars in the front with the weight of the train mostly in the rear.  Tight mountain curves add to the issues.  It is possible to pull a heavy train off of the track with a long heavy train around a tight curve.  Again distributing the load keeps that from happening.

My 2 cents, spend wisely!  Russ

For the same reason I do it with a long O-gauge consist, easier on the couplers.   I have often wondered how you can pull several hundred cars without distributed power, the loads on the first part of the consist couplers must be immense!

gunrunnerjohn posted:

I have often wondered how you can pull several hundred cars without distributed power, the loads on the first part of the consist couplers must be immense!

The big 4000-4500 HP six axle diesels built in the last 20 years can produce 100,000-150,000+ pounds of continuous drawbar pull at low speed.  A coupler knuckle or drawbar is designed to take something over half a million pounds of pull.  Three big units on the head end is the limit in a minimum speed/maximum drawbar pull operation.  If your train needs more pull you need distributed power.

Gregg posted:

I believe it also  extends the life of the  rail by a few years. (a big savings)   

It definitely does extend the life of rail on curves as well as reducing flange wear.  Trains with all the power on the head end put all the wear on the rail on the inside of a curve.  With distributed power the cars on the head end of a train place less wear the rail on the inside of a curve and the cars ahead of  units that are pushing put wear the rail on the outside of the curve.  Cars in the middle of the train operated with distributed power experience very low lateral forces on curves and produce little rail wear.

Also not yet mentioned is improved braking.  Distributed power units in the middle or rear of a train will release air and apply the brakes from the rear of the train at the same time as they are applied from the head end.  They reduce slack action and improve the speed with which brakes can be applied.

from Union Pacific: http://www.up.com/aboutup/envi...technology/index.htm

Tom

UP: Technology

CSX has recently started to use DPU's on the Popes Creek Branch (Benning yard in DC to two power plants in southern MD) in order to increase from 100 to 130 car trains.  The run is 34 miles, which I understand is the shortest on the system where DPUs are used.  At least at first, the crews hated them; they spent too much time getting them set up and running; sometimes, they gave up and just used four GEVOs to drag the trains.  But it seems recently they've gotten it down, with two units in front and one in the back.  This not only does all the things mentioned above, and reduces the number of crews needed for the branch.

Bob

catnap posted:

I think the mid-consist helpers are distributed power units (DPU's) that assist in pulling a heavy train. I haven't seen many where I live (western PA) but have seen videos of trains out West (BNSF and UP) with them when moving long stack trains.

Back in the 90's, Conrail used to run unit coal trains through Pittsburgh with DPU in the middle and end of the trains.  These were special trains that were run for Detroit Edison.  It was neat seeing these long trains running with power in the middle and end - especially in the South Side section of Pittsburgh where you don't normally see helpers.

Living in northern NJ not far from NYC it mainly commuter trains. Occasionally a 3-5 car NS local freight with a unit at each end. I assume its so they don't have to do any run around movements to spot the few cars and tie up the track.

In winter, the air brake features of Distributed Power are especially helpful, even here on the southern high plains.  In Wyoming and farther north, where it gets brutally cold and stays that way for months, Distributed Power's air brake functions are essential to the operation of trains of today's lengths.

On my iPhone, I have a weather app which can track several locations.  I always have Havre, Montana, as one of my locations, so that I can be glad that I'm not trying to charge the brake pipe for an air brake test on a train there.

In the middle seen in Marias Pass...most helpers still at rear.  When the train reaches Summit the engines on the rear can uncouple "on the fly" (still in motion) to allow the train to continue--no momentum loss/extra fuel to get going again.

You are talking about Helper-Link. It is basically a radio air brake connection that allows uncoupling on the fly. Here at Sheridan Wyoming coal and grain trains usually have 1 or 2 DPUs on the rear end but also get a manned helper set of 2 units that shove on the rear end to get them over the worst hills. Yes the manned helpers shove on the unmanned DPUs. So the train ends up with 3 or 4 units on the rear. When they reach the top of the hill the manned helpers cut off on the fly using Helper-Link. The first few times you see this it is quite odd because you don't usually see loco "consists" come apart on the fly
Helper Link equipment

 Isn't it amazing how we used to cut off on the fly every trip before the mid-1980s crackdown on safety rules and before Helper-Link. I personally did it probably a couple of thousand times. (Even coupled up on the fly a number of times!) 

Utah Railway always put on a good show with DPU trains...and they all smoke!! 

Engines at both ends are common here in the Dakotas, but mostly only on certain kinds of trains.  Most grain trains (~110 cars) will have two engines on one end and one on the other.  All coal trains have that configuration  (if not three engines one end & one on the other end.)  Some ethanol tanker trains do.  There seems to be three reasons, most already discussed.  One is to reduce pressure on the lead engines' coupler.  Another is to help push through curves and grades.  And I think another is the only trains I see with DPU around here are unit trains, so having an engine at each end means you can run them from origin to destination and back without having to switch engines from one end to the to other.  I can't recall seeing any manifest trains that had engines anywhere but up front.  In Canada I did see trains in the Rockies that had engines up front, one in the middle, and at least one on the rear.  They have some long grades and tight S curves to deal with.  All the trains I saw going through the Spiral Tunnel had that configuration.  some railroads here, such as RCPE, don't use DPU despite having very long trains.   They don't have enough DPU qualified crew.  The local railroad Dakota & Iowa (DAIR) runs heavy rock trains up a long grade near me but have all engines up front for that.  They do add a rear DPU half way through their route to negotiate some tight curves.  OTOH, I don't see UP running DPU on Minnesota branch lines, but they do on their Transcon and at least one granger line in Iowa and Nebraska.

Kent in SD

Wyhog posted:

You are talking about Helper-Link. It is basically a radio air brake connection that allows uncoupling on the fly. Here at Sheridan Wyoming coal and grain trains usually have 1 or 2 DPUs on the rear end but also get a manned helper set of 2 units that shove on the rear end to get them over the worst hills. Yes the manned helpers shove on the unmanned DPUs. So the train ends up with 3 or 4 units on the rear. When they reach the top of the hill the manned helpers cut off on the fly using Helper-Link. The first few times you see this it is quite odd because you don't usually see loco "consists" come apart on the fly

I've watched this on a number of occasions at Crawford Hill, NE.

Kent in SD

UP (DPU) Train....................January 10, 2010

A test 18000 ft Stacktrain, bound for Long Beach, runs thru Ontario, CA on Union Pacific's Alhambra Subdivision. The train has 3 units on the point, 2 separate sets of DPU's in the middle and 2 more on the rear...............9 engines!