Odd Locomotive Arrangement

[hammersley]

The other day I saw a train with 4 loco's, pretty sure they were AC 4400's, but way in the middle of the train was another lone 4400, or a Dash 9, (don't remember) - then a lot more cars. Now you RR guys are sure to have an answer, but I've seen a lot of trains, and this is the first time in this country, that I've seen this arrangement. Under what conditions would this be used????

 

[EMDDIESEL]

Its called DPU, by putting a unit mid train (Operated by remote control) you can pull more tons up grades without fear of pulling your train in two. It also helps to speed up applying and releasing the brakes. There are limits to how many axles you can have pulling your train (Depending on weight) and that will usually limit how long your train can be. But by putting the mid train units in, its almost like having 2 trains in one. The more you can move with one crew, the happier the RR is.

 

[KatDiesel]

I missed this one... .....



EMD explained alot of it.



Being I dispatch Colorado I deal with DPU trains constantly... . 80% of my trians are DPU.



It takes six 4400hp AC's to move a a 105 to 115 cars of a coal load (15,000 tons or so). When pulling that weight you have physics becomes involved. If all the horsepower was on the headend, then when you try to pull that weight up a 2% grade... . snap... you get knuckles (couplers) or even drawbars out of the car. By using DPU consists you can move whole trains without addtional crews..... and skirt around some of the physics involved. However DPU consists brings up its whole set of own problems... ... . if a locomotive dies... . or acts up. . a crew member has to walk back to get to it. Or if a "controlling" unit goes kaput you gotta replace it with another operating controlling unit. Not ever locomotive is setup to be a "controlling" dpu locomotive. One section of my railroad has about 32 tunnels within a 10 to 15 mile piece of track, so if a train "loses" comm meaning the remote link is lost... theres no chance they get it back in the tunnels and will take three crews to move.



my most common configuration is 2x1x2 and 2x2x2.



Hope this helps? Hope I made it make sense for a non-railroad person.

 

[Doubleclutch]

Talk about Doc's Land Train... What becomes the practical limit for train length if trains can be "combined" by the use of DPUs?

 

[KatDiesel]

Originally posted by Doubleclutch

Talk about Doc's Land Train... What becomes the practical limit for train length if trains can be "combined" by the use of DPUs?

If its single track, you gotta keep the trains to a certain length to meet other trains.



Also on the coal trains the mines in colorado usually can't load more then 115 cars ... . due to time and tracks available.



In 160 miles or so, I have about 10 sidings I can use to make train meets with 6000+ft trains.



On the flat lands an whatnot, they like to run upto 9,000feet of trains... ... ...