I’ve been noticing that a lot of current intermodal doublestack trains have one or two locos at the rear end of the train, with the last loco pointing backwards. Are the rear units simply there to pick up the slack, or is the entire train designed to reverse itself easily after it reaches its destination?
Where are you seeing these? I’ve seen those on unit coal trains in certain areas around NC/ SC
Richard
The locomotive(s) on the rear are controlled by the head end engineer through a radio link. I see this all the time on the Union Pacific Sunset Route here in SE Arizona.
Canadian Pacific has been doing that for years here in Southern Ontario. I’ve seen the odd Canadian National train doing the same thing but not near as much as CP. Usually CN will put a loco in the middle of the train.
Some years ago, the Union Pacific brought its Challenger to the Chicago area for an excursion. While they were planning the routing for the excursion, it was discovered that the big, “latest and greatest” road engines*, that had been operated three units on the point, exceeded bridge ratings in the area. Shortly after that, they began operating trains two engines on the front, and one on the rear. I got this nugget of joy from a co-worker who was involved in steam locomotive restoration.
The answer, or part of it, anyway, is that today’s newest diesels are so large and heavy that more than two at a time exceed the weight limits for bridges.
*I have at best a limited interest in present-day railroading, and I know little to nothing about diesels built after the GP-50.
You were told a complete falsehood. Even the salt-air corroded, 100-year old, pin-connected trusses and standard open-deck timber pile trestles on my Class I railroad, designed to Cooper E-60 ratings for the steam locomotives of 1910, will carry as many AC4400s or SD70ACes in a row as you might want to couple together. Virtually every principal main line in North America – the main lines on which you might see double-stack trains and DPUs – do not have any bridge restrictions like you describe.
The reason for DPU is to improve train handling, enabling longer trains. It also improves fuel consumption.
Rarely are the DPUs useful to enable the train to reverse. Intermodal trains are almost always broken up at destination. Unit bulk trains (grain, coal) are either unloaded on a loop, so what heads in also heads out, or are also broken up at destination.
RWM
Addressing the question of, “Why does the rearmost unit face backward?” The usual reason is so that the consist won’t have to be turned to get a cab at the front end when they are dispached in the return direction.
Chuck (Modeling Central Japan in September, 1964)
More on the 2/3 locos on one end and 1 on the other and then just reversing, using the single loco on the head end.
From what I know it wouldn’t make good sense to basically be pushing the train. Trains do better when pulled around curves, etc. especially when long and heavy. But as we know up to a point, obviously there are push/pulls in commuter and other psgr service on a daily basis. I’ve ridden them in several areas. But I don’t think that is comparable to mile or longer train with lots of curve and grade challenges. In many cases I’ve seen the head end locos (in coal service) circle back around a loop to the front again.
Nearly every intermodal train I see here in California is like that!
I guess all the more reason to go DCC. I can get away with doing a doubleheader MU in DC, but if I want some DPU action on my stack trains, DCC is the only way to go!
What’s also interesting is that not that long after the FRED made the caboose obsolete, now we see DPU locos making FREDs obsolete!
There have been occasional problems when the linkage fails between the lead unit and the DPU. If all units are required to pull the tonnage, the rear unit get moved up to the head-end where it can (hopefully) still work in regular MU mode. If there is no FRED available to replace the unit at the rear, typically there is a severe speed restriction on the maximum speed the train may travel. That’s a good way to continue to plug up a busy piece of line, so often a spare FRED is carried in one of the units.
As Railwayman indicated, it is very rare that they are located to simplify reverse movements, although there are some isolated places where that indeed happens.
John
DPU has been used for decades in coal and is now common in virtually all types of trains. A DPU train has better braking, better fuel economy and higher capacity.
It has absolutely nothing to do with bridges in Chicago.
The direction of the rear unit is more or less random. Very few DPU trains “reverse drection”. The majority that do are coal trains that have to saw onto a conection or interchange to get to a power plant.
To MU/consist locos with DCC is one of the reasons I went DCC. Speed matching is critical however to have two or three up front and one pushing. As are the individual car weights being to NMRA specs. Cars being too light or heavy can cause problems. Sound and knowing my locos has helped me run DPU consists. Since I can’t be at both ends of a 20’ long train at the same time and I want to make sure things are going well, listening to the loco sounds as well as wheels and watching the train bunch/unbunch makes for some interesting action. That’s true for powering up or putting on the brakes. BTW, the Soundtraxx F11 brakes can make this just that much more interesting.
Richard
Here’s two up front pulling the two below are pushing. Southbound from Roberts bank coal terminal just North of the U.S./Can. border.
Brent
The facing of a DPU is essentially totally random. It had nothing to do with having a train return in the opposite direction, since 99% of trains don’t do that. The train will get broken down, switched, resorted and its cars can go in 10 different directions from there.