Train engines at both ends of a freight train- how is the rear engine regulated so as to not be a drag ?

Question

Train engines at both ends of a freight train- how is the rear engine regulated so as to not be a drag ?

Answer 1

UK question...? Well here's a UK answer.

Most often you will see this arrangement of locos on engineers trains rather than on regular freight trains. The need to have a loco at each end is to make movements much easier by removing the need for the train to be "propelled" (e.g. pushed with the engine at the rear). However, under such circumstances the loco at the rear is indeed shut down and being hauled around as part of the train by the leading loco. This is well within the capabilities of the loco to do this, so it is not a huge drag.

It is possible to operate the rear loco under remote control from the front loco, but that would require the entire train to be "through wired" to allow the control signals to be passed down the train from front to back. Some UK engineers trains have such capability (most notably the railhead treatment trains run throughout the autumn), but most do not.

Answer 2

Andy is absolutely right about the rear DPU being remote radio controlled from the front, engineers have the option to operate them electronically linked to the head end power so as to operate the same or he can unlink them and manually issue different commands if conditions require it.

Depending on where you are at, you may also have seen helper locomotives back there, they have a separate engineer on them and are used primarily to help a train for short distances over a very heavy grade.

These would not be left on the train for it's entire journey, only the worst places.

The engineer on these is in contact with head end engineer via the radio and he knows when the train needs more power or less through experience and knowledge of the terrain.  

Answer 3

The throttles are linked electronically so they both work together.

Answer 4

That is known as DPU or distributed power.The rear engines are pushers that are controlled by the engineer on the head unit.They are electronically linked by radio control.They can be run linked so that the pushers do whatever the head end power is doing or they can be run split screen.In split screen the engineer runs the units separately from each other.For example he can have the head end in dynamic brake and have the rear consist pushing.They use DPU because it greatly reduces buff and draft forces in heavy trains like coal trains that can weigh 20,000 tons.It also allows trains to be run using less power than they would need if all the units were on the head end.