Regarding the use of multiple locomotives on heavy trains, one answerer indicated that the locomotives were ''ganged'' together.l wonder if the same is true when a particularly long train in mountainous areas has locomotives in the middle and at the end of the train.

They are now. Is not multifrequency remote control wonderful.

yes & no

There r still the traditional ''helper'' locomotives that r used primarily for mountain grade in short distance.
They have to be added & removed & it is still better to have a crew on them for this purpose.

A lot of what u see now is remote controlled or DPU (commonly called ''dupe'') consists. These usually stay with the train for longer distances & allow the railroads to run larger trains than they did before with strictly head end power.

They work pretty well, but when they mess up, & believe me, they do. it can be a nightmare.
They r nowhere near as good as the manufacturers claim although they r much much better than the first generation of locotrol we had back in the 70's.

As Rango said they are DPU trains.They are all run from the head end of the train.The engineer has the choice of how to control them.They can be run all together which means whatever he does on the lead unit is mimicked on the rear units.Or he can put up a ''fence'' and run the consists separately from the head end. l have never run one with units in the middle and the end but they all operate the same way.