Question for all you engineers out there...

On the UP, the rules is no more than two units in DP consist. BUT, if a manager OK's the move then you can have whatever they say.

Dan 

Did you mean isolated units in the remote consist?  Or perhaps you were referring to slave units?  Either would be permitted, although the best results come from more or less comparable locomotives.  Slaves don't have diesel-electric power plants, but consume amperage from the master unit, and therefore do not run as fast uphill as two powered units.  Were all four of the remote units running and producing power?

These days, with cabooses almost nonexistent, DPU remote units are usually at the rear of the train for  convenience.  The ideal situation would be for the remote to be cut into the train at a point where it pulls 1/3 of its rated tonnage and shoves 2/3, but that is not often done these days, due to the time consumed in placing the remote in the train.  Most railroads are too busy now to have a train sitting and occupying track for the extra time required to cut the remotes in and out of the train.

Railroad Special Instructions (which go with the timetable and modify the consolidated operating and air brake/train handling rules for that individual railroad's preferences) normally have a section on how to calculate the maximum number of powered axles that can be used on Distributed Power remote consists.

Tom,

I don't know if all 4 DPUs were running, I'm on the 5th floor of an apartment building about 500' from the tracks.  ALL the trains with DPUs I have seen in the last 3 months on the rear, never cut into the consist.  I have never seen 4 units on the rear, hence my question.

ChipR