Can someone please tell me why Union Pacific is using DPU's on their stack trains.

Question

I live in the Dallas?Ft. Worth area and when i see international stack trains with 2 engines on the front, they always have 1 on the back. But on the domestics, they have no DPU. What is the point for the DPU?

Answer 1

DPU has a number of advantages, when they work properly.

On heavy trains they reduce the coupler strain on the head end of the train by moving some of the power away from the front.

DPU also allows for much faster application and release of air brakes, instead of all brake functions happening through an air coupling at the front of a train, now it happens at both ends simultaneously.

On very long heavy trains there are forces generated that can derail a train during acceleration and braking around curves, these are greatly reduced by moving some of the power away from one point.

in short, when they work properly, DPU allows a larger train to be operated than with strictly head-end power.

And when they dont work properly . . . . . . . . . well, they can make an awful mess.