Placement of helpers

[athelney]

When CP were using helpers over the Rogers Pass , they were placed about 30 cars from the rear of the train on normal consists .

[Anonymous]

On CP rail here they run 99% of their coal trains (into Roberts Bank) with a single unit on the front and a single unit on the very end.

CN doesn't run remote locomotives anywhere here in Canada, as they have basically no grades.

[csxengineer98]

helpers are placed on trains when the tonnage of the train is to great for the power to pull it over the grade...or if the trailing tonnage is to great...trailing tonnage is the tons behind the first empty long car...(auto rack..TOFC flat car) or if the tonnage is just to great behind the engins... rail roads post the trailing tonnage reqiermtns in thier time tables and specail instructions...... also..the same rules that we use for HAZMAT placement for the head end also go for the placment of a helper on the rear... you have to have at least 5 cars befor an engin for any loaded HAZMAT car...so sometimes if the block of cars on the rear are all HAZMATS..sometimes you have to cut the helper in... meaning..you have to place it someplace in the middel of the train... to meet the HAZMAT rules...and the tonnage rules...
csx engineer

[wayne]

What considerations do railroads use (type of terrain, type of train, amount of tonnage, length, etc.) to determine where to place helpers within a train? Does the use of DPU's make a difference?