Another example of doubling, from my (ancient) past.
The C&NW branch I grew up on was an “out one day, back the next” schedule carrying pulpwood south to the mills in Green Bay & the Fox Valley area. 90 miles, mostly at minimum speed. About halfway (say MP 34-36) was a short strecth of 1+%. Occassionally, a southbound (loaded) train would have to double the hill to make it. Now, that did cut into their schedule and add to their crew time-inefficient, yes. However to compare it to the alternatives…
- Upgrade the track for a “running start” (the grade was short, maybe 1-2 miles). You’d have to add a lot of new ties, dump new ballast and maybe replace rail (70 year old, 90# IIRC) for enough distance to get up speed, for thegrade itself and for a sufficient distance afterward to allow a safe slow down after cresting the hill.
- Add power. That would have tied up a locomotive for the better part of two days, perfectly unneeded for the out bound trip and for almost 90% of the inbound.
- Helper. A locomotive and crew that would be needed only occasionally and that for, at most, a couple of hours a week.
…it was the least expensive way of using the resources available (maintenence, crew time, motive power, etc.). Not that it didn’t add any expense-but some extra expense was unavoidable. Granted, this is kind of an extreme case but that might help illustrate the considerations involved.