[Alberta's Child]

Here’s where your post is misleading: There will always be a minimum need for ONE locomotive on each group of cars up to 50.

Let’s look at your example. If one locomotive can pull 50 loaded 100-ton cars, then a train with 75 cars will need two locomotives — because they can’t put half a locomotive on the train. In effect, there is “unused” pulling power for 25 cars. What the railroads are doing is organizing their trains so that they are putting as many of them out on the system in sizes of 50 cars, 100 cars, 150 cars, etc. — thereby minimizing the “wasted” pulling power on their trains.

[glorgau]

Pretty straightforward linear optimization problem. Surprises me that they are just doing this now.