[wny]

sheer ignorance. longer trains do not mean fewer locomotives. and it’s weight being pulled, not length of the train that matters. a locomotive is rated for a given tonnage over the road. this figure varies with the location....grades, curves, etc. less tonnage uphill of course. but over the same section of railroad from point A to point B it’s the same. so if one of those units can pull 50 loaded 100-ton cars, you will need two of those units to pull 100 loaded 100-ton cars.

[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.

[Dilbert San Diego]

I know nothing of trains, but, someone once told me, that some of the long freight trains can have 2 diesel engines pulling, and one in back pushing. Apparently the weight or volume of such trains are helped by having an engine push as well as pull.

[crz]

Then there is this..

https://www.youtube.com/watch?v=XhgHrDbN4EU

and this...

https://www.youtube.com/watch?v=RU9uEwSGp9M

All with just 4 and 2 cylinders respectively.

[crz]

Of course, then there is this..

https://www.youtube.com/watch?v=c2BoMFZcnDI

[SGCOS]

so if one of those units can pull 50 loaded 100-ton cars, you will need two of those units to pull 100 loaded 100-ton cars.

that amount of power always amazes me. just incredible