Why do freight trains have multiple engines at the front and rear?

Question

I always wondered what the extra locomotives are for on modern freight trains, are they for extra power?

In: Engineering

Answer 1

Already some good answers here but there’s one more to consider: train slack and load on the couplings. If we have a 250-car train needing 4 engines and put them all at the front, that’s a lot of load on the couplings toward the front and also a lot of slack which is hard on those couplings. If you instead do 2 in front pulling and 2 in back pushing you can control your slack a whole lot better. Even 2 in front and 2 in the middle is better than doing all 4 up front.