Big freight train with 8 engines speeds through Weatherford, TX. 

That is a really good comment. In short, yes. I added a note to the remarks. I am not an expert so maybe someone else with first hand knowledge can add to this. But locomotive pooling is common across American railroads. It is done to save time and money in avoiding changing locomotives when a train changes railroads. Apparently the agreements on power exchanges are complex but it still works. There is a short write up on this link: www.trains.com/trn/train-basics/ask-trains/diesel-locomotive-pooling/ I understand there are additional leasing possibilities that could also cause locomotives from one railroad to end up elsewhere. Again, not definite or expert info. I wonder what they do about rail cars that keep switching railroads. Thanks for your note and for stopping by. Greetings from the other side of the world!

@@JoshRawlin thank you for the link . It explained everything you said about loco pooling .