Hi Chris.
The reason we back the extra down the hill is this. The regular train is nine cars long and is equiped with more modern ( mostly ajax racheted types of hand brakes.).We can safely and effectively tie down the regular train while the engine is run around the train. while the cars on the extra train is still equiped with the old style "Stem winders"hand brakes.) Because of the old systems in place it is much safer not run around the extra train, but to keep the locomotive coupled on the west end.
Here at the Loop the line runs up 3 1/2 % to 4% grades with curves as tight as 30 degrees not to mention very tight clearences. Standard gauging the line is not an option.
As for the diesel locomotives usually both are "fired up" if some switching chores need to be done. besides it is a good thing to exerisise these two locomotives now and again.
Phil Reader