How do they know...

Hello!!
I have one question. I was wondering, how does the CTC controller, or who ever watches the whole line know which train should go into the hole if two trains are passing? I know that if it’s a hotshot it takes the main, but what about others?
Thanks!!

Back in olden times most RRs had one (or both) of two systems. One would be to stipulate that trains of the same class would be superior in one direction (generally eastward) to trains of the same class in the opposite direction. The other would be (SP used this) to make trains in one direction second class and trains in the opposite direction third class.
In practice all sorts of factors could enter into it. If a grade was involved the DS would tend to favor the up hill train or loaded trains might be favored over empties, or the crew on one train might be getting short on the Hours Of Service Act, etc.