To re start a saved driver session use the saved session option, select the name you saved it under and resume session.
You can turn any route into an Ai driver session. Highlight the route, then select create session. Place a 2 consists at either end(or wherever you want) of the route, place and name a track mark on the track next to either consist. Save as attempt 1 for eg.
So now you should have a driver session to go with the route, so click on the route twice select your attempt 1 and select drive.
Command each driver to navigate/drive to the track mark at the other end of the route from where they are.
Go from 1 to the other to see they are ok, if 1 gets stuck note the place, exit without saving and back into session surveyor. Find the spot and put a track mark down, name it.
Re start the driver session, command is now drive via new track mark, drive to end track mark. Other driver gets the original command.
Follow them until 1 gets stuck and you now repeat the process.
Once you get about 6 track marks down in either direction, in session surveyor, main menu (top left) use edit session, add. Scroll down and select schedule library. Now go to driver commands and tick copy commands from. Back to the schedule library and select edit. Now you can name a schedule say southbound, now put in the track mark names in order. Make another called northbound and do the same.
Back into the driver session, give driver A-copy commands from-library schedule-northbound. Driver B gets southbound. If you need to add more track marks do so, and add them to the schedule.
That should keep you busy for a week or so. We'll get to loading at an industry when you've mastered that lot.
Do not alter trackwork in session layer only route layer.