Hi,
Not 100% sure what you mean, but have you tried 'track priority' markers?
Track priority markers are not 1 train gets the right of way over another but if a train has a priority of say 3 and you place a track priority marker and set it to 3 also, then the driver will attempt (if he can) to drive on that track.
I use these myself to make sure drivers/trains are on the correct track where they need to be, like going through a complex junction.