It appears TrainSims are moving away from AI trains and moving to multiplayer.That is why I repeat myself until blue in the face, if Trainz wants to move further into the prototype simulation area, it is absolutely essential that sooner rather than later a proper autonomous and dynamic signalling/routing AI is built in along with easy timetable creation/operation. Free roam and navigating yourself around a "layout" might work for the model railway orientated but after 11 years of doing this, maybe it's time for Trainz to move on.
Trainz and the upcoming Run8 and OpenRails are featuring multi-player.
Railworks is probably on Steam to eventually move in that direction.
Harold