Hi
I am sorry to say that the system does not have very good support for these kinds of more complex behaviours.
It is possible to create one way links, which might solve your problem, but anything more complex than that cannot be handled well, it is better handled by more specialised pathfinding systems.
I would like to simply instruct the character object to keep walking straight and then turn left everytime it reaches a left junction/road....if the character just turns left, how is the character supposed to get to the target (the character might have to turn right for example). If you just want this behaviour (always turning left, not doing any pathfinding) then you are not really looking for pathfinding, but you are looking for a FSM system or something similar.