Just had a though on this while reading the tread. Utterly untested and based on the implimentation details of the path finding algorithm
############################
...HLHHHHHHHHHHHHHHHHHHHH...
...H####################H...
...HHHHHHHHHHHHHHHHHHHHLH...
############################
. = Floor
# = Wall
L = Low traffic zone
H = High traffic zone
Route cost is the same in both directions but depending on how the path finding explores different paths i could see it prefering one route for one direction and the other route for the other direction.
Someone else may need to do the science, I dont have a computer with DF on with me.
What if you took this idea, but take the walls out of the center, and just use a couple of low traffic zones, like so:
############################
...LHHHHHHHHHHHHHHHHHHHHH...
...HLHLHLHHHLLLHHHHLHLHHHLH...
...HHHHHHHHHHHHHHHHHHHHHL...
############################
So dwarves going east-west will prefer the bottom route, then go up to the middle at the end. Dwarves going west-east should do the same with the top route. Generally, the middle will only be used for avoiding other dwarves going too slow on the preferred route. Maybe making the middle all medium traffic would accomplish the same thing, I'm not sure.
I think it'd only be useful for aesthetic reasons, if you prefer to see dwarves going one way on one side of the tunnel, and one way on the other side, since you'd probably get the same speed of traffic flow you'd see with an easier to set up high traffic middle.
Again, this does nothing for the idea of a true 1 way corridor, but I think that's impossible, unfortunately