I haven't used the one way railroad mod so I don't know for sure.
I can see that it would have certain advantages if the roundabout ran in a single direction, be that clockwise or anti-clockwise, but I don't know how much control the mod gives over what areas are/aren't one way, or how effectively the trains would account for that.
My best suggestion would be to test it, and preferably to let me/others know how the test went.

Would using the one way railroad mod make this more efficient?