Nothing at all to prevent you from using a "common" bus for the other rail on each of those tracks.I have a 12-track staging yard. . . . . . . . However, respecting the second bus wire for each track back rail, is there anything that prevents that wire being common to several/all of the tracks? I.e. could I wire, in the extreme, all 12 back rails to one common bus feed? I had already assumed I'd run a wire for each track, but it occurs to me that that may be excessive. <<<<
If you think about it, whether you install a second "block" bus for that other rail or tie them all together to a single block bus for the yard the logical flow of electricity is the same.
I'd run that common "block" bus down the middle of the yard, six tracks on one side, six tracks on the other - will reduce the overall length of the individual track feeders.