With a 3 or 4 track mainline are the mile markers placed on each track ? or just each outside track ?.

I have a track chart to follow so i know where to place them roughly but this is for the Powder River Basin which has a lot of it that is Bi-Directional ( I think that is the correct term ).
Thanks for any help.
Cheers Mick.

I have a track chart to follow so i know where to place them roughly but this is for the Powder River Basin which has a lot of it that is Bi-Directional ( I think that is the correct term ).
Thanks for any help.
Cheers Mick.