
Though to be fair that check would be a bit slower - instead of check if one item (current railtype) is present in an array (as done with VarAction2; the NML check probably compiles to VarAction2 as well), it'd have to check if an array (current railtype + alternative + compatible) would have any common member with the MY_AC_RAILS array. All of this would be done for each train, for each track piece. I think the pathfinder caches the results, but still
