To me its
obvious that the AT ditch can be placed, and I see no reason for a Perry sez.
tearlech got it right. The RB RR has nothing in common with the B32 RR. The former is a modified wall, and thus a hexside feature, the latter is a modified road and thus a hex feature. So the hexes that have RB RR's at some hexsides
may be a paved road hex, but may also be an OG hex or a shellhole hex or whatever. But none are RR hexes.
O2 says
Each hexside (including vertices) crossed by the gray and black railway depiction-but not the depiction itself (i.e., not the artwork)-is treated exactly like a wall for all purposes
.
So when looking at how the RRs affect the game, look at the wall rules, not at the B32 RR rules or paved road rules.
If Sam or anyone else still think different, then take a look at the B32 rules and tell how to apply the movement, LOS etc. rules that you find there to the RB RR.
OK, but where in O2 does it say that you can place entrenchments on the RR? The absence of the statement never means that you can do something.... "concentrate on what the rules allow".
O2 says that the RR is treated as walls - and that means that you can do everything that you can do where there is a wall - simple as that, and the rules allow trences and AT-ditches to be placed in a hex containing wall hexsides.