I think the bridge-through-the-wall idea is very clever and inventive.
But it still seems to me that it would be much easier, and just as effective, to put
some trees along the foreground edge of the benchwork. They make a darn effective viewblock
for a track punching through a hole.
Here's one:
Forget the foreground stuff like the trestle. That whole scene back there with the trees blocking the fact
that the tracks go through the backdrop is only 13" deep.
How high off the floor is your benchwork? That's another factor. The higher it is, the easier it's going to be to
conceal that hole.