Digging in at the MSR hexes etc.

[Liebchen]

I think that he meant in real life, a bunker or trench line actually in the road would be visible from far away.

As for the game, the improvements are visible when they are in view of a friendly unit, although they won't be visible during actual movement unless you bump right up against them.

There is no general intel in these games. In fact, as someone was grumbling about only recently in these forums, you can lose track of your own improvements/defense measures once they're out of sight of your own units.