Why can't I assault this hex?

[wildb]

I just got the game today. Ran some tests.

There are several hexes like that and it appears to be an elevated RR line.

You can only enter them by following the elevated RR in travel mode. I was moving the German units positioned in that area. You have to follow the RR until the RR is no longer in the elevated mode. That is, you cannot just move off the elevated RR line where you want to. This applies to infantry, artillery, and vehicles. You can also have only one unit in travel mode on the elevated RR. No stacking allowed.

If you put the infantry unit in foot mode it can move into the hex from any direction and stack with another unit.

I just looked at the information box and it shows elevation as 50+5m - my guess is that the 5m is the height of the elevated RR.