So, here's the problem.
I built a bridge and set a demolition order for the middle sections, but it turns out this is impossible because the vehicles simply can't get there.
If you demolish the sections using "Unity," after complete demolition, there remains a section of terrain with a visually impassable path for vehicles, but in reality, you can apparently drive through, and in some cases this area eventually disappears.
Next, I started building a new bridge and ran into the issue that only the center section and the entry/exit were built, but the adjacent sections can't be constructed because vehicles again can't reach them for some reason, even though the center section somehow got built (I have no idea how). The same goes for demolition.
The question is: Can bridge sections only be built and demolished with "Unity," or is this some kind of bug?