Vehicles blocked with no obvious obstacle

Issue description

I have two medium bridges next to each other. No vehicles will navigate across the bridges, and show a broken route halfway across. There are no buried pipes or other things in the area (or anywhere else on the map). I have demolished and rebuilt both bridges, but it hasn't sorted the problem out.
Attached images showing blocked route for normal and mega excavators, plus save file

Reproduction steps

Unsure - I've never seen it before, and I have other bridges aligned exactly the same way that don't have this issue.

Game version and build number

v0.6.4d (b347)

Operating system

Windows

Attachments

mike8 post nuke - Copy.save

I did it.

mike8 post nuke - fixed.save

What was the cause - how did you fix it?

I just deleted both and built them one at a time. Perhaps it depends on the order of construction.