Catan Road Eligibility for Diplomat with Knight In Between?
Oddly this is clarified in the FAQ under When is a ship “open”?
The full answer is that a knight will interrupt a continuous road, but will not make the road &quot;open&quot;, while this is a slightly confusing aspect of the rules it's there to prevent &quot;orphaned&quot; roads, which were not handled in the rules until the advent of volcanoes.
Essentially a road is only open if it is at the end of a trade route, not if both ends are connected to other pieces from the same player.