I built a road way from city A to B, and a year later, a house was built next to my way (belonging to one of connecting cities), changing its ownership from me to private.
Apparently, I did not get any fund from this. i.e. the way is effectively given to the (private) house for free.
Consequently, I cannot build private barrier on that road anymore, and other player could build no-entry sign on that road, blocking any traffic (including the original player) and effectively making the road unusable. Though, I don't have to maintain the road anymore, reducing inf. maintenance cost.
Is it by design or anything?
This is intentional: as in real life, when the area becomes urbanised, the local authority adopts the highway. As to the possibility of other players placing no entry signs, I should be interested in views on permitting players to place signs on roads that they do not own in general.