Neighbor is putting up personal traffic cones in the middle of the street. Is that allowed

Location: Idaho. As I was driving home from work today I was entering my roundabout and noticed that my neighbor has put up personal traffic cones all the way to the middle of the roundabout, effectively cutting it in half.
The road is a public road in a neighborhood close to a shopping center so it’s not private property at all. And I don’t know why he is doing it because we are not on the best of terms and don’t talk (unrelated personal things)
I am just wondering if this is allowed, because with his vehicle placement and now personal traffic cones it makes it hard to see a good chunk of one side of the roundabout as I’m coming home from work.