volcanoguy:How about calling the category Roundabout Art? We are getting quite a few roundabouts here and many of them have some nice art pieces in the center.
There are a lot in neighborhoods of Seattle that are landscaped, but common. But you're right, some of the newer ones do have large sculptures in the center. The first abstract sculpture (here) that I waymarked is a kinetic piece in a traffic circle. It's called Hi-5 and it "waves" to the folks passing by below on I-5.
The thing is that most of the art or statues in these traffic circle's would be waymarkable in other categories.