I don't think they are roundabouts, looking from above (correct me if I'm wrong). Sure, it looks like there are 9 or so big roundabouts. But for every roundabout there are 50 semaphore 4way intersections.
It feels like modern cities, at least here in Europe, are trying to effectively remove traffic from their centers. They do this, seemingly, by making car traffic a burden, and public transit easier and often free! I'd say La Plata would be perfect for this!