Traffic engineer here. The purpose of the landscaping in the center island of a roundabout is to block the view across the roundabout and to stop people from dr

Traffic engineer here. The purpose of the landscaping in the center island of a roundabout is to block the view across the roundabout and to stop people from driving directly over the central island. The purpose to blocking the view is to make traffic flow better. There are many people that will wait for any vehicle in the circulating lane regardless of that vehicle blocking their path. By blocking the view across the central island, those entering the roundabout can only see so far upstream as matters to their flow. Stopping people from traversing the central island may not be a large issue in an urban environment but in rural settings that is different. The state I live in is very rural and we have some roundabouts that are not near a water supply for irrigation. As such the state DOT tends to use just a mound of gravel (roughly 3/4 to 1 inch aggregate.) It is very common to see tracks going right through the central island, likely lifted trucks thinking it is awesome. Having landscaping in the central island ads something to hit.