Not necessarily. Some roundabouts have the center circle partially paved so that oversize loads can drive right through if needed. There are curbs, speed bumps

Not necessarily. Some roundabouts have the center circle partially paved so that oversize loads can drive right through if needed. There are curbs, speed bumps and road pillars that make it obvious for normal traffic not to take the shortcut. It also doesn't fully protect vehicles already inside the roundabout. My father got rear-ended once while inside a roundabout by a possibly distracted driver and the car was a near write-off. The main advantage of roundabouts is traffic fluidity. When compared to intersections with stop signs or traffic lights, unless it is full you can often enter a roundabout without coming to a complete stop first.