Correctly designed roundabouts - with a central reservation between the opposing directions on each approach road, and with the approach road bending as it merges with the roundabout to guide people in the proper direction - virtually eliminate direct straight-on "T-bone" crashes and it makes it much easier for people to go the correct direction around the roundabout as opposed to turn backwards (almost a U-turn) to go the wrong way. Sideswipes (at relatively shallow angles) and rear-enders, sure, but those have much less severity. The problem is that such a roundabout takes space, and in a city with everything fully developed around it, it's not happening. All of the rural roundabouts (and in new-development urban areas) have these design features.