Samm
170
Yes, the number of accidents can go up when a roundabout first goes in, but the severity of accidents goes way down because the speed is lower and the vehicles are going in the same general direction. And accident rates at a new roundabout tend to fall after people get used to it.
Also, you may not be aware of all the accidents at any specific intersection. The design engineer has access to all reported accidents for as many years back as they care to look at (generally about ten years or back to the last significant change of configuration to that specific intersection and/or stretch of roadway.) That data includes both the type of accident (side swipe, head-on, t-bone, etc.) and the contributing factors (speed, DWI, darkness, weather, etc.) for consideration in demonstrating the need for the project and the design of the new intersection. They don’t just plop these things down out there on a whim.