"roundabouts"??? You must be from overseas. Here in Jiosey, they're just called circles, and most of them have been eliminated because nobody understands the basic rule: Once you're on the circle, you have the right-away over anyone entering the circle.
I think you have too many uncontrolable variables contributing to the outcome (crashes) to make a sensible statistical probable outcome. You'd have to control the speeds and entrance & exit intervals of the cars at the circle, and that could only be done with stop lights all around and in the circle. So why not just give up and make it a cross intersection with a normal set of lights.?
IF you really want to keep traffic flowing without risk of crashes, get rid of the circle AND the lights and build overpasses and ramps.
I HATE traffic lights................
