"The death penalty seems a little extreme for driving over a traffic circle." Cate - I never advocated that but really there is absolutely no condition where you can drive fast with traffic circles in place safely. If you do you endanger everything and everyone around you. Simple solution, don't drive over the traffic circle. Boulders are an obvious deterrent, they are large and quite easy to see.
What you say? What if they can't see the boulders? Like because they are going so fast they don't have time to look, or they are driving with there headlights off?
OK, you win, yes, death penalty for driving over traffic circles is a fair compromise. I have no problem with that, again they voted for the Darwin award with their own foot, nobody forced them to do something stupid, unless you want to blame soft drink manufacturers.
Again, Cate - You could ONLY get hurt if you drove over or into a boulder (as described) at high speed. Any normal driving over the boulder would only result in a fair amount of damage to your vehicle. I'm sure you are not against that.