As has been said, you charge a fee and hire cops. That's not simple though. No real good answer really. My personal solution is to hang as far back as I can as those sorts of obstacles are approached and watch the carnage if any. I try to give myself stopping room and listen for the sound of crumpling metal or cracking carbon.
On my rides, I chew out folks who bunch up across the lane on climbs and ban them if they don't quit doing it. We stop for lights and do the Idaho Stop, now legal here, at stop signs. If part of the group misses the light, we wait or softpedal. Those practices are designed to make risk-running unprofitable.
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Results matter