Jean, you are advocating a Utopian ideal that doesn't/hasn't worked so far --at least on any path I've been on. They are constantly filled with joggers, runners, skateboarders, In Line skaters, walkers 2/3/4 abreast who act as though a bike rider ,even if he's just leisurely pedaling along, has no right to a portion of the path because it interferes with their conversation. It may be different in other places, but that is and has been my experience.
People, basically, are very selfish. They want the facilities they want and resent anyone else who might also want to share them. How to overcome this in a society dominated by the individualist attitude "All for me and to heck with you" is probably more than political compromise about bike paths will achieve in the foreseeable future.
But your vision is certainly a wonderful one and worthy of implementation. Convincing the majority of riders and walkers and runners and other users of these paths that's it's time to share respectfully and unselfishly is a formidable task. I'm not one willing to fight the fight or devote the time to such a task, I'm too busy dodging cars on the roadway. And I suspect that 99% of the population is just like me.
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ljbike