I think a big issue is how quickly things are changing in terms of what vehicles are used. There is an explosion in commuter vehicles now, both of the rentable

I think a big issue is how quickly things are changing in terms of what vehicles are used. There is an explosion in commuter vehicles now, both of the rentable and privately owned variety. I think the rentable ones are probably experiencing the most rapid change. Motorized scooters, semi-motorized bikes (the ones that "flatten hills"), "hoverboards," motorized skateboards along with those one-wheeled self-balancing things that I want so badly. :) Haven't seen motorized roller skates in the real world but I'm betting on them arriving soon. And then there are the self driving cabs that we know are coming soon. Combined with the rentable scooters and bikes, these can allow mixing it up in interesting and practical ways. It seems like thinking of cars, bikes and pedestrians as 3 distinct categories is not going to work for long. Maybe a bit fanciful, but I could almost imagine rainbow stripes drawn on the roads, with red being for cars, purple being for pedestrians, and if you're using a motorized skateboard or a bike, you'd tend to ride in the greenish area.