a sibling comment is imagining a future where automated cars will be so good (and pervasive) that we no longer design cars to survive catastrophic crashes and can build them in any size, down to a single seat. I am going to take it a step further and say that lanes will become obsolete at this point, and we just pack them together as close as allowed by width.
in this vision for the future, is it still necessary to chisel out 6ft on every surface street for humans to ride self-propelled bicycles?