[gensym]

The roads were built for multi-ton automobiles and bicycles. Because automobiles are less flexible than bikes in terms of radii and lane widths, their needs set the constraints for those factors. By "posted speeds", I assume you mean the designated upper-limit. No one is proposing that cyclists should be able to ride on roads with minimum limits that cyclists cannot maintain. This isn't that difficult to understand.

Bicycles can travel safely with automobiles. Automobiles, on the other hand, can often not travel safely with each other. Perhaps you mean "quickly" rather than "safely"?

Is your username some kind of a joke?