bicycles are unparalleled in their ability to transport humans efficiently over short or even medium distances in a city. all the advantages of cars and more, with the important caveats of course that they are unusable by the non able bodied and they cant really haul loads. and many of the disadvantages of bicycles melt away when not forced to share road space with the accurséd car. there are already real world examples of primarily bike oriented commuter systems, in for example Denmark