Using the handy heyday magazines as a guide, one would think that there was no place for a two, three or four-wheeled vehicle in the future. Wesley Treat took a deep dive into the Popular Science and Popular Mechanics archive to give an exhaustive view of the single wheeled future envisioned by those magazines.
Similarly, I suspect a study of monorails would discover an equally impressive number of covers.
Scale was such a common theme of future transportation discussion in these old magazines. The future was either very small and personal -- compact submarines, helicopters that fit in your home garage and, of course, jet packs -- or huge -- massive dirigibles with cutaways showing elegant suites, giant ships presaging container shipping, and space stations with cornfields.
Wesley Treat's Study of Monowheels
Popular Mechanics Archive
Popular Science Archive