Old issues of Popular Science are a rich repository of gonzo, never-was transportation. Ogle such curious conveyances as the skiing cubicle, the tuba-equipped jungle cruiser, and a truck with a steam engine in every wheel.
Even today Popular Science and Popular Mechanics has always been a good source of science fictional vehicles that may never get built or mass produced.
Over a decade ago, I remember reading in one of those mags the proposal, along with wonderful illustrations, to convert all oil supertankers from surface ships to submarines. This was suggested for, among other reasons, a way to prevent delays in oil shipments due to bad weather in the deep ocean.
If we looked through the archives, I bet we'd find proposals for nuclear powered dirigibles that would never land, jet packs and fleets of flying cars that could also work as boats or submarines.