If the science fiction writers of the 1950s had been right, most of us today would travel around in flying cars and pneumatic trains. We would commute to work on high-speed moving sidewalks and zip across town in horizontal elevators. For short hops, we would wear personal jet packs or anti-gravity belts. Well, here we are in the early 21st century and we’re still waiting for buses, stuck in traffic jams and trying to walk across busy streets without being hit by a cab. Transportation has changed, but not in the ways predicted by science fiction. Many of the most important changes have been invisible.