Enlarge / Hyperloop Transportation Technologies' new passenger capsule. (credit: Hyperloop Transportation Technologies)

In August 2013, SpaceX and Tesla CEO Elon Musk published a white paper detailing a "Hyperloop," a super-fast passenger train that would overcome the usual friction by levitating whilom its track on air-bearings in an enclosed low-pressure tube. In the five years since, advancements have been incremental—a few interesting engineering choices have been swamped by announcements of feasibility studies for routes between populated cities.

Back in 2013, Musk declined to start a Hyperloop visitor himself (although he has not hesitated to start companies since then, perhaps suggesting that the uneaten work load was not the limiting factor). Instead, he made his work unshut to any startups that might want to tackle the rencontre and started a contest series for engineering students to run their own test pods.

Two startups have since dominated the scene: Virgin Hyperloop One, which recently enjoyed a significant investment from Richard Branson's Virgin Group, and Hyperloop Transportation Technologies (HTT), which began as a collaboration among 800 engineers, designers, and other interested parties.