A decade ago, Elon Musk proposed a new form of transport that would shoot passengers through vacuum tunnels in levitating pods at almost the speed of sound -- he called it "hyperloop".
Since then, cities from Abu Dhabi to Zurich have been touted as destinations, research projects have gobbled up millions of dollars and a host of commercial ventures have sprung up -- even Richard Branson got involved.
"The transportation network has not had a new mode for over 100 years," said Rick Geddes, a transport infrastructure expert at Cornell University in the United States, who compared the excitement to the early days of aviation.
But nobody has come close to making the hyperloop work.
The difficulties have ranged from costs and finding suitable locations, to simply persuading people that travelling through a narrow tunnel at speeds faster than a jet plane is a good idea.
Musk's initial proposal would have been a "barf ride", transport blogger Alon Levy wrote at the time.
Despite all the problems, though, the hyperloop idea still energises university campuses, corporate board rooms and city halls across the world.
Hidde de Bos, a 22-year-old engineering student, first heard of it four years ago.
His university at Delft in the Netherlands excelled in competitions run by Musk's SpaceX firm, which invited students to develop pods to fire through vacuum tunnels.
"It made me really excited to see what the possibilities were," he told AFP.
He is now chief engineer of Delft Hyperloop, a non-profit university spin-off.
De Bos said the SpaceX competitions, which were discontinued in 2019, were too focused on speed and became like "drag races in a tunnel".
Now, his team is taking part in a student-led competition, European Hyperloop Week, which he
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