What will the mass transit of the future look like? Elon Musk, founder of space transport company SpaceX and electric-car company Tesla Motors, thinks he knows — and he calls it the Hyperloop. But ...

Of all the crazy idea Elon Musk came up with over the years, that of a tunnel system for transport pods to be used to help with congestion in crowded cities (and between them) surely sits at the top ...