Which significant design change did Hyperloop Transportation Technologies make to Elon Musk's original Hyperloop concept to improve safety and feasibility?

The transportation industry has been on the cusp of a revolution with the development of the Hyperloop concept - a proposed high-speed transportation system for both passenger and freight transport. But how well do you know the product design challenges and progress behind this potentially game-changing transportation technology?

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They replaced the air bearings with magnetic levitation technology
They added underwater tunnels to connect continents
They switched from vacuum tubes to pressurized air chambers
They eliminated the tube structure for an open-air maglev system