A 420-meter (quarter-mile) white steel tube running alongside a railway line in the windswept northern Netherlands could usher in a new era in the transportation of people and freight. The tube is the heart of the new European Hyperloop Center that opens Tuesday and will be a proving ground in coming years for developers of the evolving technology. Hyperloop, once trumpeted by Elon Musk, involves capsules floating on magnetic fields zipping at speeds of arund 700 kph (435 mph) through low-pressure tubes.