We also experience G-forces when we go around a curve. This “centrifugal force” is what flings you from side to side on fairground rides. Again, about 0.5G is the limit for comfort. Travelling at speeds of 1,220kph sets the minimum curve radius to about 23km, which means that the track has to be pretty straight. It must be very level, too, because vertical hills and bumps also give rise to G-forces.
With the right site, these constraints could be manageable. The real challenge for hyperloop will be dealing with earth movements. In all large-scale engineering, allowances are made for thermal expansion, ground water and seismic activity – things that make the ground shift around. Normally, these aren’t too much of a problem. There are expansion joints in bridges and pavements, and even when subsidence causes cracks to appear in a wall, we shrug our shoulders and say “so what?”.
But movement in the hyperloop track could cause real problems, when the pods are travelling at such high speeds. That’s why Musk favours a track on columns, so that it can be adjusted and realigned in the event of ground movement. Indeed, we already do this kind of realignment with conventional railway tracks: the rails on sleepers are loosely supported on ballast and regular “tamping” ensures that the track is kept straight.
With such demanding specifications, actually constructing a hyperloop will not be cheap. But the days of aircraft and ships are numbered, unless we can find a way to power them with electricity or hydrogen fuel. Perhaps we could even learn to live with nuclear-powered ships. Hyperloop offers a novel vision of the future of long-distance travel – one that might just catch on.