New ideas for transportation need to be explored, but the hyperloop in its proposed form is hugely flawed. Some of the issues may be addressed down the road, but it may take another 10-20 years to do so. At best, it may provide another technique for freight in the short term which may be a decent accomplishment in itself. Passenger travel would take a lot of re-design I would think.
The main issues are buckling as any exposed surface area will get sun radiation on top but not below. Also due to normal expansion during different temperature days, there has to be some relief joints similar to what bridges have. The issue is, they have to simultaneously be flexible and sturdy enough to support traffic, and be at near vacuum. You can't have only bolted together straight pipes.
Running at close to vacuum levels causes an immense amount of stress to that 3 inch?wall. As it has to both endure regular pressure from the atmosphere and negative from inside. Any form of collision on a tube wall would be catastrophic. If there are any issues at all, passengers would suffocate because there would be no oxygen and no means to escape a solid tube. Any accident at the speed of 600 mph would be instant death not just to the car(s) involved, but every other car in the system. Also running any type of propeller at near vacuum would be near useless.
Even if the tube isn't at vacuum level but partially below atmosphere pressure, it would require an immense amount of energy to both achieve and maintain at the lengths proposed. That leaves doubt as to the economic projection of the incomplete plans.
