If it uses evacuated tubes, does it really even have to bother with being a loop? Musk's Hyperloop is something completely different.

My guess is hyperloop probably uses air pressure waves (e.g. extremely low frequency sound waves). Those would travel at the speed of sound (cross between a concord and an air hockey table). And it could use cheap mirror based solar to generate the waves via thermoacoustics.

The waves could store energy as well which was also part of Musk's picture. Frictional losses with the edges of the tube could be minimized by increasing the tube diameter. The perimeter to area ratio (of a cross section) shrinks when you do that (perimeter grows as X, area within as X^2).

To visualize, see: http://en.wikipedia.org/wiki/File:Schematic_diagram_of_trave...