The problem here is the "evacuated" part. It's hard to hold a vacuum in a large vessel: think of how few giant vacuum chambers exist. Most of them were built for the Apollo program, and just get maintained. How hard is it to maintain a meaningful vacuum in thousands of kilometers of tubing? Every weld, every seal, have to be spaceship-quality.<p>Then there's the tube itself. To hold off sea-level collapse pressure, you'll need a relatively stout tube, probably with ring-stiffeners every so often to keep any buckling from ruinging a continent-long length of tubing.<p>So, pumping the tube system, the tubes themselves and the valves, seals, and welds, plus ongoing intensive inspections. This is like jetpacks, helicopter taxis and fusion power: always at least 10 years in the future.