[tptacek]

Civil engineers have looked at the Hyperloop proposal and declared themselves unable to determine how Musk proposes to reduce the costs of long runs of overpass, or of tunneling.

A simpler way to make the same argument:

If Musk can actually build a Hyperloop across California at his proposed cost, he's made revolutionary improvements to civil engineering that will be far more impactful than the Hyperloop itself; the same techniques should revolutionize, well, much of conventional civil engineering! Why isn't that happening?

[fit2rule]

Rockets = big long tubes. Big long tubes = something robots can make easily?

[Avshalom]

The tube isn't the problem. Among various problems include: the building access roads to every pylon base, conducting site surveys and environmental impact studies for each site then figuring out what to do when those studies and surveys declare a patch of dirt to be unacceptable. The original route was also going to need something on the order of kilometers of tunnel through mountains.