[coderjames]

I'm clearly missing something important because otherwise somebody would have built this already, but instead of using the fans for levitation as proposed, why not keep using the magnets?

I'm imagining a tube with (8?) magnets equally-spaced around the perimeter so that the carriage inside automatically stays centered in the tube. We already know how to toggle the magnets to produce forward motion (see maglev trains). Could still use the partial-vacuum to keep drag down. And you remove the single-point failure mechanisms of the fans on the carriage and minor misalignment of tube segments.

[throwaway41597]

I think it's because you'd need a continuous line of magnets over the full tube, as opposed to accelerators at intervals so it's probably orders of magnitudes cheaper. I don't know about the reliability of compressors but I'd say you could have a couple onboard if they're an issue.