This seems interesting:
The Hyperloop would send multi-person passenger pods through an above-ground tube at 760 miles per hour—nine-tenths the speed of sound. The tube would sit on 20-foot-high pylons that would mostly follow the route of California Interstate 5. Musk estimates the cost of the project to be around $6 billion, or less than a tenth of the estimated cost of the proposed California high-speed rail project, which Musk calls too slow and too expensive. The LA to San Francisco trip would take about 30 minutes of a turbulent-free and quiet ride.
This impressive thing about this — if all this is right — is the sensitivity to cost, which usually seems to be completely lacking in high-speed rail projects.