I've met Daryl Oster, the guy behind ET3, even contributed a few ideas crudely sketched out on a notebook -- stuff I'm sure somebody involved had already considered. Anyway, he seemed nice, smart, legit. I really love the basic idea and goals of ET3. I was a little bit concerned that it wasn't farther along in terms of implementation versus theory. But he did say that he's worked with folks in China and they were generally much more receptive to it there, whereas in the US there's more bureaucracy and legacy inertia. There's right-of-way issues, NIMBY, legal stuff. I think all the edge case scenarios are riskiest -- those need to be addressed in the design, if they can be, things like what happens if a tube is pierced, what happens if a passenger has a crisis and needs to get out of it quickly, etc. But the basic physics of it are pretty attractive because of the efficiencies and economies of scale.