Seems like there should be a separate competition for designing the tube. For example why should the radius of the tube be what it is, why have a center rail instead of two rails or side tracks, should the tube have some sort of inner coating? What if it should be a double tube, a tube within a tube, for sound/temperature isolation and to reduce vibrations, and to reduce the risk of depressurization due to outside impact kinda like a double-haul oil tanker? Can it be made out of glass (that'd be kinda cool to look at/out of)? How close to vacuum the pressure and thick the walls of the tube should be?

Can someone double check my work here: In the webcast they mentioned it will take 30mins to depressurize the tube. The length of the tube is 1mi. For example from LA to SF is roughly 400 miles if the final pump is twice stronger it'll take 6000mins or 4 days to depressurize, I'm assuming they will only need to do this once and have gates to maintain the main tube's pressure near areas of loading/unloading.