A beautiful idea, but how long did it take them to build that tunnel in Boston? And how long was that, a mile and a half or something? The geniuses building the LA subway spent a kazillion dollars of taxpayer money for a mostly useless tunnel to nowhere underneath the city which as I recall kept catching fire and exploding on them. Americans should perhaps stick with bridges, and let the Europeans dig the tunnels. If the project was given the green light today, I would expect to see it finished sometime about the year 2380.
Also, it occurs to me that by the time this transcontinental habitrail was completed the Greenland ice sheet might well have melted, raising sea levels by twenty feet, and sinking both New York and Los Angeles.