[paulsutter]

Haven't you just proven that your initial post above is irrelevant to an undersea rail system?

I'm not saying an undersea rail system is practical or smart. I'm just asking the relevance of your comparisons to US urban construction costs to begin with.

As a suggestion, a different tone might make your post seem more useful and less trollish. For example "An undersea tunnel will require serious construction breakthroughs to be practical. As a comparison, today's costs...". That would be a lot more constructive than attacking the people behind the article.

[ChuckMcM]

Great feedback, thanks. The conversation wandered a bit, and while I don't think of my style as trollish I can certainly see how my emotion on rail interferes with my communication.

My initial point is a prima facie argument, the proposal is impractical by inspection. I certainly stand by that assertion, but as part of the supporting argument we've been discussing land based construction with the implicit, albeit not as well supported, stipulation that sea based construction would always be more expensive than land based.

An interesting way to approach the problem would be to outline the design space in terms of operation cost, development cost, and rate of return and see what sort of solutions, if any, might fit inside that box.

[paulsutter]

What conceivable technologies might make it practical someday?

How can we get back to a society that is able to engage in large scale projects again? Look at the rapid low-cost subway construction in China today.

I think you're a super smart guy with really broad interests, experience, and knowledge. I think you could make the impossible happen if you applied yourself to it.