No mention of expenses for passengers. Given transportation to/from the coast, I'd guess a plane ticket in/out of here would be prohibitively expensive in both time and money. And building a 4 story metropolis underneath doesn't make sense unless there is a reason to visit. Hotels, conference centers and shopping centers, wouldn't be enough, at least for me.
"No mention of expenses for passengers." Nor of the time factor involved. Commercial flights already take the better part of a day, even for short jumps. I can't imagine having to arrive at the ferry terminal 4-5 hours before my flight so that I can get to the terminal in time to spend 2 more hours waiting for ticketing and security and all the other delays. "And building a 4 story metropolis underneath doesn't make…
Not even close. San diego is not really that big. For example, it is a 30 min drive from downtown to alpine which is a small town in the middle of nowhere, where the more sensible plans put the new airport. That travel time can be shortened with high speed rail and it would still be many times cheaper than that ocean pipe dream.
Oh and 30 min in a car or on a train will be soo much better than 45 min on a shaking sickness inducing ferry.