Earlier quoted context omitted.
Though if they really dug that much tunnel under a city in such a short time, maybe there's an actual innovation in a better way to make subway tunnels? I think putting cars in these tunnels is silly and that subways are obviously the best answer personally, but I'm also watching two new light rail lines being put in next to my house. It does not seem quick (though they're elevated). It'd be lovely if those tracks we…
If there were an actual innovation in tunneling, I feel like they’d be able to give actual specific metrics to rebut critics who argue that it’s apples to oranges. But AFAIK the bottleneck in tunneling is not a mechanical engineering one.
I think the only time it's moving close to high-rises again is over by the University.
Edit: I believe they went so deep because of the volume of glacial deposits in this area. Otherwise they would have been going through gravel. That made building the stations a bit of a pain (the Beacon Hill station still has chronic problems with water. It smelled like a moldy towel for a long time).