[retrovm]

No, it's just a lot smaller. A 12-foot-wide tunnel is, shockingly, much cheaper than a 21-foot-wide tunnel. It also has essentially zero capacity, much like a hyperloop. If you want to punch useless holes in the earth, Elon Musk is your man without a doubt.

[jjeaff]

According to an analysis I saw on youtube somewhere, they were able to find companies that dig similar sized tunnels (Boring Co. is just using off the shelf tunnel digging equipment.) They were running comparable if not a bit slower than similar projects that have been done many times before.

[ClumsyPilot]

This is the most important factor - the amount of people such a tunnel can move is borderline insignificant, compared to a proper subway with a train.