Re: "it's a [..] electric bus that automatically switches between tunnels and lifts"
Even if you could dig straight down in hundreds of places easily (you can't, any decent sized city has all sorts of infrastructure down below, not all of it properly documented) and lower a 14x faster tunnel borer you're still left with the problem that its speed is limited by all the work required before it can drill anywhere.
You may need to go a hundred feet or more below ground level (in some cities multiple hundreds of feet) to get below existing subway tunnels, piles driven into the ground for skyscraper foundations, etc. If you go down deep enough that you know FOR SURE there's no infrastructure there, you have higher pressures, more heat, more water, and of course potential voids (i.e. caves) subsidence, etc.
Where I live is nothing remotely close to a major city like London or NYC, but there are caves 20-30 feet underground in multiple places downtown. Back in the 1800s they were used as beer cellars by breweries operating in the area. If there are caves at such a shallow depth, who knows what there would be if you went down 60 or 70 feet to get below the lowest possible depth of the foundations of the tallest "skyscrapers" in town (like 15 stories or so) You might be tunneling along and your borer drops 100 feet into a massive cave. Or might remove just enough rock in a certain area that a massive subsidence causes damage to the foundation of a building above.
This Boring plan is ludicrous. I used to have a lot more respect for Musk but he's totally lost it with Hyperloop and then this boring idea! What's next, personal airplanes for traveling into major cities that require using EM catapults on the roof of tall buildings and arrestor cables for landing? Makes me wonder how much involvement he really had with Tesla and SpaceX, versus just doing a good job hiring people who could actually make his dreams a reality. Because there is no one he can hire to make the Boring company a reality.