So, the key ideas are: - Smaller diameter tunnels. 14' is suggested. This is slightly larger than the deep London Tube lines. - Electrically powered TBMs. Those exist. However, often the business end of the machine is hydraulically powered. Musk is probably thinking of going all electric, at least for the cutter head. After all, he has lots of experience with high-torque electric motors. - Do cutting and tunnel ring…
From where?