It seems to me that there were two technical details of TBC. One was "We can build a tunnel cheaply". That seems as far as I can see to have been entirely down to digging smaller tunnels- which doesn't seem like innovation to me, especially since some of the cost saved is by not building the escape tunnels that traditionally are built for safety not capacity. The second detail was "These tunnels will be fitted in a way that allows super-efficient transportation". That seems to have entirely disappeared.<p>I would really hope to see some evidence of their efficiency of digging tunnels being legitimately better than traditional methods now. Otherwise you've got to fear that this all ends in a dozen people dying in a tunnel because the safety precautions weren't sufficient.