As a former tunnel boring engineer, I can attest that mining tunnels through consistent rock is vastly easier than through mixed geologies such as Manhattan isl

As a former tunnel boring engineer, I can attest that mining tunnels through consistent rock is vastly easier than through mixed geologies such as Manhattan island. Also there is less stuff (utilities, metal debris, etc) underground in Austin. There are undoubtedly historical reasons why Austin lacks sane transit but technical difficulties while boring is almost certainly not one of them.