This idea assumes that there aren't already a maze of tunnels under cities: there are. It thinks they're cheap, which they absolutely are not. It thinks they'

This idea assumes that there aren't already a maze of tunnels under cities: there are. It thinks they're cheap, which they absolutely are not. It thinks they're reasonable to get permission to dig, which is, er, nope. And it absolutely won't work outside dense cities. The "van + drones" model scales out.