> sure, but what technology could be applied in this case?
A big problem with tunnels has traditionally been land rights (less so than with highways/but still a problem). If your tunneling costs are 10-100x lower, suddenly landowners who would otherwise try to extract exorbitant prices have a lot less leverage because you have more freedom in where you build the tunnels and entry/exit points.
A big problem with tunnels has traditionally been land rights (less so than with highways/but still a problem). If your tunneling costs are 10-100x lower, suddenly landowners who would otherwise try to extract exorbitant prices have a lot less leverage because you have more freedom in where you build the tunnels and entry/exit points.