[Tuckerman]

I agree! Total tunneling is preferable, because infrastructure of significance can be built over it. Costs are high though and I don't know how much rock lies under the connector and at what depth. One can look at the MARTA tunnel at Peachtree Center to see that going deep might be quite an undertaking. I guess this is something for the techies to figure out. I think of the huge and long auto and train tunnels through mountains in Europe which managed it.