[Quix]

I think I've read that assertion from more than a source or two.

I'm curious . . . what are the diameters of the long distance tube train tunnels? And the distances between the cars and the tunnel walls?

[Chris Talk]

I do not know and have never heard any opinion expressed on the size of the transportation tunnels, though common sense should be one's guide.

The sheer volume and multiple levels of the tunneldom out West boggles the mind.

Maybe this planet would ring like the Moon sooner or later too, once it would be so hollowed out.