"By building a system on pylons, _where_the_tube_is_not_rigidly_fixed_at_any_point"
[...]
"A telescoping tube, similar to the boxy ones used to access airplanes at airports would be needed at the end stations to address the cumulative length change of the tube"
So, the tube is lying loose on the pylons, and he assumes it will keep its shape while expanding.
I think that is highly optimistic for a tube that is a straight line, even more so for one that is curved.
If he manages to accomplish that, the end stations will move over 300 meters, in total. Hopefully, when the tube contracts again, the motion will be reversed perfectly. Otherwise, that end station in LA could slowly move north or south over the years.
From what I cited: "A telescoping tube, similar to the boxy ones used to access airplanes at airports would be needed at the end stations to address the cumulative length change of the tube"
I guess that's because accordion-like flexible sections and carriages moving at 1000 km/h on a tiny air cushion don't go well together, or because such sections, being a lot leakier then welds, would let too much air in.
So, the tube is lying loose on the pylons, and he assumes it will keep its shape while expanding.
I think that is highly optimistic for a tube that is a straight line, even more so for one that is curved.
If he manages to accomplish that, the end stations will move over 300 meters, in total. Hopefully, when the tube contracts again, the motion will be reversed perfectly. Otherwise, that end station in LA could slowly move north or south over the years.