Fair question. I would build 3 tubes instead of 2. That would help with repairs as well as with handling asymmetry in demand (for example, if more people want SFO->LA in mornings and LA->SFO in evenings)

I was thinking the same thing. Eat the up-front build costs, but assure yourself a persistently-functional loop. Probably the type of thing best determined as part of the review-process, and not listed a requirement in the technical draft.