[soyiuz]

See my comment above. An elevated (or submerged) tube with rails (or a track) inside cannot be less expensive than those rails or track elevated (or submerged) alone. I get the pipeline metaphor, but a pipeline with infrastructure inside is just infrastructure + pipeline. So instead of a train system the proposal has always been to build a train system inside a pipeline, which has to be more expensive than either. We have no indication of cost savings here.

[sroussey]

I agree, though in city, it would be cheaper to use air rights than on the ground or underground.

[Schiendelman]

It never works that way - agencies have tried with elevated systems for a century. You have to buy the land.