The HS2 cut and cover tunnels were all in greenfield: https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ ; much of the cost there goes on planning and documentation, an under-appreciated cost. It's also questionable as to whether they were needed at all; a plain cutting with embankment open to the air would have been fine from a civil engineering point of view, or even in many places just flat track, but the tunnels were planned because people objected to a railway running through fields.
>There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"!
At least for Vancouver, there was absolutely an industry arguing for the slower-more-expensive TBM option on a route that followed exactly a road (the Broadway line extension) - local businesses along the route. The previous line which was mostly done by Cut-and-Cover (the Canada Line) had a very major impact on businesses along the route for years.
There are plenty of people who will acknowledge that something is cheaper _overall_ but the impact on a small group being higher can make them extremely vocal, and that has to be managed in public projects.
There isn't some industry saying "yes we could cut and cover here, but we prefer the slower more expensive option of a TBM"!
(I see NATM mentioned; there have been safety issues https://www.hse.gov.uk/pubns/natm.htm )
The HS2 cut and cover tunnels were all in greenfield: https://www.hs2.org.uk/building-hs2/tunnels/green-tunnels/ ; much of the cost there goes on planning and documentation, an under-appreciated cost. It's also questionable as to whether they were needed at all; a plain cutting with embankment open to the air would have been fine from a civil engineering point of view, or even in many places just flat track, but the tunnels were planned because people objected to a railway running through fields.