Clive D.W. Feather wrote:
The so-called Heathrow Hub is an imaginative idea,
which has usefully opened up thinking about the way the airport operates,
but for the reasons we explain is less attractive from a noise perspective.
The Northwest Runway scheme is technically feasible and does not involve
massive, untested infrastructure.

"massive untested infrastructure"?

[I'm intrigued by the phrase but don't have time to read the report.]

It just means that the novel extended double runway idea would be a world's
first, and so all the safety analyses would have to be carried out from
scratch. New operating procedures would probably also be needed.

The much more expensive and disruptive northwest third runway scheme is
entirely conventional, which is the main reason the commission favoured it.