Richard J. wrote:
Recliner wrote on 08 Jun 2018 at 20:03 ...
Roland Perry wrote:
In message
-sept
ember.org, at 14:12:06 on Fri, 8 Jun 2018, Recliner
remarked:

I thought the whole idea of airport expansion was that the airport was
expected to pay for it themselves

They a the expansion will be privately funded by HAL, ultimately funded
by airline access charges (currently around £20/passenger, but which may
rise). But TfL has warned that HAL may not be so willing to pay for
infrastructure and public transport upgrades outside the airport.

Are HAL paying the whole cost of the M25 tunnel (after the runway's
finished, it'll be within the airport's footprint).

I'm not sure. It's not even clear if there will be a tunnel.

As I understand it, the runway will cross the M25 on a bridge or viaduct,
and will have a slight uphill gradient towards the west in order to clear
the motorway. Such gradients on runways are not uncommon, with
Birmingham being a notable example (see for example
https://www.youtube.com/watch?v=lP35ULU6IcQ )

That's one of the possibilities. There are several competing proposals.

The airlines are afraid that HAL will go for the most expensive option, as
that allows it to charge them more, so they're campaigning for a cheaper
option, such as the viaduct runway over an undisturbed M25, and no new
terminal.