Jabird
Now in very crude figures - if, and it is a very big if, you could build this airport for £50bn, and the airport could make a clean PROFIT (not PSC) of £10 out of each one, unless my calculator is having a very bad day, I make that 50 years to pay back at 0% APR.
And what was the pay-back time for the M1?
More importantly, what was the increase in the GNP (and quality of life) that the M1 provided?
These are the questions that need to be answered.
Globetrotter:
The best thing to do IMHO would be to accept that South East England already has enough airports, whatever their problems and limitations, and concentrate simply on first building a proper rail network, integrated into the normal rail ticketing at standard prices, to link all four London airports together.
Taking the price of land-space around London into account, I think you will find that this 'solution' costs three times as much as a new Thames airport. The advantage of Boris Island, is that the freehold on the land is 'free'.
Jabird
The terminal should provide sufficient separation to allow simultaneous approaches on each side of it, but all we have for now is a concept sketch, not a detailed plan unless you can give us a link for one?
Here is the primary proposal.
Thames Estuary Airport
You will have to forgive the website, as a shortage in funds meant that much of it was put together by Shoeburyness Primary School. And many of their crayons were broken. But you will get the idea.
Like every successful British enterprise, the plan was made on the back of an envelope ... I think I still have it, but if not, it will be down the back of the sofa
Please forgive the deliberate error of the runways being too close together, and the terminals located at the end of the runways. We were just testing Boris' sense of humour.
.