While three runways may be sufficient for a 30 year horizon airports inevitably develop and change over time and a new hub airport needs the ability and space to expand and adapt as the aircraft that use them also change. On the Goodwin sands there is the space for long term expansion and ultimately five or even more runways could, with further land reclamation, be accommodated there.
Airports may also change in their specific configurations, as successor generations of aircraft present different requirements, and as the nature of what is carried by air (i.e. passenger or freight) changes.
A key precedent at Hong Kong is shown below â€” HKG â€” has been developed through land reclamation and can be seen as a purpose built â€˜clean’ large capacity design. Starting as a two runway airport an additional runway and satellite terminal is now planned, and for this, the island it stands on will be extended through further land reclamation.
The precedents at other airports show how terminal and airport facility space becomes constrained by runway placement. Typically, this can be resolved by construction beyond the runways: however, this assumes land availability and additional land area cannot be easily obtained onshore.