Almost all of the major airports in the United Kingdom are single-runway (or functionally-single-runway) installations, with only two of the very busiest (Heathrow and Manchester) having as many as two runways (although Heathrow has a third under construction).
(In addition, even for the three major UK airports that have two runways, the two runways are always a parallel set, with no provision made for crosswind operations.)
This is - with few exceptions - far fewer runways than would be normal for airports of their size. Taking the seven airports in the UK with more than ten megaemplanements in 2018 and comparing them to similarly-sized airports elsewhere:
- Heathrow (two runways, with a third under construction) v. O'Hare (seven runways, with an eighth under construction)
- Gatwick (two [functionally one] runways) v. Newark (three runways)
- Manchester (two runways) v. la Guardia (okay, two runways)
- Stansted (one runway) v. Baltimore-Washington (two air carrier runways1)
- Luton (one runway) v. Calgary (four runways)
- Edinburgh (one runway) v. Norman Mineta (two runways)
- Birmingham (one runway) v. Raleigh-Durham (two air carrier runways1)
Having so few runways not only increases congestion and severely limits the number of flights that can use the airport without infringing on safe separation distances between aircraft, but also poses the risk, for the four single-runway airports,2 of an unserviceable runway (for instance, due to snowplows, potholes, trespassers, flocks of birds, wayward deer, or a disabled aircraft) shutting down the entire airport, potentially for a prolonged period of time.
Why do the UK's major airports have so few runways compared to the norms for airports of their sizes?
1: Plus one general-aviation runway each for Baltimore-Washington and Raleigh-Durham.
2: And, to a lesser degree, for functionally-single-runway Gatwick, as its emergency backup runway is close enough to the main runway for a single debris event to potentially affect both.