Nestled in the outskirts of London, Heathrow Airport began life 83 years ago as a modest facility for testing and assembling aircraft. It didn’t serve commercial flights until a decade and a half later, when the conclusion of World War II made it available to civil purposes, but since then it has rapidly grown in importance to become one of the world’s preeminent transport hubs. Like the centerpiece in a global matryoshka doll, Heathrow can be found at the heart of many overlapping spheres of interest. It’s the nexus of transatlantic business and trade, the landing spot for millions of tourists every year, and the departure point for British royalty and subjects alike.

Heathrow’s unplanned beginnings and burgeoning popularity have combined to create a chronic problem for the airport: demand for its services continually exceeds the available supply. In a March 2013 submission to the UK Airports Commission, Heathrow Airport Limited reports that it’s “already operating at its permitted capacity.” What’s more, it goes on to note, estimates from the Department for Transport “indicate that by 2020 there will be 11M of un-served passenger demand at Heathrow and 28M by 2030.”

Multiple efforts to accommodate the increasingly globalized traveler community have resulted in the opening of the £4.3 billion ($6.7BN) Terminal 5 and the currently ongoing £2.5 billion ($3.9BN) refurbishment of Terminal 2. Despite their immense cost, these projects will only marginally improve Heathrow’s capacity, primarily by routing passenger and aircraft flows more efficiently. Ultimately, if the airport wants to fully live up to its dual role as an international hub and a gateway into London, it’ll have to grow to include a third runway.