Expansion of London's Heathrow Airport

For many years, Heathrow Airport in London held the title of world's busiest airport when measured by international passenger traffic, as well as the busiest in Europe by overall passenger traffic. By the early 2010s, it was handling 70 million passenger journeys per year (though Dubai International would eventually overtake it) and forecast to reach 85 million by 2030. As the airport began to reach 100% capacity at peak times, concerns were raised about overcrowding and the need for expansion. Globally, air traffic in general was growing rapidly – due in large part to booming demand from the emerging markets of the Asia Pacific and Middle East regions – and the number of planes in service was projected to double between 2015 and 2035.

In 2009, the UK's Labour government announced that it would support the expansion of Heathrow and encouraged the airport operator (BAA) to apply for planning permission. However, these plans were cancelled the following year by the new coalition government of the Conservatives and Liberal Democrats. Following several more years of planning and reviews, the Airport Commission recommended a third runway and sixth terminal. A full report was finally published in 2015 that confirmed a new expansion to the northwest as the chosen proposal. After further revisions, and with estimated costs of £14.3bn (funded privately), this northwest runway and terminal plan was approved by the government in 2018.

The new infrastructure would increase Heathrow's capacity from 85 million to 130 million passengers annually. It was predicted to create 180,000 new jobs and generate £200bn in total economic benefits by 2050. Up to 40 new long-haul routes would become available. In addition to the airport itself, a number of access improvements were planned – such as the 118 km (73 mile) Cross rail line running all the way from east to west London, along with a refurbished Piccadilly line providing more spacious, air-cooled trains at higher frequencies than before.