If Heathrow finally builds its third runway, Londoners can expect hundreds more planes flying overhead each day. But greater congestion on the ground will be a problem too. Under Heathrow’s £33bn expansion plan, 100,000-200,000 more passengers would eventually be travelling to or from the airport each day.

The most eye-catching problem has been moving part of the UK’s busiest motorway, the M25, to make space for a new 2.2-mile (3.5km) runway. A thornier one may be getting motorists out of their cars, and finding more sustainable ways for the extra passengers – and thousands of staff – to travel to and from Heathrow.