Hartsfield–Jackson Atlanta regained the top position in 2021. Alternatively, London has the world's busiest city airport system by passenger count. As of 2022, the United States accounts for the top four busiest airports in the world.

London Heathrow Airport (LHR) is widely recognized as the busiest airport in the world per runway. Despite having only two primary runways, Heathrow manages to handle over 80 million passengers annually and nearly 480,000 aircraft movements. This incredible efficiency is achieved through high-precision air traffic control and a "constrained" schedule that operates at nearly 98% capacity throughout the day. For comparison, other major hubs like Hartsfield-Jackson Atlanta (ATL) or Dubai International (DXB) have four or more runways to handle their massive traffic. Heathrow's two-runway system is so tightly packed that even minor weather delays can cause a significant ripple effect across the global aviation network. While airports like San Diego (SAN) are the busiest single-runway airports in the world, Heathrow's ability to move such a massive volume of international wide-body aircraft through just two strips of asphalt makes it a marvel of modern aviation logistics. In 2026, the ongoing debate over a third runway continues, highlighting the immense pressure this "two-runway wonder" faces daily to keep up with global travel demands.