Domestic versus international routes
Domestic air routes, defined as commercial flights between two airports that are in the same country, tend to be busier than international air routes. Even the busiest international air route – Hong Kong to Taipei – recorded less than half the number of flights in 2017 than the busiest domestic route.
Causes of air traffic
Population is clearly a factor for high levels of air traffic, with just over half of the busiest domestic air routes involving the most populous global megacities. However, a lack of alternative travel infrastructure can also play a major role. For example, Brisbane, Melbourne and Sydney – which together account for two of the busiest air routes, despite their relatively small populations – are yet to be linked by high-speed intercity rail.