The busiest route in the world for international air travel? It's Singapore-Kuala Lumpur.
That's according to flight-data firm OAG, which has a new report identifying the world's 20 busiest airline routes as measured by passenger flights.
Coming in at No. 2 in the OAG rankings was Hong Kong-Taipei. That route was followed by three other intra-Asian routes to round out the top five: Singapore-Jakarta; Hong Kong-Shanghai; and Kuala Lumpur-Jakarta.
No Australian route made the top 20.
The highest North American route in the rankings was New York LaGuardia-Toronto Pearson, which placed eighth. (Scroll down for the full top 20 rankings)
For those taking a deeper dive into the OAG rankings, there are some significant caveats.
For starters, the rankings are measured by numbers of flights between the cities -- not by the number of passengers flying the routes. For example, OAG's data shows that 2.5 million more passengers flew on its No. 2 route between Hong Kong and Taipei (6.5 million) than on its top Singapore-Kuala Lumpur route (4 million).
But, by passenger flight operations, the 30,537 airline "frequencies" that operated on the Singapore-Kuala Singapore route between March 2017 and February 2018 topped the 28,887 frequencies the flew during the same period between Hong Kong and Taipei. The LaGuardia-Toronto route that placed eighth had 16,956 frequencies during the period.
Other caveats: The OAG report counted only jet flights -- turboprop operations were excluded -- and included only international routes. The latter creates an inherent bias against flights operating in large populous nations, excluding busy domestic routes in countries like the United States and mainland China. (Hong Kong is not counted as domestic destination for mainland China).
When domestic flights are included, Australia is high on the list, with Melbourne-Sydney the second-busiest route in the world and Brisbane-Sydney eighth busiest.
The international focus favours major airports in smaller countries that have more of a focus on international operations than domestic service. From Singapore, for example, there are no domestic flights within that small city state -- meaning every flight there is counted as international. Singapore showed up on four of OAG's top 20 routes. Other airports in smaller countries with limited domestic routes also showed up in the rankings, including Dubai, Amsterdam, Taipei, Kuwait, Dublin and London Heathrow.
Still, even with the OAG's international-focused parameters, two additional routes involving North American airports made the top 20: New York JFK-London Heathrow (13,888 frequencies) and Chicago O'Hare-Toronto Pearson (13,100).
OAG also provided some interesting breakdowns about where passengers were actually headed on the routes.
On the LaGuardia-Toronto route, OAG found that 71 per cent of passengers flying from Toronto were destined for New York itself. The other 29 per cent were connecting, with Richmond, Va., the top destination. Charlotte, Raleigh/Durham, Norfolk and West Palm Beach rounded out the top five connecting "flows" for Toronto passengers via LaGuardia.
In the other direction, 73 per cent of passengers flying to Toronto Pearson did not connect, according to OAG's data. Of those who connected there, Vancouver was the top destination, followed by Calgary, Edmonton, Ottawa and Winnipeg.
Looking at the JFK-Heathrow route, found 61 per cent of JFK-bound passengers were ending their journeys there. Of the 39 per cent who connected, Orlando was the top destination followed by Raleigh/Durham; San Juan, Puerto Rico; Los Angeles and San Francisco. In the reverse, 59 per cent flying from JFK were bound for London. Of the 41 per cent who connected, the top destination was Lagos, Nigeria, followed by Delhi; Manchester, England; Dublin; and Rome.
World's busiest international flight routes
1. Kuala Lumpur-Singapore (30,537 frequencies from March 2017 through February 2018)
2. Hong Kong-Taipei (28,887)
3. Jakarta-Singapore (27,304)
4. Hong Kong-Shanghai Pudong (21,888)
5. Jakarta-Kuala Lumpur (19,849)
6. Seoul Incheon-Osaka/Kansai (17,488)
7. Hong Kong-Seoul Incheon (17,075)
8. New York LaGuardia-Toronto Pearson (16,956)
9. Dubai-Kuwait (15,332)
10. Hong Kong-Singapore (15,029)
11. Bangkok-Singapore (14,859)
12. Bangkok-Hong Kong (14,832)
13. Hong Kong-Beijing (14,543)
14. Dubai-London Heathrow (14,390)
15. Osaka/Kansai-Taipei (14,186)
16. New York JFK-London Heathrow (13,888)
17. Osaka/Kansai-Shanghai Pudong (13,576)
18. Seoul Incheon-Tokyo Narita (13,517)
19. Amsterdam-London Heathrow (13,170)
20. Chicago O'Hare-Toronto Pearson (13,100)