Is it Chicago’s O’Hare International Airport, or Dubai International? Both apparently. But it depends on the metric.

If you go by number of flights, then O’Hare is the world’s busiest airport (881,933 flights in 2014), dethroning Hartsfield-Jackson Atlanta International Airport (868,359) after 10 years at the top – by this way of measuring. However, if you go by number of passengers passing through a given airport, then it’s Dubai that just snubbed Heathrow for that honor, and the way things are going, it’ll likely keep that pole position for a while to come.

You may have read about the “third runway” drama regarding whether or not Heathrow should expand and build out, but ultimately environmental objections seem to have stalled that project indefinitely. Meanwhile, Dubai International logged 70.5 million passengers in 2014 (a 6.1% increase), compared to Heathrow’s 68.1 million. According to a Heathrow spokesperson, "Britain has benefited from being home to the world’s largest port or airport for the last 350 years. But lack of capacity at Heathrow means we have inevitably lost our crown to Dubai.” Whether or not this is a veiled barb against those opposing a third runway is for you to decide, but with a 6.1% increase in traffic, it is clear Dubai is racing ahead.

Some might be surprised to see U.S. airports O’Hare and Hartsfield-Jackson fighting for most flights, but in fact U.S. cities take all the top 5 spots worldwide. O’Hare alone had a peak of 2,861 departures and arrivals on August 5th and 7th, its two busiest days of 2014. The reason for this includes the U.S. being a large country with over 300 million people spread out, along with lots of hub-and-spoke airline models, few high-speed rail lines, which all together accounts for a large number of flights. But again, if you go by passenger numbers, then it is Dubai that is number one, with Heathrow following.

So what does this all mean in terms of transport and energy? Well, while airlines have tried to cut fuel costs by adopting a wide range efficiency measures as well as manufacturers responding to demand with leaner burning aircraft, overall traffic is increasing and related CO2 emissions along with them.

So as traffic shifts, the overall picture is the same, but there are some things to look out for in the coming years:

  • Entrenched efficiency: as aircraft have a lifetime of 25-30 years (rough average), fuel efficiency measures put in place by Boeing and Airbus among others will benefit airlines (and hopefully consumers) for a long time to come, irrespective of oil price fluctuations.
  • Modal competition: as high-speed rail investment ramps up, certain air routes might face stiff competition from those wanting to avoid the hassles of airports, and look for alternative routes. With new city links coming online, it will be interesting to see what shares rail versus air capture.
  • Strategic location: with Middle Eastern airlines taking up market shares quickly due to their strategic location between Europe and Asia, how will European and North American airlines respond? More alliances or more protectionist measures?