December 12, 2013

Fly? You fools!

It’s time for our annual holiday drive-vs-fly post.

Last year I looked at safety: for trips where either flying or driving is feasible, flying is much safer.

This year, let’s look at fuel economy and carbon emissions.  Holiday flights tend to be  full, which makes them more efficient. According to random people on the internet, a Boeing  737 with winglets uses about 3 litres/seat/100km, and according to more reliable sources, Air New Zealand’s smaller turboprop Q300’s will use about 5 litres/seat/100km. (Car and jet fuels are different, but they both have an energy density of about 36MJ/litre and roughly two hydrogens per carbon, so are similar for this purpose.)

There are two further complications: firstly, take-off and landing use more fuel (based on Figure 3 in this report, they add about 250km of effective distance). And secondly, the global warming impact of emissions at high altitude is greater than the same amount of CO2 at ground level, by a factor that is uncertain, but in the range 1.3-2.9.

According the Ministry of Transport national fleet data, the average car in NZ seems to use about 10 litres/100km in real life. In terms of fuel use for long-distance flight, a car with 3-4 people would be comparable to flying on a full 737, and a car with 2 people would be comparable to flying on a full Q300 turboprop. For short NZ distances, the take-off/landing cost adds a good 50%, and the extra impact of high-altitude emissions means that cars win out, though by a relatively small margin if there’s only one person in the car.

A direct comparison like this misses the real emissions problem with planes, though. Hardly anyone drives to the Cook Islands or Australia over Christmas — planes let you travel further.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »


  • avatar
    Robbie Price

    On the up side of planes, they don’t use roads, and roads, bridges, and tunnels take a reasonable amount of carbon to build and maintain. Fewer accidents on planes mean fewer ambulance, police and helicopter trips dealing with broken people.

    So, these holidays, why not take a bus, train, walk, or best of all – ride a bicycle there instead.

    4 years ago

  • avatar

    Have you read It’s very good, full of these kinds of arguments.

    4 years ago