Fly away home
With the summer holiday season approaching we’ve had requests for a post on the relative safety of driving and flying.
To a large extent this depends on where you are going: if you’re heading from Auckland to the Coromandel then I’d recommend driving, but if you want to spend some time on a beach in the Cook Islands your chances of getting there safely by car are distressingly low.
Clearly we need to rephrase the question. Two possibilities are:
- for a destination where either flying or driving makes sense, which one is safer?
- if you compare a typical holiday road-trip to a typical holiday flight, which is safer?
We should also think about what risks to include: for a long plane flight the chance of a pulmonary embolism is higher than a crash, possibly much higher depending on your other risk factors.
The risk of a `fatal incident’ on a flight is largely independent of the length of the flight, and based on US data is about eight deaths per hundred million flights. The risk is probably lower in NZ, since the figure includes the September 11 terrorist attacks.
The risk of death from car crash when driving in the US is about 4 per billion kilometers. I don’t have good figures for NZ, but it’s a bit higher here. On the other hand, there’s a lot of variation depending on how you drive.
So, for a trip of 500km (eg, Auckland-Wellington), we’re looking at an average figure of about eight deaths in crashes per hundred million flights and about 200 deaths in crashes per hundred million car trips. Flying wins by a huge margin
University of Otago research estimates the risk of pulmonary embolism at about 0.5 per million short flights and about 1.3 per million long flights. Estimates of the risk of death with pulmonary embolism in modern times seem to be around 10-20%, giving death rates of about
50-100 5-10 per hundred million short flights or 120-250 12-25 per hundred million long flights. Flying still wins for the Auckland-Wellington route, even if driving doesn’t increase pulmonary embolism risk at all (it probably increases it but by less than driving)
If you compare a 500km drive with a long-haul intercontinental flight the numbers get less clear. Flying to London could possibly be more dangerous than driving to Wellington, especially if you are a safe driver but at relatively high risk of blood clots.
After all these calculations it’s important to keep a sense of perspective. Driving is pretty safe. Flying is even safer.
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. See all posts by Thomas Lumley »