Debate Settled: Flying Is Way More Efficient Than Driving

When I moved to San Francisco from New York last year to join WIRED, my new boss scolded me for flying instead of enjoying an epic road trip. (“Are you driving cross-country?” he implored. “Please tell me you’re driving cross-country.”) I booked a flight because I don’t own a car, and new research only reaffirms that I was right and my boss was wrong: Here in the US, traveling by car uses more than twice the energy you need to fly.

That’s according to a study by Michael Sivak at the University of Michigan’s Transportation Research Institute. The numbers are based on how many BTUs (British thermal unit, equal to 1,055 joules) are needed to move one person one mile. In 1970, flying was twice as energy intensive as driving, but that has reversed. In 2012, the most recent year counted, driving one person one mile took 4,211 BTUs, while flying required just 2,033.

The numbers for driving are based on the average fuel economy of all light-duty vehicles (that’s passenger cars, SUVs, pickups, and vans, which averaged 21.6 mpg), using data from the US DOT. Sivak counted only cars with internal combustions engines—no plug-in hybrids and EVs, which comprise less than 1 percent of the American fleet. The flight figures count major, large national, and large regional airlines, adjusted to account for freight and mail carried on passenger flights.

While cars have gotten more efficient in recent years, the aviation industry has made tremendous progress on cutting down fuel use. In 1985, it took about more than two gallons of fuel to move one passenger 60 miles, according to the International Civil Aviation Organization. Now that number’s below 1.3 gallons. That’s because airlines are obsessed with cutting their use of expensive jet fuel. They’re operating newer planes with better engines, and taking every opportunity to get more miles out of their aircraft (no matter how miserable it makes us).

If you feel bad about driving when you could be flying, there’s good news: Any car that gets more than 44.7 mpg beats the plane. These days, that opens up some options. There are all the electrics, of course, and the plug-in hybrids, along with the Toyota Prius and hybrid versions of the Volkswagen Jetta and Honda Accord and Civic.

There’s another way to match the efficiency of flying while on the ground: Ride with passengers. Sivak crunched his numbers based on a vehicle load of 1.38 people per car, based on DOT data. In a earlier version of this study he published last year, based on data through 2010, he found that increasing the number of people in a car to 2.3 would make a car as efficient as a plane. Sivak hasn’t done that calculation for the latest data, but says that because flying’s gotten more efficient in the past few years, 2.3 people wouldn’t be quite enough.

Fortunately, all of the hybrids mentioned above seat at least four people.