No, Flying Is Not Greener Than Driving


The headline of an article in the Washington Post on Tuesday might have gotten a lot of people excited about the fact that air travel may be more environmentally friendly than driving.

Unfortunately, the analysis out of the University of Michigan featured in Tuesday’s article leads to some false conclusions, according to the International Council on Clean Transportation (ICCT).

The new study, from Michael Sivak of the University of Michigan Transportation Research Institute, says that if you average out the data, flying has become more efficient while driving has become less efficient. The crux of his argument rests on the fact that we are now packed like sardines into planes, which reduces carbon emissions per passenger mile.

Specifically, Sivak found that “the average energy intensity of driving a light duty vehicle, such as a car or SUV, in the United States was 4,211 BTUs (British thermal units) per person mile, while the energy intensity of flying domestically was 2,033 BTUs per person mile.”


Of course, 4,211 is greater than 2,033, so driving must be twice as inefficient as flying, right? (For the record, gasoline and jet fuel have nearly identical CO2/BTU emissions).

Wrong. These numbers aren’t considering the different kinds of trips we make, according to ICCT program director Dan Rutherford. For short trips — like most people’s daily commute — flying isn’t even sensical, much less environmental. For longer trips, where flying might be an option, packing just a few people into a car is going to offer significantly less carbon per person mile than flying will.

The real issue is what question you are trying to answer, Rutherford told ThinkProgress. “All that data is just averaged. He hasn’t really made an attempt to compare competing trips.”

So for those of us interested in keeping a low carbon footprint, what questions really matter? Is it whether you drive to work every day, or whether you fly? How about whether your family will drive to Puerto Rico for vacation, or will they take the train?

Nope, those obviously aren’t the questions. The only sensible comparison between air and car transportation is for trips where both means are viable options.


“What’s the greenest way for me to get to my relatives for Thanksgiving dinner is a very different analysis,” Rutherford said.

The Washington Post takes the research to its furthest conclusion, saying, “If you carpool with a large group of people over a moderate distance — say, driving from D.C. to Detroit for Thanksgiving — you may still beat flying on an energy intensity basis.” (Emphasis added).

That’s wrong. By driving, you will beat flying on an energy intensity basis.

“The average occupancy for vehicle travel is 2.2,” Rutherford said. “Anything above 2.2, you will will get even better numbers for cars.”

Using the averaged data, two people in a car emit roughly the same amount of carbon as they would by flying. If you have three people, driving is about 15 percent more efficient. A family of four in a car cuts their carbon footprint in half over air travel.

In other words, it is true that air travel is less carbon-intense now that more people are fitting on planes. (So the next time you feel the urge to dump your drink on the passenger who reclined in front of you, just remember that your kneecaps are collateral damage in our collective fight to lower our emissions.) But if you are choosing between flying and driving with more than one person — or, even better, in a hybrid car — it’s still more environmentally friendly to pile into the car.

Of course, for people who truly want to cut their emissions, there is another directive here: Take the bus.