A new analysis from Michael Sivak of the University of Michigan Transportation Research Institute, offers a surprising conclusion about which is a greener mode of transport: airplanes or cars?
Notably, Sivak found that driving today is actually much more “energy intensive” than flying, where energy intensity is defined as “the amount of energy needed to transport one person a given distance.”
The reason? While airlines and cars have both become more energy efficient over time, one key factor in determining the energy intensity of a particular form of travel is how many people are being transported per trip. This means that jam-packed modern passenger planes have cars totally beat.
“Flying domestically in the U.S. used to be much more energy intensive than driving, but that is no longer the case,” said Sivak “One of the main reasons is that the proportion of occupied seats on airplanes has increased substantially, while the number of occupants in cars and other light-duty vehicles has decreased.”
His analysis was based on data from the Department of Transportation and found that in 2012, the average energy intensity of driving 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. Thus, on average, driving is more than twice as energy intense.
The analysis follows on his report last year, which found that driving is 57 percent more energy intensive than flying. Now, Sivak has gone back to update his analysis through 2012. He also added some corrections to the data on the energy intensity of flying. As a result of these corrections, “the advantage of flying has increased even further.”
One key takeaway is that these are averages. If you drive a car full of people it is significantly better for the environment than air travel.
The study is interesting, as it shows it is more about the capacity utilization of the transportation method, not the method itself, which drives how clean it is. Travel in any sort of vehicle that is under-occupied and it will be bad for the environment.