by Michael Sivak, Sivak Applied Research.
The energy intensity of a transportation mode is calculated by dividing the amount of fuel used by the number of passenger miles traveled and converting the result into a common measure—Btu (British thermal units) per passenger mile traveled. Until recently, the energy intensity of domestic flying was higher than the energy intensity of driving light-duty vehicles (cars and light trucks). However, the energy intensity of flying became lower than that of long-wheel-base light-duty vehicles starting in 1995, and of short-wheel-base light-duty vehicles starting in 2005. (A detailed discussion of the issues related to the comparison of the energy intensities of flying and driving is presented in a recent report.) The purpose of this brief note is to examine the energy intensities through 2020—the first year of the pandemic.
The annual energy intensities during a 10-year period from 2011 through 2020 are shown in the table below. The flying data are for domestic operations of U.S. certificated air carriers. All data are from the Bureau of Transportation Statistics, except that the entry for 2020 is an estimate from the Energy Information Administration. The main findings of this analysis are that the energy intensity of flying in the United States doubled from 2019 to 2020, and in 2020 it substantially exceeded the energy intensity of driving.
Energy intensities of flying and driving, in Btu per passenger mile.
Certificated air carriers
The main reason for the huge increase in the energy intensity of flying in 2020 is that, as flying decreased because of the pandemic, the passenger load factor (the percentage of seats occupied) decreased substantially. Specifically, the passenger load index dropped from 85.1% in 2019 to 58.9% in 2020. (There are other factors that have likely contributed to the increase in the energy intensity of flying in 2020, including the use of smaller and thus less fuel-efficient planes.)
In conclusion, the energy intensity per passenger mile flown in 2020 doubled from that in 2019. Consequently, flying passengers in 2020 contributed approximately twice the emissions per mile flown than those in 2019.
Michael Sivak is the managing director of Sivak Applied Research and the former director of Sustainable Worldwide Transportation at the University of Michigan.