by Michael Sivak.

The usual focus of analyses of road transportation is on vehicle-distance traveled, without taking into account the number of passengers in the vehicle. In contrast, air-transportation analyses typically include passenger-distance traveled among the variables of interest. The present analysis examines the changes in passenger-distance traveled in both of these two transportation modes during a 45-year period from 1970 to 2015. Furthermore, the focus here is not on total distances but on distances per person, because the U.S. population increased by 57% during the period studied.

The Bureau of Transportation Statistics was the source of the total passenger-distance information for both light-duty vehicles (cars, SUVs, vans, and pickup trucks; both short-wheel-base vehicles and long-wheel-base vehicles) and domestic operations for all four large certificated air-carrier groups (majors, nationals, large regionals, and medium regionals). The calculated average passenger-distances traveled per person are shown in the table below, along with the average occupancy rates from the Bureau of Transportation Statistics.

From 1970 to 2015, the average passenger-distance traveled in airplanes per person increased by 291%, from 511 miles to 2,000 miles. In contrast, the average passenger-distance traveled in light-duty vehicles per person increased by only 23%, from 9,692 miles to 11,930 miles. (The decrease in passenger-distance traveled in light-duty vehicles per person from 2000 to 2015 is the consequence of both the decrease in vehicle-distance traveled and the decreases in the average vehicle occupancy rates for both short-wheel-base vehicles and long-wheel-base vehicles assumed by the Bureau of Transportation Statistics.) Because of the greater increase in passenger-distance traveled in airplanes than in light-duty vehicles between 1970 and 2015, passenger-distance traveled in airplanes per person as a percentage of passenger-distance traveled in light-duty vehicles per person increased from 5% in 1970 to 17% in 2015.

Michael Sivak is the managing director of Sivak Applied Research and the former director of Sustainable Worldwide Transportation at the University of Michigan.