For example, a study by the University of Michigan Transportation Research Institute states the energy intensity of car transportation is on average 57% higher than air transports. In other words, a car emits more CO2 than the average planes because they consume more energy to transport the same amount of passengers.

In 2026, the answer depends on occupancy and distance. On a "per passenger mile" basis, a long-distance flight on a modern, fuel-efficient aircraft like an Airbus A350 often emits less CO2 than a single person driving an average internal combustion engine car for the same distance. However, for short distances (under 300 miles), cars—especially Electric Vehicles (EVs)—are significantly better for the environment than planes. Aviation has a unique environmental impact because it releases emissions at high altitudes, which has a higher "radiative forcing" effect on global warming. Furthermore, the total carbon footprint of a flight is concentrated into a few hours, whereas car emissions are more dispersed. For 2026 travelers, the "greenest" option for medium distances is almost always a high-speed train, followed by a fully-loaded car, and then a flight.