StoneBridge & K-Syran - Starry Night

by Michael Sivak.

Compared with cars, SUVs consume more energy per vehicle mile. Consequently, SUVs emit more carbon dioxide per vehicle mile than do cars. However, in the United States, the typical occupancy is higher for SUVs than for cars. The issue of interest in this study was the resultant energy usage per occupant distance. In other words, does the higher occupancy of SUVs compensate for their higher energy consumption per vehicle distance when considering energy consumption per occupant distance?

The analysis used the following data for cars and for SUVs:

• Average real-world vehicle fuel economy for model year 2017 vehicles (based on the information from the Environmental Protection Agency)

• Average vehicle occupancy in 2017 for privately operated household vehicles (from Oak Ridge National Laboratory)

The results are shown in the table below.

The final step of the analysis (with the results shown in the last row of the table above) took into account the fact that the increased occupant weight being carried by SUVs results in slightly lower fuel economy. The Environmental Protection Agency estimates that an extra 100 pounds in a vehicle can reduce fuel economy by about 1%. Given that the difference in the average occupancy between SUVs and cars is 0.29 persons, and assuming the weight of 100 pounds for an average occupant (including men, women, and children), the calculations were rerun assuming a reduction of the average fuel economy of SUVs by 0.29% (from 23.3 mpg to 23.2 mpg).

In conclusion:

• For model year 2017 vehicles, the average fuel consumption per vehicle distance is about 30% higher for SUVs than for cars. For example, the average SUV consumes 42.9 gallons of fuel per 1,000 vehicle miles, compared with 33.1 gallons for the average car.

• However, taking into account the increased occupancy of SUVs, as well as the increased occupant weight, results in the average fuel consumption per occupant distance for SUVs being only about 10% higher than for cars. For example, the average SUV consumes 23.6 gallons of fuel per 1,000 occupant miles, compared with 21.5 gallons for the average car.

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