U-M Study: Cars Lag Planes and Trains in Energy Efficiency


A new study from the University of Michigan reveals that airline flights and train trips are substantially more energy efficient than light-duty vehicles.

Michael Sivak, a professor at the U-M Transportation Research Institute, studied the amount of energy needed to transport a person in a light-duty vehicle, such as a car, SUV, pickup truck, or van, versus a person on an airplane or a train. He found that, in order for light-duty vehicles to match the energy efficiency of flying or train travel, the entire fleet of vehicles would need to achieve at least 33.8 miles per gallon, up from the current 21.5 mpg, or carry at least 2.3 persons, rather than the current 1.38.

“It would not be easy to achieve either of these two changes,” Sivak says. “Although fuel economy of new vehicles is continuously improving, and these changes are likely to accelerate given the new corporate average fuel economy standards, changes in fuel economy take a long time to substantially influence the fuel economy of the entire fleet — it takes a long time to turn over the fleet.”

The 14.5 million light vehicles sold in 2012 accounted for only 6 percent of the entire fleet of light vehicles on the road.

Sivak says the required increase in the number of passengers per vehicle would be difficult to achieve. Vehicle load has continuously dropped since 1970.

While energy intensity, which measures the cost of converting energy into GDP, has steadily decreased over the last 40 years, the improvement for flying has been substantially greater than driving — 74 percent versus 17 percent.

“It is important to recognize that the energy intensity of flying will continue to improve,” Sivak says. “Because the future energy intensity of flying will be better than it currently is, the calculations underestimate the improvements that need to be achieved in order for driving to be less energy-intensive than flying.”

Overall, in 2010, BTU per person mile was 4,218 for driving versus 2,691 for flying. Other modes of transportation include Amtrak trains (1,668), motorcycles (2,675), and transit buses (3,347).