Extra self-driving car miles could offset energy-saving benefits, say researchers

A new study has warned that the benefits of self-driving cars are likely to induce vehicle owners to drive more, potentially offsetting any energy-saving benefits that automation may provide.

“The core message of the paper is that the induced travel of self-driving cars presents a stiff challenge to policy goals for reductions in energy use.”

Samuel Stolper, U-M School for Environment and Sustainability

Researchers at the University of Michigan (U-M) noted that self-driving cars are expected to offer significant safety, traffic flow and energy efficiency benefits, while also allowing passengers to be more productive during their journeys.

However, said the researchers, previous studies have shown that greater fuel efficiency induces some people to travel extra miles, thanks to a behavioural change known as the rebound effect.

This, combined with a likely increase in travel as a result of people’s ability to be more productive on the move, could partially or completely offset the energy savings provided by autonomous vehicles, found the researchers at the U-M School for Environment and Sustainability (SEAS).



“The core message of the paper is that the induced travel of self-driving cars presents a stiff challenge to policy goals for reductions in energy use,” said co-author Samuel Stolper, assistant professor of environment and sustainability at SEAS.

“Thus, much higher energy efficiency targets are required for self-driving cars,” said co-author Ming Xu, associate professor of environment and sustainability at SEAS and associate professor of civil and environmental engineering at the College of Engineering.

The researchers, led by Dow Sustainability Doctoral Fellow Morteza Taiebat, warned that the added miles could even lead to a net increase in energy consumption – a phenomenon known as backfire.

“Backfire—a net rise in energy consumption—is a distinct possibility if we don’t develop better efficiencies, policies and applications,” said Taiebat.

The greater productivity offered by autonomous vehicles is expected to lower the ‘perceived travel time cost’ of time spent driving, which is likely to spur additional travel. The team estimated that the induced travel resulting from a 38% reduction in this perceived travel time cost would be enough to completely eliminate the fuel savings associated with self-driving cars.

The study authors concluded that the possibility of backfire implies that net increases in local and global air pollution are also possible.

In addition to the energy reduction challenges identified in the study, the researchers highlighted another issue that may need addressing as autonomous vehicles become a reality. The study found that wealthier households are more likely than others to drive extra miles in autonomous vehicles, suggesting they stand to experience greater welfare gains from the introduction of self-driving cars.


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