Connected Autonomous Vehicles (CAVs) Don’t Save Energy?

The convenience of connected autonomous vehicles (CAVs) could prompt car owners to increase their driving mileage, and those extra miles could partially or completely offset the potential energy-saving benefits of automation, according to a new University of Michigan study.

In the coming years, driverless cars are expected to provide significant improvements in safety, traffic flow, and energy efficiency. At the same time, automation will allow drivers to use their driving time efficiently.

Previous studies have shown that higher fuel efficiency will prompt some people to drive a few more miles, and the fuel consumption caused by these extra miles will offset the fuel savings, a behavioral change known as the "rebound effect." In addition, people can make effective use of their time in self-driving cars, such as working, sleeping, watching movies, and reading, which may also lead to more driving miles.

According to a team of researchers from the University of Michigan School of Environment and Sustainability, the additional miles driven by both could partially or completely offset the energy savings from self-driving cars. The researchers say the additional miles driven could even result in a net increase in energy consumption. Their study was published in the journal Applied Energy. The core message of the paper is that the induced miles driven by self-driving cars poses a serious challenge to policy goals of reducing energy use.

The researchers used economic theory and U.S. travel survey data to model driving behavior and predict the impact of vehicle automation on driving decisions and energy use. They also said that most previous studies on the energy impact of autonomous vehicles have focused only on the fuel cost of driving, which may lead to an overestimation of the environmental benefits of the technology. In contrast, their study took into account both fuel costs and time costs. They used standard microeconomic models and statistical techniques to calculate the value of time.

Traditionally, time spent driving is considered a cost to the driver. However, since people can perform other activities inside a self-driving car, this is expected to significantly reduce this "perceived travel time cost" and stimulate additional travel. The researchers estimate that the additional miles driven induced by a 38% reduction in perceived travel time cost would completely wipe out the fuel cost savings of self-driving cars. This means that local and global air pollution could increase.