Autonomous vehicles are quickly becoming more of a reality in the developed world, as some major companies have already put hundreds of vehicles on the road. This new technology could eventually save you the trouble of driving yourself everywhere, but could it also save the environment?
A new study published in the journal Environmental Science & Technology has found that the added weight, electricity demand, and aerodynamic drag of the sensors and computers used in these vehicles are major contributors to their lifetime energy use and greenhouse gas emissions.
However, when savings from the driving efficiencies of autonomous vehicles are factored into these calculations, the net result is a reduction in lifetime energy use and greenhouse gas emissions of as much as 9 percent compared to conventional vehicles.
“This study explored the tradeoffs between the increased environmental impacts from adding autonomous vehicle equipment with the expected gains in driving efficiency,” explains Gregory Keoleian, director of the Center for Sustainable Systems at the University of Michigan School for Environment and Sustainability, and co-author on the study.
In the study, the researchers assess the lifetime contributions of the sensing and computing subsystems in autonomous vehicles to energy use and greenhouse gas emissions. Autonomous vehicles – formally known as connected and automated vehicles (CAVs) – usually include multiple cameras, radar, sonar, LiDAR, a GPS navigation system, a computer, and support structures.
The vehicles the researchers analyzed for the study are Level 4 CAVs, which are vehicles that can operate without human input or oversight under select conditions. They assessed two types of CAVs: those powered by internal combustion engines and battery-powered electric vehicles. The two vehicle types were paired with sensing and computer subsystems of three sizes (small, medium, and large) to create six scenarios. To estimate lifetime energy use and greenhouse gas emissions for each scenario, they utilized life-cycle assessment methodology.
The results showed that autonomous vehicles with electric powertrains have 40 percent lower lifetime greenhouse gas emissions than vehicles powered by internal-combustion engines. “We’ve shown in this paper that a battery-electric vehicle is a better platform for CAV components compared to the internal-combustion engine vehicle in terms of minimizing environmental impacts,” says study lead author Jim Gawron, a graduate student at the U-M School for Environment and Sustainability and at the Ross School of Business.
Their findings also showed that the sensing and computing subsystems in CAVs could increase a vehicle’s energy use and greenhouse gas emissions by between 3 and 20 percent, as a result of increases in power consumption, weight, and aerodynamic drag. This includes the added weight and power demand of the onboard computer – roughly 45 percent of the weight and 80 percent of the power – and the drag caused by exterior-mounted CAV components. Luckily, the operational benefits of these vehicles are expected to outweigh these increases in the majority of cases.
However, the conclusions of this study are based on the assumption that the operational efficiencies of CAVs can result in a 14 percent reduction in fuel consumption over conventional vehicles. But if the reduction ends up being significantly lower than 14 percent, the environmental benefits could disappear.
“Our findings highlight the need to focus on energy efficiency when designing autonomous vehicles so that the full environmental benefits of this emerging, transformative technology can be realized,” says Keoleian. “We hope this work contributes to a more sustainable mobility ecosystem.”
By Connor Ertz, Earth.com Staff Writer