The additional materials, manufacturing, assembly, weight, electric consumption, and aerodynamic drag of a connected and autonomous vehicle’s sensors and computers were found to significantly increase its lifetime energy consumption and greenhouse gas emissions – about 3 to 20 percent increase. This is according to a new study conducted by Ford Motor Company and the University of Michigan.
However, when the researchers also took into consideration the potential savings in energy consumption coming from the efficiency in self-driving, the net result was an estimated 9 percent reduction in lifetime energy use and greenhouse gas emissions in comparison with the conventional vehicles.
“This study explored the tradeoffs between the increased environmental impacts from adding autonomous vehicle equipment with the expected gains in driving efficiency,” said Gregory Keoleian, co-author of the study and director of the Center for Sustainable Systems at U-M’s School for Environment and Sustainability.
“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. We hope this work contributes to a more sustainable mobility ecosystem.”
The study, which was published in the journal Environmental Science & Technology, is a comprehensive assessment of how much energy and greenhouse gas emissions would a connected and autonomous vehicle’s (CAV) sensing and computing subsystems produce.
Two types of CAV’s were used in the study – 2015 Ford Focus to represent internal combustion engine vehicles (ICEV) and 2015 Ford Focus Electric to represent battery-powered electric vehicles (BEV). Another variable used in the study is the size of sensing and computer subsystems – small, medium, and large, which were represented by configurations of Tesla Model S, Ford Fusion, and Chrysler Pacifica, respectively. Pairing up the two variables make six situations; the lifetime energy usage and emissions of each situation were calculated using the life-cycle assessment methodology.
The assessment included the following phases of a vehicle’s lifecycle: materials production, manufacturing and assembly, use, and end-of-life management. Comparing the energy or fuel consumption of CAV’s with traditional vehicles, the additional CAV subsystem causes an additional consumption due to its production, use, weight, and aerodynamic drag.
However considering the following factors associated with CAV’s, the overall energy consumption is actually reduced: “eco-driving, platooning, light-weighting, rightsizing, reduced driving to locate parking, ride sharing, congestion mitigation…”
To summarize, the researchers have concluded the following statistics:
- In terms of lifetime greenhouse gas emissions, CAV’s with electric powertrains are 40 percent lower 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,” said study lead author Jim Gawron.
- The CAV’s sensing and computing subsystems could increase a vehicle’s energy use and greenhouse gas emissions by 3 to 20 percent due to increases in power consumption, weight, and aerodynamic drag. In a medium-sized sensing and computing subsystem, the computer represented 45 percent of the weight, consumed 80 percent of the power, and caused 43 percent of the greenhouse gas emissions.
- Considering the operational efficiencies of CAV’s, the reduction in emissions and energy consumption is expected to be much higher than the 3 to 20 percent increase brought by sensing and computing subsystems.
- The resolution of the navigation maps is a significant factor in emissions and energy consumption. Standard-definition maps result in lifetime greenhouse gas emissions that are 35 percent lower than those of high-definition maps.
The net reduction in greenhouse gas emissions and energy use brought by CAV’s can only be fully realized if the assumptions made in the study are followed (or better) in actual:
- The operational efficiencies of CAVs in comparison with traditional vehicles result in a reduction of energy consumption by 14 percent.
- The power requirement of onboard computers is 200 watts.
- The CAV’s are Level 4, that is, they can operate without human input or oversight under select conditions.
- 100 percent adaption of CAV’s.