Fleet-wide spatial and temporal life cycle assessment of light-duty vehicles in the United States: Lightweighting vs. Electrification

Automakers are actively pursuing technological solutions to improve fuel economy, including both electrification of the drivetrain and mass reduction through materials substitution. Although these technologies improve the... [ view full abstract ]

Automakers are actively pursuing technological solutions to improve fuel economy, including both electrification of the drivetrain and mass reduction through materials substitution. Although these technologies improve the nameplate fuel economy of the vehicle, the effect of their deployment on total actual greenhouse gas emissions varies significantly and is strongly influenced by spatial context. Additionally, vehicle sales are not regionally homogeneous. To guide limited engineering and sales resources, it is important to be able to characterize which solutions are most effective in which contexts. Therefore, this work focuses on investigating the potential of lightweighting compared to, and in conjunction with, electrification of the drivetrain in order to reduce life cycle greenhouse gas (GHG) emissions of the light-duty vehicle fleet in the U.S. To analyze this, a temporally and spatially-explicit fleet-based life-cycle assessment (LCA) model was developed. This model integrates a state-level vehicle stock sub-model and a life-cycle sub-model in which both vehicle production and use perspectives are taken into account. Spatial and temporal differences are considered by capturing regional (state-level) differences in 1) market penetration through 2040 for alternative powertrain vehicles and 2) use phase GHG emissions due to a) electricity grid mix, b) ambient temperature, c) patterns of vehicle miles traveled (VMT) and d) driving conditions for both urban and rural

The preliminary results of the analysis indicate, unsurprisingly, that significant vehicle mass reduction will lead to life cycle GHG emissions reductions regardless of region. Moreover, lightweighting strategies are more effective in regions where conventional powertrains constitute a larger market share. We also find that, compared with an increasingly lightweighted ICEV fleet, electric vehicle deployments offer more leverage for GHG reduction in regions with moderate temperature (e.g., CA and AZ) and relatively clean power sources (at or below national averages).  Conversely, vehicle GHG emissions in regions with cold climates (e.g., the Northern Midwest) and high grid emissions can be more substantially reduced through vehicle lightweighting.

The outcomes of this paper emphasize on the importance of the fleet market trends and regional variations during the vehicle service life when assessing the potential benefits of various strategies to reduce vehicle emissions.