Lightweight materials equal lightweight greenhouse gas emissions?: A historical analysis of greenhouse gases of vehicle material substitution

Abstract

Abstract The impacts of greenhouse gases (GHG) to vehicles through improvements in fuel efficiency via material substitutions and their historical trends were analyzed to assess if lightweighting actually provides its expected benefits. Data for the weight and fuel efficiency of American and Japanese cars over the past 30 years was used for trend analysis. Also, the impacts of GHG in substituting steel for high strength steel, aluminum, carbon fiber reinforced polymer, and magnesium were analyzed. This study shows that while the amount of low-density materials in a vehicle has increased, the weight itself has increased because of the “rebound of design” reflecting the consumer demands. In lightweighting strategy, the material substitution of steel for high strength steel is the most promising option to reduce GHG emissions. Based on recent historical trends, this analysis shows that the GHG payback miles have increased and will continue to increase unless the reduction in GHG emissions occur at higher rates than that of fuel efficiency improvement from steel-based vehicles. This suggests that the competition over steel will become severer in the future for other materials with low densities. To reverse the result, it is necessary to reduce GHG intensities of materials at higher rates than that of improvement of fuel efficiency.