Incorporating Time-Corrected Life Cycle Greenhouse Gas Emissions in Vehicle Regulations

Beginning with model year 2012, light-duty vehicles sold in the U.S. are subject to new rules that regulate tailpipe greenhouse gas (GHG) emissions based on grams of CO₂–equivalent per mile (gCO₂e/mi). However, improvements in vehicle technology, lower-carbon fuels, and improvements in GHG accounting practices which account for distortions related to emissions timing all contribute to shifting a greater portion of life cycle emissions away from the vehicle use phase and toward the vehicle production phase. This article proposes methods for calculating time-corrected life cycle emissions intensity on a gCO₂e/mi basis and explores whether regulating only tailpipe CO₂ could lead to an undesirable regulatory outcome, where technologies and vehicle architectures with higher life cycle GHGs are favored over technologies with lower life cycle emissions but with higher tailpipe GHG emissions. Two life cycle GHG assessments for future vehicles are presented in addition to time correction factors for production and end-of-life GHG emissions. Results demonstrate that, based on the vehicle designs considered here, there is a potential for favoring vehicles with higher life cycle emissions if only tailpipe emissions are regulated; moreover, the application of time correction factors amplifies the importance of production emissions and the potential for a perverse outcome.