Research Publications

Inclusion of plug-in electrified vehicles (PEVs) into light-duty vehicle (LDV) fuel economy and greenhouse gas (GHG) standards has been difficult for policy makers since the uncertainty and variation of GHGs associated with PEVs is much greater than emissions from conventional single fueled petroleum vehicles. This is primarily due to the large regional variation of the electric grid carbon intensity. The United States Environmental Protection Agency (U.S. EPA) enacted the first ever LDV GHG standards for model year (MY) 2012 vehicles sold in the U.S. and published a final rule concerning LDVs from MY 2017 out to 2025 in August 2012. For both rules, the GHG compliance value for the electric portion of PEVs is zero, up to a defined per-manufacturer cap, after which a national averaged electric emission factor is used. By utilizing a national average, this GHG accounting methodology allows for reduced effectiveness in absolute decreases of the new LDV fleet GHG, due to leakage from electrified vehicles sold in regions with high electric grid carbon intensity. Conversely, the national average emission factor undermines the ability of vehicles sold in low carbon grid regions to reflect their true emissions reduction potential, and lessens the incentive for auto manufacturers to focus marketing efforts of PEVs in these regions to reduce their overall fleet GHG compliance value. This research focuses on how a more detailed methodology using regional accounting could be employed in vehicle standards to lessen the possibility of leakage in high carbon grid areas over-running the potential gains from PEVs. An evaluation using energy and emissions projections of the future U.S. electric grid and new vehicle fleet is used to see how PEVs will fit into future more stringent U.S. LDV GHG standards and how a regional standard can address the shortcomings of using a national average emission factor.