Size or mass?: the technical rationale for selecting size as an attribute for vehicle efficiency standards

This white paper summarizes the differences between size-based and mass-based efficiency standards, discusses their relative advantages and disadvantages, and provides guidance on the development of future standards. Specifically, the paper argues that size-indexed standards are more effective in promoting efficient technologies, and more neutral with respect to technology. They also escape the problem of rewarding larger engines and diesels with artificially less-stringent standards and are less subject to gaming. These advantages argue for a fundamental reconsideration of the mass-based regulatory framework where it is in use and against its extension into as-yet-unregulated light-duty vehicle markets.