California's Air Resources Board has finalized regulations implementing Assembly Bill (AB) 1493, which requires "maximum feasible and cost-effective reduction of greenhouse gas emissions from motor vehicles". By 2030, when California's light-duty vehicle stock has been substantially replaced by regulation-compliant vehicles, total emissions from regulated vehicles are projected to be reduced by 27% relative to "business-as-usual", but are nevertheless expected to be 8.7% higher than 2004 emissions. If an 8.7% increase truly represents the "maximum feasible and cost-effective" emissions reduction from transportation vehicles, then global climate stabilization clearly will not be attained within limits of "feasibility" and "cost-effectiveness", and climate sustainability will only be achievable through severely draconian measures. On the other hand, if significantly greater emissions reduction would be feasible and cost-effective, then the AB 1493 regulations fail to satisfy the legislative policy mandate and the task is to find a regulatory mechanism that will. The thesis of this paper is that the regulations do not satisfy the mandate for several reasons, the most important being the conflicting policy objectives of the "cost-constrained" legislative mandate and the " quantity-con strained", standard-based regulatory instrument. Art alternative policy instrument that would better fit legislative policy and environmental objectives would be a feebate-type system (although not necessarily a conventional vehicle feebate). (c) 2005 Elsevier Ltd. All rights reserved.