Emission Simulator (MOVES) model for mobile-source emissions, to make measurements to confirm or refute the assumption that all vehicles will only meet but not exceed emission standards. In actual practice, there can be significant differences between on-road performance relative to emissions requirements and some alternative-fuel vehicles may do better or worse than expected.
The issue of indirect land-use change is central to current debates about the merit of biofuels. Regardless of whether this impact is regarded as an externality associated with U.S. or foreign biofuels production, it is important to obtain more empirical evidence about its magnitude and causes, as well as to improve the current suite of land-use change models.
Because a substantial fraction of life-cycle health impacts comes from both vehicle manufacture and fuel production, it is important to improve and expand the information and databases used to construct emissions factors for these life stages. In particular, there is a need to understand whether and how energy-efficiency improvements in these industrial components might change the overall estimates of life-cycle health damages.
As better data become available, future studies should also focus on other transportation modes—both those that are alternatives to automobiles and light trucks (transit), as well as air, rail, and marine, which are alternatives for long-distance travel and for freight.