Abstract:The impact of transportation on global climate, and hence the task of evaluating transportation plans for their impacts on global climate, is quite complex. This paper provides analysts and policy makers an analytical background and framework for evaluating certain aspects of the Tehran project by offering an overview of some of the impacts of transportation systems on global climate. It first reviews climate change and the climate-change gases and then describes an analytical tool—a lifecycle energy use and emissions model—that can help in evaluating the effects of transportation plans on climate. It then discusses the results of applying this tool to determine:

• the contribution of highway transportation to energy-related CO₂ emissions in several countries
• the contribution of motor vehicles, per passenger kilometer, compared to the contribution of single-passenger motor vehicles to CO₂ emissions
• the potential contribution of different alternative fuels and vehicles, relative to gasoline and diesel vehicles to CO₂ emissions.

Although for the second two items, the model was applied to U.S. conditions, the relative effects charted could be applied to Iran, its capital city, or indeed to most other countries and cities.

The final section of the paper first contrasts the social costs of the emissions of greenhouse gases with the social costs of emissions of urban air pollutants and then ends with a brief discussion of the implications of those costs for transportation policy.