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Addressing the sustainability of transportation systems is an important activity as evidenced by a growing number of initiatives around the world to define and measure sustainability in transportation planning and infrastructure provision. This paper reviews major initiatives in North America, Europe, and Oceania. The purpose is to characterize the emergent thinking on what constitutes transportation sustainability and how to measure it. While there is no standard definition for transportation system sustainability, it is largely being defined through impacts of the system on the economy, environment, and general social well-being; and measured by system effectiveness and efficiency, and the impacts of the system on the natural environment. Frameworks based on important causal relationships between infrastructure and the broader environment, infrastructure impacts on the economy, environment, and social well-being; and the relative influence of agencies over causal factors, are largely being used to develop and determine indicator systems for measuring sustainability in transportation systems. Process-based approaches involve community representatives and other stakeholders in planning and present opportunities to educate the public and influence collective behaviors. These frameworks can be used collectively to help agencies refine their visions as well as develop policies, planning procedures, and measurement and monitoring systems for achieving sustainable transportation systems.

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Incorporating uncertainty into transportation decision making has become a more important activity as evidenced by the popularity of scenario-based approaches in the regional transportation planning process. Particularly in decision making to promote sustainability, uncertainty and risk factors can be important elements because they can influence which alternative is perceived as the most desirable depending on a wide range of parameters. The objective of the study is to demonstrate how some of these uncertainties can be incorporated when a multiple-criteria decision-making method is used to choose the most desirable among competing alternatives. Using data from the Atlanta, Georgia, metropolitan region, this paper examines the sensitivity of the relative desirability of competing transportation and land use plans to changes in regional priorities and weights for sustainability parameters. Throughout the study, sensitivity analysis is used as a tool to incorporate the variability in criteria weights and concurrent variation in the sustainability evaluation results and final decision. These exercises could help decision makers determine how changing the emphasis on different regional priorities could most effectively result in desired regional outcomes.

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