Addressing Sustainability in Transportation Systems: Definitions, Indicators, and Metrics

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.