This section provides a brief overview of the issue of sustainability as it relates to transportation. Topics include the following:
Current and future transportation growth patterns and the way that we develop transportation systems are important factors in sustaining the world’s limited economic, environmental, and social resources and capacity.
Transportation represents 10 percent of the world’s gross domestic product, is responsible for 22 percent of global energy consumption and 25 percent of fossil fuel burning across the world, and produces 30 percent of global air pollution and greenhouse gases. As such, the transportation sector will play a key role in addressing global sustainability concerns, including depletion of resources, global climate change, disruption of ecosystems, and toxic pollution.
The American Association of State Highway and Transportation Officials (AASHTO) has acknowledged these challenges and as a result developed the visionary report “Transportation: Invest in Our Future.”
According to the AASHTO report, “America’s transportation system has served us well, but now faces the challenges of congestion, energy supply, environmental impacts, climate change, and sprawl that threaten to undermine the economic, social, and environmental future of the nation. With 140 million more people expected over the next 50 years, past practices and current trends are not sustainable.”
“To meet the transportation needs of the present and pass on a better world to our children and grandchildren, it is necessary to expand the transportation network’s capacity while simultaneously reducing the environmental footprint of the system,” the report said.
The report urged transportation decision makers to adopt the so-called “triple bottom line” approach to sustainability by evaluating performance on the basis of economic, social, and environmental impacts and allocating equal consideration to these driving forces.
The specific elements of the triple bottom line approach and the steps required to achieve them can be summarized as follows:
In the early days of highway construction (1950s) enthusiasm for the benefits of transportation facilities overshadowed attention to potential negative impacts associated with those facilities. The National Environmental Policy Act ( NEPA) of 1969 and the Clean Air Act (CAA) of 1970 focused attention on environmental concerns. These environmental laws required agencies to include citizen ideas and consider environmental and social impacts of projects as well as conventional economic impacts. These factors led to the creation of the concept of sustainable development.
The term sustainable development was first used in 1980, and in 1987 the report by the World Commission on Environment and Development (the so-called Brundtland Commission) reemphasized the importance of sustainable development and provided a classic and widely used definition for sustainable development: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” This definition contains two key principles identified by the Commission – the concept of needs and the idea of limitations. Currently numerous initiatives across the world focus on sustainable development and sustainable transportation, and this trend is accelerating with renewed emphasis on global climate change.
The overall goals of sustainable development are to meet human needs and improve quality of life; to live within the earth’s ecological carrying capacity and maintain or enhance its natural capital; and to protect future generations from reduced quality of life. These goals are achieved by addressing three dimensions of sustainability:
Transportation plays a key role in the global economy and in the challenges and opportunities associated with sustainable development. Sustainable transportation can be viewed as an expression of sustainable development in the transportation sector. Sustainable transportation addresses local, regional, national, and global issues and therefore requires considerable coordination. It is important to apply sustainable transportation in a holistic and integrated manner across the various sectors (external to transportation) to ensure that key concerns such as depletion of resources, global climate change, disruption of ecosystems, and toxic pollution are effectively addressed.
Numerous authors have developed definitions for sustainable transportation for different contexts. These definitions are based on the broader concept of sustainable development as outlined by the Brundlandt Commission, adapted to meet current and future mobility and accessibility needs without resulting in undue negative externalities. Context specific sustainable transportation definitions generally focus on the three dimensions of sustainable development – economic development, social equity, and environmental stewardship.
The figure below demonstrates the relationship between these dimensions: the resources and services provided by the earth’s natural systems (the environment) are critical for the functioning of our transportation systems and other infrastructure (social systems), and without well-functioning social systems our economic systems cannot be productive. Therefore, there is a need to address the dimensions in an integrated way while considering their relationships.
Dimensions of Sustainability
A comprehensive definition of a sustainable transportation system developed by the Canadian Center for Sustainable Transportation states that sustainable transportation:
In contrast, one state department of transportation (DOT) in the United States defines sustainable transportation concisely as “the provision of safe, effective, and efficient access and mobility into the future while considering the economic, social, and environmental needs of society.”
Goals for developing sustainable transportation systems are context sensitive – they differ depending on factors such as level of economic development (developed, developing, or undeveloped), institutional level (local, regional, state, national, or global), type of transportation system (highway, transit, marine, aviation, or intermodal), scale of facility (section, corridor, network, or system), and time frame (year, decade, or century). The following are sample goals that may help achieve sustainable transportation depending on a specific context:
Due to the broad range of goals that are applicable to sustainable transportation, several of the environmental issues included in AASHTO’s Center for Environmental Excellence website have relevance to sustainability: Air Quality, Context Sensitive Solutions, Environmental Considerations in Planning, Environmental Enhancement, Environmental Justice, NEPA Process, Noise, and SAFETEA-LU.
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