Sustainable Transport Planning: Estimating the Ecological Footprint of Vehicle Travel in Future Years

An important indicator of sustainable land use, the ecological footprint measure has proved unsuitable for many planning applications because of the limited availability of impact data at the local level of cities and counties and because of an inability to estimate the ecological footprint of future development scenarios. In light of these limitations, this paper presents a methodology for measuring the ecological footprint of a county-level transportation network in current and future time periods. With the aid of vehicle travel behavior and fleet characteristics obtained from a number of state and federal agencies, we estimate the quantity of land required for constructing county highways and remediating annual greenhouse gas emissions through forest carbon sequestration in the years 2001, 2011, and 2021. The results of our study, which focuses on Houghton County, Michigan, indicate that, despite a projected increase in average vehicle fuel efficiency, the ecological footprint of transportation will increase in future years because of projected increases in total annual vehicle kilometers of travel along the network. On the basis of these results, we argue that the ecological footprint is a viable technique for transportation and land-use planning applications. DOI: 10.1061/ ASCE 0733-9488 2005 131:3 170 CE Database subject headings: Ecosystems; Natural resources; Environmental impacts; Regional development; Information systems; Sustainable development; Transportation management; Land usage. The rapid growth of urbanized regions since World War II has brought Americans not only great material wealth but also the degradation of natural ecosystems. Fortunately, many countries have begun to treat this problem seriously and are moving toward the models of sustainable development first articulated at the Rio Earth Summit of 1992 Brady and Geets 1994 . As defined by the United Nations World Commission on Environment and Development WCED , sustainable development requires that the economic and social needs of current generations be met without sacrificing the ability of future generations to achieve an acceptable quality of life WCED 1987 . An initial step in developing sustainable models of urban growth requires that the environmental impacts of current settlement patterns be fully established. To this end, the “ecological footprint” method has been proposed as a standard methodology for evaluating the direct environmental implications of alternative development models. Developed by Mathis Wackernagel and William Rees at the University of British Columbia, the ecological footprint measure quantifies the total land area required to support human settlement. As explained by its creators, “ e cological footprint analysis is an accounting tool that enables us to estimate the resource consumption and waste assimilation rePhD Student, Urban and Regional Planning, Univ. of Wisconsin– Madison, Madison, WI 53706. E-mail: [email protected] Assistant Professor, Urban and Regional Planning, Univ. of Wisconsin–Madison, Madison, WI 53706. E-mail: [email protected] Note. Discussion open until February 1, 2006. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on July 4, 2003; approved on July 9, 2004. This paper is part of the Journal of Urban Planning and Development, Vol. 131, No. 3, September 1, 2005. ©ASCE, ISSN 0733-9488/2005/3-170–180/ $25.00. 170 / JOURNAL OF URBAN PLANNING AND DEVELOPMENT © ASCE / SE quirements of a defined human population or economy in terms of a corresponding productive land area” Wackernagel and Rees 1996, p. 9 . More specifically, the ecological footprint of a population is calculated by determining how much land and water area are required to produce all the goods consumed and to assimilate all the wastes generated by that population Rees 2000 . The principal advantage of the footprint measure for environmental impact analysis is that it adopts a physical variable—units of land area—as a common metric for comparing alternative models. In contrast to such nonphysical metrics as units of currency, the physical area required to support a community provides a resource-constrained means of quantifying impacts. Although monetary capital fluctuates from year to year and is theoretically unconstrained over time, natural capital in the form of physical land area is limited within the boundaries of a municipality, the borders of a country, or the dimensions of the planet. As a result, the ecological footprint measure provides a means of assessing the amount of a resource that is being used relative to the amount that is available. In short, the ecological footprint variable directly embodies the ecological concept of carrying capacity. As a measure of carrying capacity, the ecological footprint provides an unambiguous standard for quantifying sustainability: sustainable communities are those for which the area of land consumed in the production of resources and assimilation of wastes is less than or equal to the total available land area. Yet, despite the clear advantage of this standard over other metrics of environmental performance, the ecological footprint approach has been criticized on two important grounds. First, the ecological footprint is limited in application to spatial dimensions for which detailed resource information is available. Often collected and maintained at the state or national level, many measures of footprint intensity, such as area of productive agricultural land or the quantity of energy consumed, may not be readily available at the level of the town, city, or county Yount et al. 2000 . The need for more-