Assessing and Managing the Ecological Impacts of Paved Roads (2005) / Chapter Skim
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1 Introduction
1 Introduction
Pages 14-36
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From page 14... ...
Many of these effects persist today. The past century has seen a transformation in the magnitude and the scale of paved roads in the world in general and in the United States in particular.
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All phases of road development -- from construction to vehicle use -- change ecological conditions of an area. Roads change abiotic characteristics of the environment -- from physical to chemical soil conditions to alterations in water flow and water quality.
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recommended a number of ways to mesh conservation and transportation objectives, including integrated planning, conservation banking, agency coordination, wildlife crossings, and native vegetation management. As more resources go toward road construction and management and as knowledge about the ecological effects of roads increases, the conflicts between the societal goals of developing transportation infrastructure and maintaining ecological goods and services (for example, soil production [a good]
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See Box 1-1 for details of the charge to the committee and Box 1-2 for the committee's definition of paved roads. In 2002, the NRC formed the Committee on Ecological Impacts of Road Density, a panel of 14 members that included a experts in environmental engineering, highway construction and engineering, land-use change, wildlife ecology, endangered species, habitat evaluation modeling, habitat impact assessment, economic development and planning, environmental law and policy, and biodiversity conservation (see Appendix A)
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Cumulative effects will be considered. The proposed study will also provide a conceptual framework and approach for the development of a rapid assessment methodology that transportation and regulatory agencies can use to assess and measure ecological impacts of road density.
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The focus of the committee's work was on the ecological effects of federally funded, major paved roads within the United States road network -- for example, highways in urban and rural locations. The committee limited its focus to highly urbanized street networks.
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This report strives to highlight the ecological effects of highways that should be evaluated throughout the decision-making process in the planning, design, construction, and maintenance of highways. The term road density is used in the charge to the committee.
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The concept of road density was developed as a way of quantifying one aspect of a road network, and therefore the term is applicable only at scales larger than a road segment or for a system of roads. The term road density may be appropriate for measuring the structure of some existing road networks (especially those few urban or rural systems in a rectilinear grid)
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, defines components of ecological systems in terms of how they benefit and support human life. Ecosystem services include water purification, flood and drought mitigation, climate stabilization, carbon sequestration, waste treatment, biodiversity conservation, soil generation, disease regulation, pollination, maintenance of air quality, and the provision of aesthetic and cultural benefits.
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From page 23... ...
Roads change the local physical environment by interacting with underlying topography, aspect, geology, soils, ecological conditions, and land cover. For example, new patterns of water runoff can develop as the local topography is altered, and those changed patterns can result in altered storm hydrographs, changed groundwater recharge, and increased delivery of sediments and contaminants.
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Although most current and foreseeable road projects in the United States are along established roads, the selection of sites for new roads carries the potential for new ecological effects. New roads can affect the movement of plants and animals and change the physical environment, as can increases in traffic volume on existing roads.
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Therefore, scale is defined here by two components: the grain and extent. As a demonstration of these meanings of scale and its relevance to road ecology, consider the set of Figures 1-1 through 1-8.
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First, as the extent and grain of scale increases, distinct objects appear and persist over distinct scale ranges and are replaced by others that are either aggregates of objects at smaller scales or new objects. For example, the double strip marking in the center of the road is no longer visible at extents of a kilometer, and road segments visible at smaller extents aggregate to become road networks in larger extents.
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The sequence of photographs suggests that road structures and attributes vary with scale. The attributes of paved roads (materials of asphalt, gravel, and concrete)
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At scales of a few meters, the structures of pavement width, shoulders, travel lanes, and paved envelope are germane. Many of the ecological effects are contained within a kilometer of the paved roads, an area often referred to as the road-effect zone.
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for understanding ecological systems. The components of a generic forest ecosystem also cover wide ranges of scale, as
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Emissions from the combustion of fossil fuels can aggregate to produce global scale effects. A human social system is defined as a group of people who share understanding, norms, and routines to accomplish activities or fulfill key functions (Westley 2002)
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ORGANIZATION OF REPORT This report addresses and is limited to the statement of task as agreed on by the NRC and FHWA. To address how ecological consid
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Chapter 2 also describes the current status of pavement, bridge conditions, and future projections of spending and other required capital investments. Chapter 3 addresses the effects of roads on ecological conditions by using spatial scale to sort ecological effects.
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time frames. Ecological conditions are affected not only by the construction of the road and road appurtenances (bridges)
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Road projects need only permits to affect certain types of ecological features -- wetlands, endangered species, and migratory birds -- and generally at a small scale. Moreover, the permit programs generally only consider direct effects of road construction or use on the protected resource.
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Integration of environmental concerns into transportation planning should be done earlier in the planning processes. Such organizations as the metropolitan planning organizations should conduct firstlevel screenings for environmental considerations in transportation improvements before the development of a transportation improvement
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Federal transportation agencies, such as FHWA and Federal Transit Administration, require that all projects using federal funds come from an adopted transportation improvement program. Transportation and conservation planning at the state level should be integrated.
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