ment in the early 1900s relied on local or private sources of funding. Funding is now derived from a variety of sources, and a large percentage originates from federally collected sources, particularly user-related fees on gasoline and transport equipment. Since the passage of the Transportation Equity Act for the Twenty-First Century (TEA-21), investment in highway infrastructure has increased; for example, investment increased by 14% between 1997 and 2000 (FHWA 2002a). Capital spending on highways totaled about $64 billion in 2000, but that amount is unlikely to meet future needs for maintenance (FHWA 2002a).

The process by which these monies are spent to administer, plan, select, and build projects and maintain roads is a complicated maze of bureaucracy. The process is centered in states—with some variation among states in planning and implementation—and involves five interacting groups: federal government, state government, metropolitan planning organizations, local government, and the public (Forman et al. 2003). These governments share funding of administration, construction, planning, and maintenance in various ratios. Governments construct and maintain roads to provide a number of social benefits, such as providing mobility, transporting goods and people, and sustaining economic growth. One of the considerations in the process of road development is the recognition and management of environmental concerns.

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. Vehicle use on roads contributes to air and water quality degradation (Forman et al. 2003). Other direct changes to the biotic components of ecosystems include alteration of habitats, increased wildlife mortality, and dispersal of nonnative pest species (plants and animals). At larger scales, roads can affect migration patterns (Forman et al. 2003).

Integration of environmental effects into all phases of transportation efforts has been part of an ongoing process for several decades. These efforts attempt to form a bridge between the transportation policy arena and the environmental science community. Federal legislation has long directed the Federal Highway Administration (FHWA) and recipients of federal funding to consider environmental factors when planning transportation systems and specific road projects. During the 1990s, the Intermodal Surface Transportation Equity Act and the TEA-21 (FHWA 2001a) contained provisions addressing environmental considerations for both transportation planning and project implementation. Combined



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