Figure 1 is a conceptual diagram (three stages) of the environmental impacts of transportation from a life cycle perspective. Phases (Stage 1) of transportation include fuel production and delivery, infrastructure development and operation, vehicle1 and parts manufacture, travel, maintenance and support, and disposal of vehicles and parts. Activities occurring during the phases result in environmental outcomes include land consumption and alterations, emissions of air pollutants, generation and release of hazardous and nonhazardous materials, noise and transportation of species. Outcomes can, in turn, affect the environment and human health, creating impacts (effect2 on: habitat, wildlife, ecosystems, human health and public welfare) that are usually negative (e.g., cancers, birth defects, asthma, stunted tree growth, and fish kills). Impacts, which can be chronic or acute, are highly dependent on two variables: concentration and exposure.
1 Vehicle here includes highway vehicles, airplanes, marine vessels, railroad cars and locomotives, and transit equipment.
2 Dependent on ambient levels or concentrations of pollutants and exposure to those outputs.
SOURCE: U.S. Department of Transportation, Bureau of Transportation Statistics, based on U.S. Environmental Protection Agency,Indicators of the Environmental Impacts of Transportation (Washington, DC: October 1999), figure 1-1.