The personal automobile is a central component of life for most Americans. The majority of Americans rely on their cars to get from their homes to workplaces, schools, stores, and other destinations. There is evidence that this dependence is growing. For example, the total miles Americans traveled in their cars grew by more than 40 percent between 1983 and 1990.

The popularity of cars carries a cost, however. Many environmentalists have argued that automobiles cause significant damage to the environment. Automobiles create air pollution, including greenhouse gas emissions that may contribute to global warning. They also leave behind toxins and chemicals such as petroleum residues on roads, which run off and contaminate groundwater. The increasing number of cars requires the construction of paved roads and parking lots, resulting in the loss of wild habitats and other open spaces. On the global scale...