Chapter 6 - Transportation and the Environment

While transportation enhances the quality of our lives, it also generates undesired environmental impacts that can lead to human health problems and ecological damage. Overall, most transportation air emissions, such as carbon monoxide and particulates, have declined since 1980 despite significant increases in U.S. population, Gross Domestic Product, and vehicle-miles traveled. Only nitrogen oxides, which contribute to the formation of ground-level ozone, and ammonia remain above their 1990 level.