These emissions cause or contribute to many human health and environmental impacts; all but CO₂ are regulated by the Clean Air Act Amendments of 1990. New vehicles sold in the United States must meet or exceed federal emission standards that restrict the release of these pollutants.

Tier 1 standards are the prevailing federal vehicle emission standards established and enforced by the U.S. Environmental Protection Agency (standards more stringent than Tier 1 have been imposed in California, New York, and Massachusetts). Under these standards CO, NO_x, VOCs, SO₂ and PM/PM₁₀ are restricted. Greater restrictions on these vehicle pollutants have been proposed; at the federal level, Tier 2 standards currently are being evaluated. Use ACEEE's Green Book. The Environmental Guide to Cars and Trucks to identify those vehicles that meet or exceed the most stringent emission standards. Using vehicle emissions and other measures, the Green Guide scores all 2000 cars and trucks sold in the United States.

Vehicle manufacturers are also developing, and offering to a limited market, vehicle alternatives that significantly improve fuel efficiency and/or reduce vehicle emissions. Known collectively as advanced technology vehicles, these alternatives are environmentally superior vehicles that you might consider in the near future. Electric and hybrid-electric vehicles are two examples of these advanced technologies. Although these alternative vehicles are available now in only a few markets (e.g., as leasing options, as fleet vehicles, and only in certain regions), they soon will be available nationally. Certain automakers have announced plans to market hybrid-electric vehicles in the United States beginning as early as 2000.


Problems with Diesel
Diesel-powered motor vehicles are a significant source of very fine particles, which are a unique public health hazard. These particles, or soot, easily make their way past the upper airway, and penetrate into the deepest tissues of the lungs, where they can accumulate. Add to this grim description the mixture of chemicals attached to the surface of these particles. Dozens of these chemicals are recognized human toxicants, carcinogens, reproductive hazards, or endocrine disrupters. Despite these data, diesel-powered vehicles are permitted waivers that allow them to pollute more than their gasoline counterparts do. Furthermore, because of its higher energy value, diesel is being considered by vehicle manufacturers to achieve next-generation fuel economy goals of 80 miles-per-gallon.


Global Warming and the Link to Fuel Economy
Carbon dioxide (CO₂) is the primary by-product of fuel combustion, and the major component of vehicle exhaust. Though not regulated as a pollutant, carbon dioxide is a greenhouse gas and contributes to global warming. There are few, if any, end-of-pipe technologies that can control CO₂. Your vehicle choice and your driving behavior, however, can minimize CO₂ emissions and your resulting contribution to global warming. By opting to buy a lighter, more fuel-efficient vehicle, you reduce the amount of CO₂ generated per mile; by driving less, you further reduce the generation of CO₂. Use our Tailpipe Tally to estimate your contribution to greenhouse gas emissions.


Emissions from Vehicle Manufacturing
To help prevent pollution at vehicle assembly facilities and protect the communities that host them, choose a vehicle with a single color of paint rather than a two-tone paint job. Two-tone paints jobs require more processing and generate nearly twice the chemical air releases of a single color paint job.

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