Many factors determine the environmental impact of a passenger car or truck. A vehicle’s tailpipe emissions level and fuel economy are chiefly important, though other factors will also play a role.
Exhaust from a vehicle’s tailpipe is a veritable stew of harmful and toxic emissions. Four regulated pollutants, carbon monoxide (CO), particulate matter (PM), hydrocarbons (HC), and nitrogen oxides (NOX), have been associated with numerous ailments including cancer, respiratory disease, nervous system damage, and premature death. While these pollutants are regulated by the government, real-world tests have shown most vehicles’ emissions to be higher than the standard to which a vehicle is certified. These excess emissions occur for a variety of reasons: inaccuracy of the tests; malfunctioning emission control systems; and deterioration of the catalytic converter and other components.
A vehicle’s fuel economy affects its environmental performance in a number of ways. First, the amount of carbon dioxide (CO2) emitted by a vehicle is essentially proportional to the amount of fuel it burns. So from a global warming perspective, the more fuel-efficient a vehicle is, the lower its global warming impact will be. Second, a significant amount of pollution also occurs in supplying vehicles with fuel. These so-called “upstream emissions” occur during the extraction, refining and transport of fuel from the well head to the fuel pump. Upstream emissions associated with a vehicle are proportional to its fuel consumption. Third, the levels of a vehicle's non-regulated pollutants, such as methane and nitrous oxide, are affected by the amount of fuel a vehicle consumes.
Because energy use and emissions also occur when a vehicle is being produced, the manufacturing process of a vehicle plays a role (albeit to a much lesser degree than tailpipe emissions or fuel economy) in a vehicle’s environmental performance.
Vehicle Environmental Ratings
The American Council for an Energy-Efficient Economy (ACEEE) produces an annual environmental guide to cars and light trucks, including ratings of all new models.
ACEEE’s Green Book® Online uses three types of vehicle-specific data to form the basis of its ratings:
- Tailpipe Emissions — given by the emissions standard to which a vehicle is certified;
- Fuel Economy — based on EPA test cycles
- Vehicle Weight
ACEEE’s Green Book Online applies adjustment factors, similar to those used in EPA's vehicle emissions calculation models, to determine the expected lifetime average emissions from every car and light truck on the market today. It uses fuel economy to estimate each vehicle’s global warming, upstream emissions, and non-regulated pollutant impacts on the environment. To estimate impacts of a vehicle’s production and manufacturing phases, ACEEE’s Green Book Online uses vehicle weight together with average manufacturing-sector emission factors and average breakdowns of vehicle materials by weight.