Passenger vehicles contribute about 20 percent of all U.S. carbon dioxide emissions, so increasing fuel efficiency helps reduce greenhouse gas emissions.
Source: National Highway Traffic Safety Administration, US

First enacted by Congress in 1975, the purpose of CAFE is to reduce energy consumption by increasing the fuel economy of cars and light trucks. NHTSA administers the CAFE program, and the Environmental Protection Agency (EPA) provides the fuel economy data. NHTSA sets fuel economy standards for cars and light trucks sold in the U.S. while EPA calculates the average fuel economy for each manufacturer. This site contains an immense amount of information about the CAFE program including a CAFE overview, rulemaking actions, fleet characteristics data, compliance activities, summaries of manufacturers? fuel economy performances since 1978, and related studies.