The fuel economy of an automobile, measured in miles per gallon (MPG), is the distance it can move using one gallon of fuel. In 1975, in the midst of concerns about oil consumption, the U.S. Congress passed a law establishing the Corporate Average Fuel Economy (CAFE) standards, which required an increase in the fuel economy of all new cars and light trucks starting in 1978. The law required that each manufacturer meet the same standard but that a manufacturer's cars and trucks be treated differently since trucks were primarily used for work at the time. It mandated an average fuel efficiency of 27.5 MPG for cars by 1985, roughly doubling car fuel economy over ten years. The car standard remains the same as of 2003. The law also directed the Department of Transportation (DOT) to establish a standard for light trucks, defined by the DOT to include sport utility vehicles (SUVs), minivans, and pickups. The DOT established a fuel economy standard of 20.5 MPG for light trucks by 1987, an increase of about 50 percent. Small changes in light truck standards were made thereafter, with the standard increasing to 20.7 by 1996 and then, in 2003, being set to increase to 22.2 MPG by 2007.
This government-driven improvement in fuel economy has helped to limit the increase in fuel use by the United States to 30 percent over the last twenty-five years, despite the fact that vehicle miles traveled have nearly doubled over that time. In 2000 the increased fuel economy of the U.S. car and truck fleet resulted in a savings of more than forty billion gallons of gasoline, representing a 25 percent reduction compared to what the demand would have been if fuel economy had not increased. This amounts to a savings of more than 430 million metric tons of carbon dioxide, the heat-trapping gasses that cause global warming.
Vehicle travel over the coming decades is projected to rise at nearly unprecedented rates, and fuel economy is not expected to improve sufficiently to compensate for this trend. Due mostly to the explosion in sales of SUVs and other light trucks for passenger travel, the average fuel economy of a new vehicle sold in the United States has actually been declining since 1987 and by 2002 was at a two-decade low of less than twenty-four MPG.
Many factors contribute to a vehicle's fuel economy, including aerodynamics, weight, tire inflation, and engine efficiency. Simple steps that can be taken by drivers, such as properly inflating and rotating tires and keeping engines properly tuned, can improve a vehicle's MPG. Conventional technology improvements, such as continuously variable transmission systems and the use of high-strength steel and aluminum, can also make a vehicle go farther on a gallon of gas, as can advanced engine technologies such as low-friction, variable vale control engines. These and other conventional technologies can increase fuel economy by 40 to 70 percent.
Even larger improvements in fuel economy can be achieved by combining conventional technology improvements with hybrid electric technology. Hybrid electric vehicles obtain driving power from both a gasoline or diesel engine and an electric motor/battery system. When combined with conventional technology improvements, hybrids can achieve more than a doubling of today's car and truck fuel economy. As of 2003 every major automaker had either put into production or announced the planned production of at least one hybrid car or truck in small volumes.
The issue of fuel economy is a controversial one, and is directly linked to the economic and environmental costs of U.S. passenger vehicle travel. In 2000, American drivers consumed over 120 billion gallons of gasoline at a total cost of more than $185 billion, and passenger vehicles accounted for 40 percent of the oil products that the nation consumed. Cars and trucks are also the largest single source of smog-forming air pollution in most urban areas. Most of this pollution comes from a vehicle's tailpipe, but emissions from fuel production and delivery, so-called "upstream emissions," are also a problem.
Also involved in the debate over fuel economy standards is global warming. The production, transportation, and use of gasoline for cars and light trucks in 2000 resulted in over one-fifth of the U.S. emission of the heat-trapping gases that scientists say are contributing to global warming. In the year 2000, U.S. cars and trucks emitted more of the heat trapping gasses that cause global warming than the individual emissions from every country other than the U.S., China, Russia, and Japan from all sources combined.
Supporters of increased fuel-economy standards say that if the mileage performance of the U.S. fleet of light trucks and cars was improved, it would help reduce the cost to drivers at the gas pump, the economic and military risks resulting from our nation's reliance on foreign oil, changes to the global climate, and would improve consumer choice. Those opposed to significant increases in fuel economy say that the auto industry could not economically withstand the cost of technology improvements to their fleets, consumers are not interested in better fuel economy and consumer choice would be reduced, and that better alternatives exist, such as increasing gasoline taxes. Both sides of the debate also raise opposing perspectives on the safety impacts of changes to fuel economy standards.
see also Energy Efficiency; Vehicular Pollution.