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Green Cars

Vehicle Use: Fuel Economy

Since the 1970's, vehicle manufacturers have improved fuel economy by designing vehicles with front-wheel drive, more efficient engines and transmissions, and other weight-saving and streamlining refinements.

For your purchase decision, vehicle class is a simple measure of vehicle weight and associated fuel economy. An automobile in the compact or mid-sized vehicle class, for example, will be lighter and more fuel efficient than a pick-up or sport utility in the light truck vehicle class. You should avoid buying a larger, more powerful vehicle than you really need – not only will it generally cost more, but it also will be more polluting.

Within a vehicle class, there also is a range (often a large range) of fuel economies from which to choose. Buy the most fuel efficient vehicle within a vehicle class, but avoid diesel-powered vehicles. Even though diesel fuel improves fuel efficiency, it also creates very fine particulate matter that poses a significant human health risk (see also, Vehicle Emissions) – one that outweighs the gains made in fuel efficiency. To help you with your purchase choice, use ACEEE's Green Book. The Environmental Guide to Cars and Trucks. Using fuel economy, vehicle emissions, and other measures, the Green Book scores all model-year 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 choose 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, or only in certain regions), they soon will be available nationally. In fact, certain automakers have announced plans to market hybrid-electric vehicles in the United States beginning as early as 2000.

Choice of Options
Your choice of engine, transmission, and other options and accessories can affect the fuel economy of a vehicle. Larger, more powerful engines (i.e., 6 or 8 cylinders) decrease fuel economy and increase vehicle emissions. If you think you need the additional power and torque offered by a larger vehicle, you should know that your fuel efficiency will suffer during all types of driving. Four-wheel drive, for example, adds substantial weight to a vehicle and consumes more energy than does a similar two-wheel drive vehicle. These characteristics of four-wheel drive can decrease fuel economy by as much as 15 percent. An automatic transmission consumes 5 percent more fuel than does a properly driven manual transmission. While decreasing your vehicle's fuel economy, these options also make your vehicle more expensive.

When buying a vehicle and choosing options and accessories, consider the following:

Weight – Avoid heavy options and accessories that decrease fuel economy. These options include 6 or 8 cylinder engines, four-wheel drive, and automatic transmission.

Drag – Keep your vehicle's profile as aerodynamic as possible because wind resistance, or drag, lowers fuel economy. For example, roof racks sit above the aerodynamic profile of a vehicle and can decrease fuel economy by 1 percent empty, and as much as 25 percent when loaded.

Energy – Avoid, whenever possible, using options which draw power from the engine whenever possible. For example, air conditioning can lower fuel economy by as much as 12 percent when used in stop and go traffic.

Vehicle Weight and Life-Cycle Considerations
While conserving fuel, lighter vehicles generally require less material and environmental resources to be manufactured, reducing life-cycle environmental impacts. The lightest, gasoline-powered automobile weighs 1,900 pounds (i.e., sub-compact); heavy automobiles and trucks can weigh 5,000 pounds or more, with the new Ford Excursion -- a nine-passenger, 19 foot vehicle that exceeds the light-truck weight classification -- topping the scales at nearly 8,000 pounds. Generally, 71 percent of this weight is iron and steel, 9 percent is aluminum and other metals, and 7 percent is plastics (the remaining weight is made up of rubber, glass, and fluids). The extraction and processing of each of these materials destroys natural habitats and contributes to air and water pollution. For example, because plastics are manufactured from petrochemicals, they also cause the environmental impacts of petroleum refining processes and so must be considered from a life-cycle perspective. Therefore, using less material to manufacture a vehicle will tend to decrease the up-stream life cycle environmental impacts.

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