BIODIESEL: For heavy-duty vehicles, it can be produced from a variety of natural oils, with soybeans being the most prominent source in the United States. The most commonly used biodiesel blend in government fleets is known as B20 (20 percent biodiesel and 80 percent diesel).
Advantages: Reduces dependence on fossil fuels. Reduces levels of emissions by 10 to 20 percent. When used in states where soybeans are grown, supports local farmers.
Disadvantages: Generally costs more than standard diesel; combination of fuel price and lower fuel economy can lead to high per-vehicle premium. Communities often need to install new equipment in storage tanks to prevent filter clogs. Can produce cold-weather start problems, but this is more of a concern at higher biodiesel concentrations than B20.
COMPRESSED NATURAL GAS (CNG): Consists mostly of methane drawn from gas wells or in conjunction with oil production. As of 2002, one in five transit buses in the country operated on CNG.
Advantages: Considerably cheaper than gasoline or diesel--in Seattle last October, it was half the cost of gasoline. Clean-burning fuel with a variety of emission-reducing benefits.
Disadvantages: CNG vehicles cost more to purchase than their gas- burning counterparts. More frequent refueling is required. Many vehicle manufacturers have ceased factory conversions for CNG.
ETHANOL: Fermented from plant sugars (mostly from corn in the United States), ethanol is generally mixed with gasoline for transportation uses. The most common blend in public-sector fleets is E85 (85 percent ethanol, 15 percent gasoline).
Advantages: Uses domestic product that helps reduce dependence on foreign sources of energy. Burns cleaner than gasoline and can improve engine performance. Some jurisdictions receive per-vehicle rebates for ethanol use.
Disadvantages: Not as available in some areas of the country as it is in Midwest. Ethanol vehicles operate at only about 80 percent of the range of gasoline vehicles, requiring more frequent fueling. With some vehicles, there are startup issues in extremely cold temperatures.
ELECTRIC/HYBRID VEHICLES: Vehicles have both an electric motor and a separate gas-powered engine. Hybrids have a significant presence in the passenger-car portion of many government fleets.
Advantages: Substantial fuel and maintenance cost savings, although full potential of technology not yet realized. Significant emission reductions on car models; not as big a difference in trucks.
Disadvantages: Per-vehicle price differential can offset fuel savings over the life of the vehicle. Difference in handling, with some describing the performance of some models as similar to that of a manual-transmission vehicle.
OTHER: Propane, a byproduct of natural gas processing and petroleum refining, has been used in some fleets; more than half of the Texas Department of Transportation's on-road fleet runs on either propane or natural gas. Liquefied natural gas offers a clean-burning option used prominently in the waste management industry and for bus fleets in places such as Phoenix and Orange County, California. Use of fuel cells made of hydrogen to power vehicles may be part of alternative fuels' next wave. The city of Las Vegas' fleet currently includes two fuel cell vehicles: one for a parking enforcement supervisor and the other for the city manager's office.