Summary: To help reduce air pollution in U.S. cities, various alternative fuels have been proposed for use in transit buses, including compressed natural gas, liquified natural gas, methane, ethanol, biodiesel fuel, and propane. GAO found that alternative fuel buses account for a very small, but growing, portion of the nation's transit bus fleet. Five percent of the nation's 50,000 transit buses ran on some type of alternative fuel in 1997. The most commonly used alternative to diesel fuel is compressed natural gas. Transit operators are also beginning to test new propulsion system technologies -- hybrid electric systems and fuel cells -- in their transit buses. Data are limited on the extent to which alternative fuels in transit buses have improved air quality in urban areas. Transit operators pay more to buy, maintain, and operate buses that use compressed natural gas than they pay for diesel buses. When deciding whether to switch to alternative fuels, transit operators consider a range of factors, including the need to adhere to more stringent emissions standards, public concerns about transit bus pollution, and the higher costs and reduced reliability of buses that use alternative fuels.
