Alternative fuel vehicles
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Public transit is often called upon as a measure to reduce environmental impacts of travel, both by consolidating travelers from single-occupant vehicles into one environmentally-efficient vehicle, and by using modern technology for cleaner propulsion. Many technologies have been adapted for bus and rail transit since their advent in the late 1800s, including electricity and battery, natural gas, and hydrogen.
Standard Fuels: Gasoline and Diesel
The most common fuels for all vehicles in the U.S. include unleaded gasoline, and diesel. Federal regulations attempting to reduce the impact of these fossil fuels on the environment have mandated supply of ultra-low sulfur diesel and the use of ethanol in gasoline. (SOURCES) Some agencies now use biodiesel as a means to reduce harmful emissions without the added expense of purchasing hybrid electric buses.
Practically all bus manufacturing firms offer diesel options, and cutaway buses are commonly available in either gasoline or diesel configurations. The manufacturers producing diesel and biodiesel-compliant engines for buses available in America include:
Natural gas is used as a fuel in both liquid (LNG) and compressed-gas forms (CNG). (Explain engine differences). Santa Monica, California's Big Blue Bus includes a fleet of buses powered by LNG. Los Angeles County Metropolitan Transportation Authority (LACMTA, or Metro) operates the country's largest fleet of CNG buses.
Bus Manufacturers with Natural Gas Offerings
Electric power for buses is one of the oldest propulsion technologies, adapted from electric streetcars. Buses powered by overhead wires are commonly called "trolley-buses" and still operate today in some cities such as Seattle, San Francisco, Dayton, Boston, and Philadelphia. Buses can also be powered by electric battery without external power such as overhead wires, but the range of these vehicles tends to be limited. The most common application of electric power for buses today is the hybrid-electric.
Hydrogen Fuel Cell
Hydrogen fuel cells has been researched as a power source for buses using Federal funding . AC Transit of California has participated in a hydrogen fuel cell bus testing program since 2000 using Van Hool buses and a power plant developed by UTC Power of Connecticut. In 2013, UTC Power was sold to another company which chose not to continue the fuel cell bus program.