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The growing need to reduce fuel consumption and lower emissions
in the United States transportation sector has spurred urban transit
bus operators to pioneer the adoption of alternate fuels and new
drive system technologies. One of the most promising technologies
to receive attention is hybrid-electric drive, which consists of
two or more onboard fuels that supply energy to electric traction
motors that in turn drive the wheels. By contrast, conventional
drive employs an internal combustion engine to generate rotational
force that is then only mechanically transferred to drive the wheels.
A growing number of companies are developing and beginning to supply
commercial hybrid-electric drive products to the truck and bus markets.
Most of these commercially-available hybrid buses combine an internal
combustion engine and traction battery, although there are many
possible drive system configurations.
The electric drive improves drive system efficiency, reduces energy
consumption, recovers energy, reduces emissions, and improves driveability.
Hybrid systems are being used in transit bus applications where
pure battery-electric drivetrain is not yet feasible because the
power and energy requirements associated with typical urban transit
bus drive cycles exceed the performance capabilities Ð primarily,
range -- of current battery technologies. Transit operators are
implementing hybrid buses since the hybrid drive systems can easily
meet and exceed the urban transit bus drive cycle requirements while
still improving fuel economy and emissions.
The global hybrid bus population has increased dramatically in
just a few years. In a report for the Transportation Research Board,
the NAVC estimated that more than 300 hybrid buses had been built
worldwide as of 1999. More significant are the transit operators'
planned hybrid bus purchases for 2001 and beyond. In the U.S. alone,
the number of planned hybrid buses purchases will increase the bus
market from approximately 65 in 1999 to over 300 in 2001.
Hybrid bus demonstration and deployment
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