BACKGROUND: A hybrid electric bus that weighs half as much as conventional buses, boasts three times the fuel economy, and can carry 20% more passengers, could debut by the middle of 2008. The bus would also be quieter and would have less environmental impact than standard diesel-powered buses, resulting in significant cost savings. It is being developed by a collaboration between Autokinetics, Oak Ridge National Laboratory, and the Department of Energy's FreedomCAR and Vehicle Technologies Program.
LESS IS MORE: At the heart of the bus is an ultra-high-strength stainless steel body and chassis that would be up to 30% less expensive to build than the standard bus body. The lighter weight of the bus improves fuel efficiency by reducing drag. The weight (technically, the mass) of the vehicle determines how much energy is needed to get it moving, or to change direction. As the vehicle accelerates, it gains speed, but it also experiences an increase in drag, the friction from the air passing by. It takes extra energy to overcome that drag. A similar effect happens on a bicycle: it takes more exertion on the part of the rider while biking into a strong headwind, than when the wind is at the rider's back. So any decrease in drag that a vehicle experiences will result in better fuel economy.
WHAT ARE HYBRIDS: Gasoline-powered cars are the most common type, although there are some battery-powered electric cars available today. A hybrid vehicle is a combination of the two, attempting to reap the best of both approaches. Current hybrid engine systems have a single mode of operation, using a single gear set to split the engine's power into two systems -- routing it to drive the wheels or charge the battery -- for both city and highway driving. A hybrid engine also captures energy from braking that would otherwise be lost and shutting off the engine at a stop. The battery alone can power the vehicle at low speeds. The electric motor can double as a generator while braking and only has to run part of the time. One disadvantage is that the gasoline engine must therefore run at varying speeds, which reduces its energy efficiency.
CRASH TEST: Scientists at Oak Ridge National Laboratory have performed computer simulations of collision scenarios to ensure that the buses meet safety standards for reducing the impact of a collision. Every vehicle has what is known as a 'crumple zone,' that absorbs energy upon impact. It increases the amount of time it takes to come to a complete stop, spreading the force over a longer period of time. Because they yield during a collision, crumple zones change the energy of the impact into heat and sound, reducing the chance of injury to passengers.
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