Most promising green technologies number nine: compressed air

Who would have thought that a concept as simple as compressed air could be a viable automotive technology? Sure, we all fill our tires with the stuff, but some automakers - MDI, for one - are considering compressed air as an energy carrier, like a battery. Whether a vehicle is engineered to run solely on air power or if the energy is stored as part of a hybrid system, the very air we breathe could provide propulsion for our vehicles.

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