Pneumatic Hybrids: Urban Powertrain Of The Future?

Hybrid technology propels most fuel-efficient vehicles currently on sale in the U.S., but with costly battery packs and not-so-easy-on-the-wallet pricing; Are gas-electric hybrids long for this world? Could pneumatic hybrids be a cost-effective replacement? » 6/16/09 2:00pm 6/16/09 2:00pm