The 21st-century equivalent of the cavalry has come charging in to rescue cities in China and South Asia in their battles against air pollution and global warming. And it's also beginning to help out on the traffic-choked streets in London, New York, São Paulo and Los Angeles. This is the electric bicycle, or "e-bike," a technology that blends the simplicity and mobility of a traditional bicycle with the speed of a moped or motorized scooter, but without the internal combustion engine. Go to story #1