By Michael Bristow
BBC News, Beijing
Office worker David Dai is one of a growing army of Beijing residents returning to two-wheeled transport.
But the 28-year-old does not rely on his own pedal power - like hundreds of thousands of others, he has bought an electric bike.
These battery-powered, and virtually silent, machines have become increasingly common on the streets of the Chinese capital.
With roads often clogged with cars - there are now four million vehicles in Beijing - they offer a speedy way to get around.
But not everyone seems to like them: government officials are unsure about how to deal with this explosion of electric bicycles.
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more:
http://news.bbc.co.uk/2/hi/asia-pacific/8538221.stm