To get a sense of how large a problem this is, imagine if you fell off your bike and had a head injury such that your doctor ordered some tests.

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Leslie lost her leg and her eyesight after serving in Bosnia, and this is her first time back on a bike.

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But if public safety and common sense don't compel you, know this: Headphones atop a bike is an insult to an extraordinary, all-sensory city.

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In other news, pedal-powered transportation geared up for the future as we showcased a chain-less hybrid bike with an out-of-this-world design and a molded bamboo bike that is grown from the ground up.

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"I haven't biked since I was 13, and I was avoiding buying a bike, so this is a really good opportunity to find out how it'll go, " said Jessica Sheridan, 36, an architect who lives on Manhattan's Upper West Side and is a bike-sharing program member.

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This is comparable to a higher end off -the-rack steel bike, and less expensive than buying a stock steel frame from a prestigious Italian manufacturer like Colnago and building it up.

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This month Cohen will add the City of Boston, which is launching a 600-bike system (sponsored in part by athletic-shoe maker New Balance).

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This system of impromptu bike renting is helping urban areas reduce automotive traffic and pollution while providing locals and tourists with a convenient, cheap and healthy means of transport.

BBC: Bike sharing around the world