Bicycles go hand-in-hand with the green movement. Riding one, instead of driving a car, reduces one's carbon footprint exponentially (as a bicycle has virtually none).

 

Cycling just eight miles prevents 15 pounds of air pollutants from contaminating the air. Since auto emissions are such a huge source of pollution (water and especially air), substituting car trips for bike rides is highly encouraged by environmentalists. (Source: NHTSA, Photo: Flickr)