Every Sunday, more than a million people in Bogota join what has become a weekly ritual: congregating on the city’s main roads temporarily turned into a network of bike paths known as the "Ciclovia".  In a city of 7 million people, Sunday mornings are not for cars, they are for exercise.  More than 120 kilometers of highways are closed. In many locations, there are free aerobics, yoga and exercise classes.  This 36-year success is now being copied in several large cities around the world.  Producer Zulima Palacio recently spent time on the paths and prepared this story.