On the last Friday evening of every month, the streets of hundreds of cities around the world are transformed. The cars, trucks and buses that usually dominate the landscape slow down, because they are overrun by... bicycles. It started in San Francisco. Now, as they have for over a decade, cyclists from all over the city, the Bay and sometimes the world come together at the foot of Market Street in San Francisco's financial district. They are racers in spandex, messengers with canvas bags, children, seniors and all in between. Shortly after the clocktower at the Ferry Building strikes 6, the group of people begins to move, to revolve around the concrete park... to reach a boiling point of excitement: A critical mass. Then one person takes off into the traffic, followed by another... and more... until hundreds, or even thousands, of bicycles fill the downtown roadways, forcing all the motorized vehicles to stop Ben Trefny (TREFF-knee) and Zoe Corneli (ZOEY corr-KNEE-lee) of KALW News in San Francisco joined the Critical Mass, and spoke with three of the founders, to find out how a collection of like-minded people can make the world spin a little differently.

On the last Friday evening of every month, the streets of hundreds of cities around the world are transformed. The cars, trucks and buses that usually dominate the landscape slow down, because they are overrun by... bicycles. It started in San Francisco. Now, as they have for over a decade, cyclists from all over the city, the Bay and sometimes the world come together at the foot of Market Street in San Francisco's financial district. They are racers in spandex, messengers with canvas bags, children, seniors and all in between. Shortly after the clocktower at the Ferry Building strikes 6, the group of people begins to move, to revolve around the concrete park... to reach a boiling point of excitement: A critical mass. Then one person takes off into the traffic, followed by another... and more... until hundreds, or even thousands, of bicycles fill the downtown roadways, forcing all the motorized vehicles to stop Ben Trefny (TREFF-knee) and Zoe Corneli (ZOEY corr-KNEE-lee) of KALW News in San Francisco joined the Critical Mass, and spoke with three of the founders, to find out how a collection of like-minded people can make the world spin a little differently.