By closing off stretches of a neighborhood's streets on Sunday, the City of SF creates space to celebrate local flavor. Pedestrians & bicycles roam free, and nearby businesses and organizations coordinate activities along the car-free streets.
Sunday Streets gives San Franciscans a chance to explore and appreciate new neighborhoods. In a densely populated city, it's a chance for families to let their kids bike on wide roads. Activities along the 10-12 block routes are neighborhood specific: Sometimes the police force will set up a demonstration, or a group of auto aficionados will designate an alley for a display. Street food vendors set up shop and businesses bring their goods outside for the day. It gives each neighborhood the chance to show itself at its best.
San Francisco's Sunday Streets is proof that it's scalable: it orginiated in Bogota, Colombia as Ciclovia, a day to promote free health- and community-oriented events.