The big "Ciclovia" style block party is this Sunday in San Francisco. A big stretch of 3rd Street and The Embarcadero will be closed from 9 AM to 1 PM on Sunday. The T-Third and F-Market Muni lines will be FREE from 8 AM to 2 PM for access to Sunday Streets.
Sunday Streets is modeled after the Ciclovia program in Bogota, Columbia. More here.