Back in April the SF Transit Riders Union challenged the mayor and Board of Supervisors to use Muni for their daily commutes for 22 consecutive days in June. Since then, they've gotten eight supervisors to pledge to do this, along with the mayor, and they kicked things off today with a rally and press conference on the steps of City Hall, led by transit-oriented Supe Scott Wiener.

The number 22 was chosen to mark the 22nd anniversary of Proposition AA from 1993 which requires all "city officials and full-time empoyees [to] travel to and from work on public transit at least twice a week." The non-binding ordinance isn't really policed, and thus the challenge is meant to remind everyone about it, and to get city officials more in touch with the transit woes of common folk.

All the participants in the challenge have to tweet while riding, or waiting for, Muni with the hashtag #OnBoardSF, and they'll be tracked on an interactive leaderboard.

Supervisors Wiener, John Avalos, London Breed, David Campos, Julie Christensen, Mark Farrell, Jane Kim, and Eric Mar have all signed on, with possible participation from Katy Tang and Norman Yee. (Tang previously noted that, as an SF native, she has ridden Muni her entire life.) If any of them fail to use transit one of the next 22 days, they have to tweet the reason for it.

Says Ilyse Iris Magy of the Transit Riders Union, "This is an opportunity for our city officials to promote their own commitment to public transportation, showcasing that they care about the future of Muni, which is the future of San Francisco."