If you were planning to take public transportation in the Bay Area Sunday, you may spot some riders without pants.

The event, “No Pants! Subway Ride 2013,” was expected to have a similar turnout as it did a year ago, when more than 600 BART and San Francisco Municipal Railway riders rode pants-free.

Riders were scheduled to come in two waves, and all will convene in from of City Hall in San Francisco for a group photo, according to the event's Facebook page, www.facebook.com/events/471254752925571/.

The first wave, coming from all stops on BART and MUNI will arrive at about 1:15 p.m. at Montgomery Station in San Francisco, according to the event page.

While that group walks down Market Street, the second wave of riders will meet up with them at about 1:35 p.m. at the Civic Center Station.

The event was described as improvisational to get reactions from people unaware of the day's plan.

Pants-free people were encouraged to walk into stores, bars, bathrooms and malls to get reactions from people, all while acting as if they were unaware why people are looking at them curiously.

This annual events has Facebook pages on events dating back to 2010, and was intended on being a light-hearted display.

Anyone interested in joining the pants-free participants were advised of four requirements: have a willingness to take pants off before boarding the subway; are able to keep a straight face; have at least $10 to ride on BART or MUNI (plus extra for bar visits); and absolutely no nudity.

The event can be followed through its Twitter feed at www.twitter.com/NopantsSF.