SEPTA customers may think they have seen it all, but Sunday riders can expect an eyeful.
Passengers will go pantsless while taking the Broad Street and Market Frankford subway lines for two hours as part of the 13th annual No Pants Subway Ride.
"Our riders seem to get a laugh out of it," said Andrew Busch, a SEPTA spokesman.
The Philadelphia Urban Playground is organizing the local event, which will take place from 3 p.m. to 5 p.m.
At least 58 people plan on exposing their thighs while riding the train Sunday, according to a Facebook page for the event.
Urban Playground is instructing anyone interested in participating to gather at the southwest corner of Broad and Arch streets. From there, the still-clothed crowd will head to the City Hall subway stop to board the Broad Street Line towards AT&T Station.
Once inside a car, they'll drop trou.
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The pants-free passengers will circle back north on the orange line, then transfer to the blue line at City Hall. They'll head eastbound to the Frankford Transportation Center, where they will wrap up the ride and their legs.
Urban Playground warns all participants to "please wear underwear" while riding sans slacks.
Busch says the eye-catching event has not caused any problems in previous years, but security will step in if the partakers take it too far.
SEPTA employees will remain dressed, he added.
Philadelphia is one of more than 50 cities participating in the worldwide event.
Improv Everywhere, a New York-based prank collective, launched the pantsless public transit ride in New York in 2002. The group had a simple mission when they created the No Pants Subway Ride - to make others laugh and smile.