On the west side of South Philly, the 25th Street Elevated rail viaduct clearly defines it the boundaries of the Grays Ferry and Point Breeze neighborhoods. Over a dozen trains, including oil trains like the one that derailed over the Schuylkill River recently, rumble its weathering 86-year-old bones every day. Chris Dougherty goes back a century to find the Elevated’s origins in the heyday of the rail industry—and civic reform