In all U.S. cities with over a 1 million population, Philadelphia sports the highest percentage mode of bicyclists. In 2012, the U.S. Census estimated Philadelphia’s bicycle commuting rate at 2.3%, higher than Chicago (1.6%) or New York (1.0%)
It's just about always been that way. In a city that doesn't have a lot of fancy newfangled bike lanes or bike infrastructure, that often surprises many. But there are a myriad of reasons why.
For one, Philadelphia has a very narrow street grid which - unfortunately - doesn't allow for ample room to paint bike lanes in many neighborhoods, but it does have the effect of producing streets where cars and bikes are sharing the road at a reasonable speed. That means bikes are sometimes squeezed but that the slower pace makes biking feel more like a negotiation with drivers. Street users come to frequent stops at intersections thanks to 4-way stops. The traffic light sequencing is short. And the city's residents also tend to live closer to their jobs than most other places, making biking more of an option.
Thanks to Alex Doty, the Executive Director of the Bike Coalition of Greater Philadelphia, you'll hear many more reasons why there are a good many cyclists in his city. But in the end most people use the bike because it is the fastest, most logical option.