There is a bus in Philadelphia which SEPTA does not talk about.  It is not listed on the website.  It has neither schedule nor route.  It drives the city in a pattern known only to its driver, and perhaps not even to him.  Its electronic reader board never displays a number, only “SEPTA.”  People who know it call it the Zero, the Random Bus, the Wandering Bus, or just The Bus.  It is not a bus for people who know where they want to go.  It is a bus for departures.