Though we are generally free to go where we choose, there are still certain places we are unlikely to go.We have boundaries that we are unlikely to cross, the result of prejudices, routines, and networks of other people that create these boundaries and put both physical and psychological space between ourselves and others.

Trains, on the other hand, will cross boundaries that people typically will not. The Red Line of Chicago's elevated train, known as the “L,” travels a straight line from north to south. Unlike other lines, it doesn't eventually bend to the west and it doesn't split and offer you a choice of branches. Nor does it circle around, like the trains in the downtown Loop, sending you back where you came from. If a Red Line train starts on the north side of the city, there is nowhere to go but south. Coming from the south side, there is nowhere to go but north. Either way, the train crosses a boundary that its riders typically do not.

In Chicago, the boundary between north and south is the boundary between white and Black. It is not a sharp boundary like an international border; there are complexities, such as the racially integrated Hyde Park neighborhood and an Irish-Catholic neighborhood, Mount Greenwood, on the South Side. But everyone in Chicago knows the boundary is there and most accept that the other side is a place you shouldn't go. For a white person in Chicago, the South Side is a void, populated only by stereotypes.When a tourist – usually white – unfolds a map of Chicago, the South Side isn't even shown. Chicagoans don't travel from north to south or south to north because there is not only a physical distance between these two parts of the city, but also – and much more importantly – a psychological distance.