Photo a Whenever: Photo 124. This is a picture of the Interborough Rapid Transit (IRT) 7 train Flushing Line elevated track at Court Square in Queens, NY.
The NYC subway system was built by three different companies, the IRT, the Brooklyn–Manhattan Transit Corporation (BMT), and the Independent Subway System (IND), which was run by the city. Because the subway system was built by competing companies, they didn’t build transfers between their lines, and would even go out of their way to make it difficult to transfer or for the other company to build competing service.
Where this picture is taken, there is also underground service from two IND lines, serving three other trains, the G, E, and M. It wasn’t until June 3rd 2011 that a transfer was built between the IRT 7 line and the IND G,E, and M lines even though the stations are right above one another.