History: The New York City Subway, United States

At most of the system's entrances and exits sits a lamp post or two bearing a colored spherical lamp. Before the introduction of the MetroCard in 1994, these lights indicated the station's availability. A green lamp meant that the station was open and running 24 hours a day, a yellow lamp meant that it was open only during the day, while a red lamp meant that it was an exit-only. The yellow lamp was phased out and replaced by red lamps, which takes over the role of both a part-time entrance and exit-only.
• Platforms
A typical subway station has waiting platforms ranging from 500 to 600 feet (150 to 180 m) long. Due to the large number of transit lines, one platform or set of platforms often serve more than one service. Passengers need to look at the overhead signs at the platform entrance steps and over each track to see which trains stop there and when, and at the arriving train to see which one it is.
There are a number of common platform configurations: