A railroad apartment (or railroad flat) is an apartment with a series of rooms connecting to each other in a line. The name comes from the layout's similarity to that of a typical (mid-20th century or earlier) passenger train car.
This style is most common in New York City, San Francisco, and their surrounding areas. Railroad apartments are common in tenement buildings or even modern apartment blocks, and are sometimes found in subdivided brownstones.
Railroad apartments first made an appearance in New York City in the mid-19th century, and were designed to provide a solution to urban overcrowding. Many early railroad apartments were extremely narrow, and most buildings were five or six stories high. Few early buildings had internal sanitation, and bathrooms emptied raw sewage into the back yard. In some cases, one family would take up residence in each room, with the exterior hallway providing communal space.
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