Cincinnati Subway

The Cincinnati Subway is a set of unused tunnels and stations for a rapid transit system beneath the streets of Cincinnati, Ohio. It is recognized as the largest abandoned subway tunnel in the United States. Construction took place in the early twentieth century, but the project was not completed so it never hosted a paying customer.

The project has been described as "one of the city's biggest embarrassments," and "one of Cincinnati's biggest failures." Some argue that because rapid transit was never completed, that Cincinnati is smaller, forces its citizens to be automobile-dependent, has its downtown area dominated by highways and parking lots, lacks "walkable communities," motivates people to live outside of the city, and has spawned today's traffic jams. Others say it would have been abandoned anyway due to waning ridership, as was the case with the city's original streetcars and the Mount Adams Incline.

Proposals to complete the subway have been near continuous since its initial failure, but all attempts to use the tunnels for transit have failed thus far. Many Cincinnatians do not know subway tunnels exist under their city.