The Cincinnati Subway has an astonishing history. In the early 20th century, Cincinnati, Ohio suffered from major traffic congestion and so it was suggested that a subway system be built to help relieve the problem. Using bonds issued before the outbreak of the World War I, construction was started however after being halted for a time, the costs had doubled and even though construction resumed following the war, the money ran out with 11kms of subway tunnels dug out but with no tracks laid.
The subway was constructed in a disused canal on top of which the Central Parkway boulevard was built. It opened in 1928. To date there have been no solid plans to finish construction however lots of photos and videos exist as the underground tunnels have become a favourite destination for urban explorers.
Some FAQs about the Cincinnati Subway from http://www.cincinnati-transit.net/subway.html where there is lots more information for those interested -
1. Where is the subway?
The main subway tunnel runs under Central Parkway for two miles, between Walnut St. and an anonymous spot north of the Western Hills Viaduct. Three underground stations were built and still exist at Race St., Liberty St., and Brighton's Corner. An extension of this tunnel under Walnut St. south through downtown with a station at Fountain Square was planned but never built. Additionally, several miles of surface running line were graded and three of roughly a dozen planned above ground stations were built. Significant portions of today's I-75 and the Norwood Lateral follow the path of the line. A stretch of I-71 near the Dana Ave. interchange was built where the subway loop's eastern half was planned.
2. When was it constructed?
1920 through 1925. The $6 million bond issue in 1916 was exhausted in 1925, no further money was obtained, and construction never resumed.
3. Can the tunnel still be used?
Yes. It has been continuously maintained and will likely be usable for the next hundred years, if not longer. The 2002 "Metro Moves" sales tax would have funded a rail transit network that planned to use the tunnel, but it was defeated by a 2-1 public vote.
Location: Cincinnati, Ohio, USA