"America's abandoned subway" -- The Cincinnati subway was started around the turn of the 20th century as a project to solve 2 problems: 1) Make use of the remains of the Miami-Erie canal. 2) Give the city of Cincinnati a transit system that would serve her population's needs over the next century.

The Miami-Erie canal was in declining use in the early 1900s due to the increasing national importance of the railroad and its inability to handle bigger and faster ships. So plans were made to drain its water and lay subway tracks down instead. The plan was to use 8 miles the canal, covered, as the main portion of a subway that would ultimately loop around and pass through the city center, to meet up with itself again.

Construction was begun on the canal portion, but due to projections of insufficient usage, the plan was reduced in scope, to one which would have a spur splitting off the end of the canal, and only run to downtown Cincinnati, rather than loop all the way around. Come 1917, the USA got involved in World War I and halted all government bonds, which the city had been relying on to fund construction. So construction halted, until after the war.

Construction was resumed, but corruption slowed progress and the Great Depression hit before work was started on anything beyond the canal section. Construction was halted again, and by the time the Depression was over, as well as World War II, automobiles were the predominant mode of transportation. This, combined with the cost of the project (steadily growing over the past 40 years), finally forced a complete shutdown of tunnel construction.

So, as there was still no link to the city center, and no spur at the far end of the canal, the Cincinnati subway ended up being a subway from nowhere important to nowhere important. While the canal section was complete, including tracks and stations, nothing else was.

Its fate was cemented when, after the Eisenhower Interstate system was initiated, the I-75 was built over significant portions of the intended route. And later, in the early 1970's, a major water main was run through most of the existing tunnel, rendering it unusable for trains, or much else.

To this day, all eight miles of the Cincinnati subway remains shut off and abandoned (although in perfect shape), a relic of turn of the century hopes and optimism, with not a single train ever having known its tracks.