Throughout history, there were plenty of city plans that never really worked out. As an example, look no further than the subway system of Cincinnati, Ohio.
In contrast to the current decline of the city, at the beginning of the 20th century, things were looking bright for the booming town.
It was decided that the streetcar system needed to be replaced. A subway system was drawn up and constructed to fit the bill. Only two problems—it was never finished, and it never provided service to a single passenger!
WWI, then the Depression, and finally WWII postponed the subway indefinitely.
In hindsight, the whole ordeal is seen as a shameful and humiliating period in Cincinnati's history. As if all the waste weren't enough, the failure to complete the subway potentially caused a loss of growth. Its residents have become highly reliant on automobiles, leading to expansive areas in the city being cluttered up with roadways and parking lots. Traffic jams have become an all-too-common problem. Residents are therefore forced to deal with the many inconveniences of Cincinnati's infrastructure.
Various proposals have been made to complete the subway, but nothing has gotten off the ground. Only time will tell if it will ever be put to good use a century after it's inception.