When the Erie Canal was rerouted around downtown Rochester, New York in 1918, city leaders were left with an immense piece of obsolete infrastructure: the Broad Street Aqueduct and miles of open canal bed cutting directly through the urban core. Rather than filling in the massive ditch, the city embarked on an ambitious engineering experiment in 1921 by building the Rochester Industrial and Rapid Transit Railway directly inside the abandoned canal channel. To preserve valuable surface real estate, engineers roofed over the downtown section of the canal bed, creating a new street level above while turning the former aqueduct and ditch below into a rapid transit subway tunnel.
Opened in 1927, the line stretched over seven miles, serving both as a commuter subway for local residents and an interurban freight connection that allowed interurban electric trolleys and freight cars to cross the city without clogging surface streets. However, the subway's success was short-lived. The rapid rise of post-WWII private automobile ownership, expanding suburban highways, and the decline of interurban trolley traffic severely eroded ridership.
Because the route followed the old canal path rather than expanding residential neighborhoods, it failed to serve postwar commuters effectively. In 1956, passenger service was officially terminated, leaving the cavernous concrete aqueduct and subterranean tunnels abandoned to graffiti artists and urban explorers.