In the early 1920s, the city of Rochester, New York, faced a unique urban planning dilemma paired with an unprecedented opportunity. The original route of the Erie Canal passed directly through the heart of downtown Rochester, running along a stone-lined channel and across a massive stone aqueduct over the Genesee River. When the state constructed the enlarged New York State Barge Canal in 1918, it rerouted traffic south of the city, leaving the downtown canal bed completely dry and abandoned.
Rather than filling in the massive trench at immense cost, Rochester city engineers conceived a bold scheme: convert the drained canal bed into an underground rapid transit system. From 1921 to 1927, workers roofed over the open canal ditch, turning it into a covered subway tunnel, and built a deck on top to serve as Broad Street. The electric streetcars and interurban trains running inside the former canal bed alleviated surface congestion while connecting the city's rail lines.
The system operated for nearly three decades until private automobile dominance led to its shutdown in 1956. Today, the abandoned canal-bed subway remains one of America's most famous subterranean ghost networks, showcasing a unique era of infrastructure adaptive reuse.