Chicago Deep Tunnel (1975-present)
Chicago began building the Tunnel and Reservoir Plan in 1975, a network of deep tunnels designed to capture stormwater and sewage that previously flooded basements and polluted waterways. The system now spans more than 100 miles of tunnels.
The tunnels captured increasing volumes of overflow as sections came online, reducing flooding and pollution.
The project is still being completed decades later, with costs far exceeding initial estimates.
Shows how deep tunnel sewer projects can take decades and grow in scope, offering a cautionary comparison for Pittsburgh's timeline.
