The New York subway became the word’s largest mass transit system shortly after it opened in 1904. Today, it carries fully one-third of all mass transit passengers in the United States. But after decades of neglect, New York’s once great subway is nearing collapse.

An enormous renovation effort will transform the city’s subways and commuter rails into the most technologically advanced mass transit system in the world – that is, if all goes as planned. Structural engineers grapple with the difficulties of updating the transit system whilst still keeping it open to the public, and city planners work to strike a balance between attracting even more people to the city and transporting them effectively.