The New York City subway system rebounded from the 1970s, when the city teetered on the edge of bankruptcy, crumbling cars routinely broke down and rampant crime scared riders away.

It survived the Sept. 11, 2001, terror attacks and Hurricane Sandy in 2012, which led to years of costly rebuilding and service disruptions. And it turned a corner after a spate of meltdowns and accidents in 2017 — including a derailment injuring dozens of riders — that prompted Gov. Andrew M. Cuomo to declare a state of emergency.

But now, the subway faces its worst financial crisis yet — one that threatens to hobble the system and have a lasting impact on the city and region.

As the coronavirus pandemic has shut down New York, over 90 percent of the city’s subway ridership has disappeared — along with critical fare revenue — leaving behind escalating expenses and an uncertain timeline of when and how the city’s transit lifeline will recover.