On March 18, 2020, as the Covid-19 pandemic began to rage in New York, and two days after the city shuttered its schools and four days before the city forbade white-collar workers from coming to their offices, New York’s Metropolitan Transportation Authority, which runs the regional subway, bus, and commuter-rail system, warned investors in its nearly $44 billion in municipal debt: “People may permanently alter their commutation behavior after this crisis.”

The statement proved prophetic. Three years later, even as American life has mostly returned to normal, with planes and restaurants full, the nation’s mass-transit systems still struggle with double-digit ridership declines. American public transit faces its biggest crisis since city dwellers deserted cramped apartments and sweaty subways for suburban homes and the private car, beginning a century ago. The transit crisis is also an urban crisis. Successful cities thrive on density; transit enables it. Unless Congress, governors, and mayors figure out how to get more people back on trains and buses regularly, the already brittle urban success story of the twenty-first century will crack.