“The federal aid gives them three years to restructure their operations to be more efficient,” said Andrew Rein, the president of the Citizens Budget Commission, a financial watchdog. “If they don’t use this time to do that, they are going to be back to where they started, which is not having enough money to run the system because it’s too expensive.”

In New York, transit officials said that the latest infusion of federal aid will allow them to bring back some service on the Metro-North Railroad and the Long Island Rail Road, which suffered higher ridership losses than the subway or buses.