Transit agencies received $30.5 billion in pandemic relief from the American Rescue Plan passed in March. : (Bloomberg) -- With commuters slowly coming back and Congress considering a major infusion of cash for public transportation, mass-transit operators suddenly have a rare moment to invest for the future. But looking out over a sea of dire problems—including aging infrastructure, a backlog of repairs and the need to rebuild ridership in a Covid-scarred world—how is a system manager to decide what to tackle first? Researchers using an in-depth case study of the Massachusetts Bay Transit Authority in Boston have come up with an equation to prioritize repairs.