For generations, New York City transportation planners have dreamed of a unified, regional transit system that would allow commuters to ride from New Jersey to Long Island without transferring. Gone would be the days of buying separate tickets from separate agencies run by separate states.

The idea to unite New York and New Jersey’s busiest railroads has long been dismissed by elected officials on both sides of the Hudson River for logistical and political reasons. But now the time may finally come. As President Donald Trump pushes ahead with a federally run renovation of Penn Station and crews build a new set of rail tunnels beneath the Hudson River, supporters say there’s a rare opportunity to reorganize the entire rail network.

Most of the attention to Trump’s redevelopment of the nation’s busiest train station has focused on converting its labyrinthine layout into an architectural marvel filled with natural light. One plan under consideration would move Madison Square Garden across the street. But the much-needed aesthetic improvements to Penn have arguably distracted from a more pressing problem: In the coming decade, Penn Station is going to run out of room.