Under the plan by the Grand Penn Community Alliance plan, Penn Station will move above ground while Madison Square Garden is relocated.

Expanding the train station, the busiest in the nation, is a pressing issue because construction has just begun on a $16 billion pair of rail tunnels under the Hudson River, the centerpieces of a project known as Gateway, which would double the current cross-Hudson capacity.

With no movement on plans to redesign and renovate Penn Station, a public interest group is suggesting moving Madison Square Garden across the street and replacing it with a much bigger train station and park.