As Amtrak studies how to bring bullet trains to its frantically busy Northeast Corridor, one design team is suggesting a radically new route requiring a roughly 18-mile-long tunnel beneath Long Island Sound.

Trains speeding from Washington to Boston would run through the heart of Long Island, cross into Connecticut through a tunnel emerging in Milford, head to Hartford and then race east toward Worcester on new tracks running alongside I-84.

Amtrak is focusing on its own “NextGen High-Speed Rail” map for the corridor, a proposal that would skip the Long Island section and cost an estimated $151 billion. But PennDesign’s plan isn’t off the table.