Task: Question Generation
Input (English): Union Station is further served by four Amtrak lines: the Northeast Regional and the high-speed Acela Express provide service to New York, Washington, D.C. and Boston, and rank as the first and second busiest routes in the country; the New Haven–Springfield Line provides service to Hartford and Springfield, Massachusetts; and the Vermonter provides service to both Washington, D.C., and Vermont, 15 miles (24 km) from the Canadian border. Amtrak also codeshares with United Airlines for travel to any airport serviced by United Airlines, via Newark Airport (EWR) originating from or terminating at Union Station, (IATA: ZVE).
Output (English): Which transit lines out of Union Station are ranked as the busiest routes in the U.S.?