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 <answer>United Airlines</answer> for travel to any airport serviced by <answer>United Airlines</answer>, via Newark Airport (EWR) originating from or terminating at Union Station, (IATA: ZVE).
In additions, the train line is also connected with which airline services?
United Airlines