Question: which Amtrak's flagship service along the Northeast Corridor is  currently the only services in the country
Sentence (from "Acela Express"): The Acela Express ( ; colloquially abbreviated to Acela) is Amtrak's flagship service along the Northeast Corridor (NEC) in the Northeast United States between Washington, D.C. and Boston via 14 intermediate stops including Baltimore, Philadelphia, and New York City.
Relevant evidence: Yes