Question: BWI Rail Station is served by which Amtrak flagship service?
Context: The BWI Marshall Airport Shuttle is a free bus service provided by Baltimore–Washington International Airport, that connects the airport terminal to BWI Rail Station.  The free shuttle connects airport passengers to Amtrak and MARC trains, hence connecting the airport to Baltimore and Washington, D.C., as well as the rest of the Northeastern United States. BWI Airport station is a train station located in an unincorporated area within Anne Arundel County, Maryland.  It is served by Amtrak intercity services (frequent "Northeast Regional" and "Acela Express" trains plus the daily "Vermonter" and "Palmetto") and MARC Penn Line regional rail service. The Greenbelt–BWI Thurgood Marshall Airport Express Line (commonly shortened to the Greenbelt–BWI Airport Line), designated Route B30, is a weekday-only bus route operated by the Washington Metropolitan Area Transit Authority between Baltimore-Washington International Thurgood Marshall Airport and the Greenbelt Metro Station of the Green Line of the Washington Metro.  The line operates every 60 minutes five days a week along the Baltimore-Washington Parkway between these two locations with no intermediate stops, with the exception of the BWI Business District Light Rail Stop, and the last bus leaving BWI at 10:01 pm.  The trip is approximately 29 minutes long. The BWI Business Partnership LINK Shuttle is a free bus service provided by the BWI Business Partnership that circulates the BWI Business District surrounding the Baltimore–Washington International Airport, as well as military installations and defense contractors located at Fort Meade.  The free shuttle provides last mile connections for employees and visitors in the area by connecting businesses and hotels to the BWI Rail Station, served by the MARC Penn Line and Amtrak, as well as the Baltimore Light Rail at the BWI Business District Light Rail station. 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.  The route contains segments of high-speed rail, and Acela Express trains are the fastest trainsets in the Americas; they attain 150 mph on 28 mile of the route. Burbank-Bob Hope Airport is an unstaffed Amtrak and Metrolink rail station at Bob Hope Airport in the city of Burbank, California.  It is served by both Amtrak's "Pacific Surfliner" from San Luis Obispo to San Diego and Metrolink's Ventura County Line from Los Angeles Union Station to east Ventura.  The ten "Pacific Surfliner" trains that serve the station daily and 29 Metrolink trains that serve the station each weekday connect arrivals from the airport to downtown Los Angeles' Union Station in about 30 minutes.  Amtrak's "Coast Starlight" which travels between Seattle, Washington and Los Angeles also stops here. Coatesville is an Amtrak rail station located in the far western suburbs of Philadelphia at Third Avenue and Fleetwood Street in Coatesville, Pennsylvania.  It is served by most Amtrak "Keystone Service" trains.  An old railroad station building exists at the stop, but is not currently used.  There is no ticket office at this station.  Coatesville is one of the least-used stations on the Keystone Corridor east of Harrisburg.  This may be due to a lack of parking as well as its proximity to Thorndale Station on the SEPTA Paoli/Thorndale Line.  SEPTA once served this station until 1996 when the agency was forced to close a $75 million gap and has since truncated its service. BWI Business District station is a Baltimore Light Rail station in the BWI Business District, north of the Baltimore-Washington International Airport in Linthicum, Maryland.  There are currently 36 free public parking spaces and connections can be made to MTA Maryland's Route 17 and 99 buses, WMATA's B30 express bus, and Howard Transit's Silver Route from this station.  Additionally, portions of the BWI Trail can be found across the street from the parking lot. Linthicum station is a Baltimore Light Rail station in Linthicum Heights, Maryland.  This station is the last station on the light rail's trunk line; southbound trains depart onto branches to BWI Marshall Airport station and Cromwell station.  There is currently no free public parking or bus connections at this station. Fresno is a California High-Speed Rail station being constructed in Fresno, California; the groundbreaking ceremony for the system was held at the station site on January 6, 2015.  The first purpose-built high speed rail station in the United States, it is part of the system's Initial Construction Segment.  The facility is located in Downtown Fresno at H Street between Fresno and Tulare Streets, and is about 7 blocks south from the existing Fresno Amtrak station.  The high-speed rail line runs along the right-of-way of the Union Pacific Railroad at this location.
Answer: Acela Express