Possible Clues:

• Metroliner's successor
• Metroliner successor
• Speedy Boston-Washington connection
• Amtrak service
• Amtrak's express train
• Metroliner’s successor
• Amtrak express train between Washington, D.C., and Boston
• Amtrak service since 2000
• Northeast Corridor express
• Train for a game in Boston or D.C.?