Amtrak's Downeaster ACSES Test Train, with 50th Anniversary P42DC #46, ducks under the Boston University Bridge as it crosses the Grand Junction Railraod Bridge on the MBTA Grand Junction Branch in Boston, Massachusetts during the afternoon of July 21st, 2021. The train is heading back to Southampton Street Yard after completing a round trip to Portland on the Downeaster route and is crossing to the "south side" via the Grand Junction Branch. This area is one of the few places in the world where a boat can sail under a train running under a car driving under an airplane.