When the Three Rivers operates from New York to Philadelphia it uses an electric locomotive (usually an AEM-7) due to operation through the tunnels in New York and local law prohibiting diesel trains in Manhattan. On this portion of the route, the train is actually run backwards with the coach seats facing the wrong way.
At Philadelphia, the electric locomotive is removed from the south end of the train and diesel locomotives are put on the opposite or north end of the train. This was the end that was the back of the train coming from New York. When the train leaves Philadelphia, now facing forward, it exits the Amtrak Northeast Corridor at a large junction called “Zoo” located about 2 miles (3 km) from the Philadelphia station and heads west on the Amtrak Harrisburg line. West of Harrisburg it runs on tracks owned by the Norfolk Southern RR and still later, CSX Transportation.