Switching locomotives at Union Station, Wash DC

The passenger train tracks north of DC comprise what is called the Northeast Corridor. Fully electrified, this is the busiest rail corridor in the US. The electrification ends at DC though, so when traveling south it is necessary to change the train's locomotive from an electric traction unit to a diesel unit. Here engineers switch an electric EMD AEM-7AC for a diesel GE Genesis P42DC engine.