What is a deadhead train?

Answer: B — passenger train without any revenue passengers

A deadhead train refers to a passenger train that is operating without any revenue passengers on board. This situation can occur for various reasons, such as when a train needs to return to its originating point after completing its schedule or when a train is being repositioned for service. The term "deadheading" typically signifies that the train is not actively generating fare income during that journey. Understanding the context of why the other options do not apply is helpful. A train carrying freight only does not align with the concept of a deadhead train, since deadheading specifically involves passenger trains. Likewise, operating outside of scheduled hours describes a different operational condition that does not inherently suggest the absence of passengers. Finally, a maintenance train used in yard service pertains to trains designated for track upkeep rather than passenger transport, making it distinct from the idea of deadheading.