What defines a controlled block?

Answer: B — block governed by a series of controlled signals in CTC territory

A controlled block is characterized by being governed by a series of controlled signals, particularly in Centralized Traffic Control (CTC) territory. This indicates that the movement of trains within these blocks is directed and managed through signals, ensuring that the traffic flow is orderly and efficient. The use of controlled signals allows for real-time adjustments to be made based on the operational needs, improving safety and facilitating better coordination of train movements. In contrast, other options focus on specific circumstances or characteristics that do not encompass the broader definition of a controlled block. For example, a block between two block limit signals primarily defines the physical separation of train movements but does not indicate whether the signals are controlled or not. Similarly, a block occupied by deadhead trains or one used only for light engine movements describes particular situations but does not relate directly to the control mechanisms in place within that block. Thus, the essence of a controlled block lies in its governance by active signal control, making option B the accurate definition.