Upon receiving a signal to slow down due to work on the tracks, what distance can a train operator expect the resume speed signal to be placed beyond the work?

The appropriate distance for a resume speed signal to be placed beyond track work is typically determined by safety regulations and operational protocols established by railway authorities. The correct answer reflects a standard practice within the industry, which designs this distance to ensure that the train has enough time to safely accelerate back to its normal operating speed after the area of work.

The placement of the 600 feet distance takes into account multiple factors, including the train's speed, braking capabilities, and the physics of train movement. This buffer zone allows for a smoother transition back into normal operations, minimizing the risk of accidents or operational issues that could arise if trains sped up too soon. Additionally, the signal placement at this distance aligns with established safety measures aimed at protecting both the crew and any workers present on or near the tracks.

In contrast, the other distances provided in the options do not align with these safety considerations, as they may not provide adequate time for the train to respond and resume a safe speed. This makes 600 feet the most appropriate choice based on standard protocol in train operations regarding work zones.