What might the signal indicating restricted speed advise about the conditions ahead?

The signal indicating restricted speed specifically advises that the crew should prepare for conditions that may not be ideal ahead, such as a switch or track work. Restricted speed requires a train to operate at speeds that allow it to stop short of any obstruction or hazard. This is crucial for safety when approaching track areas that may have changes in alignment or ongoing work that could affect train operations. The indication of potential track work or a switch suggests that trains should proceed with caution, ensuring they can react to any unexpected situations.

In this context, the other options do not accurately reflect the implications of a restricted speed signal. For example, a dangerous situation in the next block refers to an immediate risk, while clear visibility and absence of track limits would not necessitate a reduction in speed. These options do not align with the fundamental purpose of the restricted speed signal, which is to ensure safe operations in uncertain or changing conditions ahead.