What is the maximum authorized speed on a secondary track or siding?

The maximum authorized speed on a secondary track or siding is considered restricted speed unless otherwise provided. This means trains must proceed cautiously, ensuring they remain vigilant of any potential obstacles or conditions that could affect safe operations. Restricted speed is particularly important in less controlled environments where the risk of encountering work zones, other vehicles, or differing track conditions is higher.

This speed guideline ensures that train crews are prepared to stop within half the range of vision, which adds a significant layer of safety by allowing for quick reactions to unexpected situations. In contrast, the other options suggest speeds that do not prioritize these safety measures, indicating higher speeds without the necessary precautions that restricted speed mandates.