What do restricted speed instructions indicate?

Answer: B — Trains must proceed slowly to avoid obstructions

Restricted speed instructions are critical for ensuring safety in rail operations. They indicate that trains must proceed slowly to avoid obstructions that may be present on or near the tracks. This concept emphasizes the importance of caution under specific circumstances, such as when approaching a work zone, navigating through areas where visibility may be limited, or when the potential for obstacles exists, such as other trains or equipment on the tracks. By following restricted speed instructions, train crews can react adequately to unexpected situations, ensuring safety for personnel, equipment, and rail infrastructure. This approach helps in preventing accidents and provides a necessary margin of safety when operating under potentially hazardous conditions.