What must be operational for trains operating over public crossings at speeds greater than 20 mph?

The requirement for trains operating over public crossings at speeds greater than 20 mph to have at least one operable auxiliary light is grounded in safety protocols designed to enhance visibility and alert motorists and pedestrians of an approaching train. Auxiliary lights serve as a warning mechanism, and their operation is crucial in reducing the risk of collisions at crossings. The designated speed of over 20 mph indicates a higher risk level, thus necessitating additional safety measures such as having at least one operable light.

While options suggesting the use of two auxiliary lights, no auxiliary lights, or a flagman at each crossing may seem plausible under certain circumstances, they do not meet the specific requirement set for the conditions presented in this scenario. Two lights may enhance visibility further, but the minimum requirement is just one. Not having auxiliary lights would not fulfill safety requirements, and relying solely on flagmen is not a standard practice for every crossing due to resource constraints and operational efficiency. Therefore, ensuring that at least one auxiliary light is operational is the essential focus for enhancing awareness at public crossings when trains operate at higher speeds.