When is it acceptable to sound the whistle signal less than 15 seconds before a crossing?

The correct choice indicates that sounding the whistle signal less than 15 seconds before a crossing is acceptable when the crossing is clearly visible and safe. This is grounded in safety regulations and practices that prioritize the well-being of both train operators and the public.

When a train approaches a crossing that is clearly visible, the crew can assess the area and determine whether it is safe to sound the whistle signal at a shorter notice. This area of visibility allows for better situational awareness, enabling the crew to confirm that there are no obstructions or hazards that would compromise safety. Essentially, the primary goal is to ensure that the warning is effective while still complying with safety protocols designed to alert anyone near the crossing of the train's approach.

The other choices do not align with safety practices. Approaching a station typically involves more complex operational considerations that may not justify compromising the standard whistle signal timing. Disturbing nearby residents is not a valid reason to modify safety signals, as the priority remains public safety over community noise concerns. Lastly, leaving the decision to whenever the crew decides lacks a foundation in established procedures, which are vital for consistent and safe operational standards.