What is the role of a "whistle board" in rail operations?

The role of a "whistle board" in rail operations is to indicate the location for sounding the whistle near public crossings. This is crucial for safety as it alerts motorists and pedestrians of an approaching train, thereby reducing the risk of accidents at intersections. The placement of the whistle board serves as a reminder for train crews to sound the whistle when they reach this designated point, ensuring that the warning is given at the appropriate time and location. This practice enhances public safety by making the presence of the train more noticeable to those near the track.

The other options do not accurately reflect the specific function of a whistle board. While some might involve aspects of train operations or safety, they do not pertain to the purpose of warning about crossings, which is the primary focus of a whistle board.