What does a round, black on yellow warning sign indicate?

A round, black on yellow warning sign is specifically used to alert drivers about the presence of railroad tracks. This design serves as a clear signal that the driver should slow down, look for any trains, and listen for any sound indicating an approaching train. This is critical for ensuring safety at railroad crossings, where vehicles may encounter trains unexpectedly.

The choice indicating a school crossing typically uses a pentagon shape and is designed in a different color scheme to ensure visibility during times when children are likely to be present. A low overpass warning, which helps drivers anticipate height restrictions, is represented with a rectangular sign, not a round one. Lastly, a hospital zone warning would typically be marked with a different symbol and coloration and would not use the round, black on yellow configuration. Therefore, the round, black on yellow sign is distinctively designed to focus on train crossings and convey the appropriate caution needed for those situations.