You must stop 50 feet, but not less than __________ feet from the nearest rail of the railroad when a human flagger is warning of an approaching train.

When a human flagger is warning of an approaching train, the law requires that you stop at least 50 feet from the nearest rail of the railroad tracks. This rule is put in place to ensure safety and provide enough distance for the flagger and oncoming trains to operate safely. Specifically, the requirement stating "but not less than 15 feet from the nearest rail" ensures that drivers maintain a sufficient buffer zone to avoid dangerous situations when a flagger is present. Stopping too close to the railroad could result in accidents, especially if a train approaches unexpectedly.

Maintaining this 15-foot minimum distance helps give drivers enough reaction time and avoids any potential for vehicles to be caught too close to the tracks while waiting for the flagger’s signal. Ensuring compliance with this distance is vital for the safety of both drivers and train operators. Other distances provided in the choices are less than this minimum requirement and do not offer adequate safety measures under these circumstances.