What method of communication should be used if a customer train must be run from other than the head end on the road?

The appropriate method of communication in the scenario where a customer train must be run from a location other than the head end on the road is the use of a sound powered-telephone or radio. This method is essential because it allows for clear, direct communication between crew members who may be positioned at different points along the train. Such communication is critical for ensuring safety and coordination, particularly when the train is being operated in a way that could lead to unexpected situations.

Sound powered-telephones are self-powered communication devices that work well in environments where other forms of communication might fail, such as during power outages or in areas with poor radio signal. Having this reliable method enables the crew to maintain constant communication while executing necessary operational adjustments or responding to any issues that arise during the train's movement.

While ground-based radios provide a similar method of communication, they may not always be available or functioning, making sound powered-phones a safer fallback option in emergencies. Other methods such as visual signals are limited in their ability to convey complex information and might not be effective over long distances, especially when immediate response coordination is required. Smoke signals, while historically significant, are impractical and not used in modern train operations due to their limitations and the invention of more efficient communication technologies.