If a pusher locomotive is not used on a trip, what is required?

When a pusher locomotive is not utilized on a trip, it is essential for the locomotive operator to have an assistant to ensure safe and effective operation. The presence of an assistant helps to enhance communication, facilitates a higher level of situational awareness, and provides support during the trip, particularly in terms of monitoring the train's performance and handling any operational challenges that may arise. This requirement acknowledges that the absence of a pusher locomotive may introduce additional risks, and having an assistant can help mitigate those risks, promoting overall safety in locomotive operations.

Regarding the other options, while having a radio communication device is certainly important for safety, it is not a direct substitute for having an assistant. Similarly, additional signage along the track or enhanced safety training might be beneficial under certain circumstances, but they do not fulfill the immediate operational and safety needs that an assistant can provide during a trip without a pusher locomotive.