Is it permissible for a train operator to reverse the car motors?

Reversing the car motors can be a complex action depending on the operational protocols and safety guidelines in place for train operations. The correct answer indicates that reversing the motors is permissible under specific circumstances, such as to prevent a collision. In high-pressure situations where safety is at immediate risk, the ability to quickly reverse motors may be crucial in avoiding accidents, allowing for an effective response to unexpected obstacles on the tracks.

This practice emphasizes the critical nature of decision-making in emergency situations, where the priority is to ensure the safety of passengers, crew, and infrastructure. Operators are trained to assess their environment and make rapid decisions that prioritize safety, and reversing motors can be a tactical move to mitigate danger in such scenarios.

The other options highlight situations that either impose unnecessary restrictions or lack the immediacy required in emergencies. For example, requiring a supervisor's instruction might delay the necessary reaction time, while prohibiting such actions outright fails to recognize emergency exceptions. Thus, the correct answer incorporates the essential principle of judicious action in emergency scenarios while ensuring the safety of all involved.