Why must a train not proceed on a hand signal against fixed signal indications?

A train must not proceed on a hand signal against fixed signal indications because the hand signal may be incomplete or misunderstood. Hand signals rely on visual communication that can be subject to various interpretations based on factors like visibility, the operator's situational awareness, or even environmental conditions. If a train were to take action based solely on a hand signal that is misinterpreted or not fully understood, it could lead to dangerous situations, such as collisions or other accidents.

In contrast, fixed signals are standardized and designed to provide unequivocal guidance to train operators. They convey clear instructions regarding whether a train should proceed, stop, or prepare to change its speed. This clarity is crucial for maintaining safe operations on the railway. Therefore, the inherent potential for error with hand signals emphasizes the importance of adhering strictly to fixed signals to ensure safety.