When must a train not pass a stop signal?

A train must not pass a stop signal as a fundamental safety measure to ensure the railway operations remain safe and controlled. The conditions provided by the choices outline specific scenarios where passing a stop signal may be permissible, but generally, the rule dictates that under regular circumstances, a train must halt.

In the case of having the proper signal indication, it is crucial to understand that the signal indicates whether it is safe to proceed. When the signal is at stop, it means that the train must halt, as proceeding could lead to potential collisions or other safety hazards.

Authorization by Rule 241 or Form L is another important context. These mechanisms provide specific instances where a train may pass a signal at stop, usually pertaining to a controlled or authorized movement under certain conditions that ensure safety.

Traveling at less than 10 mph is also significant, but it does not inherently allow a train to disregard a stop signal. The underlying principle remains that regardless of speed, the signal's indication must be respected.

Each of these aspects contributes to the overarching rule that a train must not pass a stop signal unless specific authorized conditions are met. Therefore, recognizing the necessity of compliance with signals to ensure safe operations is paramount in the operational rules of the LIRR.