What speed must a train proceed at when moving past a Stop signal that has been authorized to move?

When a train is moving past a Stop signal that has been authorized to move, it is required to proceed at a restricted speed. This speed allows the train to remain under control, ensuring it can stop quickly if necessary, such as when encountering other trains, obstructions, or hazardous conditions on the track.

Restricted speed is defined by rail regulations and typically means traveling at a speed that permits the train to stop within half the range of vision. This context is crucial for maintaining safety in rail operations, particularly in areas where visibility may be limited or where other unexpected conditions may occur.

The other options propose various speeds that do not prioritize the safety and control necessary in situations where a Stop signal was previously displayed. Full speed, medium speed, and half speed all imply a greater speed than what is advisable when approaching potentially unpredictable situations after a Stop signal.