When is a train allowed to foul a main track according to switching protocols?

A train is allowed to foul a main track when the switch is connected with movement aligned. This means that the switch must be set in a position that allows the train to safely proceed without encountering any obstruction on the main track. This protocol ensures the safety of both the train and the operations on the main line, minimizing the risk of accidents that could occur if a train were to enter a section of track that is not properly aligned or if it were to conflict with another train's movement.

The importance of having the switch correctly aligned is paramount in maintaining operational safety and efficiency. When the switch is properly set, it directs the movement onto a track that is clear for passage, thereby preventing unsafe fouling of the main track where there may be other train movements.