Which condition allows a main track switch to remain open?

A main track switch can remain open when attended by a crew member because the presence of an individual directly overseeing the switch provides safety and control. The crew member can ensure that the switch remains in the correct position for movements, allowing for safe operations. This supervision helps prevent accidents that could occur if the switch were left open unsupervised, where it could pose a danger to trains traveling along the main track.

In railway operations, there are strict protocols governing the status of switches, and having a crew member physically present mitigates risks. The presence of personnel allows for immediate action in case any unexpected situations arise. Therefore, this condition reinforces the importance of human oversight in areas where safety is paramount.