What is the normal position for a main track switch to allow movement on the main track?

The normal position for a main track switch to allow movement on the main track is when it is lined and locked. "Lined" indicates that the switch is set in the correct position to direct trains along the main track, ensuring that they can pass through safely without being diverted onto a siding or a different track. "Locked" means that the switch is secured in that position, preventing accidental movement which could lead to derailments or collisions. This combination of being both lined and locked is crucial for maintaining safety on the track and ensuring smooth operations for trains traveling on the main line.