What is indicated by a spring switch indicator showing that the switch is properly lined?

A spring switch indicator that shows the switch is properly lined indicates that the switch is aligned correctly for the route that a train will take. This means that when the indicator is in the correct position, it assures that the rails are set in such a way that a train can proceed safely without the risk of derailment or obstruction.

This safety feature is critical for rail operations; it acts as a confirmation that the train can navigate through the switch without encountering issues. The presence of a properly lined spring switch indicator enhances safety and operational efficiency, allowing trains to move smoothly along their designated tracks.

In contrast, the other options do not accurately represent the implications of a correctly lined switch. For instance, asserting that signals are unnecessary neglects the importance of communication and coordination in railway operations. Train operations still rely on signals to manage traffic and ensure safety across the network, regardless of the switch indicator status. Similarly, saying that further inspection is required would suggest uncertainty, while a properly lined indicator clearly indicates that the switch is ready for safe use.