What is the procedure to pass an automatic signal displaying 'Z' or 'D'?

When an automatic signal displays 'Z' or 'D', the procedure requires the train operator to stop short of the signal and request permission to pass. This is crucial for maintaining safety protocols and ensuring that any potential hazards or unknown circumstances ahead are properly assessed.

The 'Z' signal indicates that the signal is in an intermediate position, and the 'D' signal typically indicates difficulty or a conditional proceed, meaning that there could be restrictions or other trains occupying the track ahead. Stopping gives the operator a chance to confirm conditions ahead either through communication with the dispatcher or by observing the track conditions directly. It helps to ensure that safety is prioritized and that the train can proceed only when it is safe to do so.

This procedure is part of adherence to signal rules governing train operations, which are in place to protect both the train and the passengers it carries. The necessity of waiting for permission is a key principle in the operational guidelines that govern safe rail travel.