Automatic Signals are of two types:
One with ‘A’ marker
Another with plate marking.
Fig: ‘A’ marker signal
Fig: Plate marker
Difference between ‘A’ marker and Plate marking.
Automatic signals are normally not monitored by the signal man. In case of failure of the system the signal might continue to display the danger aspect while the track is clear ahead. In such a situation driver might stop at defective signal & wait for the signal to clear. But as signal man is not monitoring the signal no one might realize about the defective signal. Because of such a possibility drivers are allowed to pass automatic signals at danger after waiting for 1 min during day time & 2 min in night. However some signals are required to work some times in automatic as well as manual mode. Such signals are provided with ‘A’ marker light. When the ‘A’ marker light is lit the driver is allowed to pass the signal at danger. If the ‘A’ marker is extinguished then driver has to wait till proper authority is to proceed is given (memo). If fixed ‘A’ plate marking is provided the signal is assumed to be in permanently automatic.