That is Distant Signal (Inner) & relies on Next Signal either Home Signal or Gate Signal if any to change its status to Yellow. There is no track circuit to detect the passing of train. Also this is Permissive Signal, meaning there is no Red here. Just Yellow, Double Yellow or Green.


Watch the video till the end again, As soon the...
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Loco crosses the Home Signal, which is the next signal after this, This Distant signal turns to Single Yellow.

There will be another signal behind this called Distant Signal or (Outer Distant/First Distant) that may also change or Stay as it is depending upon which line Train is received in Station. Will be Green for Main line pass or Stop or will be Double yellow if Loop line stop or Pass through. Default status will be Double Yellow only.