Yellow Red

What does the red, green, yellow light along a track mean, I know it is a signal for the engineers but forwhat

Now that they started a coummuter rail service in our area they had to install signals along the tracks where only freight trains would run before. It is one light that changes colors: yellow, red, green.

Green means the track is clear red means there’s a train coming I’m not sure about yellow, maybe it means it’s in the process of switching.

Red And Yellow – Escapist Trailer