Hi all, wonder if anybody with knowledge can educate me about this. I'm joining Network Rail as a signaller soon so I've been paying extra attention to signals etc when out and about in anticipation.

I was on a train yesterday, watching the signal aspects change through the window. A couple of times when passing I saw the signals go from clear to caution. I was under the impression that once the track circuits or axle counters told the system a train was occupying that block, the protecting signal would go to danger.

Is there any reason why the signal would go to caution instead? Could it be that it cycles through the aspects for some reason? Or possibly that they are distant signals rather than stop signals?

This is on the Merseyrail network and they are new style colour light LED signals, if it helps.