Think about the effect of the aspects seen on the way the driver would drive his train. IF he is due to stop in the station, and intends to have a "normal" sort of brake application to achieve that, he will start braking at normal braking away from the platform. Up to that point he has been on green (he only sees the YY because he is catching up the stopping train which is about to move away) and hence until the sighting point of the YY the presence of the train ahead is of no consequence to him. The brake application at this point does not affect his time to clear the section becasue he has to brake for the station anyway.
I hope I have managed to explain that clearly.
Peter (the other one)
I hope I have managed to explain that clearly.
Peter (the other one)