Train from Cardiff arrives at Ystrad Rhondda station. The train stopped at the platform on the left has been waiting for the arrival of this train, because the line ahead is single track (just beyond the stop signs with a large red spot). The Cardiff-bound train cannot proceed until the train from Cardiff has cleared the section. As an essential safety measure, there is a token (one only!) that has to be carried by the driver of the train occupying the single section of track. The driver of the arriving train will hand the token to the driver of the waiting train, who will then be assured of a clear track ahead to Porth station, where the line becomes double track again.