They drop buses totally from the timetable if running close to one of the other buses and send the empty bus via a quicker route back to the other terminus in order to get back on time. How can anyone disagree this is unethical?
I've been on plenty of NCT buses where the football traffic has bunched them up and, after the driver has checked with the passengers, one of the buses has continued through the estate and the one I'm on has carried on down the main road - those passengers waiting for the first would have been delayed anyway, and those waiting for the second get on the first at the same time the second would have arrived; but more importantly passengers on later services get one which is operating much nearer the schedule that otherwise.