Perhaps the bus that caught up to the full bus should pass it, and relieve the next stop - presumably there are extra passengers waiting at that one too, since

Perhaps the bus that caught up to the full bus should pass it, and relieve the next stop - presumably there are extra passengers waiting at that one too, since the bus is late. This way the bus that caught up will now risk slowing down (dealing with fuller stops), but the original full bus that was slow is likely to not speed up that much, having an above-average number of potentially disembarking passengers.