The protagonist in Charles Dickens's short story "The Signal-man" is the signal-man because he is the character who comes into conflict with opposing forces and is affected in some way.
Since the train has disturbed nature with the carving of the tunnel as well as by the intrusion of the looming black machine, supernatural forces are released; moreover, these forces are too strong for the signal-man to control. For, they seek what may be retribution. This signal-man is at odds with the spirits of the area; consequently, he sees ghosts warning him of disaster. The narrator describes him in this way:
His pain of mind was most pitiable to see. It was the mental torture of a conscientious man, oppressed beyond endurance by an unintelligible responsibility involving life.
The signal-man tells the narrator about the apparitions that have appeared to him, but to no avail. For, on the day that the narrator has arranged to visit again, he sees instead a group of officials who are conducting an investigation of the death of the signal-man. Evidently, he had been standing on the line, peering down the tunnel when a train bore down upon him. The conductor reports that he shouted, “Below there! Look out! For God’s sake, clear the way!”
Furthermore, the engineer of the train has waved his arm in warning even as he has covered his face to keep from witnessing the train strike the signal-man. The narrator notes the remarkable similarity between the driver's actions and the actions of the phantom as the signalman has earlier related.