The Signal Man is a conscientious, dark-haired railway worker stationed in an isolated underground box. He spends his long shifts managing telegraph messages and warning flags to ensure train safety on the line. Despite squandering early academic opportunities, he remains highly intelligent and uses his downtime to study mathematics. He harbors a deep anxiety regarding a recurring supernatural presence near the tunnel entrance.

The Narrator is an unnamed, middle-class traveler staying at a local inn who possesses a newly awakened interest in railway infrastructure. He enjoys leisure time and long walks, eventually discovering the isolated station worker below the cutting. Initially operating on class-based assumptions about manual laborers, he quickly revises his views upon recognizing the worker's intelligence. He applies a rational, skeptical mindset to the supernatural events described to him.

The Ghost is a mysterious spectral figure that haunts the railway cutting near the tunnel entrance. The entity manifests in human form but obscures its face while performing desperate, urgent arm gestures. It occasionally manipulates the railway's electric bell, creating a strange vibration audible only to specific individuals. Its vague warnings create profound distress for those trying to decode its true meaning.

Tom is an engine driver who commands trains passing through the dark tunnel and surrounding railway lines. He watches the tracks ahead and depends entirely on the station workers' flags and lamps to operate safely. His occupation demands sharp reflexes and a loud voice to alert individuals who might wander onto the dangerous rails.