Railroad Signal Systems
Introduction
In this section, we present the basics of Track Signal Systems and how they are used.
Signal System Objective
The basic objective or railroad signal systems is to maintain safe separation between trains.
Approach
Dictate speeds of trains through specific sections (Blocks) of track.
sections (Blocks) of track.
• Eastern U.S. railroads use Speed only.
• Western U.S. railroads include some indication of Route.
In this section, we present the basics of Track Signal Systems and how they are used.
Signal System Objective
The basic objective or railroad signal systems is to maintain safe separation between trains.
Approach
Dictate speeds of trains through specific sections (Blocks) of track.
sections (Blocks) of track.
• Eastern U.S. railroads use Speed only.
• Western U.S. railroads include some indication of Route.
Types of Signal Systems
ABS - Automatic Block Signals: Track is divided into a
series of blocks (sections) and signals control entrance into
each block.
• Track circuits determine if the block is occupied.
• Interlocking: A collection of turnouts and signals that are
mechanically or electrically interlocked to insure their
movements are coordinated. Often a Control Tower is
present.
CTC - Centralized Traffic Control: A system of controlling
signals and turnouts from remote locations.
ABS - Automatic Block Signals: Track is divided into a
series of blocks (sections) and signals control entrance into
each block.
• Track circuits determine if the block is occupied.
• Interlocking: A collection of turnouts and signals that are
mechanically or electrically interlocked to insure their
movements are coordinated. Often a Control Tower is
present.
CTC - Centralized Traffic Control: A system of controlling
signals and turnouts from remote locations.
Definitions
• Rule - A numbered provision of a recognized set of rules for conducting transportation on a specific railroad that defines a particular aspect, its name and the associated indication.
• Aspect - The physical appearance of a signal such as color of lights, the geometric arrangement of lights and the position of semaphore blades to indicate a specific rule.
• Indication -The meaning of the signal aspect, such as, "Proceed not
exceeding Normal Speed" or "Stop"
• [Aspect]Name - The formal name of the aspect. It is essentially a short form of the indication conveyed by the aspect. Examples are: "Clear", "Approach" and "Stop".
• Rule - A numbered provision of a recognized set of rules for conducting transportation on a specific railroad that defines a particular aspect, its name and the associated indication.
• Aspect - The physical appearance of a signal such as color of lights, the geometric arrangement of lights and the position of semaphore blades to indicate a specific rule.
• Indication -The meaning of the signal aspect, such as, "Proceed not
exceeding Normal Speed" or "Stop"
• [Aspect]Name - The formal name of the aspect. It is essentially a short form of the indication conveyed by the aspect. Examples are: "Clear", "Approach" and "Stop".
Speed Nomenclature used in Signaling
• Normal - The maximum speed allowed for a specific
section of track. Can be different for passenger trains
versus freight trains.
• Limited - Varies, but typically 45 mph.
• Medium - Varies, but typically 30 mph.
• Slow - Varies, but typically 15 mph.
• Restricted - Commonly defined as speed at which train can
stop in "half the visual range". Typically 15-20 mph
• Normal - The maximum speed allowed for a specific
section of track. Can be different for passenger trains
versus freight trains.
• Limited - Varies, but typically 45 mph.
• Medium - Varies, but typically 30 mph.
• Slow - Varies, but typically 15 mph.
• Restricted - Commonly defined as speed at which train can
stop in "half the visual range". Typically 15-20 mph