Train Control

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This page was last updated on September 28, 2026.

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Rule Books

Operation of a railroad is governed by rules, issued to employees in the form of a rule book. They usually follow a more or less standard form.

These books of rules specify general duties of various employees in the Operating Department and attempt to formalize their actions in any situation that may arise in operating trains.

There are several rule books currently used by railroads in the United States. They are all based on the Uniform Train Rules and Rules for the Movement of Trains by Telegraphic Orders, adopted by the American Railroad Association (ARA) in 1887, and adopted by the ARA's General Time Convention in July of 1889. (The General Time Convention was responsible for the establishment of Standard Time and the Time Zones in the United States on November 18, 1883.)

There was no coordinated effort to produce uniform rules for use by all railroads. Each railroad developed whatever rules it deemed necessary. The inconsistencies and vague instructions continued to cause deaths and injuries. During 1900 alone, 2,500 railroad employees died while on duty; many as a result of those variations in the rule books. The "Uniform Train Rules" book and its procedures continued to be further refined and evolved into a set of rules.

Standardization in the form of what later became the Standard Code of Operating Rules was the method to close the variations. It served as the standard for consistency in understanding and applying operating rules from a conceptual standpoint and also for terminology, formatting, wording and numbering.

The American Railroad Association became the Association of American Railroads in 1937. In 1938, the Uniform Train Rules and Rules for the Movement of Trains by Telegraphic Orders was renamed the Standard Code of Operating Rules, Block Signal Rules, Interlocking Rules, usually known simply as the "Standard Code" or as the SCOR.

The "Standard Code of Operating Rules" was not an actual rule book. Instead, it was a set of recommended best practices from the Association of American Railroads. It was more of a template to establish standard terminology, formatting, wording and numbering of rules. Many individual railroads reprinted it almost word-for-word as their own rule book, with modifications to suit their individual needs and circumstances.

Two actual rule books were soon developed, based on the AAR "Standard Code" book:

Both were superseded by the General Code of Operating Rules (GCOR) in 1985, and the Northeast Operating Rules Advisory Committee (NORAC) in 1988.

General Code of Operating Rules (GCOR):
First Edition – 1985
Second Edition – 1989 (Rules for Movement by Train Orders Eliminated)
Third Edition – 1994 (Rules reworded and reorganized into 16 Chapters)
Fourth Edition – 2000
Fifth Edition – 2005
Sixth Edition - 2010

Over 300 other railroads, including the BNSF Railway, Canadian Pacific and Union Pacific Railroad have also adopted the GCOR.

Northeast Operating Rules Advisory Committee (NORAC):
First Edition – 1988
Second Edition – 1991
Third Edition – 1992 (Rules Consolidated and Streamlined to be More Readable)
Fourth Edition – 1993
Fifth Edition – 1995
Sixth Edition – 1997
Seventh Edition – 2000
Eighth Edition – 2003
Ninth Edition – 2008
Tenth Edition – 2011

Approximately 60 eastern railroads have adopted the Northeast Operating Rules Advisory Committee (NORAC) Operating Rules.

As of 2012, several railroads continued to maintain their own rule books: CN, CSX Transportation, Norfolk Southern, Metro-North Railroad, and Long Island Railroad

The process could best be described as evolution or by what is called Westinghouse's Law: "The More Things We Invent, The More Things We Need To Invent." -- George Westinghouse

It can be said that the advent of railroad operating rules coincided with the need for them.

Railroading is a dangerous business. A common saying within the railroad operations community is that every rule is written in blood, meaning that railroad operating rules are constantly being updated to address unsafe conditions as technology continues to change.

E. O. Gibson wrote in January, 2019.

The Standard Code, along with later competing Consolidated Code (Northwestern railroads) and Uniform Code (Midwest Railroads), had a good run. It only was replaced en masse by the succeeding General Code of Operating Rules in 1985. Several roads instead decided to opt out and formed the Northeast Operating Rules Advisory Committee (NORAC), which came out with its own version of the rules two years later.

Since then, the Federal government has gradually and abundantly insinuated itself into "the rules", generally for the better, through the Code of Federal Regulations, Part 049. Positive Train Control will likely be the central focus of rules debate in the near future, as the unforeseen consequences of unproven technology collide head-on with the real world. That's the way it's always been.

(Read more about railroad rules by E. O. Gibson on his WX4 website)

Timetables

One of the first systems to prevent collisions between opposing movements was the Timetable Schedule.

The Timetable Schedule also provided time separation of trains moving in the same direction. As traffic increased, tracks were divided into blocks and train separation was by space interval through use of manually controlled signals at the entrance to each block.

Each train was given a printed time schedule, as shown in the timetable. Meeting points were established between trains moving in opposite directions.

Under timetable authority, neither train could leave the meeting point until the other train arrived. The system worked well as long as there were few trains, and trains ran on schedule. If one train was delayed in arriving at the meeting point, delays to many trains could result and eventually paralyze the railroad.

In today's railroad operations, a railroad timetable is an authoritative, published document that outlines the scheduled movement of trains, line characteristics, and operating rules for a specific section of a railway network.

Telegraph

A telegraph is a communication system that sends electrical impulses or signals over wires (using codes like Morse code) to transmit text messages quickly over long distances. Telegraph wires ran alongside railroad tracks, allowing messages to travel faster than any train.

The first telegraphic train order was issued on September 22, 1851 on the New York & Erie Railroad, when Superintendent Charles Minot sent a telegraph to a station 14 miles west of the station where he had been expecting an eastbound train. His telegraph ordered the operator to hold the eastbound train, and to wait for an opposing train to arrive at that same station. He then wrote an order and handed it to the conductor of westbound train he was riding on, ordering the conductor to proceed to that next station, where the eastbound train was being held.

In 1837, Samuel F. B. Morse invented the electric telegraph. A simple apparatus for sending and receiving electric impulses by wire.

(Read the Wikipedia article about the Electrical Telegraph)

(Read more about Morse Code)

It was only a matter of time before the telegraph would be used by the railroads.

How The Telegraph Works

Train Dispatching: A central dispatcher used reports from station operators to track train locations and manage single-track movements safely.

Schedule Adjustments: If a train ran late, dispatchers sent new meeting points or passing instructions to other stations, preventing collisions and long delays.

Time Synchronization: Station clocks were synchronized using telegraph time signals, which created reliable, uniform timetables across regions.

Station Communication: Local operators used a clicking sounder to copy train orders, control wayside signals, and hand written orders to passing crews.

Interlocking

Once turnouts (switches) and crossings were developed so tracks could branch from and cross each other, a means to assure the route was clear had to be developed.

The switches and signals were operated, via pipe and wire pull, by a switchman using hand levers to operate the switches and foot stirrups to work the signals.

In 1843, at Bricklayer's Arms Junction in England, Sir Charles Hutton Gregory installed the first devices where signals and switches were controlled from a single nearby location.

In these early designs there was no interlocking among the switches and signals. Switches were sometimes thrown under trains and signals cleared over open switches.

In 1856, the first mechanical interlocking was developed in England. John Saxby (1821–1913) invented and patented the system by which signals and switches are controlled by one operation.

John Saxby was a British railway engineer who revolutionized railway safety with his interlocking system for points (switches) and signals. His invention ensured that signals and switches could not be set in conflicting positions, preventing dangerous movements.

Before Saxby's system, the leading cause of railway accidents was the changing of points while a train was passing over them, or signals being set to "clear" for conflicting routes.

Saxby, a former employee of the London, Brighton, and South Coast Railway, worked on his idea after an 1855 accident. He received his first patent for interlocking on June 24, 1856. The core principle was that the position of the track points dominated the signals — if a switch was set for one route, signals for conflicting routes would automatically be locked at "danger". The points and signals were "interlocked."

In 1861, Saxby left the railway company to start his own business. He later partnered with John Stinson Farmer, forming the firm Saxby and Farmer. The firm became a major manufacturer, employing thousands and exporting interlocking frames worldwide. Their US Patent (No. 80,878) for an "Improved Switch and Signal" was issued in 1868. Saxby's system became the standard for railway safety globally.

The first interlocking in the United States, imported from England, was manufactured by Saxby and his partner John Stinson Farmer. The Saxby & Farmer interlocking machine was put in service in 1870 at "Top of the Hill," a junction in Trenton, New Jersey, on the Philadelphia and Trenton Railroad.

Originally, interlockings were totally mechanical. They relied on the brute strength of the control operator. Levers in the control building or tower were connected to rods (pipes) on rollers which moved cranks and in turn moved signal arms and switches in the field.

Between the operating levers and the rods was the interlocking machine. Inside the interlocking machine a system of slots and locking bars with latches (dogs) between the levers, known as the locking bed, prevented the levers from being moved except in proper sequence. The arrangement prevented signals from being cleared until all switches in the route were properly lined and also prevented giving a signal to two opposing or crossing trains.

(Largest mechanical interlocking in North America was the State Line Tower at Hammond, Indiana. Installed in 1897, it had 128 working Levers. It was retired: August 5, 2000.)

In 1872, Dr. William Robinson invented the Closed Direct Current Track Circuit which provided the ability to electrically detect track occupancy and most track integrity problems, such as broken rails. Robinson's Closed Rail Current System was installed at Kinzua, Pennsylvania on the Philadelphia and Erie Railroad in 1872.

With the invention of the track circuit and an ever increasing understanding of electricity, mechanical locking evolved into electrical locking.

In 1911, the first Absolute Permissive Block System, more commonly called the Automatic Block Signal System (ABS) was installed on the Toronto, Hamilton & Buffalo Railway. The system allowed trains to operate on single track in either direction with full signal protection for both opposing and following movements.

In 1927, combining the Absolute Permissive Block System with electric interlocking technology, the New York Central Railroad installed several small interlockings, remotely controlled from Fostoria, Ohio by a single dispatcher, in ABS territory on the Ohio Division between Stanley and Berwick, Ohio. This created the first Centralized Traffic Control (CTC) System that allowed operation of trains on single track under centralized supervision without train orders.

(Read the Wikipedia article about Interlocking)

Timetable and Train Order (TTTO)

Timetable and Train Order is a traditional railroad operating system used before modern radio and electronic dispatching, and is used by railroads to authorize train movements and ensure safety on main tracks, especially outside of high-tech signaled areas.

How it works: Train movements were governed primarily by a printed Timetable that set regular schedules and train superiorities. When regular schedules needed to be changed, added, or restricted, the dispatcher issued specific, written Train Orders handed to train crews at stations along the route.

Characteristics: It required no direct, real-time radio interaction with the dispatcher for basic movement, relying instead on strict adherence to the printed schedule and physical train orders.

Track Warrant Control (TWC)

Track Warrant Control is a verbal and written authorization system defined by the General Code of Operating Rules (GCOR) that replaced many older Timetable and Train Order systems, and is used by railroads to authorize train movements and ensure safety on main tracks, especially outside of high-tech signaled areas.

How it works: A dispatcher gives a train crew verbal permission (a track warrant) via radio to occupy a specific segment of main track between designated points (like named stations or mileposts). The train crew writes down the warrant on a form and repeats it back to the dispatcher for verification.

Characteristics: It is commonly used in "dark territory" (lines without automatic block signals) or combined with basic signal systems to manage medium- and low-density traffic safely. Unlike old train orders that gave broad authority over an entire run, track warrants generally grant authority in smaller increments.

Similar to TWC, a Form D Control System (DCS) is used by Northeastern railroads that have adopted the NORAC Rule Book. It is a variation of TWC. Canadian railroads, whose dispatchers are called Rail Traffic Controllers, use an Occupancy Control System (OCS) Clearance also similar to TWC.

(Read the Wikipedia article about Track Warrant Control)

Direct Traffic Control (DTC)

In railroad operations, Direct Traffic Control (DTC) is a verbal authorization system where a train dispatcher gives track occupancy and movement authority directly to a train crew via radio. DTC essentially replaced trainorders as a way to safely control traffic.

How DTC Works

Pre-Defined Blocks: The railroad's main track is divided into permanent, physical sections called DTC blocks, marked by specific geographic boundaries.

Radio Dispatching: Instead of using roadside telephone operators or paper train orders, the dispatcher talks straight to the engineer or conductor over the radio to grant permission to enter a block.

Types of Authorities: Authorities given by the dispatcher can designate a block as a Clear Block (no other trains ahead), Occupied Block, or Absolute Block (exclusive occupancy) depending on traffic rules.

Releasing Tracks: Once a train completely clears a block, the crew must immediately notify the dispatcher and release their authority to occupy the block.

(Read the Wikipedia article about Direct Traffic Control)

Signal Types

Railway signals are mechanical or electrical traffic control devices that guide train drivers on whether it is safe to proceed, how fast they can travel, and which route to take.

Under both Automatic Block Signaling (ABS) and Centralized Traffic Control (CTC), there are different types of colored-light signals, which replaced semaphores.

Main Types of Signals

Color Light Signals: Modern lights using red, yellow, and green lenses to direct traffic.

Semaphore Signals: Traditional mechanical arms that change physical position to indicate stop or proceed.

Ground or Dwarf Signals: Small low-to-the-ground position lights used to control low-speed movements inside rail yards.

Absolute Signals (Dispatcher-Controlled): The signals or semaphores located at the entry and exit points of sidings and crossovers were wired directly to the dispatcher's console. The dispatcher has absolute control over these signals.

Intermediate Signals (Automatic): The signals or semaphores positioned between stations functioned automatically. They relied on track circuits to detect train positions and adjusted their lights or arms automatically to show "Caution" or "Proceed" without dispatcher intervention.

Distant (Approach) Signals: Placed to warn engineers about an upcoming absolute signal. Semaphores had a notched tail (a "fish tail") to indicate their status as distant signals. Usually known as an Approach signal in modern systems. Many railroads add a 'D' plate to indicate a signal as a Distant signal.

Dwarf Signals: Low-to-the-ground signals used to govern train movements in areas with restricted overhead clearance or low-speed operations. Dwarf signals are small versions of standard high-mast signals, standing only a couple of feet tall. They are mounted close to the ground, placed directly next to or tucked between tracks where full-sized signal masts would infringe on safety clearances. They are primarily used in congested areas such as rail yards, sidings, industrial spurs, terminals, and interlocking switch limits where trains move at restricted or low speeds.

(Read the Wikipedia article about North American railroad signals)

Centralized Traffic Control

Centralized Traffic Control (CTC) is a railway signaling and command system that allows a remote dispatcher to manage train movements, track switches, and signals across an entire territory from a single central location.

How CTC Works

Remote Dispatching: A dispatcher sits at a central control console (traditionally a physical panel with levers and lights, now typically a computer workstation) to oversee operations.

Real-Time Tracking: Track occupancy circuits show block status on a display, allowing the dispatcher to see where every train is in real time.

Direct Switch and Signal Control: The system allows the dispatcher to remotely align powered switches and change wayside signal aspects (such as at sidings and crossovers) without needing local tower operators or train crews to manually handle switches.

Built-In Safety: The control software or interlocking hardware is designed to prevent a dispatcher from issuing conflicting movement authorities.

(Read the Wikipedia article about Centralized Traffic Control)

Automatic Block Signaling (ABS)

Automatic block signaling (ABS) is a railway safety system that divides a track into defined sections called "blocks" and uses automatic signals to maintain a safe distance between trains moving in the same direction.

(Also known as Absolute Permissive Block System, APB)

ABS as a series of consecutive parts of a railroad (called blocks) governed by block signals that are actuated by a train or engine, or by certain other conditions. ABS signals are not controlled by a distant dispatcher.

How ABS Works

Block Division: The railway line is split into contiguous segments or blocks using track circuits.

Automatic Detection: The system automatically detects whether a block is occupied by a train, has a broken rail, or features an open switch.

Signal Aspects: Wayside signals at the entrance of each block change aspects (such as green for clear, yellow for approach, or red for stop) based on track occupancy ahead, without needing manual input from a dispatcher.

Safety vs. Authority: ABS provides a protective safety overlay, but it does not grant train movement authority. Crews must still receive movement authorization via separate rules, timetables, track warrants, or verbal clearances.

Autonomous Operation: The system functions entirely on physical track conditions and electrical relays without external control intervention.

Collision Prevention: It prevents rear-end collisions by ensuring a following train gets restrictive or stop indications if a preceding train is still occupying the blocks ahead.

(Read the Wikipedia article about Automatic Block Signaling)

Rule 251

Rule 251 in railroad operations is an operating rule that allows trains to run in one specified direction—known as the "current of traffic"—on signaled tracks where block signal indications override the standard superiority of trains. Rule 251 is used as part of Automatic Block Signaling (ABS) systems.

How Rule 251 Works

Direction: Trains move only in the designated compass direction or proscribed flow for that specific track (typically found on multi-track lines).

Signals as Authority: The automatic block signals (ABS) govern train movements in the same direction, meaning train crews do not rely on traditional timetable superiority or train orders to follow other trains in that direction.

Against the Current: Moving a train in the opposite (counter) direction requires special extra authority, such as manual block directives, form orders, or a specific mandatory instruction from the train dispatcher.

Comparison: Unlike Centralized Traffic Control (CTC or Rule 261), where signals allow movement in either direction on demand under direct dispatcher control, Rule 251 traditionally applies to fixed multi-track directional running where signals manage following trains via track occupancy rather than active individual dispatcher lever control.

Semaphores

A railway semaphore signal is a trackside mechanical visual device used to direct train engineers on whether to stop, slow down, or proceed safely along the tracks.

Semaphores were used as part of Centralized Traffic Control (CTC) as well as Automatic Block Signaling (ABS). While it is common to associate CTC with modern color-light signals, semaphores and CTC overlapped significantly during the mid-20th century.

How Semaphores Work

Movable Arm (Blade): A tall pole holds a painted metal arm that pivots.

Daytime Signals: The angle of the arm tells the engineer what to do. Horizontal means stop, a 45-degree angle means caution or proceed slowly, and a vertical or dropped position means clear to proceed.

Nighttime Signals: Colored glass lenses move in front of lamps (originally oil, later electric) behind the arm to display colored lights like red, yellow, or green.

Fail-Safe Design: They use heavy counterweights. If a control cable breaks, gravity pulls the arm back to the safe "stop" position.

The modern form of semaphores use signal aspects to identify the position of semaphore arms. Under the modern General Code of Operating Rules (GCOR), signals may display color light aspects or semaphore arms and color lights in which the color of lights, flashing of lights, position of lights, or any combination provides the needed indication. Aspects may be qualified by marker plate, number plate, letter plate, or marker light.

Automatic Cab Signal (ACS)

An Automatic Cab Signal (ACS) or Cab Signaling System (CSS) is a railway safety technology that displays track conditions and signal aspects directly inside a locomotive cab.

How ACS Works

In-Cab Display: Colored lights or digital screens inside the locomotive cab continuously show the status of the track ahead.

Signal Transmission: Track status is transmitted from the rails (using coded electrical currents) or via wireless data to onboard equipment.

Real-Time Updates: The display updates instantly when track conditions change, even if external wayside signals (trackside traffic lights) are hidden by weather or curves.

ACS Aids Engineers: It removes the need for train crews to rely solely on memory or visibility of distant wayside signals.

Brake Enforcement: When paired with an Automatic Train Control (ATC) or speed limiter, the ACS system sounds an alarm and will automatically apply the train's brakes if the engineer ignores a required speed reduction.

Modern Transition: Traditional rail-based cab signals have largely been supplemented or replaced on major lines by computer-based Positive Train Control (PTC) systems.

Train Dispatchers and Control Operators

A train dispatcher is a professional railroad employee who directs and coordinates the safe, efficient movement of railroad traffic over an assigned territory. Train dispatchers work from central control centers to manage the flow of both passenger and freight trains.

Train dispatchers are usually the final authority over train movements and track permits. Under their direction, there are also Levermen, Towermen and other employees formally known as "Control Operators" who control a formal control point.

Control operators are under the direction of the train dispatcher when their duties concern handling track warrants, track bulletins, lineups, the movement of trains and any other instructions issued by the train dispatcher.

Train dispatchers supervise train movement and any employees connected with that movement.

(Read the Wikipedia article about Train Dispatchers)

Protecting Track Workers

Each system of train movement authority must also include provision for protecting maintenance vehicles and workers, as well as any work trains that may be moving back and forth within a section of track.

Under CTC, the usual procedure is for the dispatcher to grant "Track and Time Authority" to the track foreman, vehicle operator, or work train. This authority protects the worker's use of a designated track between locations where signals are controlled by the dispatcher (called control points). These signals can't be cleared into the track and time limits.

Another method requires train crews to contact a foreman before passing through (or on multiple tracks, adjacent to) work zones. This is called a "Form B Track Bulletin" on Western roads. Rule 251 territory has similar procedures.

In TWC, DTC, and DCS territory, work crews and vehicles are treated in the same manner as trains. Verbal authority from the dispatcher is required to occupy or obstruct the tracks.

The Rules Today

The following was posted to Trainorders.com by "Topper".

That operating rules today are so dumbed-down and revised so frequently, as well as compromised by operating management for convenience, that understanding in the context of historical perspective is an exercise in futility.

The General Code of Operating Rules is a product of the evolution of the "old" Consolidated Code of Operating Rules, Uniform Code of Operating Rules, and books of rules used by carriers such as ATSF, SP, WP, UP, and DRGW. The original General Code, issued in 1985, was the product of five years of discussions and negotiations as well as hell of a lot of compromising.

There are significant differences between "track-and-time", "track permit", and "work-and-time" only by virtue of the territories in which they are employed. Otherwise they are quite the same in providing *protection* for men and equipment and/or trains working upon a *main track*.

  1. Track-and-time is used within Centralized Traffic Control (CTC) and manual interlocking limits.
  2. Track permits are used within double-track (current of traffic) limits where controlled signals exist at both ends of such limits.
  3. Work-and-time *was* used within Direct Traffic Control (DTC) limits.

Further, two operating rules have stood the test of time for well over 100 years:

  • "Safety is of the first importance in the discharge of duty".
  • "In case of doubt or uncertainty, the safe course must be taken".

Many rules in existence today have undergone periodic revisions as technologies advanced or expired and craft agreements were negotiated. And many rules have come into existence over the past 15 years simply because of the application of a multitude of computer processes to all manner of operations.

Operating rules exist because they are written in human blood. Regardless of how simple or how complex an operating rule or rules might be perceived, the weakest element will always be the human element, regardless of whatever technological sophistication might be incorporated into any operating practices or policies.

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