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Centralized traffic control (CTC) is a signalling system used by railroads. The system consists of a centralized train dispatcher's office that controls railroad switches in the CTC territory and the signals that railroad engineers must obey in order to keep the traffic moving safely and smoothly across the railroad. In the dispatcher's office is a graphical depiction of the railroad on which the dispatcher can keep track of trains' locations across the territory that the dispatcher controls. Larger railroads may have multiple dispatcher's offices and even multiple dispatchers for each operating division. It has been suggested that safeworking be merged into this article or section. ...
This is the top-level page of WikiProject trains Rail tracks Rail transport refers to the land transport of passengers and goods along railways or railroads. ...
This article belongs in one or more categories. ...
A railroad switch is a mechanical installation enabling trains to be guided from one set of rail tracks (or tramway tracks) to another. ...
A railroad engineer or train driver is a person who operates a railroad locomotive. ...
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Development and technology CTC was designed to enable the train dispatcher to control train movements directly, bypassing local operators and eliminating written train orders. Instead, the train dispatcher could directly see the trains' locations and efficiently control the train's movements by displaying signals and controlling switches. It was also designed to enhance safety by detecting track occupancy and automatically preventing trains from entering signal blocks already occupied by other trains (see interlocking). Interlocking in railway terminology (US) is a term used to describe an at-grade crossing or other junction of two or more railroads, or any railroad switching complex in which the switches and the signals controlling train movement over those switches is interlocked so that it is impossible to give...
The basic component of a CTC system is detecting track condition and occupancy. The track at either end of the signal block is electrically insulated, and within the block a small electrical current passes through the track. When a train passes a signal and enters a block, the metal wheels and axle of the train short-circuit the current, which causes a relay associated with the track circuit to itself become de-energized. (See track circuit and rail circuit.) Additionally, any fault in the rail or failure in the signal system, such as a broken rail, a cut wire, or a power failure, will cause the relay to de-energize. When this relay is de-energized, the system understands the track to be occupied or damaged, and the signals show it as such to prevent a train from proceeding and encountering harm. It has been suggested that Wheel and Axle be merged into this article or section. ...
An axle is a central shaft for a rotating wheel or gear. ...
It has been suggested that Rail circuits be merged into this article or section. ...
Signals and signal blocks The most prominent feature of CTC is its signals. Signals govern movement over the section of track, or signal block, between that signal and the following signal. A signal is a mechanical or electrical device that indicates to train drivers information about the state of the line ahead, and therefore whether they must stop or may start, or instructions on what speed they may drive their train. ...
When calculating the size of the blocks and, therefore, the spacing between the signals, the following has to be taken into account:
- Track speed (the maximum speed the train is allowed to travel)
- Gradient (to compensate for the assistance or otherwise afforded to deceleration)
- The braking characteristics of the train(s) that travel on that line
- Sighting (the ability of the engineer to see the signal)
- Reaction time (of the engineer)
A signal is placed where signal blocks meet. Separate signals are placed for trains traveling in opposite directions. Signals are generally placed on the right side of the track; however, opposing signals may both be mounted on the same signal mast in opposite directions or may be located on an overhead support system. A signal is a mechanical or electrical device that indicates to train drivers information about the state of the line ahead, and therefore whether he or she must stop or may start, or instructions on what speed the train may go. ...
These signals are one of two types: an absolute signal, which is directly controlled by the train dispatcher and is located at a control point, or an intermediate signal, which is automatically controlled by the conditions of the track in that signal's block and by the condition of the following signal. Train dispatchers cannot directly control intermediate signals.
Signals have aspects and indications. The aspect is the visual appearance of the signal; the indication is the meaning.
Switches and control points The majority of control points are located at electronically-operated switches. These switches are called dual-controlled switches, as they may be either remotely controlled by the train dispatcher or by manually operating a lever or pump on the switch mechanism itself (although the train dispatcher's permission is generally required to do so). These switches may lead to a passing siding, or they may take the form of a crossover, which allows movement to an adjacent track. A siding, in general rail terminology, refers to a section of track distinct from a through route such as a main line or branch line or spur. ...
A crossover is a pair of switches that connects two parallel rail tracks, allowing a train on one track to cross over to the other. ...
Sidings are located at stations. A station is a place along the railroad designated by name in the railroad's timetable, which is a publication with instructions governing train movements--as opposed to a passenger timetable, which details the arrival and departure times of passenger trains--and does not necessarily refer to a place where a passenger train stops to allow passengers to get on or off.
Operation Although some railroads still rely on older, simpler electronic lighted displays and manual controls, in modern implementations, dispatchers rely on computerized systems to view the location of trains and the aspect, or display, of absolute signals. Typically, these control machines will prevent the dispatcher from giving two trains conflicting authority. Modern computer systems generally display a highly simplified mock-up of the track, displaying the locations of absolute signals and sidings. Track occupancy is displayed via bold or colored lines overlaying the track display, along with tags to identify the train (usually the number of the lead locomotive). The signal aspects are represented by colored circles corresponding to the signals that train crews see.
Absolute signals at a switch contain two signal heads, one on top of the other. The top signal governs movement over the straight or main track, and the bottom signal governs movement over the diverging route.
Normally, signal blocks touch each other. However, control points located at switches do not touch; instead, the area between the opposing signals is all considered to be the control point, and track occupancy in the control point is displayed separately on the control machine.
Applications in the U.S. CTC-controlled track is significantly more expensive to build than non-signalled track, due to the electronics and failsafes required. CTC is generally implemented in high-traffic areas where the reduced operating cost from increased traffic density and time savings outweigh the capital cost. Most of BNSF Railway's and Union Pacific Railroad's track operates under CTC; the portions that are not are generally lighter-traffic lines that are operated under Track Warrant Control (BNSF and UP) or Direct Traffic Control (UP). The BNSF Railway (AAR reporting mark BNSF), headquartered in Fort Worth, Texas, is one of the largest railroad networks in North America (only one competitor, the Union Pacific Railroad, is comparable in size). ...
The Union Pacific Railroad (AAR reporting marks UP) (NYSE: UNP) is the largest railroad network in the United States. ...
Track warrants are systematized permissions used on some rail lines instead of or in addition to signals. ...
Direct Traffic Control (DTC) is a system for authorizing track occupancy used on some railroads instead of or in addition to signals. ...
East of the Mississippi River, CTC is generally applied only to single track railway with passing sidings; double-track railway is generally operated under Rule 251. In the western United States, most signaled track, whether single, double, triple or more is generally operated under CTC. This allows the dispatcher greater flexibility in managing traffic by having some trains "cross over" to another main track to pass slower or stopped trains or allow access by trains moving in both directions to spurs and industries on both sides of the track. The Mississippi River, derived from the old Ojibwe word misi-ziibi meaning great river (gichi-ziibi big river at its headwaters), is the second-longest river in the United States; the longest is the Missouri River, which flows into the Mississippi. ...
A single track railway A single track railway is one where traffic in both directions shares the same track. ...
A crossing loop is a place on a single line railway where trains in opposing directions can cross each other. ...
It has been suggested that safeworking be merged into this article or section. ...
Suppliers There are several companies offering individual components as well as turnkey systems that comprise the elements of a CTC system. These suppliers include: Alcatel SA is a global company, headquartered in France that provides hardware, software and services to telecommunications service providers and enterprises. ...
Alstom (formerly GEC-Alsthom) (Euronext: ALO) is a large French company whose businesses are power generation and manufacturing trains (e. ...
GE Transportation is a division of General Electric, comprised of GE Aircraft Engines and the much smaller GE Transportation Systems. ...
George Westinghouse founded Union Switch & Signal in 1881, consolidating the assets of companies that had pioneered closed track circuits and interlockings. ...
Siemens AG (FWB:SIE, NYSE: SI) is the worlds largest electronics company. ...
See also Direct Traffic Control (DTC) is a system for authorizing track occupancy used on some railroads instead of or in addition to signals. ...
Track warrants are systematized permissions used on some rail lines instead of signals. ...
Advanced Train Control System, usually called ATCS, is a set of specifications designed to document the stated requirements of railroad operational and technical professionals concerning ATCS hardware and software. ...
External links - Railroad Empire a CTC simulation
- Logic Rail Technologies, maker of a CTC system for model railroads
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