Direct traffic control (DTC) is a system for authorizing track occupancy used on some railroads instead of or in addition to signals. It is known as "direct" traffic control because the train dispatcher gives track authority directly to the train crew via radio, as opposed to through wayside personnel via telephone or telegraph, as in train orders.
A DTC block sign for the Luthman block on the Alaska Railroad.
In DTC, controlled tracks and sidings (those requiring authority from the train dispatcher to occupy) are divided into pre-specified blocks. In addition to being listed by milepost in the railroad's timetable, block limits are delineated by conspicuous signs along the tracks. Every portion of controlled track belongs to a block, as blocks are laid out back-to-back along the entire length of the rail line.
For example, a 30-mile (48km) length of main line track may be divided into three blocks, Anna, Bess, and Cloy, each 10 miles (16km) long. At milepost 10, there will be a sign displaying the end of Anna block and the beginning of Bess block, and a similar sign between Bess and Cloy. A train authorized in Anna through Bess blocks must stop before Bess block ends and Cloy block begins.
For example, a length of track may consist of three blocks. Anna, Bess, and Cloy. There is a siding at Bess, and this siding is specified as Bess Siding. Both Bess and Bess Siding blocks extend to the switches at either end of the siding. Anna and Cloy blocks begin on the other side of their respective switches. Neither Bess nor Bess Siding blocks may be occupied without authority from the train dispatcher.
In this example, a train may have authority straight through from Anna through Cloy. Or, it could have authority in Anna through Bess Siding, in which case it must throw the switch between Anna and Bess and enter the siding - this will usually be done to clear the main track for an opposing train to pass. After clearing its authority in Anna siding and the opposing train passes, it might then get authority from Bess Siding through Cloy, in which case it will throw the switch between Bess and Cloy and reenter the main track.
Lengths of DTC blocks vary, but usually take about 10 minutes to traverse. The siding itself is not considered a DTC block per se, but in some situations sidings must not be occupied without authority from the train dispatcher. However, in DTC territory all sidings operate as non-controlled, restricted speed track and there is no safety consideration in a train occupying it without central authority to do so. For traffic flow purposes the dispatcher needs to record which sidings are occupied. If a train could not use the main track in Bess (due to maintenance, a stuck switch, a disabled train, or an obstacle blocking the track), it would also be possible for the train to have authority from Anna through Bess Siding through Cloy. This is not done when the main track is available, as there is a speed disadvantage to having the train traverse the slower siding track (including having to stop to throw the switches to enter the siding).
While most DTC blocks are laid out back-to-back, the blocks actually do not touch at sidings. Instead, there is a "gray area" over the siding's switches, and the main track's and siding's DTC blocks begins at approximately the clearance point of the switch. The area over the switch must not be occupied unless authority is granted in blocks on both sides of the switch. For example, a train authorized only in Anna block must stop at the End Anna Block sign, which is a short distance from the switch points. A train authorized in Anna through Bess or in Anna through Bess Siding may proceed past the End Anna Block sign, over the switch, and then past the Begin Bess (or Bess Siding, as applicable) Block sign.
Blocks are typically named after a distinguishing feature within the block, such as a station, town, or river.
Procedures
Normally, only one train or piece of equipment may occupy a given block at a time, and a train must release their authority in a block for the dispatcher to authorize another train into that block. Barring human error, this ensures that no two trains are ever authorized on any given piece of track at the same time, thereby preventing collisions. (In certain circumstances, dispatchers will authorize more than one piece of equipment—as in the case of track maintenance vehicles—into the same block. When this occurs, the authority is marked as "joint," and all movements must be made at restricted speed, which allows stopping within half the range of vision.) Another key feature of DTC is that only one authority is in effect for any given train at any given time. When a dispatcher issues a new authority to a train, the previous authority becomes invalid and must not be used.
In modern implementations, dispatchers rely on computerized systems to monitor trains that have received authority. Typically, the computer will prevent the dispatcher from giving two trains authority over the same track. The computer system generally displays a highly simplified diagram of the track, displaying the block limits 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).
To receive or change a train's authority, the train dispatcher communicates by radio with the train crew and gives "mandatory directives" authorizing occupancy in a specified number of blocks. A member of the train crew, usually the conductor, copies the dispatcher's mandatory directive onto a prescribed form. The crew member will repeat the directive back to the dispatcher, who monitors the repeat for any errors. If the crew member correctly repeats the mandatory directive, the dispatcher finalizes the directive by saying, "That is correct," followed by the dispatcher's initials. A mandatory directive cannot take effect until the dispatcher has said, "That is correct," reducing the potential for human error to cause an accident.
Numbers are always repeated in an alternate format to ensure clarity and prevent misunderstandings. Numbers from zero to nine are spelled out, while numbers greater than ten are given by their individual numerals. For example, the number six would be given as, "Six, s-i-x," while the number 14 would be given as "fourteen, one-four." Engine numbers such as 2001 are usually read first as "two thousand one," while numbers such as 4321 are usually read as "forty-three twenty-one," although this is mostly a personal preference about what is easiest to say. Regardless, the repeat will give the individual numerals, as in, "Engine twenty-eight oh eight, two, eight, zero, eight."
A sample issue format would be as follows:
Train dispatcher: "This is mandatory directive to engine forty-three twenty-one, four, three, two, one, with engineer Johnson. You are authorized to proceed westward in three, t-h-r-e-e blocks, Anna through Cloy, over."
Train crew member: "This is a repeat of mandatory directive issued to the forty-three twenty-one, four, three, two, one, with engineer Johnson. We are authorized to proceed in a westward direction in three, t-h-r-e-e blocks, Anna though Cloy, over." Dispatcher: "That is correct, S.D.K., over. Crew: "That is correct, dispatcher S.D.K. Thanks, dispatcher, forty-three twenty-one, out."
Dispatcher. "Thanks, train dispatcher out."
When trains must meet en route, one train must be authorized into the siding. For example, train 5432 may be authorized from Anna into Bess Siding:
Train dispatcher: "This is mandatory directive to engine fifty-four thirty-two, five, four, three, two, with engineer Smith. You are authorized to proceed westward in two, t-w-o blocks, Anna through Bess Siding, over."
Train crew member: "This is a repeat of mandatory directive issued to the fifty-four thirty-two, five, four, three, two, with engineer Smith. We are authorized to proceed westward in two, t-w-o blocks, Anna through Bess Siding, over." Dispatcher: "That is correct, S.D.K., over. Crew: "That is correct, dispatcher S.D.K. Thanks, dispatcher, fifty-four thirty-two, out."
Dispatcher. "Thanks, train dispatcher out."
An opposing train will be authorized in two blocks, Cloy through Bess, using a similar format:
Train dispatcher: "This is mandatory directive to engine forty-three twenty-one, four, three, two, one, with engineer Johnson. You are authorized to proceed eastward in two, t-w-o blocks, Cloy through Bess, over."
Train crew member: "This is a repeat of mandatory directive issued to the forty-three twenty-one, four, three, two, one, with engineer Johnson. We are authorized to proceed eastward in two, t-w-o blocks, Cloy through Bess, over." Dispatcher: "That is correct, S.D.K., over. Crew: "That is correct, dispatcher S.D.K. Thanks, dispatcher, forty-three twenty-one, out."
Dispatcher: "Thanks, train dispatcher out."
Once train 5432 has fully entered the siding and restored the switch for movement along the main track, they will call the dispatcher and release Anna block, using the following format:
Train crew member: "The fifty-four thirty-two, five, four, three, two, would like to release our authority in one block, Anna, over."
Train dispatcher: "Engine fifty-four thirty-two, five, four, three, two, is releasing authority in one block, Anna, over." Crew: "That is correct, dispatcher." Dispatcher: "All right, thanks. Dispatcher out."
Crew: "Fifty-four thirty-two out."
After the 5432 has released its authority in Anna, the dispatcher may issue a new authority to the 4321 authorizing them through Anna block. Since only one authority is valid at any given time, if the 4321 is still in Cloy block, the dispatcher will give the new authority containing Cloy through Anna. Once the 4321 is fully within the Bess block and has cleared Cloy block, the conductor or other crew member will call the dispatcher and release Cloy. The dispatcher will then issue a new authority to the 5432, giving them authority from Bess Siding block through Cloy block. This generates additional radio traffic but ensures that there is no confusion as to which train is allowed to enter a given block at any given time. Some railroads have instituted a practice which allows a train to enter a block contingent upon the passing of the opposing train, although the National Transportation Safety Board has recommended against this practice. A DTC authority given under this practice will include a phrase such as "This line is not in effect until after the arrival of train 7940."
In the case of two trains traveling the same direction, the dispatcher will only authorize the following train in blocks that the leading train has released. In the case of closely spaced trains, the dispatcher may opt to reduce his or her workload and implement a "radio blocking behind" authority, which lets the two trains talk to each other directly to discuss which blocks the leading train has cleared. Caution must be exercised by the leading train not to release authority on track that the train still occupies, as this could result in a rear-end collision if the leading train slows down or stops or if the train becomes separated and a portion is left standing on the main track.
Entering a block in which the train is not authorized or releasing a block which the train still occupies is considered a main-line violation by the Federal Railroad Administration and carries stiff penalties for all crew members, which may include time off from work and the suspension or revocation of the engineer's license.
Use
The Southern Pacific Railroad, now the Union Pacific, implemented DTC on several of its lines formerly controlled by train orders (most of the rest of UP's lines use Centralized Traffic Control). The BNSF Railway does not use DTC; it uses mostly CTC with track warrants in its non-signalled territory. The Alaska Railroad changed its Track Warrant Control territory to DTC and is also implementing CTC in high-traffic areas. Queensland Rail in Australia uses the DTC system in some of the lower traffic areas in the western area of the state. CSX uses DTC on their former Georgia railroad mainline from Scottdale, just east of Atlanta, to Augusta.
A railroad switch (AE), turnout, or [set of] points (BE) is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.
A railway signal is a visual display device that conveys instructions or provides advance warning of instructions regarding the driver’s authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal might inform the driver of the speed at which the train may safely proceed or it may instruct the driver to stop.
Railway signalling is a system used to direct railway traffic and keep trains clear of each other at all times. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormous weight and momentum of a train, which makes it difficult to quickly stop when encountering an obstacle. In the UK, the Regulation of Railways Act 1889 introduced a series of requirements on matters such as the implementation of interlocked block signalling and other safety measures as a direct result of the Armagh rail disaster in that year.
Rail terminology is a form of technical terminology. The difference between the American term railroad and the international term railway is the most significant difference in rail terminology. There are also others, due to the parallel development of rail transport systems in different parts of the world.
Rail transport operations are the day-to-day operations of a railway. A railway has two major components: the infrastructure and the rolling stock
A track warrant is a set of instructions issued to a train crew authorizing specific train movements. The system is widely used in North America. The warrant is issued by the train dispatcher and delivered to the train crew via radio. The train crew copies the instructions onto a pre-printed paper form and reads back the warrant to ensure that nothing was misunderstood.
A siding, in rail terminology, is a low-speed track section distinct from a running line or through route such as a main line or branch line or spur. It may connect to through track or to other sidings at either end. Sidings often have lighter rails, meant for lower speed or less heavy traffic, and few, if any, signals. Sidings connected at both ends to a running line are commonly known as loops; those not so connected may be referred to as single-ended or dead-end sidings, or stubs.
Centralized traffic control (CTC) is a form of railway signalling that originated in North America. CTC consolidates train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that controls railroad interlockings and traffic flows in portions of the rail system designated as CTC territory. One hallmark of CTC is a control panel with a graphical depiction of the railroad. On this panel, 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. These offices are usually located near the busiest yards or stations, and their operational qualities can be compared to air traffic towers.
Train order operation, or more accurately timetable and train order operation, is a largely obsolete system by which the railroads of North America conveyed operating instructions before the days of centralized traffic control, direct traffic control, and the use of track warrants conveyed by radio. The system used a set of rules when direct communication between train dispatchers and trains was limited or non-existent. Trains would follow a predetermined operating plan, known as the timetable, unless superseded by train orders conveyed to the train from the dispatcher, through local intermediaries. Train order operation was a system that required minimum human overhead in an era before widespread use of technology-based automation. It was the most practical way for railroads with limited capital resources, or lines with limited traffic, to operate. To this day, many short lines, heritage railways, and railroad museums continue to use Train Order operation.
Catch points and trap points are types of turnout which act as railway safety devices. Both work by guiding railway carriages and trucks from a dangerous route onto a separate, safer track. Catch points are used to derail vehicles which are out of control on steep slopes. Trap points are used to protect main railway lines from unauthorised vehicles moving onto them from sidings or branch lines. Either of these track arrangements may lead the vehicles into a sand drag or safety siding, track arrangements which are used to safely stop them after they have left the main tracks.
Standards for North American railway signaling in the United States are issued by the Association of American Railroads (AAR), which is a trade association of the railroads of Canada, the US, and Mexico. Their system is loosely based on practices developed in the United Kingdom during the early years of railway development. However, North American practice diverged from that of the United Kingdom due to different operating conditions and economic factors between the two regions. In Canada, the Canadian Rail Operating Rules (CROR) are approved by the Minister of Transport under the authority of the Railway Safety Act. Each railway company or transit authority in Canada issues its own CROR rulebook with special instructions peculiar to each individual property. Among the distinctions are:
A train dispatcher (US), rail traffic controller (Canada), train controller (Australia), train service controller (Singapore) or signalman (UK), is employed by a railroad to direct and facilitate the movement of trains over an assigned territory, which is usually part, or all, of a railroad operating division. The dispatcher is also responsible for cost effective movement of trains and other on-track railroad equipment to optimize physical (trains) and human resource (crews) assets.
Automatic block signaling (ABS) is a railroad communications system that consists of a series of signals that divide a railway line into a series of sections, or "blocks". The system controls the movement of trains between the blocks using automatic signals. ABS operation is designed to allow trains operating in the same direction to follow each other in a safe manner without risk of rear-end collision. The introduction of ABS reduced railways' costs and increased their capacity. Older manual block systems required human operators. The automatic operation comes from the system's ability to detect whether blocks are occupied or otherwise obstructed, and to convey that information to approaching trains. The system operates without any outside intervention, unlike more modern traffic control systems that require external control to establish a flow of traffic.
The Brühl train derailment happened on 6 February 2000 at Brühl, railway station on the West Rhine railway. A train negotiated a low speed turnout at three times the correct speed and derailed, killing 9 people.
The Plymouth Subdivision is a freight railroad line in the U.S. state of Michigan. It is owned by CSX. It connects the Plymouth Diamond at milepost CH 24.5 to Grand Rapids at CH 148.1, passing through the Lansing metropolitan area en route. Other towns served include Brighton, Howell, Williamston, Grand Ledge, and Lake Odessa. Operationally, it is part of the CSX Chicago Division, dispatched from Calumet City, Illinois.
The Callahan Subdivision is a CSX Transportation railroad subdivision within the Jacksonville Division on the former Seaboard Air Line Railroad. The sub extends northward 20 miles from Baldwin, Florida, where the Jacksonville Terminal Subdivision's S Line and Florida Gulf & Atlantic Railroad meet just north of Baldwin Yard, a classification yard. According to Jacksonville Division Timetable Number 4 published in 2005, the sub runs from milepost SM 0.18 to milepost SM 20.0, where it joins the Nahunta Subdivision, a former Atlantic Coast Line Railroad, in Callahan, Florida. The line serves as a bypass to Jacksonville.
The 2002 Farragut derailment occurred on the morning of Sunday, September 15, in Farragut, Tennessee. Norfolk Southern freight train 15T derailed 27 cars, resulting in the release of oleum or fuming sulfuric acid. Roughly 2,600 residents were evacuated from nearby homes for three days until hazardous materials crews were able to mitigate the scene. No fatalities or major injuries were reported as a result of the derailment, but property damage and losses were calculated at US$1.02 million. 17 people were injured.
On February 4, 2018, the southbound Amtrak Silver Star No. 91 passenger train from New York City to Miami collided with a stationary CSX Transportation freight train in Cayce, South Carolina, just south of the state's capital of Columbia on CSX's Columbia Subdivision. Two Amtrak crew members were killed and 116 other crew and passengers were injured.
The Harvey train collision took place on October 12, 1979, when the Shawnee train operated by Amtrak between Carbondale and Chicago Union Station crashed into a parked Illinois Central Gulf freight train, leading to the death of two crew members.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
