Introduction 1002
Control Panel 1002
Elements of cTc Operation 1005
Non-Coded cTc 1005
Elements of Coding 1006
Stepping Principles 1008
Capacity 1010
Carrier Control Operation 1010
Implementation of Coding Systems 1011
TypeJ Coding System 1011
Type Dl Coding System 1011
Type E2 Coding System 1012
Type Li Coding System 1013
System4000 1013
Datatrain 1015
Traffic Master Control Centers 1015
Traffic Master 1016
Micro Traffic Master 1016
Traffic Master II 1017
Operating Technique 1017
Operations Reporting System 1017

Centralized traffic control,* or cTc as it is generally
known, is an original development of the General
Railway Signal Company. It was first installed in
1927 from Stanley to Berwick, Ohio, a distance of
40 miles, on what was then the New York Central
A centralized traffic control system is made up up of a succession of interlockings, all controlled from a single console. Automatic block signals are usually provided on the intervening trackage. Such a system may be adapted to any existing signal installation and may be applied to single or multiple track. The control console, located in an office within, adjacent to, or remote from the installation, provides means for initiating the desired controls and for displaying the indications which keep the operator informed of train movements and track conditions. Important switches and crossovers are power operated to expedite the movement of trains into and out of sidings, junctions, etc.
Since the introduction of the Traffic Master Il® type of control center, many new installations of cTc have been furnished with that kind of video display and computer assisted control facility. The Traffic Master Control configurations are described later in this section. Smaller installations and additions to certain existing installations may still specify control consoles - sometimes called “control machines” - with panels similar to Figure 1001. We shall first describe cTc operation based on such a control machine, as the operating principles (which are the same for Traffic Master) can be more easily demonstrated - and, of course, the majority of control machines presently in use are of this type.
cTc provides controls for all power-operated switches (and, if desired, all electrically locked hand-operated switches) and for all interlocked signals, that is, signals located at controlled points such as ends of sidings, crossovers, junctions, etc.
*In 1950, the Interstate Commerce Commission broadened the term to “traffic control system” defined as “a block system under which train movements are authorized by block signals whose indications supersede the superiority of trains for both opposing and following movements on the same track.”

The automatic block intermediate wayside signals located between controlled points operate inherently as a part of the system, but their individual controls are simply field circuits, arranged for automatic operation. Other wayside facilities such as employee call devices, switch heaters, tunnel door locks, etc. may be placed under the control of the cTc operator if desired.
Figure 1001 shows a typical panel of a cTc control machine. Above the panel is a supplementary track diagram which shows car capacities of sidings, lengths of intermediate tracks, and other information helpful to operation. At the top of the panel are the names of the controlled points or sidings. Below these and above the track diagram are located the power-off lights, one for each controlled point or field location. These lights are normally dark. When steadily illuminated (red), a light indicates that the a-c power is off at that location. If the installation is coded cTc, the light will be lighted throughout the duration of an indication cycle from the field location. Should the a-c power be off and a light is burning steadily, then it will be extinguished for the duration of an indication cycle from its respective field location. This feature keeps the operator informed as to power conditions at the field location and also enables him to readily identify the field location sending in an indication. Both are valuable in event of an operating abnormality.
The track diagram is laid out in geographic representation of the territory controlled. Adjacent to it are signal symbols with identifying numbers and the number or name of the switch or crossover or other controlled facility. Within the track line itself are located the track-occupancy indicating lights for different sections of track circuited track. For sections not track circuited, token holes are provided so that the operator may post pertinent information. For example, a work train or a damaged car may be on a non-track-circuited siding. By posting a token bearing the train number or the word “cripple,” he can keep himself and other operators informed of this condition. White lights are generally provided for approach and intermediate track sections and red lights for the “OS” track sections (detector track sections within controlled points). These lights are normally dark and are illuminated during track occupancy or in event of a broken rail or any other condition that causes the track relay to open its front contacts. An audible signal, bell or buzzer, may be provided to work with the OS lights or important approach lights. These are usually arranged to sound momentarily at the time the track-occupancy indication is first displayed.



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Figure 1001. Typical control panel.



Below the track diagram are the employee-call switches, usually one for each controlled point. Such a device (at the field location) may be a horn, ringer or light, or a combination thereof. The switches controlling such devices are two-position, on and off.
Next are the signal-clear indication lights, two for each signal lever. These indications are directional, that is, the light representing the signal governing movements in one direction will light when the corresponding signal is clear in the field.
Next are the signal levers, which are three- position rotary switches. Their normal position is center (vertical) which calls for the corresponding group of signals to display their stop aspects. Turning a lever to the right calls for a signal governing movement toward the right to clear; to the left, for a signal governing movement toward the left. Where two or more signals govern in the same direction, selection of the one to clear is a field function, controlled by local signal selection circuits taken through switch-repeater relays. cTc controlled signals are usually arranged for stick operation, that is, they are automatically put to stop upon acceptance by a train. They will remain at stop until again cleared by the operator. Non- stick operation may be provided if desired.
Below the signal levers are the switch levers, one for each switch or crossover associated with the signals governed by the lever above. These levers are also rotary switches, normally two-position as shown, having the vertical position as normal. Turning 90 degrees to the right calls for the switch reverse. Engraved letters N and R show normal and reverse positions.
Each rotary switch used in GRS control machines is designed to accommodate a lamp in its barrel which, when lighted, shines through a translucent insert. This is known as the switch-correspondence light. When lighted, it indicates that the switch or crossover in the field is not in correspondence with the position of its controlling lever. Some roads prefer to use this lamp to indicate that the associated switch is electrically locked in the field. In such case, the switch-correspondence light is located in the panel directly underneath the lever.
At the bottom of the panel are shown the start buttons, ordinarily used only if the cTc system is coded. When controls are to be sent out, say for example, to reverse switch 18 and clear signal 17R at Ridgeton for a train to enter the siding, the operator turns signal lever 17 and switch lever 18 to the right. Then he pushes the start button directly below these levers. The transmission of the controls to the field will not begin until after the start

button is pushed. The control message, received and deciphered in the field, will ask for switch 18 to reverse and then for the lower unit on signal 17R to clear, indicating that a diverging route is set up. The execution of these controls will, of course, be subject to the local interlocking circuits at the location, including detector locking, approach locking, track and block conditions, etc. as described in the section on relay interlocking.
At the time switch lever 18 is turned to the right, the switch-correspondence light in the barrel of the lever is lighted, indicating to the operator that the switch in the field is not in correspondence with the position of the lever. This light remains lighted until an indication message is received in the control office to the effect that the switch is over (reverse) and mechanically locked. When an indication message is received to the effect that signal 17R has cleared, the signal-clear indication light above and to the right of signal lever 17 is lighted.
The foregoing control panel description is of an assumed typical panel. Variations according to the individual railroad’s preference may be made. For example, some roads prefer one lamp in the barrel of the signal lever to indicate signal-clear, whether right- or left-hand signal, instead of the two directional signal-clear indication lamps shown. Another feature sometimes provided is a lock light for each switch lever. This lamp may be carried in the barrel of the switch lever, with the switch- correspondence lamp located directly below the lever, or vice versa. When lighted, the lock light indicates that the switch is electrically locked in the field and will not respond to controls asking for a change in its position. Signal and switch levers may be transposed, the switch above and the signal below. Switch levers may be three- position, arranged to call for the switch reverse with lever horizontal to the right or to the left. In this way, if a train movement is to be made toward the right, all levers being positioned (other than normal) for such a move may be positioned toward the right; if to the left, all levers would point left. Another pushbutton may be added to be operated in conjunction with the signal lever when a non- automatic (call-on) signal is to be cleared. Such an arrangement ensures against the displaying of such an indication except when deliberately executed by the operator.
Local field circuits may be arranged for either of two basic schemes of cTc operation: with or without preconditioning. With preconditioning permitted, the controls required to change a route for a second train may be transmitted to and stored at a field location in preparatio,-for the second train while a first train is occupying a conflicting route.


With this arrangement, the stored controls will automatically change the route as soon as the locking circuits are released by the departure of the first train. This means that with preconditioning, controls can be initiated by the operator to line up the second route as soon as indications on the control panel show that the first train has occupied the first route.
Sometimes exit lights are incorporated in the control machine. Exit lights assist the operator in readily determining if he has lined up the desired route in its entirety before he pushes the start buttons and sends the controls to the field for execution. This is of particular value for layouts where a number of possible routes diverge from any given entrance point. When the operator desires a certain route, he first positions all required switch and signal levers. At this time an exit light will be lighted at the point on the engraved track diagram showing the point to which his route lineup leads or, in other words, at the point where the train will exit. He is thus assured that he has positioned all levers properly and may then push the required start buttons to begin the transmission of the controls to the field.
If the system is coded cTc, a succession of controls may be initiated on the control panel at one time. The system will store such initiated controls and release them, one at a time, for transmission to the field in rapid succession without further attention on the part of the operator. Any controls so stored, awaiting their turn to be transmitted, may be cancelled by the operator, if desired.
If it is considered necessary to verify the indications from any field location, a recheck switch provided on the control machine’s master panel may be operated in conjunction with the start button for the particular field location. By means of this facility, a complete check of the indications from a field location may be made without disturbing any of the field functions, that is, without changing the position of a switch or the indication displayed by a signal.
If some abnormal condition at one of the field locations causes that station to repeatedly transmit indications into the control office and thus occupy the line to the exclusion of other stations, a “field cancel” switch provided on the power and test panel of the cTc machine may be manipulated, and the impaired field location will be made to retire and free the line.
A facility often added to machines controlling extensive territories is an automatic train recorder. The recorder may be installed as an integral part of the control machine. Records of train move-

ments are automatically made on a constantly moving chart, which is marked with time graduations. The chart is also provided with location identifying lines by means of which the various siding ends, crossovers, junction points, etc., may be identified. Provision is usually made to record the occupancy by a train of each OS track section in the territory. Signal-clear or other desired information may be recorded if desired. The operator, at his convenience, may connect all recording marks made by a train, and in this way the chart becomes a graphic train sheet. (With Traffic Master II, this is printout data.)
Space for telephone, telegraph and other desired apparatus may be provided in the control machine as required. Telephone communication circuits are often combined on the cTc control line with the code circuits. Such facility may be supplemented with the employee call facility, generally provided for use when the operator desires to call a particular field location, and by a voice-actuated call device which will audibly signal the operator when parties call from the field.
Detailed description of an actual cTc circuit would take far more space than is available in a book of this nature. What are described here are elementary principles of operation. For details of a particular system, refer to the appropriate GRS publication.
Non-Coded cTc
In this elementary circuit, Figure 1002, note the line circuit in which a three-position control lever, a neutral indication relay, a polarized relay, an OS track relay contact, and a switch repeater relay contact are all connected in series. The track relay contact and the switch repeater relay contact are used to control the indication relay.
This basic line circuit is duplicated to each field location. It performs four irpportant functions:
(1) controls the switch to normal or reverse, (2) controls the signal to stop or clear, (3) indicates the switch in transit, and (4) indicates track occupancy.
The eastbound train is approaching the siding and the operator intends to direct the train into the siding at Luckey. Throwing the three-position lever 1 upward polarizes control relay 1, and the switch operates to the reverse position. The lower arm of signal 1R assumes the yellow aspect, being controlled through the neutral contact of the control relay and detector contacts of the switch machine.




When the train accepts the signal and moves into the siding, it shunts the OS track section, thereby releasing the track relay. This de-energizes indication relay 1 in the office which, in releasing, lights the track occupancy light on the panel (this part of the circuit is not shown).
When the operator is ready to let the train proceed out on the main line, he raises lever 2 controlling the switch and signals at field location 2. This action reverses the switch. Dwarf signal 2RB will clear after the switch completes its movement and permit the train to enter the main track.
While this first train was in the siding, the operator could have directed a faster train to move past the siding in either direction on the main line.
Of course, additional refinements are incorporated in the practical application; such as, signal stick, signal selection (both direction and route), both approach and detector locking of the switch, and others as desired.
From the signal circuit point of view, cTc is a communication system whereby the man at the control machine can directly impress a supervisory control over the orthodox and time proven signaling elements
- track circuit control of signals, automatic block, and all the types of locking that have been developed for safety of operation, with all safety features incorporated in the field between

the functions. These circuits are shown in the section on interlocking.
This non-coded cTc system requires a separate control wire to each location and a common wire to all locations. It is obvious that the amount of line wire increases very rapidly as the number of functions to be controlled and the length of the installation increase. As a result, techniques were developed to reduce the amount of line wire and increase the transmission distances. Such systems are known as “coded” cTc.
Elements of Coding
The basic object of the coded systems is to transmit the controls and indications between the control office and the field locations over a minimum number of line wires by a series of relatively short current pulses, arranged in code formation. This is distinctive from the sustained energization or deenergization of numerous, separate line circuits. Outbound controls and inbound indications share the same line wires, using them only for short periods of time.
Figure 1003 is a simplified, elementary scheme which illustrates the basic principles of a coded system. Imagine that there isa step-by-step device




Figure 1002. Elemental principles of unit-wire cTc.





Figure 1003. Elemental principles of coded cTc for one field location.

at the control office and another at the field location. Also, imagine that they are capable of being so synchronized that arms A and B can be moved simultaneously to make contacts 1, 2, and 3. At the
office, levers Li, L2, and L3 are connected to contacts 1, 2, and 3. At the field location, polar relays Ri, R2, and R3 are connected to contacts 1, 2, and 3 and may be used to govern the operation of switch machines, wayside signals, etc. The lever contacts are connected to a split battery, the common wire of which is connected to all three relays in the field.
Assume the step-by-step devices are set in motion, stopping for a moment when arms A and B touch contacts 1. Now if lever Li is placed in the down position, relay Ri will change and its neutral contacts, not shown, will close.
When the devices move to position 2, lever L2 is connected to relay R2, but this relay will not operate to call for a change in its controlled functions, since lever L2 was not changed.
On step 3, lever L3 is connected to relay R3, and the stepping cycle is complete. At this point the step-by-step devices could be restored to their original position ready to start the cycle all over again when a new control is to be sent out.
It should be understood that a ‘control” is the action necessary to operate a two-position field function or device, such as a polar relay. Also, an “indication” is the action necessary to describe the condition of a two-position field function or device, such as a track relay.
Figure 1004 is another elementary diagram having two field locations. It shows how one location is selected from among many.

Levers Li, L2, and L3 are to control relays Ri, R2, and R3 at location i, and levers L4, L5, and L6 are to control relays R4, R5, and R6 at location 2. Again there are synchronized stepping devices, one at the control office and one at each field location. When the arm on the master device moves to contact 0, the other synchronized devices do the same.
One step is used to select the location. The 0
contact of the master device is connected to plus
or minus through a front contact of location relay
1 or 2, depending on which relay is energized. The
O contacts of the field step-by-step devices are
connected to the station relays.
The basic principle of selecting the right location to which to send controls is to apply the proper polarity on the line when the arms touch the 0 contacts. This will cause the proper station relay to close its contact and connect the control relays to the line for the controls that follow.
Assume the operator desires to send controls to location 2. When he presses the code start button on his panel, location relay 2
is energized. Note how minus polarity is connected to contact 0 on the master device, so that when all the movable arms touch the 0 contacts the station relays at both locations are polarized to the right. The polar contact closes at field location 2, but remains open at field location 1. Location 2 is thus automatically selected.
The next step, with contacts 1 closed, is similar to the action described for a single location. The desired field location having been selected, lever L4 is connected to relay R4. On step 2, lever L5 is







connected to relay R5, and on step 3 lever L6 is connected to relay R6. In positions 1, 2, and 3, the positions of the levers determine the positions of their respective relay contacts in the field.
In actual practice the basic schemes shown in Figures 1003 and 1004 are substantially amplified as follows:
1. Banks of stepping relays (or electronic circuits) perform the function of the step-by- step devices.
2. Sensitive line relays respond to line circuit energizations and control operation of other relays by local batteries. In electronic coding systems, receivers and transmitters are used.
3. Other relays and circuits or electronic configurations are added to provide starting of the transmission cycles, station selection and registration, and other standard and special features.
Stepping Principles
It has been noted that the step-by-step device must be capable of being synchronized accurately with similar devices remote from it. Several methods were developed, some with rotary switches like the wipers used in telephone exchanges. Then the all-relay type of stepping was developed and has been used extensively although electronic means are now common. The basic principles of the relay type will be described, with the understanding that it is only one of several ways that synchronization can be accomplished.

Referring to the simplified circuit in Figure 1005, the control office and field locations are connected by two line wires, which join the F relays in a continuous circuit so that when energy is applied to the line circuit all F relays are energized.
The stepping circuits are shown for a field location only, for simplicity. They are practically the same in the control office, and, of course, would be the same at each field location in the system.
As far as the stepping action is concerned, it makes no difference whether the code pulses on the line are distinguished from one another by polarity or by their length. Therefore, although the circuit shows a polar line relay for the stepping circuits in the field, a neutral repeater of the F relay, called FA, is used to actuate the stepping.
The SA relay is a repeater of the FA and is used to apply energy to the stepping circuits. Because it is slow-release it remains picked up during the short intervals when the line is de-energized between pulses, known as OFF periods. At the end of a complete cycle, the SA relay releases. Its function then is to remove energy from the stepping relays and restore them all to their original position, ready for the next cycle. In effect it returns the movable arm of the step-by-step device to the starting position. The rest of the relays, the V relays, are concerned with the stepping action, and therefore constitute the relay equivalent of the step-by- step device.




Figure 1004. Elemental principles of coded cTc for two field locations.



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operator starts the action by pressing the start button. The cycle begins with a “conditioning period,” when certain relays are prepared to transmit and receive. The line is energized, as are also the F relays. The FA relay and the SA relays in both office and field pick up, followed by the VP relay. Upon picking up, the VP causes the line circuit to open at the office, thus ending the conditioning period.
The opening of the line starts the first OFF period. The F relays and the FA are de-energized. However, the SA remains picked up, since it is slow-release. Therefore, relay VI will now pick up, through a back contact of V2 to make certain the stepping proceeds in proper sequence. Once Vi relay is picked up, it remains up for the rest of the cycle by a stick circuit through a front contact of the SA relay.
At this point all the Vi relays are up, at the control office and all field locations. This is the equivalent of closing contact 1 on all step-by-step devices.
During the first OFF period, the VP relay is held up by a stick circuit through a front contact of SA relay and a back contact of FA.
As soon as the Vi relay in the office picks up, the line is again energized, thus starting the first ON period. Both F relays are energized. The FA relay picks up and re-energizes the SA. The stick

circuit to VP relay is opened and VP releases. This, as before, causes the line circuit to open at the office, thus ending the period.
The second OFF period is now started. The F relays and the FA are de-energized, but the SA stays up because it is slow-release. The V2 relay now picks up, checking that V3 is released and Vi is picked up. All V2 relays are thus picked up all along the line, the equivalent of closing contact 2 on the step-by-step devices.
When V2 relay in the office picks up, the line circuit is again energized, starting the second ON period. Again both F relays, the FA and the SA are energized. The VP relay picks up through a back contact of V3 and a front of V2 relay, checking their proper position in the cycle.
When VP picks up, the line circuit opens at the office, starting the third OFF period
- and so on, until the system steps through the entire cycle and the last step relay is picked up. At this point the line is de-energized and remains de-energized long enought to cause the slow-release SA relay to release and restore all the step (V) relays to normal.
The number of step relays in a system depends upon the number of controls or indications to be transmitted, and the number of field locations to be selected.


Figure 1005. Stepping circuits.





In the simplest form, each step can be considered as a channel on which either of two things can be done to provide character.
In such a system, the capacity in stations is 2 to the nth power, where n is the number of steps used in the station selection portion of the code. That is, 2 selections on 1 step, 4 on 2 steps, 8 on 3 steps, and so on.
The common siding end location requires 3
steps for controls:
1. Switch normal
- switch reverse.
2. Signal left stop
- signal left clear.
3. Signal right stop
- signal right clear.
There is often an additional switch or other control, such as a maintainer’s call, required. Therefore, 4 steps are generally allocated for controls.

Modern code systems using electronic stepping techniques and line currents of carrier frequencies enormously increase the speed and capacity of coded control systems.
Carrier Control Operation
It should be borne in mind that modern electronic coding systems are basically carrier systems. We are speaking here of carrier superimposed upon a relay type code system.
It was often necessary to divide a large relay coded centralized traffic control territory into two or more sections, each handled independently from the same control office. This would ordinarily have required a separate pair of line wires for each cTc section.

Figure 1006. Schematic diagram of GRS carrier control, showing how a number of remote cTcsections may be controlled over one pair of line wires. The length of each section depends on local requirements.

This converts carrier codes of frequency for section 3 into d-c. codes, and vice versa. Carrier frequencies for sections beyond are by-passed.

First Converter Unit
This converts carrier codes of frequency for section 2 into d-c. codes, and vice versa. Carrier frequencies for sections beyond are by-passed.

Control Office Units These convert conventional d-c. codes into carrier codes (and vice versa) for control of sections 2, 3, etc.


However, by means of carrier control, Figure 1006, one pair of line wires serves the whole territory. Carrier control consists of providing carrier- frequency currents that act as a connecting link between a control office and one or more remote sections of coded cTc. The first cTc section is usually handled directly from the control office without the aid of carrier. The second section is remotely controlled from the same control office by means of carrier currents superimposed on the line wires of the first section. A third section can be controlled by means of carrier currents of a different frequency superimposed on the same line wires of the first and second sections. Additional sections can be controlled in a similar manner if required.
Carrier control can also be used to control remotely a complete cTc territory from a control office located some distance from the controlled territory. In all of these applications, simultaneous and independent operation of each of the cTc sections is an inherent feature of the system.
The characteristic pulses of the cTc codes are converted into pulses of coded carrier currents for transmission to and from the control office. At the beginning of each carrier section there is a code unit which converts carrier current impulses into d-c code impulses and vice versa for sending back indications to the control office. A similar code unit at the control office converts carrier impulses into d-c code impulses and vice versa, for the control of cTc sections beyond the first section.
There are usually a variety of ways of implementing a technical concept such as coded communication, and this is true of cTc coding. GRS has developed a number of coding systems since introducing cTc. These have reflected changes in communication technology, and also have reflected expanding railroad requirements for field location capacity, number of control and indication functions, speed of operation, and adaptability to specific types of communication plant, e.g., dedicated wire line, telephone circuit, microwave, etc.
Coding systems for cTc are specialized applications of communication science, one of the most rapidly advancing areas of technology. It is to be expected that GRS coding systems will change to reflect these advances. Descriptive literature will be available from GRS as such developments occur.

Major features of the principal GRS coding systems available at the date of publication are summarized in brief descriptions below. The order of listing is roughly in increasing order of system speed and capacity, recognizing that some overlap exists. Choice among alternative coding systems capable of handling a proposed installation requires an analysis of factors pertaining to each installation.
System capacities indicated in the descriptions are typical single-system maximums. In general, if the number of field stations required decreases, the number of controls and indications available per station increases, but not in proportion. Moreover, systems may be installed end-to-end to provide station capacities in excess of those indicated.
Type J Coding System
1.The Type J coding system, Figure 1007, is suitable for use in single-track territory, or low- density double-track territory.
2. System capacity permits 64 stations, with 9 controls and 10 indications per station.
3. Step-by-step relay coding is used for controls and indications. Controls are transmitted as d-c polar codes on a two-wire line circuit. Indications are sensed at the office as marks and spaces (line shunted or unshunted at the field location) over the same line. The control office drives the field location for both controls and indications.
4. Control or indication cycle transmission time is approximately 4.5 seconds. Controls and indica tions are not transmitted simultaneously.
5. Coding units employ a single type of economical plug-in relay, GRS Type J, minimizing cost and simplifying maintenance.
6. Installations may be expanded, up to maximum capacity, by adding relays in increments of two. Carrier link may be used to extend operations.
Type Dl Coding System
1.The Type Dl coding system, Figure 1008, is suitable for use in double-track territory with moderate traffic. Capacity is sufficient to handle consolidation of moderate-size interlockings.
2. System capacity permits 64 stations with 12 controls and 12 indications per station for a single cycle (19 steps). With double-cycle operation (38 steps), capacity is 64 stations with 29 controls and 30 indications per station.




3. Step-by-step relay coding is used for controls and indications in conjunction with solid-state electronic counters and FSK (frequency shift keyed) carrier.
4. Controls are transmitted over a two-wire line via FSK carrier, Indications are returned, by FSK carrier on another channel over the same line, in respons to a roll call of field locations initiated at the control office.
5. Locations having changes to report respond by generating an indication when reached in the roll call. Scanning is suspended during control and indication cycles.
6. Control and indication transmission time is approximately 2 seconds for a single (19-step)

cycle and 4 seconds for a double (38-step) cycle. Controls and indications are not transmitted simultaneously.
7. Line battery is not required. The system is readily applied to commercial telephone circuits, leased lines, or microwave links.
Type E2 Coding System
1.The Type E2 coding system, Figure 1009, is capable of handling heavy traffic on single track, moderate traffic on multi1e track, and consolidation of interlockings.



Figure 1007. Organization ofTypeJ coding system.




Figure 1008. Organization of Type Dl coding system.







2. System control capacity permits 64 stations with
12 controls per station for a single cycle (19 steps). With double-cycle operation (38 steps), control capacity is 29 controls per station.
3. System indication capacity permits 62 stations with 10 indications per station.
4. Step-by-step relay coding is used for controls. Single-cycle control transmission time is approximately 2 seconds. Controls are transmitted as d-c polar codes on a two-wire line circuit, or as frequency shifts when carrier is used.
5. Indications are continuously scanned and are transmitted from field stations via carrier. An additional FSK carrier, transmitted from the office, synchronizes the indication function. Typical time for a complete system scan and indication update for a 62-station system is 4.6 seconds, and is independent of control code activity.
6. Relays and electronic modules are plug connected, simplifying maintenance and facilitating system change or expansion.
Type Li Coding System
1. The Type Li coding system, Figure 1010, is capable of handling dense traffic in multiple track territory, including rapid transit lines.
2. Control capacity permits 62 stations with 10 controls per station.

3. Indication capacity permits 62 stations with 10 indications per station.
4. Controls utilize electronically generated mark! space codes transmitted via carrier. Time to transmit a control depends on the code-bit rate of the office-field communication link, but is typically on the order of 150 milliseconds.
5. Indications are continuously scanned and are transmitted from field locations on a second carrier channel. An additional carrier channel, transmitted from the office, synchronizes the indication function. Typical time for a complete indication update for a 62-station system is 4.6 seconds, and is independent of control code activity.
6. Relays and electronic equipment are plug connected, simplifying maintenance anf facilitating system change or expansion.
System 4000
i.System 4000, Figure 1011, is an electronic coding system capable of handling consolidation of territories with heavy traffic. Micrologic integ rated circuits provide flexibility of function and permit compact “packaging” to minimize the number of modules required. Operation may be on open-wire line, via telephone circuit, or over teletype channels.



Figure 1009. Organization of Type E2 coding system.






Figure 1010. Organization of Type Li Class M coding system.

Figure 1011. Organization of System 4000.

2. Control capacity is flexible. Up to 50 stations can be accommodated, with a substantial number of controls per station, depending on the amount of data to be sent.

3. Indication capacity is also flexible. Up to 62 stations can be accommodated, with a substantial number of indications peT station, depending on the amount of data to be sent.







APPL CAT ION _______





4. Control and indication codes are transmitted at high speeds via carrier at rates up to 600 code bits per second. Actual message time, control or indication, depends on message length.
5. Modular design permits changes and expansion without disturbing the basic circuit structure.
6. Field and office code unit modules are interchangeable, and a complete system check is possible by means of only two plug-in test modules. Simplified maintenance results.
1. Datatrain, Figure 1012, is a maximum-performance coding system capable of handling large- scale consolidations with heaviest traffic. LSl (large-scale integration) logic circuits provide information-handling capacity and flexibility of application necessary for such projects. Operation is by carrier over open-wire line, cable, telephone carrier, or microwave.
2. A small digital computer (minicomputer) provides message formatting, indication scanning, code validity check, and information processing. It is possible to use an existing computer in the system.
3. Controls and indications are transmitted as mark/space codes. Transmission speeds normally range from 110 to 1800 bits per second, with

9600 bits per second attainable. Actual transmission time per control or indication code depends on message length and bit rate.
4. Control capacity for a 62-station system is up to
256 controls per station.
5. Indication capacity for a 62-station system is up to 320 indications per station.
6. Applicability to expansion projects is facilitated by ability to interface directly with existing computerized systems, and by easy adptability to interfacing with other types of cTc systems.
7. Modular design facilitates future changes or expansion. Circuit boards interchangeable between office and field locations simplify maintenance and minimize maintenance parts inventory.
The advantages of cTc provide a strong incentive to expand areas under control and, beyond that, to consolidate at one control center the supervision of cTc territories originally installed as isolated segments. High-capacity high-speed coding systems and efficient communication links offer the technical means of implementing large-scale cenFIELD STATION 1

Figure 1012. Organization of Datatrain coding system.









tralization. But a limiting factor could be the ability of personnel to absorb information efficiently from the system, and to transfer to the system commands for the functions to be implemented.
Consideration must thus be given to the interface between the cTc system and personnel. The primary interface is at the control console, between the operator on duty and the cTc system. But in a broader sense, avariety of interfaces exists, including those with personnel at management level who need information, such as schedule performance and other operating data, for managing the business aspects of the railroad and for planning procedures aimed at improvement.
The Traffic Master control centers described below help to facilitate the flow of information and command decisions across the man/system interface.
Traffic Master
When a cTc installation includes a large number of controlled locations, or incorporates complex interlockings, the panel space required for panel- mounted control levers increases. Thus not all levers may be within easy reach of the operator. The resulting inconvenience and possible fatigue can adversely affect operator efficiency.
The GRS Traffic Master control console, Figure 1013, recognizes this problem. The console includes a track indicator panel, auxiliary panel, and pushbutton panel. The track indicator panel is generally similar to that for individual lever control, showing the geographical track layout for the controlled territory, with panel lamp indications for track occupancy, switch position, signal clear and

Figure 1013. Typical Traffic Master control console.

other functions. The auxiliary panel shows siding capacities and contains jacks which provide track and switch blocking (out of service) when tokens are inserted.
The pushbutton panel includes an essential feature of Traffic Master: concentration of control at the operator’s fingertips regardless of system size.
An operator’s control actions comprise two elements: (1) selecting a field location; (2) generating a command (cTc control) which orders the cTc system to carry out functions at the chosen location. With individual lever control, selection of field location occurs when the operator moves his hand to a specific panel position. The command function occurs when he operates panel-mounted controls at that position. Controls are duplicated for each panel position as field functions require.
With Traffic Master, locations are selected by pressing location-selection buttons on the pushbutton panel. All locations are thus “reachable” with equal ease. After the location is selected, field functions are controlled by operation of additional buttons on the pushbutton panel. Only one set of pushbuttons is needed for control purposes, since the same button may be used to control similar functions, such as a switch or signal, at any location.
Micro Traffic Master
Micro Traffic Master derives its name from the combination of Traffic Master control center design with the use of electronic microprocessors to implement the office code system and application logic.
A movable, desktop keyboard unit provides for entering commands. Indications are displayed on a track diagram, which may be large-scale, wall or pedestal mounted, or may be of miniaturized design for direct mounting on a console. Microprocessors read keyboard input and generate corresponding codes to the cTc system. Similarly, incoming indications are decoded and indication lights (or audible tones) are actuated by microprocessor output.
Micro Traffic Master control centers interface readily with all cTc code systems in common use, thus are usable with existing installations. Conversion of older control center installations is facilitated by the ability to share control with existing control machines durin the transition period.



Multiple systems can be linked locally or by data communication lines for multi-division consolidation. In a similar way, multiple control offices can be linked to a minicomputer system to establish an Operations Reporting System (described later under Traffic Master II) offering full monitoring, reporting, and management interface capability.
Traffic Master II
Traffic Master II, Figure 1014, brings the flexibility and information-handling power of computer technology to control centers for cTc and NX interlockings. Fingertip location selection and control are combined with computer-generated color video displays which replace the fixed diagrammatic control panel. With computer-generated video display, changes in track layouts in controlled areas, extensions of territory, and consolidation of territories can typically be handled without physical changes at the control center. Modifications in computer programming take care of changes in track diagram displays and other information.

train-describer identification numbers, alarm conditions, and a variety of plain language system messages.
Operating Technique
A typical operator’s keyboard is shown in Figure 1015. The operator uses the keyboard to communicate command requests to the computer. Locations and functions to be carried out are identified by pressing appropriate keys.
The requested commands are repeated in English (abbreviated to save space) on the display unit. If the commands are as the operator desired, he presses an EXECUTE key. The system, through the computer, processes the command including a check on its appropriateness in the light of field conditions. If the command is not compatible, a message is displayed to aid the operator in making corrections. If acceptable, the command is translated into the cTc control codes required to carry out the field function. Five commands can be entered and stored for automatic execution in proper sequence when field conditions permit.
Figures 1016 through 1019 illustrate a typical control/display sequence for two trains making a meet.
Figure 1020 shows how track and switch blocking are displayed on the operator’s video unit, and the appearance of special alarm and information messages.
Traffic Master II includes a train describer system which provides specific identification of trains operating throughout the territory. Each train is assigned a number which the system uses to keep track of the train as it moves over the railroad. The same identification number is used for references and records that the system is called upon to furnish. By assigning priorities to the trains as identified, Traffic Master II is capable of completely automatic dispatching of trains in accordance with such priorities.
Operations Reporting System
The Operations Reporting System (ORS) is a capability of Traffic Master II that automatically acquires train performance information, consolidates train performance data, and outputs reports as required. The need for manual record keeping is greatly reduced, allowing operators to concentrate effort on the primary task of efficient train dispatching.

[ZT 1

Figure 1014. Typical Traffic Master II control console.
One or more overview video displays are included that show the entire territory, with indications of routes, track occupancy, and related information. Each operator has at his work station a keyboard, and a video display unit is located in his immediate field of view. The operator can call up on his video unit, essentially instantaneously, a display in large-scale format for any desired location. Included are details on routes, track occu pancies, switch alignments, signal aspects,



Figure 1016. The operator keys in location 4 and it is instantly displayed on the control VDU. Note that switch 2 is normal (track line not connected) and switch 4 is reverse (track line connected).

Figure 1017. The operator calls for switch 2 reverse and signal 1 R clear for a route onto the siding, and switch 4 normal and signal 3L clear for a route down the main line. After checking the commands (upper left corner of VDU), he pushes the execute key. The track lines in the called-for routes change from white to yellow, and the IR and 3L signal symbols and switch points ,flash yellow while the switch machines are in transit.

Figure 1015. Typical operator’s keyboard, Traffic Master II.




Figure 1018. After the signals clear, both the signal symbols and routes change to green. The red route in approach to signal 1 R denotes train 37 on the approach circuit.
Operating data is stored in computer memory as events occur. This information may be retrieved in specified formats, for viewing as a video display, or printed out. Typical reports include:

OS Report

Train Reports

Entry and leaving times for all trains at a station.
Progress of individual trains,
with times at all stations en


Block Report Trackage out of service (blocked), with boundaries thereof, and times blocking was set and released.

Signal Report

Signal-clear and signal-stop times, by signal and shift.

The CR5 may also be used to produce printed train sheets ready for the operator’s signature.
Multiple display and printer terminals can be installed to provide access to CR5 data as widely as desired. Supervisors with video display units or printers can use these to monitor current conditions.
If train orders are necessary for any reason, the operator can call up the requisite from on his dis pla

unit and key in the special data needed for the situation to be covered by the order. A printout can be produced immediately. It is also feasible to include mobile printers in locomotive cabs so that hard copy documents, such as train orders, can be transmitted without delay.

Figure 1019. As the trains occupy their respective routes, the signal symbols and track lines change to red.

Figure 1020. Track blocking is displayed by blue line. Switch 2 blocking is displayed by a blue track line at the point of route divergence. Maintainer call in effect (MC) and an alarm - power off (P0) - are displayed below the site name.