US3828307A

US3828307A - Automatic traffic control system

Info

Publication number: US3828307A
Application number: US00157871A
Authority: US
Inventors: E Hungerford
Original assignee: Georgia Tech Research Institute
Current assignee: Georgia Tech Research Institute
Priority date: 1971-06-29
Filing date: 1971-06-29
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06

Abstract

An automated control system is disclosed that is particularly adapted for use in regulating urban traffic flow. The system includes a central control facility linked with a plurality of remote terminals over a unitary communication channel, which is preferably equivalent to a voice grade, non-compensated telephone line. The central control facility includes a computer coupled through interface equipment with a master transceiver. The master transceiver couples the computer and interface equipment with the communication channel. Each of the remote terminals, which are coupled to the communication channel in parallel, party line fashion, includes a remote transceiver coupled through interface equipment to a traffic control device, such as a signal light. An emergency vehicle locator may also be included in each remote terminal. Vehicle detectors may be coupled to the communication channel through the remote terminals or through separate remote transceivers to provide a measure of traffic flow parameters.

Description

United States Patent 1191 1111 3,828,307

Hungerford Aug. 6, 1974 AUTOMATIC TRAFFIC CONTROL SYSTEM IBM Technical Disclosure Bulletin, M. Druckerman, [75] Inventor: Ernest Timmons Hungerford, August 1964 pages 211 &

Atlanta, Ga. Prima ExaminerKathleen H. Claff 1 [73] Asslgnee: Georgla Tech Research Insmute ASSZ'SIZI Examiner-Randall P. Myers Atlanta Attorney, Agent, or Firm-Newton, Hopkins & [22] Filed: June 29, 1971 Ormsby [21] Appl. No.: 157,871

[57] ABSTRACT 'C 340/ An automated control system is disclosed that is par- 0 ticulafly adapted for use in regulating urban traffic [58] Field of Search 340/35, 37, 40, 41 flow. The System includes a central control facility linked with a plurality of remote terminals over a uni- [56] References cued tary communication channel, which is preferably UNITED STATES PATENTS equivalent to a voice grade, non-compensated tele- 3,090,032 5/1963 Shand et al. 340/41 phone line. The central control facility includes a 3,l 19,093 H1964 willya rd 340/40 computer coupled through interface equipment with 3 3,159,817 12/1964 Hendricks et al 340/41 master transceiver. h master transceiver couples the g v l computer and interface equipment with the communi- 3247482 4x966 g g 340441 cation channel. Each of the remote terminals, which 312541324 5/1966 cascimli'21111]IIIIIIIIIIIII IIIII 340/35 are wills Eommunicatim Channel Parallel, 3,268,814 8/1966 DuVivier 340 40 Party llne P m Includes? remote transcelver 3,302,170 l/l967 Jensen et a1. 340/40 p e through Inte ace equipment to a traffic control 3,305,828 2/ 1967 Auer, Jr. et al 340/40 device, such as a signal light. An emergency vehicle 3,328,791 6/1967 Casciato 340/35 locator may also be included in each remote terminal. 3,423,733 H1969 Aver, Jr. e! 40/4l Vehicle detectors may be coupled to the communicag; Q et tion channel through the remote terminals or through en HC 5 3,506,808 4/1970 Riddle, 11. et a1. 340/35 figig to a measure of 3,594,719 7/1971 EndO et a1. 340/40 MW, M 3,605,084 9 1971 Matysek 340 40 3,675,196 7/1972 Molloy et a1 340/35 OTHER PUBLICATIONS Computer-Controlled Vehicular Traffic, Gordon D.

Friedlander, IEEE Spectrum, February 1969, pages 33 Claims, 18 Drawing Figures |{I0 ,Ii CENTRAL CONTROL FACILITY ,16 1 ,22 l I COMPUTER 1 1 A T R 1 COMPUTER INTERFACE X E mQ l EQUIPMENT 1 l 14/ g l VlSUAL l 1 DISPLAY 5 1 I BOARD I I I F REii0 l 'E 1E Rl11l1lKL 56 i I 5 REMOTE TRANSCEIVER REMOTE VEHlCLE I E 'QEF INTERFACE l TERMINAL DETECTOR I LOCATOR EQUIPMENT L l I l I 28 I 32 TRAFFIC I l 20 CONTROL I I DEVICE L I PAIENTED MIG 6 I974 IIEEI an! 14 K W N U 2 W m, C VIII T I I l I I I I I ll 4 R E mm Mm mm R Y ZI I "l C T m HEN vI A LA L UFM AILD 0 P P P m E M W m CWm W C L M. T.. I m

R E U P M O C 2% PH llllllllll IIL 6 2 T L E CN CL AE IO M R F F E N W m M W M a M RoE Mo WE TCD F M E R 0x T 2 M E F T R 0 E0 M CTI E A u HC Wm v.. L F lllllllllllll IIL R E 5 a C E 0 EU d/ vD I O I 4 2 L F I MM 0' MM m T ROI 9 cDuNT couNr T2 I n oI CENTRAL FACILITY COUNT COUNT Ito) COUNT COUNT COUNT TIMEDASE SYNC ALERT GATE 34 DATA TRANSMISSIDN GATE I DATA INPUT GATE RESPONSE GATE (b) SYNC INTERVAL COMMAND INTERVAL RESPONSE INTERVAL INVENTOR ERNEST T. HUNGERFORD B, m W A ATTORNEYS REMOTE TRANSCEIVER TIMING DIAGRAM PAIENIEDM sum sum as or 14 PAIENIEDAIIB 61w SHEET 10 (IF 14 PAIENIEDIIIB LOCAL CONTROLLER CAM SWITCHES LOG/C sum 12 0F 14 AND #| GREEN AND #ZGREEN TRAFFIC LAMP INDICATOR AC POWER SOURCE FIG. I5

OR GATE BIT LINE#2 BIT LINE#3 BIT LINE#4 BIT LINE#5 AND ATTACHED TO#I LINE OUTPUT FROM LOGIC FIG. I4

PAIiNTEU B M 3,828,307

saw 13 or 14 BITLI E2 BIT LINE 3 1 AUTOMATIC TRAFFIC CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates generally to communication networks, and more particularly to an automatic communication system for use in traffic control.

2. Description Of The Prior Art In metropolitan areas with populations greater than 100,000, the vehicular traffic and transportation environment is becoming more complex, and satisfactory control of vehicular traffic flow presents many problems. In some areas attempts are being made to solve the varied problems by implementation of centralized, computer operated traffic control systems. Whether the computer utilized is analog or digital, significant problems exist in providing adequate communications between the central facility and the individual traffic control devices which are located on the street.

Most existing systems require essentially one dedicated line of communications from the central facility to each individual remote traffic control device. A remote traffic control device may be a conventional signal light or traffic light located at a highway or street intersection, for example. Naturally, in any city of reasonable size, hundreds, or perhaps thousands of such individual signal lights are required to keep traffic flowing smoothly. Consequently, hundreds or thousands of individual communication lines are required, to make such presently existing systems operational.

In addition, where various types of vehicle detection devices are utilized, individual communication lines are also required for these units. Vehicle detection devices may detect the presence of a vehicle or measureother data related to vehicular traffic flow, such as vehicle speed. Vehicle detection devices may be located on the streets immediately adjacent to an intersection or they may be spaced along a street or arterial. The data furnished by vehicle detection devices may be utilized in a computer facility to establish, compute, or select a desired traffic flow plan for the indicated traffic conditions.

In any centralized traffic control system, this current practice of utilizing a single,'dedicated communication line to each traffic control device or vehicle detector can be extremely expensive and can result in the need for a large amount of complex interface equipment. The initial installations of the many separate communication lines required are also costly. In addition, if the lines are leased from the local Telephone Company, the continuing lease costs of many lines can be significant, particularly for the larger systems.

Consequently, there is a need for an automated traffic control system that includes an efficient and relatively inexpensive communication link between its central control facility and each remote traffic control device and vehicle detector.

SUMMARY OF THE INVENTION tomated traffic control system including a communication network which is relatively inexpensive to maintain.

Yet another object of this invention is to provide an automated traffic control system including a communi cation network which is relatively simple and inexpensive to install.

A further. object of this invention is to provide an automated traffic control system in which the central control facility is linked to a plurality of remote traffic control devices and vehicle detectors over a single communication line.

Another object of this invention is to provide, a novel computer controlled automated traffic control system.

A still further object of this invention is to provide an automated traffic control system having novel remote terminal systems.

Yet another object of this invention is to providean automated traffic control system including emergency vehicle locators.

Another object of this invention is the provision of an automatedtraffic control system which expedites the travel of emergency vehicles in urban areas.

Briefly, these and other objects of the invention are achieved by providing a central control facility includ- BRIEF DESCRIPTION OF THE DRAWINGS operation of the Remote Transceiver illustrated in FIG. I

FIG. 4 is an expanded block diagram of the Modulator and Response Receiver sections of the Master Transceiver of FIG. 1;

FIG. 5 is an expanded block diagram of the Logic section of the Master Transceiver of FIG. 1;

FIG. 6 is an expanded block diagram of the Sync Detector, Data Receiver and Response Modulator sections of the Remote Transceiver of FIG. 1;

FIG. 7 is an expanded block diagram of the Logic section of the Remote Transceiver of FIG. 1;

FIG. 8 is a block diagram of an output circuit which may be coupled to the Logic section of the Remote Transceiver illustrated in FIG. 7;

FIG. 9 is an expanded block diagram of the first logic network illustrated in FIG. 8;

FIGS. A, 10B and 10C illustrate is an exemplary circuit and logic diagram for remote control of a sixstreet intersection;

FIG..1 1 is an exemplary circuit and logic diagram illustrating on an expanded scale a portion of the circuit of FIG. 10, showing a remote control circuit for operating the indicator lights for one street of the six-street intersection;

FIG. 12 is a circuit and block diagram illustrating a system for expediting the travel of emergency vehicles;

FIG 13 is a circuit and block diagram illustrating a system for controlling a simple two-street intersection;

FIG. 14 is a circuit and block diagram illustrating an interface network for coupling response signals from traffic light indicators at a given intersection with the associated remote unit;

FIG. 15 is a schematic diagram of an burn-out detection circuit; and,

FIG. 16 is a block diagram of vehicle detector interface equipment which may be used in the instant invention.

DESCRIPTION OF THE .PREFERRED EMBODIMENT I. GENERAL Referring now to the Drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, the instant invention is shown as including a Central Facility 10 for the control of traffic and transportation. Contained within the Central Facility ware a Computer 12, Computer Interface Equipment 14, and a Master Transceiver 16. If desired, a Visual Display Board 18 may be utilized to indicate the current status of all

remote traffic devices

20, 30 and 32. The Master Transceiver 16 is connected to a Communication Link 22, which includes a single communication line. This line may be equivalent, for instance, to a voice grade, non-compensated telephone line. Such a line can be connected through a multiplicity of telephone exchanges if necessary. Also other communication links identical to 22 can be operated from the Master Transceiver 16, if desired.

Spaced along the communication line at arbitrary distances are Remote Terminals 24 which are connected to the Communication Link 22 in parallel, party line fashion. Each Remote Terminal includes a Remote Transceiver 26 for use with a locally attached Traffic Control Device 20. The Remote Transceiver 26 includes Interface Equipment 28 for coupling it to the attached Traffic Control Device 20. The Remote Transceiver permits appropriate remote control of the Traffic Control Device as well as a locally controlled operation of the Traffic Control Device. A Vehicle Detector 30 may be connected locally through Interface Equipment 28 to a nearby Remote Transceiver 26 to the Communication Link 22, or a separate Remote Transceiver maybe used to couple a Vehicle Detector to the Communication Link 22. An Emergency Vehicle Locator 32, comprising auxiliary receiver equipment, may be included in each Remote Terminal 24 such that emergency vehicle information can be appropriately transmitted through the Remote Transceiver 26 to the Central Facility, when desired.

Within the Central Facility 10, the Computer 12 may be either analog or digital. A digital computer is superior for the present purpose since its possible applications are move varied and more flexible. Based on input vehicular traffic data, the software package of the Computer 12 can be constructed for computation of an appropriate traffic control plan or for specific selection of one of several programmed traffic control plans. The appropriate control data are transmitted in the form of commands to each Remote Transceiver. In addition, the computer facility can be utilized for record keeping and appropriate production of hard copy records.

In the Central Facility 10, the Interface Equipment 14 has a two-fold function: (1) It couples coded command data from the Computer 12 to the Master Transceiver l6; and (2) it receives coded response information from the Master Transceiver and couples this data to the Computer.

In the Central Facility, the Master Transceiver equipment generates all pulse timing and frequency information for operation of the Communication Link 22. Appropriate timing signals are input to the Computer 12 via the Interface Equipment 14. In addition, output command data, via the Interface Equipment, are processed and appropriately multiplexed onto one or more Communication Links. Appropriate synchronization information is also generated in the Master Transceiver 16 and appropriately multiplexed onto the Communication Link 22.

At each Remote Terminal 24, the Remote Transceiver 26 is appropriately coupled to the Communication Link 22 in parallel with other remote units on the same communication line. Each remote unit is automatically and periodically synchronized by means of the data received from the Central Facility 10. For each remote unit, this enables specific reception of its own command data. These commands are demodulated and processed for application to the attached Traffic Control Device 20, which may be conventional traffic lights, for example. The locally processed data are coupled to the attached Traffic Control Device by means of Interface Equipment 28. This circuitry applies power to the appropriate lamp indicators of the local Traffic Control Device. This same interface circuity is responsive to the existent state of the lamp indicators. These response signals are processed and coupled to the attached Remote Transceiver 26, where they are further processed and modulated onto the Communication Link 22. Appropriate reception of these response signals occurs at the Central Facility 10, and furnishes one part of the information input to the Computer 12.

In systems which utilize vehicle detection devices, a second category of information can be input to the Computer 12. Data gathered by a vehicle detection device of Vehicle Detector 30 may be coupled by wire to a nearby Remote Transceiver 26 via Interface Equipment 28 for subsequent transmission to the Central Facility 10. On the other hand, each vehicle detection device may be utilized with its own Remote Transceiver. In either case, the data are processed and appropriately multiplexed onto the Communication Link 22 to be utilized by the Computer for generation or selection of an appropriate trafiic flow plan.

In systems where it is desired to locate emergency vehicles, additional reciever circuitry 32 can be included with each Remote Transceiver 26 at each controlled intersection. Sequential response to emergency vehicles as they proceed through a controlled intersection can be generated by the additional receiver circuitry. This information can be processed and appropriately multiplexed onto the attached Communiation Link 22. Emergency vehicle data detected at the Central Facility need not be computer processed, except for record keeping purposes. An appropriate Visual Display Board as illustrated at 18 may be used for analyzing this information The remote control and associated processing of discrete data to and from the Remote Terminals 24 can be accomplished by appropriate time division multiplexing. The circuitry discussed herein is relatively simple and inexpensive.

A timing diagram for the cyclic operation of the system as a whole provides a description of the general system operation. Referring now to FIG. 2, the Central Control Facility time base is depicted in part (a). Several count values and count periods are indicated, which will be discussed subsequently in more detail. A syn alert gate defined by each of

pulses

34 and 36 is shown in part (b of the figure. It is noted that the term pulse is used merely as a convenient term designating the rectangular waveforms shown in the Drawings. Transmitted data contained in this period are utilized for arming of Remote Transceivers 26 for subsequent sync reception. A data transmission gate defined by a pulse 38 is shown in part (c) of the figure and extends for approximately one-third of the total cycle time. All data from the Master transceiver 16 are transmitted during this time, including sync data and individual, discrete command data for each Remote Terminal 24. The syn gate defined by a pulse 40 is shown in part (d) of the figure. During this time, precise synchronization data may be transmitted in the form of a binary coded word. The data input gate defined by a pulse 42 is shown in part (e) of the figure. It is during this time that actual commands are transmitted to each remote unit. The response interval defined by a pulse 44 is depicted in part 0) of the figure. The extent of this interval comprises essentially the remaining two-thirds of the total cycle time. It is during this time that all data responses from all Remote Terminals 24 are transmitted at the remote location and received at the Central Facility 10. Vehicle Detector 30 responses as well as Emergency Vehicle Locator 32 data may be included in the response interval.

Referring now to FIG. 3, part (a), the time base of a Remote Transceiver 26 is depicted. Local counts and count periods are indicated which will be discussed subsequently in more detail. The sync interval gate defined by a pulse 46 is shown in part (b) of the figure. It is during this time that a Remote Transceiver 26 is synchronized, first by coarse sync and second by fine sync signals. The command interval gate defined by a pulse 48 is shown in part (c) of the figure. It is during this time that the particular, discrete command to a given Remote Terminal 24 is received, demodulated, and processed. The response interval gate defined by a pulse 50 is shown in part (11) of the figure. It is during this time that an individual Remote Transceiver 26 processes and modulates data for transmission back to the Central Facility 10.

Other procedural arrangements may be utilized with respect to time sharing on a communication link. For instance, an individual command could be transmitted to the first Remote Terminal or unit. This first Remote Terminal could then respond to the received command and transmit the response back to the Central Facility 10. A second command could then be transmitted to the second Remote Terminal over the same communication line used with the first Remote Terminal. This process would be repeated for each attached Remote Terminal. However, in the preferred embodiment, the procedures refer to a time base construction similar to that depicted in FIGS. 2 and 3.

II. TIMING BASE DESCRIPTION FOR PREFERRED EMBODIMENT OF THE COMMUNICATION LINK SYSTEM The communication cycle is a serial operation comprised of synchronization signals and commands, which are transmitted from the Central Facility 10, and response signals, which are transmitted from the Remote Transceivers 26. In a Remote Terminal 24, the particular command to the Remote Terminal is detected and stored during each communication cycle. The cycle length can be changed or adjusted for any practical extent in time. This cycle length is not directly related to the cycle times of traffic signal devices, and in general, the communication cycle time is less than a few seconds, while a traffic signal device cycle time may extend for many seconds, perhaps minutes. On the other hand, it is possible to maintain absolute timing of an attached Traffic Control Device to less than one second.

The Central Facility time base shown in FIG. 2 will be described in greater detail. This time base may be incremented, for instance, at a rate of 3,600 Hz, determined from a master crystal-controlled oscillator to be described hereinafter. The start of a communication cycle occurs at count 0, referenced as t in FIG. 2(a), and extends for 7,610 counts. Count 761 l is coincident with count 0, at which time the master counter is reset to zero, and the cycle repeats.

After activation of the Communication Link 22 and towards the end of each communication cycle, a Sync Alert Gate pulse 34 occurs. This is shown in FIG. 2(b) and occurs from count 7 251 to count 7301. During this time interval, a low frequency tone may be transmitted, for instance, 750 Hz. This tone may be utilized to signal all attached Remote Transceivers 26 that a synchroni zation interval will occur as the next event. Reception and detection of this frequency tone in each Remote Transceiver may be considered as establishment of coarse synchronization.

At count 7301, the Data Transmit Gate pulse 38 occurs. This gate is shown in FIG. 2(c) and extends through count 0 to count 2301. During the first part of this gate, a string of binary zones may be transmitted at the carrier frequency to count 30. Reception and direction of this signal in each Remote Transceiver establishes a stable carrier reference for subsequent data decoding.

A Sync Gate pulse 40 occurs from count 30 to 51 as shown in FIG. 2(d). During this interval a fine-sync code word may be transmitted at the carrier frequency. Reception and detection of the fine-sync word in each remote unit may be considered as establishment of fine synchronization.

A Data Input Gate pulse 42 occurs from count 51 to count 23011, as shown in FIG. 2(e). During this interval,

all command data are transmitted from the Central Facility 10 to all attached Remote Terminals 24.

A Response Gate pulse 44 occurs from count 2301 to count 7251, as shown in FIG. 20). During this interval, all response data are transmitted from all attached Remote Terminals to the Central Facility 10.

A typical Remote Transceiver 26 time base is depicted in FIG. 3(a). A remote time base may be referenced to the Central Facility 10 time base by establishment of the time T For instance, a remote unit clock circuit (to be described hereinafter) may be operated at 1,200 Hz. This frequency also may be established as the bit rate. If this bit rate is utilized, the remote clock pulses will occur at one-third the rate of the Central Facility clock pulses.

In a remote unit, reception and detection of the low frequency tone automatically establishes a sync interval as depicted by a pulse 46 in FIG. 3(b). Subsequent reception and detection of the reference carrier signal and the fine-sync code word establishes T in each Remote Transceiver. At this time, a Remote Transceiver counter is reset to zero.

The total command interval for a Remote Transceiver occurs from T to count 750, as shown by a pulse 48 in FIG. 3(0). The total response interval for a Remote Transceiver occurs from count 750 to count 2400, as shown by a pulse 50 in FIG. 3(d). Approximately at the time of count 2400, a given Remote Transceiver will receive the low frequency Sync Alert Tone, and the communication cycle will repeat.

The command data for all attached Remote Terminals are transmitted from the Central Facility commencing at count 51, FIG. 2(a). These data are transmitted serially in the form of binary ones and zeros. The command data to any particular Remote Transceiver may comprise, for instance, two, three, four, or five bits. The first bit indicates the mode of control for a particular Remote Transceiver. Thus, a binary one for the first bit signifies the Remote Control Mode, and the particular remote unit will permit the attached traffic signal device to be controlled by commands issued at the Central Facility. If the first bit is a binary zero, the Local Control Mode is indicated, and the particular remote unit will cause the attached traffic signal device to be controlled by the Local Controller at the Traffic Control Device.

If the first bit is a binary one, the remaining one, two, three, or four bits may consist of some combination of binary ones and zeros. Dependent on the number of required functions of the attached traffic signal device, these remaining one, two, three, or four bits may be utilized to convey, respectively, two, four, eight, or 16 discrete. commands. Therefore, the associated Remote Transceiver 26 may be adjusted to accept its own required number of command bits. Correspondingly, the command interval allotted to a given remote unit must be at least equal in extent to the required number of command data bits.

The response signals from each remote unit represent the existent state of any attached traffic device. Thus, the response signals can represent the existent state of on-the-street lamp indicators for an attached traffic signal device, or the existent state of a vehicle detection device, or information relating to the presence of a particular emergency vehicle.

III. DESCRIPTION OF PREFERRED MASTER TRANSCEIVER CIRCUITRY FOR THE COMMUNICATION LINK SYSTEM The Master Transceiver 16 may comprise, for instance, a Modulator 52, a Response Receiver 54, and

a Logic section 56. Block diagrams of the Modulator 52 and Response Receiver 54 sections are shown in FIG. 4. A block diagram of the Logic section 56 is shown in FIG. 5.

The Modulator section 52 accepts input synchronization and command data from a multiplexer 58 in Logic section 56 (FIG. 5) and modulates the carrier with this input. The Modulator 52 is controlled by two gate signals which are generated in the Logic section 56. These signals are labeled as the Data Transmission and the Sync Alert Gates in FIG. 4. The Data Transmission Gate enables a Bi-Phase Modulator 60, and the Sync Alert Gate enables a Sync Oscillator 62. The Sync Oscillator 62 produces a low frequency tone, for instance, 750 Hz, which is coupled to a Summing Amplifier 64. After the Sync Alert Gate, the Data Transmission Gate allows the Bi-Phase Modulator 60 to accept input data. A carrier frequency, for instance, 1,800 Hz, may be generated in the Logic section 56 and coupled to the Bi-Phase Modulator 60. The input data modulate the carrier in a synchronous manner, such that input binary zeros and ones produce, respectively, 0 and ar radians of phase shift on the carrier signal.

The Summing Amplifier 64 combines the modulated carrier and the low frequency Sync Alert signal, amplifies these signals and couples the output to an Isolation Transformer 66. The Summing Amplifier 64 produces the proper signal power and impedance levels, for instance, for driving a voice grade telephone line or equivalent Communication Link 22. The Isolation Transformer 66 may convert the unbalanced output signals from the Summing Amplifier 64 to balanced signals for transmission over the attached Communication Link 22.

The Isolation Transformer 66 also couples input response signals from the Communication Link 22 to the Response Receiver section 54 of the Master Transceiver 16. These Signals are the response signals from each attached Remote Terminal 24. These signals, for instance, may be in the form of a binary, pulse amplitude modulated (PAM) 1,800 Hz carrier. Response sig nals are coupled through an analog AND gate 68 to a Response Signal Amplifier 70. AND gate 68 is enabled by the Response Gate generated in the Logic section 56.

The Response Signal Amplifier 70 provides sufficient gain to drive a Full Wave Rectifier 72. This rectifier converts the bipolar response carrier pulses into unipolar signals. The Full Wave Rectifier 72 is coupled to a Comparator 74 which compares the rectified input signal with a reference voltage which may be set at a predetermined threshold value. The threshold value is set above the average line noise and below the minimum expected signal level. If an input signal to the Comparator 74 is above the threshold procedures convert the unipolar PAM signals into a series of constant voltage amplitude pulses. The resultant pulses are fed into a Low Pass Filter 76 which sets the signal band width and shapes the Comparator output. The Low Pass Filter output will cause a delay of about one-third of a bit time for each input data bit. Otherwise, this output represents the data bit stream-as transmitted from the Remote Terminals 24.

The remaining circuitry in the Response Receiver section 54 converts the detected response data stream into digital data suitable for processing, for instance, by digital Computer 12, via Interface Equipment 14. The response data stream is coupled to two separate circuits. One circuit generates timing signals which are utilized to decode the data, and a second circuit shapes the input data for acceptance and storage in a Shift Register circuit.

For the first circuit, response data pulses are coupled to a first Differentiator 78. The first initial input data pulse is differentiated in the first Differentiator 78 and the leading edge of this pulse is utilized to set a first Bistable circuit 80. Immediately when first Bistable circuit 80 is set the output gate from first Bistable circuit 80 releases a Master Response Bit Clock circuit 82. This clock is adjusted to free run approximately at the data bit rate, for instance, 1,200 Hz. Immediately upon release, the Master Response Bit Clock 82 generates a bit clock pulse, for instance, 10 to 25 microseconds in extent. These Bit Clock pulses continue approximately at the bit rate, until first Bistable circuit 80 is reset by means of a pulse from the Logic section 56.

The output gate from first Bistable circuit 80 also is coupled to a second Differentiator 84. The differentiated output is utilized to set a second Bistable circuit 86 and to reset a Response Counter 88 to zero. In the set state, second Bistable circuit 86 output enables an AND Gate 90 such that the Response Bit Clock pulses are coupled to the Response Counter circuit 88 and to a Bit Clock Delay-92. The Response Counter 88 accumulates six bit clock counts, which corresponds to five complete bit time intervals, including the first initial input data bit. At the end of the 5-bit interval and coincident with the sixth count, the Response Counter circuit 88 generates a reset pulse to second Bistable circuit 86. Consequently, the enable gate to AND Gate 90 is removed, and no further Bit Clock pulses are passed. In addition, a reset pulse from the Logic section 56 is coupled to first Bistable circuit 80 which resets this Bistable circuit. In the reset state, first Bistable circuit 80 disables the Master Response Bit Clock 82. The actual time of the reset pulse to first Bistable circuit 80 occurs just prior to the minimum time possible for input of the next group of response data bits in the next sequential response time interval. Precise timing distinction between the reset-time of first Bistable circuit 80 and an immediately following set-time is augmented by the slight delay of data pulses as they occur from the Low Pass Filter circuit 76. Thus, it will be impossible to attempt setting of first Bistable circuit 80 at the same time that it is being reset by the pulse from the Logic section 56. The output Bit Clock pulses from AND Gate 90 are coupled to the Bit Clock Delay circuit 92. In this circuit, a delay of about one-half bit time is generated and the delayed clock pulses are coupled to a Shift Register 94.

In the second circuit, response data pulses are coupled directly from the Low Pass Filter 76 to a Data Shaper 96. The Data Shaper 96 shapes the response data pulses and couples them to Shift Register 94. The input Bit Clock pulses to the Shift Register 94 are utilized to clock response data bits into the Shift Register Circuit. For instance, the first delayed Bit Clock pulse occurs at a time which is coincident with the time of the first data bit from the Data Shaper 96. This coindicence enables sampling of the response data bit pulse at the approximate midpoint, and permits storage of the value of this response data bit in the Shift Register 94. When five response bits have been stored in the Shift Register 94, a pulse from Logic Section 56 can be used to cause the Shift Register to dump its contents into a Response Storage Register 98. Towards the end of a communication cycle, for instance, at count 7251, the contents of the Response Storage Register 98 may be dumped into the attached Computer facility 12. Use of a Response Storage Register permits rapid dumping of all response data which have been accumulated during one communication cycle, and further enables more efficient usage of an attached, on-line, real-time, digital computer, as illustrated at 12. The response data bits may be utilized in the computer to generate appropriate output commands.

A preferred embodiment of the Logic section 56 is shown in FIG. 5. The logic circuitry may be utilized to generate all timing information for the operations of the Central Facility 10, for instance, timing for the communications cycle, synchronization signals, command signals, and response signals. The Logic section 56 contains a crystal controlled oscillator 100, which, for instance, may produce a continuous 180 kHz signal. All timing functions can be derived from or synchronized with this clock signal. The 180 kHz signal may be divided by 50, for example, in a first Frequency Divider 102 to produce a 3,600 Hz clock. The 3,600 Hz clock may be divided by 2 in a second Frequency Divider 104 to produce an 1,800 Hz clock, and by 3 in a third Frequency Divider 106 to produce a bit Clock of 1,200 Hz. Finally, the 3,600 I-Iz clock may be coupled to a fourth Frequency Divider 108 which is a gating circuit utilized with the response time interval.

A Master Counter 110 utilizes the 3,600 Hz clock input to produce a number of output timing pulses. The total communication cycle time may be determined, for instance, by the 7610 count output, which resets the Master Counter 110 to zero, coincident with the 7611th count. The 7610 count output is also utilized for reestablishing zero phase in the first, second, and third

Frequency Divider circuits

102, 104 and 106.

The 7251 count output pulse sets a first Bistable circuit 112, which generates, at one of its outputs, the Sync Alert Gate. This gate is utilized in the modulator section to release the Sync Oscillator 62. Count 7251 also resets a fourth Bistable circuit 114. In the reset state, the F ourth Bistable circuit 114 couples a logical 1 from its Q output to an AND Gate 116. Count 7301 resets the first Bistable circuit 112. In the reset state, fire first Bistable circuit 112 couples a logical 1 from its Q output to AND Gate 116. These two inputs to AND Gate 116 produce the Command Data Gate at the output of and Gate 116. The 7251 count output pulse also is utilized in the Response Receiver section 54 to dump the response data in Storage Register 98 into the computer facility 12.

The 0030 count output pulse sets a second Bistable circuit 118. In the set state, the second Bistable circuit 118 generates the control gate for use in a Sync Word Generator 120. The 0051 count output pulse resets the second Bistable circuit 1.18 which removes the control gate.

The 0051 count output pulse also sets a third Bistable circuit 122. In the set state, the third Bistable circuit

Claims

1. An automated traffic control system comprising: a central control facility, said central control facility including computer means for processing input information signals and for generating traffic control signals, and computer interface means in said central control facility coupled to said computer for applying said input information signals to said computer means and for transmitting said traffic control signals from said computer means; signal communication means in said central control facility, said signal communication means coupled to said interface means and including multiplexing means; a single communication line coupled to said signal communication means for transmitting signals to and from remote points; and a plurality of remote terminal means coupled to said single communication line in parallel, party-line fashion for receiving said traffic control signals from said computer means and for supplying said input information signals to said computer means over said single communication line.

2. An automated traffic control system as in claim 1, wherein: said communication line includes a voice grade, non-compensated communication line.

3. An automated traffic control system as in claim 1, wherein: said computer means comprises a digital computer facility.

4. An automated traffic control system as in claim 1, wherein: said signal communication means includes master transceiver means coupled to said communication line for transmittIng signals over and receiving signals from said communication line.

5. An automated traffic control system as in claim 4, wherein: said computer interface means includes input-output storage register means for temporariliy accumulating signals to be fed into said computer means and for temporariliy accumulating signals generated by said computer means.

6. An automated traffic control system as in claim 4, wherein: said master transceiver means includes a coarse synchronization signal generating means for conditioning said remote terminal means to receive a synchronization signal.

7. An automated traffic control system as in claim 4, wherein: said master transceiver means includes a fine synchronization signal generating means for preparing said remote terminal means to receive and decode data from said central control facility.

8. An automated traffic control system as in claim 4, wherein: said master transceiver means includes means for generating a stable carrier reference for enabling said remote terminal means to decode data transmitted from said central control facility.

9. An automated traffic control system as in claim 4, wherein: said master transceiver means includes means for establishing a data input gate interval for defining a period during which data is transmitted from said central control facility to said remote terminal means.

10. An automated traffic control system as in claim 4, wherein: said master transceiver means includes means for establishing a data response gate interval for defining a period during which data is transmitted from said remote terminal means to said central control facility.

11. An automated traffic control system as in claim 4, wherein: said master transceiver means includes said multiplexing means for permitting time shared use of said communication line.

12. An automated traffic control system as in claim 4, wherein: said remote transceiver means includes means for recognizing only traffic control signals which are directed uniquely to a particular one of said remote transceiver means.

13. An automated traffic control system as in claim 1, wherein: Said remote terminal means include remote transceiver means coupled to said communication line for transmitting signals over and receiving signals from said communication line.

14. An automated traffic control system as in claim 13, wherein: said remote terminal means include traffic control means for regulating traffic flow; and, terminal interface equipment for coupling said traffic control means with said remote transceiver means.

15. An automated traffic control system as in claim 14, wherein: said central control facility includes a visual display means for displaying the various conditions of said traffic control devices.

16. An automated traffic control system as in claim 14, wherein: said remote terminal means include local controller means for controlling the operation of said traffic control means according to a self-contained predetermined program.

17. An automated traffic control system as in claim 16 wherein: said remote terminal means include emergency vehicle detector means for sensing the presence of emergency vehicles; and, said terminal interface equipment includes means for disabling said local controller means in response to the detection of an emergency vehicle by said emergency vehicle-detector means.

18. An automated traffic control system as in claim 17, wherein: said remote terminal means includes sequencing means for rendering said mean for disabling said local controller means inoperative until after a prescribed signal is received from said central control facility.

19. An automated traffic control system as in claim 17, wherein: said terminal interface equipment includes means for causing said traffic control means to produce a signal indicative of the presence of an emergency vehicle.

20. An automated traffic control system As in claim 14, wherein: said traffic control means include indicator lamp means for producing visual traffic regulating signals.

21. An automated traffic control system as in claim 14, wherein: said remote terminal means include signal generator means for generating a signal in response to said traffic control means becoming inoperative.

22. An automated traffic control system as in claim 13, wherein: said remote terminal means include vehicle detector means coupled to said remote transceiver means for measuring parameters of traffic flow.

23. An automated traffic control system as in claim 13, wherein: said remote terminal means include emergency vehicle detector means coupled to said remote transceiver means for sensing the presence of emergency vehicles.

24. An automated traffic control system as in claim 13, wherein: said remote transceiver means includes data receiver means for accepting said traffic control signals from said central control facility.

25. An automated traffic control system as in claim 24, wherein: said remote transceiver means includes coarse synchronization signal detecting means for preparing said data receiver means to receive traffic control signals from said central control facility.

26. An automated traffic control system as in claim 24, wherein: said remote transceiver means includes fine synchronization signal detecting means for preparing said data receiver means to decode traffic control signals from said central control facility.

27. An automated traffic control system as in claim 26, wherein: said fine synchronization signal detecting means includes means for establishing a stable reference signal for demodulation of said traffic control signals from said central control facility.

28. An automated traffic control system as in claim 27, wherein: said fine synchronization signal detecting means includes phase sensitive means for determining whether said stable reference signal is in phase with a signal from said central control facility, or 180* out of phase with said signal from said central control facility.

29. An automated traffic control system as in claim 27, wherein: said remote transceiver means includes response modulator means for producing pulse amplitude modulation of said stable reference signal.

30. An automated traffic control system as in claim 13, wherein: said remote transceiver means includes logic means for demultiplexing said traffic control signals from said central control facility and for multiplexing said input information signals for transmission to said central control facility.

31. An automated traffic control system as in claim 13, wherein: said remote terminal means include vehicle sensing means for detecting the presence of vehicles.

32. An automated traffic control system as in claim 13, wherein: said remote terminal means include vehicle counting means for determining the number of passing vehicles.

33. An automated traffic control system as in claim 13, wherein: said remote terminal means include vehicle speed detectors for determining the speeds of passing vehicles.