US3047838A - Traffic cycle length selector - Google Patents

Description

July 31, 1962 Filed NOV. 5, 1958 G. D; HENDRICKS TRAFFIC CYCLE LENGTH SELECTOR 5 Sheets-Sheet l 'STl sra maouno OUTBOUND TRAFFIC TRAFFIC DENSITY DENSITY COMPUTER COMPUTER 1c oc 00 I AMPLIFIER VOLTAGE CYCLE LENGTH DETECTOR GENERATOR AND v0 SELECTOR cs CGA LDI 0GB 1c LD2 CGC AMPLIFIER VOLTAGE o0 DETECTOR LD3 cs0 LD4 CGE 0 L05 CGF INVENTOR. LEVEL CYCLE I K DETECTORS GENERATORS G'DONALD HENDR C s iiwA ATTO RNEY July 31, 1962 G. D. HENDRICKS 3,047,833

TRAFFIC CYCLE LENGTH SELECTOR Filed Nov. 5, 1958 5 Sheets-Sheet 2 LG El iJ e m9 D E ll OUTBOUND TRAFFIC cc\ DENSITY COMPUTER 00 VOLT A 65 CYCLE LENGTH DETECTOR GENERATOR A INBOUND v D AND SELECTOR Tlgfillgqc cs 0 I Y 00 COMPUT IC FL, c LC 7 /IST EJP1 i122 s -il 2 T10" I I T ANTENNA Ic-| GEN kI OR fl SENS'T'VE TRIZYJS- ELECTOR TSM TR oc-| cs I TONE ANTENNA GENERATOR T a Y CYCLE TIMING FM IE I TONE SENSITIVE MOTOR RECEIVER AMPLIFIER DEMODULATOR XR TSD 7 TT AMPLIFIER INVENTOR.

FIG. 5

G. DONALD HE NDRIGK 8 BY ATTORNEY G. D. HENDRICKS 3,047,838 TRAFFIC CYCLE LENGTH SELECTOR Jul 31, 1962 Filed Nov. 3, 1958 5 Sheets-Sheet 3 REED OSCILLATORS INVENTO R G-DONALD HENDRICKS ATTORNEY July 31, 1962 G. D. HENDRICKS TRAFFIC CYCLE LENGTH SELECTOR 5 Sheets-Sheet 4 Filed NOV. 3, 1958 s T K o m R Y H MW%E ME N u VH R MD 0 L/ A A T m M a A V D "F G .T Y5 B B R m R as E E F E l LE HA M AA u B PRE AMPLIFIERS 5 Sheets-Sheet 5 .2 .2 w 2 2 Nw ow m a. mm J J 3 1E M M vwvwmv wvwwwwww v m I r M C W .wo .w? m? .mi. m mg m wm3 m5 m2 mmm M a A 6-7 N mm m 0 $$$999 6. W m T July 31, 1962 G. D. HENDRICKS TRAFFIC cycuz: LENGTH SELECTOR Filed Nov. 5, 1958 aposite direction.

This invention relates to improvements on trailic supervised apparatus which automatically relates the duration of a traffic signal cycle to the volume of trafiic in the direction of heavier trafiic along a thoroughfare.

The invention relates also to improvements in tratlic sampling and control on a system of city streets forming a grid. One or more typical streets is selected for sampling, the streets chosen being representative of those within the entire grid.

It has long been realized that different volumes of trafiic can best be handled with trafiic signals set for different cycle lengths. Light tramc flows most expeditiously through a series of intersections signaled with a short cycle that does not appreciably delay a vehicle either on the thoroughfare or on the cross street. As trailic volume increases, progressively longer trafiic cycles are required to pass larger numbers of vehicles with fewer stops and starts.

Until recent years, changes in tratfic cycle length have been programmed from a central station according to a predetermined pattern established from traffic counts and other estimates. However, traflic does not always follow the predetermined pattern and may increase or decrease at various times for various reasons.

The invention relates to apparatus which permits frequent adjustment of the traffic cycle length based on a 100 percent trafiic sample thus permitting high accuracy. The sample is taken at the entry points to the grid or thoroughfare permitting anticipation of change in tratfic conditions within the grid. The apparatus in the local controllers also permits instantaneous lengthening or shortening of the cycle during any portion thereof without altering the split or offset. A change in cycle length does not disrupt the split of the cycle between the thoroughfare and the cross street, nor does it interrupt the progressive offset. The apparatus thus effects a smooth transition from one cycle length to another.

Another feature of the invention is its ability to determine cycle length from the volume of trafiic in the heavier direction along one or more throughways. Known systems base the cycle length on the total volume of trafiic in both directions on one street. It is evident that tratfic conditions are entirely different when, for example, 400 vehicles travel in each direction than when 700 vehicles travel in one direction and 100 vehicles travel in the op- The apparatus disclosed herein determines the volume of traffic in each direction, selects the higher, and determines the cycle length therefrom. Thus, a more realistic cycle length is effected.

One portion of the apparatus is embodied in a novel electronic level selector shown in its preferred form as having six levels. More or fewer levels may be employed without departing from the spirit of the invention. The level selector operates in conjunction with a number of vibrating reed type cycle generators making only one generator effective at a time to supply a particular signal frequency over an interconnecting channel to the drive motor in each local traflic controller. An amplifier is employed with the cycle selector to boost the power output of the device so that it can drive a number of local controller motors. A novel amplifier is employed in each local controller to amplify the incoming signal and to increase the potential applied to the motor in proportion to the frequency so that the motor can supply substantially the same torque at all speeds. Such an amplifier is disclosed in United States patent application 830,03 8, filed July 28, 1959, entitled Constant Current Trafiic Control Amplifier, now abandoned.

Another feature of the portion of the invention within the local controller is its ability to change the complete cycle length rather than only portions thereof. Known cycle changers alter the cycle during the variable portions and switch to constant timing power for the amber intervals, The present invention changes the entire cycle making the same percentage change to each variable portion. A second constant timing device times each constant portion of the cycle. This makes the unit easy to set upand easy to change. The cycle speeds are direct reading; there is no need to add two variable timers and two constant timers to determine total cycle length.

Within one complete traflic cycle there may be any number of variable and constant timing intervals. Additional dial keys are simply inserted in the two dials at each local controller. The device is also easy to convert from two-street to three-street operation, simply by inserting dial keys and breaking out signal-controlling cams.

Another feature of the invention is its ability to control cycle length at a number of local trafific controllers through the use of a single radio channel. The output of a tone generator is modulated by various tones from any one of the vibrating-reed type cycle generators and applied to a radio transmitter. A receiver at each local controller includes an amplifier, a demodulator, a second amplifier, and a synchronous motor which drives the signal changing device. Other signaling impulses including resynchronizing pulses, offset selecting pulses, and split selecting pulses may be transmitted simultaneously without affecting the cycle speed. The radio link is disclosed more fully in United States patent application 830,096, filed July 28, 1959, entitled Remote Control of Traffic Cycle Length.

The present invention is an improvement over any cycle determining device known in the art. 'It attacks the problem directly. It employs two tratfic density computers each of which develops an output potential proportional to the volume of tralfic in each direction along one or more thoroughfares, a voltage detector to determine the higher density, a plurality of trafiic volume level selectors, and a plurality of cycle generators any one of which may be chosen to energize a conductor connected to a motor in each local controller to drive it at one of a plurality of speeds. In another embodiment of the invention a tone sensitive modulator and a radio transmitter may be used with a radio receiver and tone sensitive demodulator in each local controller. In a third embodiment of the invention an electro-mechanical gear changer may be employed in each local controller to change its cycle speed, the gears being shifted remotely under control of the volume level selectors. Such a gear changer is disclosed in United States patent application 727,741, filed April 10, 1958, entitled Tratfic Cycle Selector Apparatus.

Objects The principal object of the invention is to provide an improved electronic traffic control device able to determine trafiic cycle length for an area including intersecting street-s from the density of traffic in the heavier direction on one or more thoroughfares.

It is another object of the invention to provide electronic apparatus for determining thev density of traffic in both directions on a street, discerning the higher, and using the higher density to select a traflic cycle length.

It is another object of the invention to provide apparatus at a central station for generating a plurality of discrete frequencies and for making any one of six frequencies corresponding to six levels of traffic density effective to control the length of a traffic cycle.

It is another object of the invention to provide apparatus at a plurality of local traffic signal controllers for receiving and amplifying any one of a number of frequencies and for operating a synchronous motor therefrom to control the duration of a traflic cycle.

It is another object of the invention to provide an amplifier at each local controller whose output potential is proportional to its input frequency.

It is another object of the invention to provide a trafiic level selector which energizes one of a group of signal generators when energized by a potential gradually variable over a wide range.

It is another object of the invention to provide a generator of discrete frequencies only one of which is amplified at a time depending upon the higher density of traffic on a thoroughfare.

It is another object of the invention to select according to higher traffic density and amplify the output of only one of a group of continuously opera-ting signal generators and to transmit the amplified signal to a group of local controllers to precisely control their speed.

It is another object of the invention to provide a tone generator modulated by various tones representive of various cycle lengths, a radio transmitter, and a plurality of local controllers each including a radio receiver, a tone sensitive demodulator, an amplifier, and a cycle timer.

It is another object of the invention to provide a level detector to determine the level of traffic in the heavier direction, a group of interconnecting channels, and a group of local controllers each having a constant speed motor, and a cycle timing unit driven by the motor through a gear train shif-table over the interconnecting channel.

Figures The invention will be described with reference to the following drawings, of which,

FIGURE 1 is a plan view of a six lane highway having traffic actuated detectors in each lane, inbound and outbound traffic density computers, a voltage detector, a cycle length generator and selector, an amplifier, and a conductor to the local controllers.

FIGURE 2. is a plan view of two one way streets having detectors in all the lanes, two traffic density computers, a voltage detector, a cycle length generator and selector, an amplifier, and a single channel to the local controllers.

FIGURE 3 is a block diagram of a cycle length selector including a voltage detector, level detectors, cycle generators, and amplifier.

FIGURES 4 and 4A are a wiring diagram of the cycle length generator and selector having five level detectors, six oscillators, six preamplifiers, and an amplifier.

FIGURE 5 is a block diagram of a system for transmitting the variable frequency signal using radio.

FIGURE 6 is an isometric view of the cycle timing apparatus in a local controller. The wiring associated with the unit is also shown.

Grid System Controlled by T rafiic on T wo-Way Streets A typical application of the invention is shown in FIG URE 1. A six lane street ST is shown for purposes of illustration; the street may have more or fewer lanes, however. The street has a number of intersecting streets STl, ST2, only two of which are shown. Local intersection trafiic controllers LC control the traffic signals S along the street ST according to a number of plans whose selection forms the subject of this invention.

A traffic density computer is employed for each direction of traffic. The inbound and outbound traffic density computers are labeled IC and OC. Traffic actuable detectors are installed in each lane of the street ST. Detectors D1, D2, D3 in the inbound lanes 1, 2, 3 feed traffic information to the inbound computer IC. Detectors D4, D5, D6 in the outbound lanes 4, 5, 6 feed traffic information to the outbound computer OC. The most accurate sampling is done with detectors in all traveled lanes, but detectors may be omitted from some of the lesser traveled and parking lanes with only a slight reduction in accuracy. Any of the known types of detectors may be used including pressure, electromagnetic, electrostatic, radar, photo electric, or infrared. Detectors of the pressure type will be used in the illustration because they are the simplest to apply, requiring no auxiliary apparatus.

Each traffic density computer as presently constructed is adapted toreceive the output of as many as five traffic actuated detectors. A complete disclosure of a traffic density computer usable with this invention may be found in United States patent application 738,327, entitled Trafiic Lane Control," filed May 28, 1958. The function of a computer is to provide a direct current output potential proportional to tratfic density in one direction. The computers receive signals from the detectors, reduce the signals to a pulse of short duration, eliminate most of the noise accompanying the signals, reduce the pulses by a factor of two, give the remaining pulses a definite duration, integrate the pulse count over a short interval, integrate the count over a long interval, and develop a potential proportional to the integrated count. The output of each computer is available for a number of purposes and may also be read on a meter entitled Vehicles per Hour.

The output of each traffic density computer IC, 0C is fed to a simplified voltage detector VD consisting of two silicone diodes. Both voltages, indicative of traffic density in each direction, are passed by the diodes with the higher voltage being effective in the cycle length selector SC. The lower voltage has no further effect. The output of either computer IC or 00 does not affect the other because of the high back-impedance of the diodes.

The output of the higher traffic density computer IC or 0C is thus applied to the cycle length generator and selector CS. This consists of a plurality of level detectors, a corresponding group of low frequency oscillators and preamplifiers, and an amplifier. If the incoming potential is not sufiiciently high to overcome the lowest level detector, a first cycle plan remains in effect. As trafiic density increases and the potential rises it overcomes successively higher level detectors. The highest level detector to be energized makes effective its corresponding oscillator-amplifier circuit and makes ineffective all lower oscillator-amplifier circuits. The output of the highest effective oscillator-amplifier circuit is amplified it amplifier A and transmitted over a single channel CC to all local controllers LC. The local controllers LC are of the type disclosed in United States patent application 642,469, entitled Multiple Program Traflic Control Systems, filed February 26, 1957. Apparatus described in the present application adapts the local controllers disclosed in application 642,469 to receive the variable frequency, amplify it, "boost its potential in proportion to the frequency, and energize a synchronous timing motor which drives the cycle dial at a speed exactly proportional to frequency. The speed of the cycle dial determines the duration of the various traffic signal intervals comprising the signal cycle. Power to operate the local controllers LC and to illuminate the signals S is taken from lines L1, L2.

Thus the duration of the traffic signal cycle within an entire area of a city is made to vary in incremental steps substantially proportional to the density of traflic in the heavier direction on a typical thoroughfare.

Trafiic System Controlled by Trafiic on One-Way Streets Another application of the invention is shown in FIG- URE 2. The invention may be used on city streets one or more blocks apart that are designated for one-way travel, or on a divided highway having intersecting streets. The street carrying inbound tralfic is labeled IST and has detectors Dll-DIS mounted in its five lanes. The street carrying outbound traffic is labeled 0ST and has detectors D16-D20 in its lane Any of the ,known types of trafiic detectors may be used; pressure sensitive detectors are shown for simplicity. In the interest of economy, one or more of the lesser traveled lanes may not be detected. This reduces the accuracy of the count somewhat, depending on the relative weight of the undetected lanes.

The output of each of the five detectors Dll-DIS in the inbound street IST is fed to individual input terminals on the inbound traflic density computer IC. The output of each of the five detectors D16-D20 in the outbound street 0ST is fed to individual input terminals on the outbound trafiic density computer 0C. In practice, each computer is built to include five individual input circuits. Individual circuits are required so that almost simultaneous signals may be differentiated and not lost.

Each pressure sensitive trafiic detector closes a circuit when actuated by traffic, the circuit usually being closed to ground potential. Two signals are initiated, one for each set of wheels passing over the detector. The signal originated by closure of the detector contact plates is characterized by contact chatter, bounce, and noise. It is the function of the input stages of each computer IC, CC to convert the noisy signal to a chatter-free pulse, one for each axle. The input stages amplify and clarify the signal, give it a very short duration, and reduce two pulses to one. The pulse is reduced to one of short duration so that pulses arriving almost simultaneously will not be imposed on top of each other and lost. Two pulses are reduced to one so that the count of vehicles, not axles, will be registered The short pulses are next given a uniform duration and amplitude, and are then integrated over a short interval. A potential is developed which represents the running average of vehicles arriving over a continuous 20 second interval. This count is next integrated over a variable, running interval which may include counts up to 9 minutes old. A potential is developed to represent the running average of trafiic density in one direction integrated over the running 9 minute interval. The computers are described in detail in application 73 8,327, noted above.

Potentials representative of the density of tratfic in each direction are fed from inbound and outbound computers IC, OC to a voltage detector circuit VD. The circuit consists simply of two diodes each of which is arranged to pass the potential impressed on it. The higher potential is applied to the cycle length generator and selector CS. The lower potential has no effect. One computer is kept from backfeeding to the other by the high back-impedance of the diodes.

In the cycle selector CS the input potential is fed to a group of successively higher biased level detectors. When the input potential is so low that it does not energize any level detector, a first oscillator and pre-amplifier is free to energize an amplifier A. The amplified signal frequency is transmitted over an interconnecting channel CC to each local trafiic signal controller LC. At the local controller LC the signal frequency may again be amplified, increased in potential and utilized to drive a synchronous motor. The motor in turn drives a cycle dial which times the duration of the traffic cycle.

When traffic density increases and the input potential to the level detectors increases, successively higher level detectors are energized which in turn make successively lower frequency oscillators eflective. Only one oscillator is effective at a time although all oscillators operate simultaneously and continuously. Only the oscillator and pre-amplifier corresponding to the highest energized level detector is switched to be effective at any time. All pro-amplifiers are connected to the amplifier A which amplifies the signal from the effective oscillator and preamplifier. The amplified signal is transmitted to the local controllers LC where it determines the speed of the synchronous cycle dial motor and thus the duration of the traffic signal cycle.

The cycle of signal change in an entire section of a city is thus made to conform to trafiic density on one typical thoroughfare, whether the thoroughfare consists of one-way or two-way streets. In the one-way street system it is important to relate the duration of the cycle to the heavier direction of trafiic and to interconnect all controllers along both one-way streets to permit the coordination of cross street traflic.

There may be instances where trafiic cycle length may be determined simply by flow of traflic in one directionas on a one-way street widely separated from. its companion one-way street. If coordination of cross street tralfic may be disregarded, each direction of traffic may have its own independent cycle length. The apparatus required for each street may be reduced to one traffic density' computer, a cycle length generator and selector CS, an amplifier A, an interconnecting cable CC, and a group of local controllers LC. Since this application would find only limited use, and since the various components are identical with those described, the single street systerm will not be further described.

Cycle Selector Having described the operation of the complete system, the cycle length generator and selector will now be described.

FIGURE 2 shows that the output of the inbound or outbound tratfic density computer, IC or OC whichever is higher, is applied to the cycle length selector CS from the voltage detector VD. The higher potential is used as a measure of traific density on the thoroughfare and the cycle length is determined therefrom.

Referring now to FIGURE 3, th voltage detector VD consists of two selenium diodes which pass the positive direct-current potential from the traflic volume computers IC, OC. The output of the circuit is a potential representative of traffic in the heavier direction and is applied to all of the level detectors LDl-LDS simultaneously. Successive level detectors are biased with successively higher biases producing a ladder effect. The bias voltage for each level is adjustable so that different steps in traffic density will be required to trigger the various level detectors. The steps may be those commonly used in trafiic control such as 100, 200, 300, 400, 500, 600 vehicles per hour per lane, for example. The steps may also be calibrated in percent of traffic volume at which the change from one cycle length to the next cycle length is to be made.

When the density of trafiic is very low, as during the hours from midnight to early morning, none of the level detectors LDl-LDS is energized and thus cycle generator CGA is permitted to operate. Cycle A is thus in effect. Cycle A may be the shortest length cycle or may permit all local traflic actuated controllers to dwell with the right-of-way signal illuminated to the main street. If trafiic actuated controllers are used they are permitted to answer calls from traffic arriving on the cross street.

Calls may be answered as they occur, or they may be delayed until a background cycle impulse indicates to successive controllers that the time reserved for main street traflic has transpired and that cross street calls may be answered. If pretimed controllers are used, the signals may be set to provide a flashing right-of-way indication to main street traflic and a flashing stop indication to cross street traflic. This permits cross street traffic to proceed with caution after a full stop, yielding the rightof-way to main street trafiic.

As trafiic density increases during the morning hours the potential from one of the traflic density computers IC, OC may be sufiicient to overcome the bias voltage on the first level detector LD1. When this occurs the first level detector LDI energizes a relay which switches plate potential from an amplifier associated with cycle generator CGA and applies plate potential to an amplifier associated with cycle generator CGB. Cycle B is thus in effect. Cycle B may be a slightly longer cycle or may be a plan which permits the local traffic actuated controllers to answer calls only at certain intermittent times. Thus, a cycle length is established.

As traflic density builds up further it may require additional change in cycle length. As the potential from either of the traific density computers IC or OC increases, it will be sufficient to overcome successively higher biases and cause one of the higher level detectors LD2-LD5 to conduct. As any one level detector LD2LD5 becomes effective it energizes its corresponding cycle generator preamplifier CGC-CGF, respectively, and deenergizes the preamplifier associated with the next lower cycle generator. Only one cycle generator is effective at any time. The cycle generators and their controlling reed vibrators are all oscillating all of the time to reduce the start-up interval and to make the full generator frequency available instantly as required. Their preamplifiers are switched on or off to make the desired cycle generator effective.

Amplifier A receives the preamplified signal from the effective preamplifier associated with cycle generators CGA-CGF. Here the selected frequency is amplified before it is sent out on an interconnecting channel CC to all the local controllers LC. In each local controller LC the signal is again amplified and increased in potential before it is applied to the synchronous motor which drives the cycle timing dial. The portion of the apparatus located in the local controller is shown in FIGURE 6 and is described in greater detail in a later section.

Cycle F, the cycle plan put into effect when traffic density is greatest, may constitute the longest cycle length employed or may be a plan for simultaneous operation of a group of controllers. Simultaneous operation may include a number of controllers operating in unison, or may include a multiple alternate offset plan. The plan chosen to be put into effect would be the plan found to handle heavy trafiic most efficiently for the thoroughfares involved. The plan found to be most eflicient in one city may not be satisfactory in another. Therefore, the plans are made flexible so that the largest number of installations can be accommodated.

The device used to adapt the cycle determining frequency to one suitable for transmission over a radio channel is shown in block diagram in FIGURE and is disclosed in detail in United States patent application 830,- 096, named above. The device used topick up and amplify the signal at each local controller is disclosed in United States patent application 830,038, also named above, and now abandoned.

Cycle Generator and Cycle Selectoir A complete wiring diagram of the cycle generator including reed oscillators, oscillator control circuits, preamplifiers, amplifier, level detectors and plate relays is shown in FIGURES 4 and 4A. FIGURE 4A may be placed to the right of FIGURE 4 in order to view the circuit diagram in its entirety. Six reed oscillators are shown at the left of FIGURE 4. Six oscillator control circuits are shown at the right. Six grid leads continue to the right border and are repeated at the left of FIGURE 4A. FIGURE 4A shows three double preamplifier tubes. Along the right border are shown five potential dividers, and five level detector tubes. Above the level detectors is a final amplifier tube and the output terminal OT. Between the preamplifiers and the level detectors are the plate circuit relays. Each level detector controls a plate circuit relay which applies plate voltage to a single preamplifier which in turn makes one oscillator control circuit effective. greater detail.

A plurality of resonant reed oscillator controls 11A- The circuit will now be described in v 11F are employed to control the frequency of oscillation of an equal number of oscillator control circuits. The resonant reed oscillator control is an electromechanical device of the type described more fully in James G. Biddle Company Bulletin 34-10, dated March 1957. The drive coil 13 is connected in the cathode circuit of triode V1B. When plate potential is applied to terminals marked 3+, tube V1B draws current through drive coil 13 located in its cathode circuit. Drive coil 13 creates a magnetic flux in the reed 14 which momentarily polarizes it allowing the tip of drive reed 14 to momentarily become a magnetic pole. The flux in the coil and that induced in the reed tip interact causing the reed to move toward the opposite pole of the coil. This motion of drive reed 14 is transmitted through the rigid metal bar 15 to reed 16. Control reed 16 is mounted inside of control coil 17; as the tip of control reed 16 moves inside coil 17 its fiux changes and induces a potential in control coil 17. This potential is applied to the grid of tube VIA causing a change in plate current through resistor R1. Increased current through resistor R1 causes a reduction in potential on the left side of capacitor C1. Now-surplus electrons on the right side of capacitor C1 flow to ground through resistor R2 increasing the negative bias applied to the grid of tube V1B through resistor R3, thus decreasing its current flow.

Decreased current fiow through the plate circuit of tube V1B results in reduced current through drive coil 13. 1f the values of capacitors C1, C2 and resistors R1R5 are properly chosen, an oscillatory condition will result causing increased motion of drive reed 14. The amplitude of travel of drive reed 14 increases with each successive current pulse until vibration at the reeds natural frequency is maintained. Oscillation of control reed 16 will control and sustain the oscillation of the tube circuits VIA, V1B through the potential induced in control coil 17. The circuit will continue to oscillate producing a signal of nearly sinusoidal waveform and at the exact frequency of reeds 14 and 16.

Resistor R5 is placed in the cathode circuit of tube V1A to reduce the cathode potential and aid cut-off. Resistor R4 limits the plate current in tube VlB. Capacitor C2 acts to smooth out the current flow through resistor R4.

The output of the controlled oscillation circuit is taken off below plate circuit resistor R1 through coupling capacitor C3. Potentiometer R6 is connected between capacitor C3 and ground. Its tap applies the controlled frequency sinusoidal signal to the grid of preamplifier tube V7A, FIGURE 4A, through grid resistor R7.

Any number of reed oscillator controlled circuits may be employed in the cycle generator, one being required for each cycle length desired. Six oscillator circuits asscciated with tubes V1A, VIB to V6A, V6B are shown, each having different values of resistance and capacitance, and each having reed oscillators 11A-11F tuned for different frequencies.

Plate voltage 13+ and filament voltage is applied to all the oscillator circuits continuously. Thus, all oscillator circuits are functioning simultaneously. Plate voltage is applied to only one preamplifier V7A, V7B to V9A, V93, FIGURE 14A, at a time. Which tube receives plate voltage depends on the position of relay switches 21-25, FIGURE 4A, which in turn depends on the condition of level detector tubes VII-V15. The condition of level detector tubes V11-V15 is determined by the level of the input potential from the higher traffic density computer 1C or OC.

Preamplifier tube V7A, FIGURE 4A, has plate volt age applied to it through resistor R3 When the input potential to the grids of the level detector tubes V11-V15 is low and none of the detector tubes is conducting. With none of the relays 21-25 energized, the plate voltage circuit is complete from terminal B-]-, through relay contacts 25A, 25B, through relay contacts 24A, 24B; 23A, 23B; 22A, 22B; 21A, 21B, through resistor R8 to the plate of tube V7A. Tube V7A conducts if grid potential is applied from oscillator tube V1A. Resistor R9 in the cathode circuit of tube V7A aids cutoff. The circuit configuration amplifies the output of the oscillator maintaining the sinusoidal waveshape of the signal.

The output of the circuit is applied to the grids of final amplifier tube halves VltlA and VltlB through coupling capacitor C4. Both halves of tube V10 are connected in parallel to increase the capacity of the tube.

Resistor R10 is a grid leak resistor associated with both grids of tube V10. Resistor R11 is a cathode follower resistor. The output potential of the cathode follower circuit is taken off through coupling capacitor C and applied to output terminal OT. Plate voltage B-lis applied to both plates of tube V continuously while the master controller is functioning. The output of the device is supplied to all local controllers over the single channel CC, FIGURES l and 2.

The operation of the level detectors will now be described. Tubes V11-V15 are of the thyratron type. They form a level detector. The potential representative of trafiic density is applied to all the grids, but through successively higher impedances and against successively more negative bias voltages. A plate circuit relay controls the plate potential to the next lower level detector tube and to the next lower preamplifier tube. (The lower level detectors are shown near the top of FIGURE 4A and the higher level detectors are shown near the bottom of the figure.) The plate circuit relay also controls power to a neon indicator A-F which shows which level is effective.

One level detector will be described in detail; the others are identical except for impedance values. A negative bias potential 105 v. is applied over line 41 to an adjustable voltage reducing network consisting of a variable resistor R12, a potentiometer R13, and a fixed resistor R14 connected to ground. A tap on potentiometer R13 applies an adjustable negative bias potential to the control grid of tube V11 through grid resistor R15.

The potential representative of traffic volume in the heavier direction arrives from voltage detector VD and is applied to the level detector grids through conductor 42 and grid resistor R16. The difference in positive and negative potentials is effective to control tube V11. Capacitor C6 is connected between the grid and cathode for tube protection purposes. The screen grid is connected to the cathode and to ground.

The plate of tube V11 is connected to a source L2 of 120 volts A.C. through the coil of plate circuit relay 21 and through normally closed contacts on the plate circuit relays 2225 of all the higher level detectors. Plate circuit relay 21 connects the plate of the lowest level preamplifier tube V7A to positive plate potential B+ through contacts 21A, 2113 when deenergized. When energized, relay 21 connects the plate circuit of the next level preamplifier tube V7B to B+ through contacts 21A, 21C. Capacitor C7 is connected in parallel with the coil of relay 21 to maintain the current therethrough during the negative half cycle of the 60 cycle supply L2.

Resistor R17 is switched into the grid bias circuit in parallel with resistor R14 by relay contacts 21G when relay 21 is energized. This permits the circuit to respond to reduction in density-representative potential and fall back to level A when density decreases.

Pilot lamp A is illuminated when the lowest level preamplifier is operating. It is energized from source L2 through contacts 25D, 25E; 24D, 24E; 23D, 23E; 22D, 22E; and 21D, 21E. Other pilot lamps B, C, D, E, F are provided to indicate higher levels and are energized through contacts ZIP-25F, respectively.

To trace a level change, assume that tube V11 is conducting, relay 21 is energized and preamplifier V7B is effective. Its signal output is taken off through coupling capacitor C4 and applied to the grids of tube V10. A sinusoidal oscillation at the frequency established by 10 reed oscillator 11B and tubes V2A, V2B, FIGURE 4, appears at output terminal OT, FIGURE 4A.

Assume now that traffic density increases to a value that permits level detector tube V12 to conduct. Relay 22 is energized and applies plate current 3+ to preamplifier tube V8A through contacts 22A, 22C. Contacts 22A, 22B open and deenergize the plate circuit of preamplifier tube V7B. Thus, the new frequency established by reed oscillator 11C is used to control the output of amplifier tube V10 and is available at output terminal OT.

Further increases in trafiic density and the potential applied to line 42 will result in further stepping of the level detector. When traffic density approaches its highest value, level detector tube V15 will conduct and energize relay 25. Contacts 25A, 25C will close and supply plate potential B+ to tube V9B making preamplifier V9B and reed oscillator 11F effective. In the application of the level detector to traffic cycle length control the lowest level oscillator will generate the highest frequency which in turn drives the cycle timing motor at the highest speed resulting in a short cycle length. The highest level oscillator will generate the lowest frequency resulting in a long cycle length.

To complete the description, assume now that traffic density decreases and that the potential from the voltage detector VD applied to the level detector grids also decreases. If level detector tube V12 has been conducting, for example, and now its bias potential is no longer sufiicient to sustain conduction, the tube will cease to conduct when the A.C. potential from line L2 goes through its negative half-cycle. Plate circuit relay 22 will be deenergized closing contacts 22D, 22E admitting L2 power to the plate of the next lower level detector tube V11. The potential from the voltage detector VD will be sufficient to permit tube V11 to conduct because traffic density cannot fall off instantaneously. When relay 22 was deenergized it removed plate potential from preamplifier tube VSA; when relay 21 was energized it applied plate potential to preamplifier tube V7B. Thus, the frequency developed by reed oscillator 11B replaces that developed by reed oscillator 11C.

Thus the appropriate traffic cycle control frequency is selected from among a group of continuously generated frequencies and made available at an output terminal for control of a number of local traffic signal cycle controllers. The output frequency is inversely proportional to traffic density level and results in a trafiic signal cycle whose duration is proportional to traffic density.

Because the output of the device is a frequency variable signal it lends itself to the common methods of transmission. Examples of methods of transmission are:

(a) Single conductor, and common return.

(b) Telephone pair.

(0) Radio.

Each of these systems will be explained further and then the local cycle selector apparatus will be described.

Transmission Systems Various known methods are available for transmitting the variable frequency signal from the cycle generator and selector in the master controller to the cycle timing devices in the local trafiic controllers. These may include one conductor plus a common return in the control cable, a leased telephone pair, or a radio link.

Normally a multi-conductor cable connects the master controller with a group of local intersection trafiic controllers. One conductor in the cable may be reserved for the cycle length control function and may have impressed on it the variable frequency signal. At each local controller the variable frequency is applied as a signal to an amplifier. The amplifier has a very high input impedance to limit the drain on the line. It may also incorporate the novel feature of providing an output frequency identical to its input frequency at a potential proportional to 1 1 frequency. The output potential is increased with frequency to compensate for higher iron and copper losses within the synchronous motor operating at frequencies up to twice or more its design frequency.

In the event a multi-conductor cable is not employed between the master controller and the local controllers, or in the event a multi-conductor cable is employed but all of the conductors are being used for other functions, a pair of telephone wires may be leased from the local telephone company. Various transmission plans may be investigated and priced. Assuming that the leased pair has been found to be most economical in this instance, the variable frequency signal would be applied to the telephone pair through an impedance matching device. Reduction in signal strength at distant controllers is not a detriment because the amplifiers in the local controllers depend on input frequency rather than voltage. Thus the variable frequency system is suitable for interconnection by wire.

A radio link is likewise a suitable interconnecting means. A frequency modulated transmitter may be installed at a central station and an FM receiver installed at each local controller. This system is shown in block diagram in FIGURE 5 and is described below. It is more fully disclosed in United States patent application 830,096, named above.

Referring now to FIGURE 5, the potential from the higher traffic density computer IC or OC arrives via the voltage detector VD and is applied as the input signal to the cycle generator and selector units CS. As described in a prior section, the various cycle generators oscillate continuously, a level detector selects one oscillator and amplifiers its output, and makes it available at output terminal OT. The output consists of one of a group of fixed frequency signals of from 30 to 120 c.p.s. depending on trafiic density. The signal frequency is applied to the tone sensitive modulator TSM. A constant frequency tone generator TG develops a tone at a constant frequency, say 3,000 cycles per second. The 3,000 c.p.s. constant frequency is amplitude modulated by one of the 30 to 120 c.p.s. frequencies from the cycle generator and selector in the modulator TSM. This signal is amplified and applied to a frequency modulated radio transmitter TR for broadcast to the local controllers.

The cycle selector unit CS is normally located in the master controller and its output is fed to the modulator TSM and transmitter TR which may be installed at a location near the antenna.

At each local controller an antenna and an F M receiver XR picks up the signal, amplifies it, detects the modulated 3,000 c.p.s. carrier, and applies it to a twin T network TT having inverse feedback. The twin T network blocks out substantially all but the 3,000 c.p.s. signal, amplifies it, and passes it to a tone sensitive demodulator TSD which may be a standard detector. The detector rectifies the signal and passes it through a low pass filter to permit only the 30 to 120 c.p.s. portion to pass to amplifier A. The 30 to 120 c.p.s. variable frequency is then amplified and applied to the cycle timing motor M. The speed of motor M fixes the duration of the cycle change at the local controller. Since each controller motor M is synchronous and is energized by a common frequency the cycle duration at each controller is identical with very other controller including the master. This is a desirable feature and has not been possible in the past except when all the timing motors were driven from 60 c.p.s. local power.

The Local Controller One form of local traffic cycle controlling device is shown in isometric view in FIGURE 6. Dial 202 determines the duration of one complete cycle of trafiic signal change and is driven through suitable gearing (not here shown) by synchronous motor 60 energized over line VF from the variable frequency power source. The variable frequency power source is the output terminal OT of 12 the cycle generator and selector CS, FIGURE 4, connected to line VF over one conductor of an interconnecting cable CC or over a radio link as shown in FIG- URE 5. Dial 202 runs continuously at a constant speed for each input frequency.

Dial 202 carries five keys 100, 101, 101, 102, 103 angularly displaced on its surface. Key 100, normally inserted in the zero slot corresponding to the zero point in a traffic signal cycle, closes contacts 1008 as it passes beneath them and momentarily energizes constant speed motor 37. Motor 37 drives constant timing dial 203 through suitable gearing (not here shown) and rotates it sufficiently to permit key 32 to move from under contacts 32S allowing them to close and energize motor 37 for half a revolution of dial 203.

Constant timing dial 203 times the duration of all intervals in the signal cycle which are not allowed to vary with changing cycle duration. Examples of signals whose duration is constant include amber trafiic clearing intervals, guaranteed pedestrian clearance intervals, advance green arrow intervals, all red clearing intervals, no left turn intervals, and similar intervals. The duration of each of the above intervals is determined by the placement of dial keys 74, 74', 78, S0, 30', and 31, and by the number of intervals broken out of its signal-controlling cam. Contact 305 is closed momentarily by keys 74, 74-, 73, S0, to energize solenoid 48 and thereby ratchet camshaft 4-6 one position. If a signal is controlled by a cam similar to cam 59 broken out for more than one interval, the signal will be illuminated for more than one interval. If a signal is controlled by a cam similar to cam 44 broken out for only one interval it will be illuminated for only that interval. The intervals may be given any reasonable duration by the relative spacing of the dial keys on dial 203 and by the speed or" dial 203 governed by synchronous motor 37 and gearing. The present form of the invention permits easy change of gears between motor 37 and dial 203 to permit longer or shorter constant timing intervals. Once the gear is installed. there is little need for change.

To illustrate a typical signal cycle assume that the green signal is illuminated to cross street trafiic and the walk signal is illuminated to permit pedestrians to cross the main street. As illustrated in FIGURE 6 key on dial 202 has just closed contact 1008 momentarily energizing motor 37 through line 57 and switch 708. Motor 37 starts to turn dial 203 and the movement of key 32 from under contacts 328 permits them to close and energize motor 37 from a steady source L2. Dial 203 begins to rotate, timing the end of the cross street green interval. Rotation of dial 203 brings key 74' under contacts 308 closing them momentarily to energize solenoid 48 and ratchet camshaft 46 one position. The pedestrian walk signal 2W is deenergized by the action of cam 44' and switch 448'. The pedestrian Wait signal 2WT is illuminated by the action of cam 43' and switch 438'.

A guaranteed pedestrian clearance interval is timed by the spacing between the keys 74 and 78. The duration of the interval desired depends upon the width of the intersection and is intended to permit safe passage for a person starting to walk across main street at the end of the walk interval. The wait signal 2WT is illuminated when the safe-passage time has expired prior to the award of righ-of-way to main street traffic.

Dial 203 continues to revolve bringing key 78 under contacts 308 which closes them and momentarily energizes solenoid 48 which turns camshaft 46 one position. Cam 44 controlling the cross street green signal 2G opens its switch 448 deenergizing the signal 2G. Cam 43 closes its switch 438 energizing the cross street amber signal 2A. Dial 203 times the duration of the amber interval. Closure of contacts 308 by dial key 80 terminates the amber interval and starts the main street green interval and the main street pedestrian interval.

Cam 43 opens switch 438 deenergizing the cross street amber signal 2A. Cam 41 closes switch 418 illuminating the main street green signal 16. Cam 41' closes switch 41S illuminating the walk signal 1W parallel to main street. Switch 435 continues to illuminate the wait signal 2WT across main street. Cam 45 closes switch 458 illuminating the cross street red sign-a1 2R. Cam 49 opens switch 498 deenergizing coil 70, closing switch 708 to line 58, transferring control of motor 37 from contacts 325 to contacts 338. Dial 203 rotates a few degrees and stops when key 33 opens contacts 338 deenergizing motor 37.. Dial 202 rotates continuously timing the main street green interval and the 'walk interval parallel to main street.

The duration of these right-of-way intervals is timed by variable timing dial 202. The beginning of the end of the walk interval is initiated when one of the split keys 101, 101, 102, or 103 closes its corresponding contact 101$, 101$, 1028 or 1038 and momentarily energizes motor 37 over conductor 58 and switch 708. Which of the split keys is effective is determined by the position of contacts 108, 118, and 118. The latter contacts are controlled by relays and 11 from a master traflic controller, not shown. The functioning of the split control is described fully in United States patent application 742,160, filed June 16, 1958, entitled Trafiic Cycle Split Selectors.

Relay 70 is deenergized and switch 70S is closed to conductor 58 during the main street green interval because its controlling cam 49 is not cut for that interval.

Therefore, when key 103 closes contact 1038, for example, power is supplied to motor 37 to start it rotating dial 203. As SOOn as key 33 moves out from under contacts 338 the latter close and supply steady L2 power to motor 37. Motor 37 is thus energized for half a revolution of dial 203 until contacts 328 are opened by key 32. Dial 203 rotates only a short distance until it brings key 80 under contacts 308 closing them momentarily and ratcheting camshaft 46 into a new position. Cam 41' opens switch 418 deenergizing the walk signal 1W parallel to main street. Cam 40 closes switch 408 energizing the wait signal 'lWT parallel to main street.

Dial 203 rotates at a constant speed and times the guaranteed pedestrian clearance interval. When key 31 reaches and momentarily closes contacts 318 the solenoid 48 is again energized and ratchets the camshaft 46' to its next position. Cam 40 closes switch 408 illuminating the main street amber signal 1A. Cam 41 opens switch 418 deenergizing the main street green signal 1G. Dial 203 times the constant amber interval which terminates when key 74 closes contacts 305 and ratchets the camshaft to its next position. Cam 40 opens switch 408 deenergizing the main street amber signal 1A. Cams 42 and 44 close switches 42S and 445, respectively, illuminating the main street red signal IR and the cross street green signal 26. Cam 44' closes switch 448 illuminating the walk signal 2W across main street. Cam 43 opens switch 438 deenergizing the wait signal 2WT across main street. Thus the cross street right-of-Way interval is in progress, its variable portions timed by dial 202 and its fixed portions by dial 203. If it had other variable intervals such as left or right turn arrow indications, they would be timed by the variable timing dial 202. If it had other fixed time intervals such as all red clearance, they would be timed by consant timing dial 203.

It is to be noted that a circuit is employed to keep the variable timing dial 202 in step with the proper phase of the camshaft 46. Key 100 times the beginning of the end of the cross street interval and camshaft 46 must be in the cross street interval to make contacts 1008 effective through switch 705. Switch 7 08 is closed to line 57 only when relay 70 is energized. Relay 70 is energized only during the cross street green interval through switch 498 operated by cam 49. Thus, key 100 always 14 times the beginning of the end of the cross street green interval, which is the same as the start of the main street green interval, and the splits always occur in the proper part of the cycle.

Another circuit is provided to keep the constant timing dial 203 in step with camshaft 46. Contacts 308 are ineffective to ratchet the camshaft during the main street green interval. Only key 31 and contacts 318 are effective to release the camshaft from the main street green interval. Switch 598 controlled by cam 59 is open during that interval, rendering contacts 308 ineffective. Thus, the camshaft 46 is kept in step with the proper interval on the variable timing dial 203 so that the intervals on the dials 202, 203 correspond with the intervals on the camshaft 46.

The circuit employed to keep dial 202 in synchronism with the master controller is not shown. It is fully described in United States patent application 768,193, filed October 20, 1958, entitled Trafiic Cycle Offset Selector, and in application 642,469, filed February 26, 1957, entitled Multiple Program Traffic Control Systems. It will be appreciated that a reference cam (not shown) in each local controller may be driven also by motor 60 at the same speed as dial 202 and a similar cam located in the master controller driven also from the same variable frequency source OT. The resynchronizing circuit maintains a zero angular relationship between the reference cam in the master controller and the reference cam in each local controller, thus keeping all controllers in exact synchronism. An offset establishing device, not shown here but described in application 768,193 named above, inserts a remotely selectable angular displacement between dial 202 and the local reference cam. Any local controller may be made to lead or lag any neighboring controller by a remotely selectable angle, and thus by part of a trafiic signal cycle. This establishes a progression for traffic moving along a thoroughfare or in a grid.

In the above discussion of the relationship between the variable portions of the traffic signal cycle, the right-ofway portion for each direction of traffic is understood to include also the fixed amber interval. The right-of-way periods are thus proportional to cycle length; the intervals during which the green signals are illuminated are not exactly proportional to cycle length because of the fixed a-mber intervals.

I claim:

1. A method of adjusting traffic cycle length on a street in relation to the density of traffic in the heavier direction thereon, comprising, counting traffic in each direction and developing an output potential proportional thereto, comparing the two potentials and utilizing only the higher, admitting the higher potential to a level detector having a succession of levels, energizing a level of one of said succession of levels corresponding to the level of the potential, operating a plurality of signal generators continuously to produce a plurality of output signals of different frequencies, the energized level of said level detector applying the output signal of one of the signal generators to an amplifier, transmitting the amplified output to a series of local traffic controllers, energizing a synchronous motor in each controller from the amplified output, driving a traffic cycle timing dial by the motor, the duration of a traffic cycle being proportional to the heavier traffic count.

2. A traific cycle length selector and frequency generator including, in combination, a plurality of successively higher biased voltage level detectors having a common input connection, a plurality of relays one for each said level detector and each of said relays adapted to be selectively energized by its corresponding level detector, a plurality of continuously oscillating tone generators one for each said level detector and each of said tone generators adapted to produce a tone having a frequency different from that produced by the other said generators, a source of potential, each of said relays when energized connecting said potential to a tone generator corresponding to the energized relay and disconnecting said source of potential 15 from any other tone generator, an amplifier, the output of all tone generators adapted to be connected to said amplifier with only the output from the tone generator corresponding to the energized relay being amplified.

3. A traffic cycle length selector as in claim 2 including an interconnecting channel to which the output of said amplifier is applied, a plurality of local tratfic signal controllers, a synchronous motor in each said local controller connected to said interconnecting channel and adapted to be energized therefrom.

4. A traffic cycle length selector as in claim 3 including a timing dial in each controller adapted to be driven by said motor, a multi-circuit signal controller intermittently stepped by said timing dial, a source of power, and a plurality of traffic signals connected to said source of power through said multi-circuit controller in a traffic controlling pattern, the duration of said pattern controlled by the speed of said motor and said tone generator.

5. A local traffic signal control device including a first synchronous motor, a first dial drum adapted to be driven by said motor, a source of input potential for energizing said synchronous motor, said input potential having a variable frequency constant for a time period usually longer than a trafiic signal cycle, a plurality of contact pairs adjacent to the surface of said first dial drum, a plurality of keys arranged in angular relationship on said first dial drum and adapted to close particular ones of said contact pairs, a second motor, a second dial drum adapted to be driven by said second motor, a first and second plurality of contact pairs adjacent to the surface of said second dial drum, a plurality of keys arranged in angular relationship on said second dial drum in operative relationship with said first and second contact pairs, a source of power, a circuit comprised of said source of power and said first plurality of contacts adjacent to said second dial drum and said plurality of contacts adjacent to said first dial drum to intermittently momentarily energize said second motor and then to maintain energized said second motor for portions of a revolution of said second dial, a solenoid op erated camshaft intermittently energized by said second plurality of contact pairs adjacent to said second dial drum, a traffic signal cycle having constant and trafiic-variable intervals, the duration of said constant intervals fixed by said second dial, and the duration of said traflic variable intervals fixed by said first dial and said variable frequency.

6. A local traffic signal controller including a variable speed dial driven by a motor energized by variable frequency power from a remote source, a constant speed dial driven by a motor energized by constant frequency power from a local source, adjustable contacts in operative relationship with said variable speed dial that place the constant speed dial motor in operation at intervals, a step switch, adjustable contacts in operative relationship with said constant speed dial that close a circuit to intermittently energize said step switch, said step switch stepped at intervals alternately timed by said variable speed dial and said constant speed dial, and traffic signals controlled by said step switch.

7. In a trafiic regulated trafiic control system, a plurality of local trafiic signal cycle controllersleaeh including first and second timing means connected respectively to fixed and variable frequency channels to time constant and variable portions of the traffic cycle respectively, a master controller connected to said plurality of local controllers, said second timing means employed also in said master controller and energized constantly from said variable frequency channel for synchronizing said second timing means in each said local controller with said second timing means in said master controller.

8. A cycle generator comprising a plurality of constant frequency generators each functioning continuously and each developing a successively lower frequency, a like plurality of preamplifiers each connected to and adapted to receive signals from each said frequency generators, but only one of said preamplifiers effective at any one time to transmit a frequency received by said frequency generators, a like plurality of voltage sensing devices each having a manually preselectable successively higher bias and adapted to detect successively higher input voltages and having circuit interrupter means connected to cut off all of said voltage sensing devices but that which is energized having the highest bias, said voltage sensing devices and having circuit switching means connected to energize its corresponding preamplifier; an input circuit common to all of said volt-age sensing devices; an amplifier having an input circuit connected at all times to all of said preamplifiers and amplifying only the output of the energized preamplifier; and an output circuit from said amplifier.

9. A cycle generator as in claim 8, each said constant frequency generator comprised of a reed vibrator and a vibrating reed signal generator and an electronic oscillation initiating and sustaining circuit to start said reed vibrating and to amplify the signal output of the vibrating reed signal generator and to feed said amplified signal back to said reed vibrator to develop and maintain oscillation, and an output circuit between each said generator and each said preamplifier.

10. A cycle generator as in claim 8, each said voltage sensing device comprising of a tetrode gas-filled tube having a cathode, a plate, a control grid, and a screen grid; the cathode and screen grid of each said tube connected together and to ground, the control grid of each said tube connected through an impedance to said common input circuit and to a manually adjustable tap on a voltage dividing network; a source of negative bias potential, a like plurality of voltage dividing networks connected between said negative potential and ground, each said tap normally set for a successively more negative bias potential; a source of alternating current potential, a plurality of relays each one in circuit with the plate of each said tube and with said AC, potential through a first ladder circuit, said first ladder circuit comprised of a pair of contacts on each of said relays and a series circuit therebetween; a source of plate potential, a second ladder circuit comprised of a second set of contacts on each of said relays in circuit with said plate potential and with the plate circuit of each said preamplifier such that only the one voltage sensing device corresponding to the value of input voltage is operative at a time to make its corresponding preamplifier effective.

11. A trafiic cycle length generator and selector including an input circuit and an output circuit; a source of plate potential and a source of bias potential; a plurality of tetrode gas-filled tubes, each having at least a cathode, plate, and grid; each of said grids connected through an impedance to said input circuit; each of said cathodes connected to ground; a like plurality of stepped, manually adjustable potential dividers connected in common between said source of bias potential and ground, each of said potential dividers having a manually adjustable tap connected to and biasing each of said grids the bias applied to each of said control grids increasing from the bias applied to the control grid of one of said tetrode tubes to the bias applied to the control grid of the next succeeding tetrode tube within said plurality of tetrode tubes; a like plurality of relays having contacts, one of said relays in the plate circuit of each of said tetrode tubes, each plate circuit including contacts on all preceeding relays in higher-biased tube circuits; each relay also having contacts which apply the plate circuit potential to the plate of its corresponding preamplifier tube, a plurality of corresponding preamplifier tubes each having a cathode, plate and grid; each of said cathodes connected to ground through an impedance; an amplifier tube having at least a cathode, plate and grid, said amplifier tube grid connected to ground through an impedance and to the plate of each of said preamplifier tubes through an impedance, said amplifier tube plate connected to said source of plate potential, said amplifier tube cathode connected to ground through an impedance forming a cathode follower, said output circuit connected also to said cathode through an impedance; a like plurality of oscillator control circuits each comprised of a reed oscillator and a double triode vacuum tube; each said reed oscillator having a primary and secondary excitation coil and two tuned reeds mechanically joined; each of said double triode vacuum tubes having first and second cathodes, first and second plates, and first and second grids; each primary excitation coil in circuit with said second cathode and ground, each secondary excitation coil connected between said first grid and ground, said first cathode connected through an impedance to ground, said first and second plates connected through impedance to said source of plate potential, said second grid connected through impedances to both said first plate and to ground, said second plate connected through impedance also to ground, and said first plate connected through impedance to the grid of its corresponding preamplifier tube, said impedances in said oscillator control circuit selected to initiate and sustain oscillation.

12. A method of determining trafiic cycle length on a thoroughfare in relation to the density of traffic moving in the heavier direction thereon, the steps of which com prises, counting traffic moving in each direction over a running interval and developing a potential proportional thereto, comprising the two potentials representative of trafiic density and selecting the higher, applying the higher potential to a multi-level voltage level detector and allowing the potential to energize one level of said multi-level detector depending upon the value of the potential, operating a plurality of tone generators continuously to produce a corresponding plurality of different output tone signals, amplifying the output tone signal of one of said tone generators corresponding to the energized level of said multi-level detector, transmitting the amplified tone signal to a group of local traffic signal controllers, operating a synchronous motor at each local controller from the transmitted amplified tone, and driving a cycle timing dial from the synchronous motor, the frequency of the transmitted amplified tone determining the speed of the motor and the timing of the traffic cycle.

13. A traffic control system comprising: inbound and outbound trafiic density computers each delivering a voltage indicative of the traflic density; a voltage detector adapted to receive and pass the higher of said voltages; a number of successive level detectors, connected to receive the transmitted voltage of said voltage detector, each said detector responsive to a higher voltage than the preceding level detector; a like number of relays each one actuated by a level detector with which it is associated, and when energized to deenergize all level detectors responsive to a lower value of said voltage; a plurality of tone generators each of which is associated with one of said level detectors, such that a tone generator transmits a tone signal when the level detector with which it is associated is energized; a conductor over which said tone signal is transmitted; a plurality of local controllers to which said conductor leads; a synchronous motor in each local controller connected to said conductor and driven at a speed determined by said transmitted tone; and a trafiic cycle timing mechanism driven by said synchronous motor.

14. A trafiic control system, comprising: an inbound and outbound traffic density computer, said computer having an output voltage proportional to traffic density; a voltage detector to determine and transmit the higher of the two said outputs; a succession of level detectors to which said higher voltage is applied for selectively energizing one of said level detectors; a plurality of re lays, each one of said relays corresponding to and associated with one of said level detectors and connected thereto, such that each one of said relays is energized when its corresponding level detector is energized and is effective to deenergize all other lower level detectors; a succession of continuously operating tone generators corresponding to said relays, each of said tone generators adapted to produce a tone having a frequency different from that produced by any other tone generator in said succession; an amplifier; said relay corresponding to the energized level detector also switching the output of its corresponding tone generator to said amplifier; a plurality of local intersection traffic signal controllers; a conductor interconnecting said amplifier with each said controller, the output of said amplifier applied to said conductor; a synchronous motor in each of said local controllers, said motor connected to said conductor and adapted to be operated therefrom at a speed proportional to the said tones; and trafiic cycle timing means in each said controller driven by said motor.

15. A traffic cycle length selector and generator, including, in combination: a source of input potential representative of traflic volume in the heavier direction of tralfic fiow on a thoroughfare; a plurality of adjustable level detectors set for successively higher values of said input potential, each of said level detectors responsive to different Values of said input potential; a plurality of fixed frequency generators, each of said generators adapted to develop and transmit a dfierent frequency; circuit means connecting the first of said frequency generators to said level detectors wherby the first of said frequency generators transmits its frequency when none of said level detectors is energized, a second of said frequency generators effective to transmit its frequency when the first of said level detectors is energized, the third of said frequency generators effective to transmit its frequency when the second of said level detectors is energized; an amplifier connected to receive the transmitted signal frequency of whichever frequency generator is transmitting, said amplifier having an output frequency substantially identical with its input frequency.

16. A local trafiic signal control device, including, in combination: a first synchronous motor; a first dial drum adapted to be driven by said first motor; a source of input potential for energizing said first motor, said input potential having a variable frequency constant for a period normally longer than a traffic signal cycle; a plurality of first contact pairs adjacent to the peripheral surface of said first dial drum; a plurality of keys angularly spaced about the periphery of said first dial drum and adapted to close particular ones of said contact pairs; at second motor; a second dial drum adapted to be driven by said second motor; a first plurality of keys arranged in spaced angular relationship about the periphery of said second dial drum; a first plurality of contact pairs adjacent to the peripheral surface of said second dial drum; a source of power; a circuit comprising said source of power and said contact pairs adjacent to said first dial drum and said first plurality of contacts adjacent to said second dial drum, said circuit adapted to intermittently energize said second motor, said first plurality of contact pairs adjacent to said second dial drum adapted also to intermittently maintain energized said second motor; a step switch device; a second plurality of keys on said second dial drum; a second plurality of contact pairs adjacent to said second dial drum, adapted when closed by said selected ones of said second plurality of keys to momentarily energize said step switch device; a plurality of signals and signal circuits controlled by said step switch through a cycle of traffic signal change having fixed and variable intervals, the duration of the variable intervals dependent on the speed of said first motor and said variable frequency potential, and the duration of the constant intervals dependent on the speed of said second motor.

17. A trafiic cycle length generator and selector including, an input circuit and an output circuit; a source of plate potential and a source of bias potential; a plurality of tetrode gas-filled tubes, each having at least a cathode, a plate, a control grid, and a screen grid, each of said control grids connected through an adjustable of said control grids, the bias applied to each of said con:

trol grids increasing stepwise from the bias applied to the control grid of one of said tetrode tubes to the bias applied to the control grid of the next succeeding tetrode tube within said plurality of tetrode tubes; a like plurality of relays having contacts, one of said plurality of relays in a plate circuit of each of said tetrode tubes; each said plate circuit of said tetrode tubes also including contacts on all said relays in the plate circuits of tubes having control-grids of higher-bias; a plurality of preamplifier tubes corresponding to said relays, each having a cathode, a plate, and a grid; each relay also having contacts which apply the plate. circuit potential to the plate of its corresponding preamplifier tube; the cathodes of said preamplifier tubes connected to ground through an impedance; an amplifier tube having at least a cathode, a plate and a grid, said amplifier tube grid connected to ground through an impedance and to the plate of each of said preamplifier tubes through an impedance, saidamplifier tube plate connected to said source of plate potential, said amplifier tube cathode connected to ground through an impedance forming a cathode follower, said output circuit connected also to said cathode through an impedance; a like plurality of oscillator control circuits, each comprised of a reed oscillator and a double triode vacuum tube, each said reed oscillator having a primary and a secondary excitation coil and tWo tuned reeds mechanically joined; each of said double triode vacuum tubes having first and second cathodes, first and second plates,

n I and first and second grids; each primary excitation coil in circuit with said second cathode and ground, each sec-.

ondary excitation coil connected between said first grid and ground, said first cathode connected through an impedance to ground, said first and second plates connected through an impedance to said source of plate po tential, said second grid connected through impedances to both said first plate and to ground, said second plate connected through impedances also to ground, and said first plate connected through impedance to the grid of its corresponding preamplifier tube, said impedances in said oscillator control circuits chosen to initiate and sustain oscillation.

References Cited in the file of this patent UNITED STATES PATENTS 1,945,666 Stewart Feb. 6, 1934 1,973,563 Friendly Sept. 11, 1934 2,199,573 Paul May 7, 1940 2,282,102 Tunick May 5, 1942 2,282,142 Barker May 5, 1942 2,291,855 Wilcox Aug. 4, 1942, 2,301,004 Adler Nov. 3, 1942 2,428,389 Singer Oct. 7, 1947 2,515,254 Nosker July 18, 1950 2,538,829 Clark Jan. 23, 1951 2,542,978 Barker Feb. 27, 1951 2,554,329 Hammond May 22, 1951 2,564,766 Oberman Aug. 21, 1951 2,612,550 Jacobi Sept. 30, 1952 2,761,119 Barker Aug. 28, 1956 2,761,120 Wilcox Aug. 28, 1956 2,892,995 Kearney June 30, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,047,838 July 31, 1962 George Donald Hendricks It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 17, line 26 for "comprising" read comparing Signed and sealed this 5th day of November 1963.

(SEAL) Attest:

EDWIN L. REYNOLDS ERNEST W. SWIDER Attesting Officer AC g Commissioner of Patents

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