US2156138A - Traffic control system and apparatus - Google Patents

Description

Patented Apr. 25, 1939 UNITED STATES PATENT OFFECE TRAFFIC CONTROL SYSTEM AND APPARATUS tion of Delaware Application July 3, 1936, Serial No. 88,724

22 Claims.

This invention relates generally to traflic control systems and more particularly to such systems of the trafiic actuated type, and provides new and improved apparatus suitable for use in a number of associations but designed primarily for use at the intersection of two or more roads or streets or at one or more of a series of intersections of cross roads spaced along a main road.

The invention has for its general object the provision of system changing apparatusfor alternately connecting and disconnecting one or more individual trafiic actuated signal controllers to or from a coordinated train-c control system in accordance with traffic conditions, the operation of the individual signal controller when so connected being restricted by the coordinated system, and when disconnected being independent of such system.

Systems of traffic control have heretofore been proposed to transfer right of way from one to another of intersecting trafiic lanes in accordance with actual trafiic conditions at the intersections. This is achieved for example by placing traffic actuatable detectors in the lanes approaching the intersection and these detectors are arranged to initiate or modify, by actuation of trafiic, the time cycle of signal changes by the signal controller. Actuation of a detector in a lane not having the right of way causes right of way to be transferred to it and actuation in a lane to which right of way is being displayed causes prolongation of right of way for a short period, continued prolongation by repeated actuation being intercepted by a maximum timing device.

Trafiic actuated signal controllers may either be full actuated in which case detectors are placed in the approaches of each of the roads at an intersection, or they may be semi-actuated, having detectors only in one of the roads, generally the minor or cross road. In the latter type of control right of way normally rests on the main road, is transferred to the cross road for a minimum period upon actuation therein, may be prolonged on the cross road for additional periods by further actuation and up to a maximum by continuous actuation, and at the end of such minimum or prolonged period is retransferred to the main road and cannot again be transferred from the main road for a minimum protective period.

0 Arrangements have also been devised for soordinating the operation of one or more traffic actuated controllers under the supervision of a master controller or timers. Such a system may coordinate traffic actuated controllers of either the full or semi-actuated type, or both, and fixed time controllers also under the same master timer. In coordinating the semi-actuated type of controllers the master timer governs the time at which right of way transfer from the main to the cross road may be made in response to cross road actuation. 5 Full actuated controllers may be coordinated by controlling the time at which right of way transfer to the cross road is made when such transfer is caused by operation of the maximum timing device, but this transfer may be made unrestricted by the master if it occurs at any time before operation of the maximum timer.

An arrangement has also been proposed for connesting and disconnecting the controller at one intersection of a group to and from the master timer, dependent on the frequency of interruption of main road right of Way.

The present invention concerns a new arrangement for connecting or disconnecting the controller at an intersection to or from a master timer in accordance with traffic conditions at the intersection, more particularly in accordance with the traffic density. When the traffic density is great, frequent and uncoordinated right of way transfer causes excessive stopping and starting of heavy traffic with consequent excessive delays. Therefore in accordance with the invention an appropriate value of traffic density is selected and when the density exceeds this value the transferring of right of way to the cross road by actuation is restricted by the master timer to periodic intervals in certain time relation at the different intersections. In light traflic conditions, however, it is desirable to obtain maximum flexibility in the transferring of right of way between the roadways, since maintenance of coordination restricted right of way transfer is not so essential and single vehicles or small groups of vehicles should not be delayed unnecessarily in waiting for coordinated right of way periods. When the traffic density is comparatively low, therefore, the signal controller is arranged to operate as a full actuated controller independent of the master timer.

The invention besides providing for full actuated operation of the controller when independent, also converts the controller to semi-actuated type of operation when the latter is under the control of the master timer. This provides a rigid adherence to the program of the master timer since any transfer of right of way from the main lane must occur at a predetermined time in the master timer supervisory cycle, and an appropriate main lane right of way period is assured under control by the master timer.

Since trafiicconditions are often uniform on both the main and cross lanes at an intersection, growing heavier or lighter on both lanes in about the same proportions, the present invention proposes to utilize the detectors in the main lane approaches to the intersection not only for their ordinary purpose of prolonging right of way and calling for accord of right of way in connection with full traffic actuated operation, but also for the purpose of determining traffic density. Accordingly apparatus embodying the invention may comprise mechanism for determining the number of main road detector actuations per unit time which is termed traffic density.

The present invention is also intended for use at a plurality of intersections along a main lane at which semi-actuated signal controllers are located, so that under light trafiic conditions, as determined by the density of main road traffic at one of the intersections, called the key intersection, the several controllers operate independently, transferring right of way back and forth in accordance with traific demands at their respective intersections, and in conditions of heavy traific the controllers operate under a master timer so that transfer of right of way is made simultaneously or in accordance with some predetermined scheme at all those intersections on which cross road traflic is waiting to proceed. This prevents multiple stopping of main road trafiic under heavy trafiic conditions. Similarly the system may also be applied to connect and disconnect a number of full actuated controllers to and from coordination of the master timer.

If desired to coordinate the individual intersection controllers into two or more groups each group having a diiferent point in the master timer cycle when right of way transfer to the cross road is permitted, a coordinated progressive system may be established which will permit continuous movement of platoons of main road traific thru the intersections.

Broadly the object of this invention therefore is to provide means for connecting a traific signal controller to a coordinated system when traffic conditions make coordinated operation advantageous to trafiic movement and to release the controller from the coordination when traffic conditions make independent operation advantageous.

More specifically the object of the invention is to provide means for connecting a traflic signal controller to a coordinated system when the traiiic density at the intersection rises above a predetermined value and to maintain said controller connected to coordination until the traffic density falls below the same or a lower predetermined value.

Another object of the invention is to provide a trainc signal control system for a single intersection, or for each of a group of intersections, which under certain conditions will operate full 'trafiic actuated so that detectors in the several approaches to the intersection are active to modify the signal cycle and under other conditions will operate as a semi-actuated control system so as to expedite traffic on the heavier travelled of the lanes, and which will change from one system of operation to the other as traflic conditions at the single intersection, or at one of the group of intersections, change.

Still another object is to provide an improved automatic traffic governed signal control system which will function in response to density of traffic fl W, so that as variat ons occur, the systerm will function in response to conditions as they exist, thereby expediting the flow of traific.

A further object is to provide a system of this character in which the critical densities of traific flow at which the control system changes from one type of operation to another may themselves be adjusted and set at any desired predetermined values.

A still further object is to provide a traliic control system for one intersection which system is of the general character described, in which the detectors in the main road approaches to the intersection will serve dual purposes, for initiating or modifying the cycle of the signal controller, and also, in connection with a counting and timing mechanism, for determining the traffic density at the intersection.

Other objects will subsequently appear.

Regardless of the conditions to be regulated or the types of control systems to be utilized under one and another trafiic conditions, apparatus for carrying out the principles of the invention may be comprised of a switching mechanism for changing over the signal controller or controllers from one system of operation to the other, as from independent to coordinated operation or vice versa, and a device for ascertaining the density of traflic, that is, the amount of traific per unit time.

The invention will be described and its operation explained in connection with the accompanying sheets of drawings in which:

Figure 1 represents schematically the intersection of a main road and cross road, a traffic actuatable signal controller, master timer, and system changing apparatus for connecting and disconnecting the signal controller to and from the master timer automatically in accordance with traihc density.

Figure 2 is a circuit diagram of an embodiment of the system changing apparatus and a master timer which may be employed in the system of Fig. 1.

Figure 3 is a circuit diagram of a common form of trafiic actuated signal controller for governing the right of way signals at an intersection and adapted for operation in a system embodying the invention.

Figure 4 illustrates a series of intersections along a common main highway provided with trafiic actuated controllers under the governing action of a system changing apparatus at a key intersection in accordance with one form of the invention.

In Figure 3 there is shown a form of full actuated type of signal controller, representing for instance the controller C shown in Figure l, suitable for ready conversion to semi-actuated type of operation by action of the system changing apparatus in accordance with the principles of the invention, and it is believed that the nature and operation of the system changer will be more readily comprehended if preceded by a description of the signal controller.

Ordinarily a signal controller of the form illustrated, operating as a full actuated controller, transfers right of way cyclically between the main and cross streets, the length of the cycle, and the portions of the right of way signal cycle accorded to the main and cross streets being dependent on or modified by actuation of the vehicle detectors in the streets. The vehicle actuated detectors may be pressure operated pavement switches which operate during the passage of a vehicle across them to close an electric circuit.

ill

Suitable photoelectric and electromagnetic detecting devices and other means of detection are well known in the art and any of these may be utilized instead of the pressure type.

The controller may by manner of example be comprised of a plurality of contact pairs operated by a cam shaft which is moved step by step thru a cycle by means of a solenoid. The contact pairs control signal illuminating circuits and control circuits. The solenoid in this embodiment is controlled from a timing circuit employing a condenser-gas discharge tube combination, permitting variation in the timing by the vehicle detectors as will be pointed out. Both minimiun and maximum timing circuits are provided.

The controller, it will be noted in Figure 3, is arranged for operation from an alternating current supply (indicated by plus and minus in a circle), and suitable rectifying arrangements are provided as for example a thermionic rectifier VLV and transformer XFR, from which suitable potentials of direct current for operating the gas discharge tubes is obtained (at the terminals indicated by plus and minus in a square).

The table at the right of Figure 3 shows a development of the several cams and shows the positions of the cam shaft in which the various cams are operating to close their respective contacts. In each position of the cam shaft a circuit for charging condenser QA is completed over one of the interval adjusting switches VNS to LEW, which are wired to appropriate tapping points on resistance 3. Maximum timing condenser QB is charged similarly over switches MXA or MXB and resistance 4 as will be subsequently explained.

Operation of this controller as an independently operating full actuated controller will now be described. Accordingly, under this type of operation, terminals and Q are connected to grounded lead 2 and terminal G is connected thru the phase A (or main road) detector DNS to grounded power. Detector DEW for the cross road is connected between terminal F and grounded power. Let it be assumed for example that both switches PEW and PNS are open, and that at the moment the cam shaft is standing in position 6, the phase A (or main road) vehicle interval. Power is supplied from AC plus power lead I over cam contacts C9 and OH to grounded lead 2 to cause the phase A (main road) green signal GA and the phase B (cross road) red signal RB respectively to be displayed.

Meanwhile condenser QA is being charged by current from the rectifier VLV over DC plus lead 8, cam contact C4, vehicle adjusting switch VNS, resistance 3, condenser QA to grounded lead 2. It will be assumed that a succession of vehicles are passing over the detector DNS, in the main road, and owing to the intermittent operation of relay E thereby a circuit shunting condenser QA over low resistance YD and cam contact C is intermittently completed at contact 62 thus reducing the charge on condenser QA. As the maximum timing circuit is initiated upon actuation of the detector in the lane not having right of way, a maximum limit to the waiting time for such actuating vehicles is assured. This maximum limit corresponds with the period of the maximum timing circuit if the actuation occurs in the vehicle interval, and if it occurs in the prior initial or amber intervals these periods are added also.

If now a vehicle arrives on the cross road and actuates the detector DEW, relay D is energized and locks-in over its armature dl, cam contacts Cl, and at armature d2 it completes a circuit over lead 5 and cam contacts C6 thru relay A and tube FA paralleling condenser QA. Also armature d3 completes a timing circuit to charge maximum timing condenser QB from D. C. plus lead 8 over cam contacts Cl, armature cit, phase A maximum interval switch MXA, resistance 4, which is substantially larger than resistance 3, and condenser QB to grounded power lead. Subsequently, due either to a gap of sufiicient size between actuations by the main road trafiic permitting condenser QA to become charged to the flash potential or ionizing voltage of the tube FA, now connected in parallel with the condenser, or due to the charge on maximum condenser QB attaining the flash potential of tube QB, either tube PA or tube FB will become conducting whereupon either relay A or B as the case may be is operated. At armature a! or bi circuit is completed from lead l thru solenoid S to lead 2 while relay A or B momentarily is operated to energize solenoid S. Energization and de-energization of the solenoid causes the cam shaft to be advanced by a ratchet mechanism to the next position, position 1. As the maximum timing, circuit is initiated upon actuation of the detector in the lane not having right of way, it assures that the actuating vehicle will be forced to wait at most not longer than the period of the maximum timing circuit before right of way is transferred.

In its energized position the solenoid completes a circuit over its armature si, condenser QA and low resistor YA short circuiting condenser QA so that whenever the solenoid operates to advance the cam shaft the next interval timed will' start with an initial condenser voltage of sub stantially zero. Similarly armature s2 completes a discharge for condenser QB over resistor YB.

In position 1 the cam contacts C9 open and C2! close so that the phase A (main road) am ber signal AA and the phase B red signal RB are illuminated and the phase A green signal GA is extinguished. Condenser QA is charged from lead 8 over cam contact Cl3, resistance 29, condenser QA and minus lead 2. Tube FA and relay A are connected across the condenser over cam contacts 05 and armature d2, and when the condenser QA voltage reaches the flash voltage of tube FA relay A and solenoid S are operated and the cam shaft is advanced to position 2 in the manner described above.

In position 2 the main road amber caution signal AA and cross road red signal RB are extinguished and right of way is accorded to the cross road. Cam contacts C25 and C22 are operated to illuminate phase A red signal RA and phase B green GB.

In order to provide a suffici nt period for the starting up of any phase B traffic which may be waiting, an initial non-extendible interval of right of way is now timed. Condenser QA is charged from. lead 8 over cam contacts Cid, resistance 3, condenser QA. grounded lead 2 until the voltage across the condenser reaches the flash potential of the tube FA, which then becomes conducting and causes the charge on the condenser to operate relay A, and this in turn energizes solenoid S, advancing the cam shaft to the phase B vehicle interval position, #3. Here no change is made in the signal indicating circuits but the lock-in circuit for relay D is broken at cam contact Cl, so that relay D now operates intermittently under the control of traffic on the oross road actuating detectors DEW thus extending the right of way period in a manner similar to that described for relay E by main road traffic actuation in position 6.

Operation of the controller thru positions 4 and 5 is similar to that described for positions 1 and 2, excepting of course that in position 4 right of way is leaving phase B and being accorded in position 5 to the phase A traffic for an initial non-extendible interval. The charging circuit in position 4 extends over cam contacts C2 and switch LEW and in position 5 over cam contacts C3 and switch INS. At the end of the interval in position 5 the cam shaft is advanced in the manner previously explained into position 6, thus completing one entire cycle of the controller, whereupon the cycle described is repeated in accordance with traflic actuation.

If transfer of right of way from one road to the other at the end of the vehicle interval positions occurs by operation of the maximum circuit relay B, armature b2 cooperates to leave the controller in a condition to remember vehicles cut off so that right of way will be retransferred to them as soon as possible. For instance if right of way is on the cross road, and waiting vehicles on the main road have energized and locked-in relay E, and if the cross road vehicle interval position 3 is terminated by operation of relay B, a circuit to energize relay D is completed from plus lead I thru relay D, armature b2, armature e1, cam contacts 013 to grounded power lead 2. Solenoid S, which operates immediately upon energization of relay B, at contacts s3'provides a lock-in circuit over armature (ii for relay D which holds until the cam shaft has moved into position 4 where the lock-in circuit over cam contacts Cl becomes operative. Similarly, assuming for the moment that switch PNS is open, if right of way on the main road is terminated by operation of the maximum timing circuit relay E is left energized to cause subsequent retransfer to the main road.

The arterial switches PEW and PNS when closed ensure that right of way will return to the associated phase even in the absence of trafiic thereon. Their effect as will be seen from the circuit is to simulate operation of the detectors while their associated phase is not receiving right of way although they cannot produce any extension effect while their respective phases have right of way.

When operating as a semi-actuated controller, the main road detectors DNS are disconnected from terminal G and relay E is operated only by switch PNS in cooperation with cam contacts Cl8. Accordingly when right of way is transferred to the cross road for the duration of positions 2 and 3, the cross road initial and Vehicle intervals, energization of relay E by the circuit from plus lead I thru the relay, switch PNS, cam contacts Cl8 to grounded power lead 2 causes right of way to be retransferred to the main road .by operation of either the minimum or maximum timing circuits. Accordingly, right of way will normally remain on the main road, being transferred to the cross road for a predetermined minimum period in response to actuation of the cross road detector DEW and remaining on the cross road for an additional period if there are fur ther actuations of detector DEW. Right of way is then retransferred to the main road from which it cannot again be transferred before expiration of a minimum period comprising the initial interval, position 5, and a Vehicle interval, position 6, in which the minimum. timing condenser QA charges, without any discharging or resetting, to the flash potential of its associate-d tube FA.

As pointed out above, methods have been proposed heretofore to coordinate the operation of semi-actuated signal controllers under a master timer. To control the cycle of a controller of the type shown in Figure 3 by a master timer, the direct connections which in the foregoing descrip' tion were assumed made from terminals and Q to grounded power are both broken, and instead terminals 0 and Q are joined together and the common lead joining them is connected thru a pair of contacts, periodically closed for short intervals by the master timer, to grounded power. The principle of this type of coordination is to control the time at which the controller may transfer right of way to the cross road in response to actuation therein, while allowing the controller to proceed thru the rest of its cycle in normal fashion as described above. Any number of semiactuated controllers may be synchronized by connecting the terminals 0 and Q in each to master timer contacts.

During the time when terminals 0 and Q are not connected directly to grounded power during the main road vehicle interval, position 6, the operating circuit for tube FA and relay A is not completed in shunt with condenser QA and the circuit thru tube FE and relay B is not completed in shunt with condenser QB. Consequently neither relay A nor B can operate to advance the controller from position 6 to transfer right of way to the cross road until terminals 0 and Q are connected by the master timer to grounded power, completing these shunt circuits, even though other conditions for carrying out such transfer may be fulfilled.

In Figure 2 a form of cyclically operating master timer I is shown. The timer may be comprised of a synchronous motor 54 driving a cam 53 to close for a short interval in each cycle the contacts 52 which connect grounded power from leads I2 and 5! to terminals 0 and Q in each of the controllers to be coordinated. At the time when contacts 52 are made, and at no other time in the master timer cycle, therefore, the controller or controllers connected thereto may transfer right of way from the main to the cross road in response to actuation of the cross. road detectors.

Where a plurality of controllers is tobe governed by this type of master timer and it is desired to coordinate these controllers to operate with a phase displacement or offset between the start of the cross street green signal at different intersections, a second cam 57' is adjusted to close a pair of contacts 56 at a dilferent time in the cycle of timer l5 for providing the desired offset. More cams and corresponding contacts may be added to care for more than two controllers or groups of controllers having separate ofisets. Under this type of coordination trafiic on the main road where the controllers are located if stopped at one intersection, should, if proceeding at the speed for which the system is designed, pass thru all the other intersections in the group without being required to stop. Obviously if the coordination is merely to synchronize operation of the controllers so that all which must transfer right of way from the main road do so at the same time, only one cam and contact pair is required for all the controllers, but in this case the individual controllers should be isolated by relays, as shown by relays Z in Figure 4.

It will be obvious to those skilled in the art that instead of having the operating contacts of the master controller concentrated at one location, individual contacts may be located at the individual intersections and maintained in any desired time relation by individual synchronous motors connected to a suitable common alternating current power supply.

Considering now apparatus embodying the present invention, the system changer, as has been pointed out above, serves in conjunction with the main road detectors at an intersection as a switching device and meter of traflic density. When the trafiic density exceeds a certain predetermined Value the system changer changes over operation of the traffic actuated controller with which it is associated from full actuated independent operation to semi-actuated operation under a master timer, and when the traffic density subsequently falls again, preferably to a second lower predetermined value, changes over to the full actuated type of operation once more.

With reference now to Figures 1 and 2, which should be considered together as illustrating the connections for operation of the traffic actuated signal controller with the system changer and master timer, it will be observed that the main lane detectors DNS (which are connected in parallel with each other) now have one contact plate connected to grounded power and the other to relay l3 in the system changing unit. A cir-- cuit from grounded power via wires 5| and i4, armature '35 of relay i3, and armature it of relay i4 and wire 11 connects grounded power to terminal G of the trafiic actuated signal controller whenever relay i3 is energized by the main road detector DNS while relay I4 is energized, as will be further described subsequently. A relay it in the illustrated embodiment of the apparatus is arranged to be operated when the associated signal controller (shown in Figure 3, for example) causes display of the amber-leavingmain road signal AA and relay i5 is connected in parallel with this signal from terminal H to grounded power. Another relay, i1, is energized in parallel with the cross road green signal GB. A relay M in the system changer, termed the coordinating relay, determines by its state of energization or de-energization whether the associated controller will operate independently or under the control of the master timer.

While relay M is in its energized position, grounded power is constantly supplied over leads '34, armature '50, contact 69, lead 6! to terminals and Q of the signal controller whereupon the latter operates as a full actuated independent controller in accordance with the description of this type of operation presented above. While relay M is in its de-energized or coordinating position, the continuous connection from ground ed power to terminals 0 and Q is broken at armature m; consequently the associated controller operates under the coordinating action of master timer i5, terminals 0 and Q being periodically connected to grounded power by cyclic operation of contacts 52.

The traffic density ascertaining mechanism comprises essentially twoparts: a timing device and a counting device for counting actuations of detector DNS over the period timed by the timing device. The present embodiment, however, for convenience utilizes under difierent conditions two separate timing devices. While relay emptied into the reservoir condenser 39.

I4 is deenergized and the signal controller operating under control of the master timer, actuations of detector DNS are counted between successive energizations of the cross road green relay l'i. Thus-the period of the signal cycle itself serves as one timer. While relay i4 is energized and the controller is operating independently of master timer i5, actuations of the detector DNS are counted over an interval measured by a periodic timing device, which will be described subsequently.

Each time the amber-leaving main road relay i is energized it completes a circuit over its armature ll to energize coordinating relay [4 for the duration of the amber-leaving main road period. If less than the predetermined number of detector DNS actuations have been registered by the counting mechanism, relay is will remain energized at the end of the amber period and will continue energized during the entire next cycle of the signal controller or as long as less than the predetermined number of actuations have been registered, but if more than the predetermined number of actuations required to place the signal controller under the coordination of the master timer have been registered, the mechanism will operate at the end of this amber period to de-energize relay is, thus coordinating operation of the signal controller for at least one cycle of the trafiic signals. Accordingly, if the signal controller is operating under the control master timer l5, relay I4 is energized once during each signal cycle to determine if the signal controller can operate independently.

Before considering further the operation of the timing devices the vehicle counting mechanism with which they cooperate will be disclosed and explained. Detector DNS, it was noted above, is arranged upon traffic actuation to energize detector relay [3 in the system changing unit. When the signal controller operates independently of the master timer, it operates as a full actuated controller, as previously pointed out, and accordingly when relay i4 is in its energized or non-coordinating position, grounded power is connected over leads l4, armatures i5, i6 and lead 7? to terminal G of the signal controller to energize relay E therein upon each actuation of detector DNS.

When relay i is in its deenergized or coordinating position and relay I3 is in its tie-energized or non-actuated position, from a potentiometer it across the direct current or output terminals of rectifiers 28, 2 i, a potential is applied to condensers 23, over contact 24, armature lead 2?, contact 28, armature 29, lead 83, armature 32, contact 35, condenser 23, leads and I2. Upon energization of relay it, which occurs when a main lane detector DNS is actuated, this charging circuit for low capacitance condenser 23 is disconnected at armature 29, and over contact 38 this small condenser is connected thru low resistance 3?, lead 33, to a larger, or reservoir, condenser 39.

The energy stored in unit condenser 23 is When the wheel of the actuating vehicle moves oil the detector, relay it becomes deenergized, and con denser 23 instantly acquires a new unit charge from potentiometer IQ for transfer to condenser 39 when relay [3 is next operated.

When the two condensers 23 and 39 are connected, the energy stored in unit condenser 23 distributes itself over both condensers and the final voltage of each is equal and is dependent both on the difference in size or capacitance of the condensers and the original difference in potential between them. In the present embodiment, by making the difference in capacitance large, and the ratio between the initial voltage of condenser 23 and the final voltage, after successive transfers, of condenser 39 also large, variation in the size of the unit charges transferred into reservoir condenser 39 is minimized, the voltage on condenser 39 being at any time substantially proportional to the number of vehicles which have passed since the condenser was last discharged. The number of passing vehicles may of course be half of the number of actuations for example, if the front and back wheels of twoaxle vehicles actuate the detector separately.

In similar fashion, when relay I4 is in its energized or non-coordinating position, unit charges for transfer into reservoir condenser 39 are formed on unit condenser 22 by a potential applied from potentiometer I8.

Artery amber relay [6 may be considered a testing relay for non-coordination, since each time it is energized it completes over its armature i"! a circuit to energize coordinating relay [4, thus bringing the latter into its non-coordinating position once in each signal cycle. Relay l4 thereupon looks over its armature 48, lead 49, armature 59, leads l 2, and subsequently remains energized throughout the amber leaving artery period and until the cross street green position, in which a relay I! is energized from the key controller. Over armature 40 the relay l7 completes a circuit shunting the condenser 39 thru relay 42 and the anode circuit of an electron discharge tube 43 Whose characteristics will 'be described below.

When this circuit is closed by armature 40 the potential difference across the plates of condenser 39 also exists between the anode 44 and cathode 45 of tube 43. If a predetermined number or more actuations of the main lane detectors have been received since the last energization of relay 42, the voltage across condenser 39, which as pointed out exists across the tube 43, will be sumcient to initiate conduction thru the tube, and this current thru the tube serves to energize relay 42 which at armature 59 breaks the lock-in for relay [4, and the latter again assumes its de-energized or coordinating position. The tube 43 has such a characteristic that once conduction or discharge thru it has been initiated, it direct current is used in the anode-cathode circuit as in the present embodiment, this discharge will persist until the energy stored in condenser 39 is no longer suflicient to maintain the current thru the tube. In this type of tube the potential of the grid or control electrode controls the initiation of conduction thru the tube, but has little effect once discharge has started. The discharge continues until the potential between the anode and cathode declines to a low value, whereupon the current in the circuit is no longer great enough to maintain relay 42 energized. At the end of the cross road green period relay I1 is also ale-energized and the counting condenser 39 begins to accumulate the unit charges from condenser 23 upon operation of relay l3 by trafiic actuation.

Relay M has by the breaking of its lock-in circuit at armature 59 resumed its de-energized or coordinating position. The signal controller may transfer right of way to its cross lane only in accordance with the cycle of master timer 15.

Consider now another alternative at the time when relay H is energized, at the start of the side street green period, and relay I1 completes over armature 40 the circuit paralleling condenser 39 thru the tube 43 and relay 42. If tramc is so light that there have been up to this time an insufficient number of transfers of unit charges to condenser 39 to raise the potential of i5 and is free to transfer right of way to its cross road upon actuation of detector DEW at any time after the minimum period of right of way on the main road has expired. The release from co-ordination in periods of light traffic benefits the cross traffic which now obtains right of Way at the first gap in main road traffic instead of having to wait for the cyclic closing of contacts 52.

While relay !4 is in its energized position, and the traffic signal controller is operating independently of the master timer [5, the traffic density is determined by the counting or reservoir condenser 39 counting actuations during periodic intervals timed by the periodic timing unit, instead of during the time between successive energizations of relay [7. This periodic timer may conveniently be of the electrostatic.

type shown or any other suitable type and in this embodiment comprises a condenser 59 which is charged by a direct current from rectifiers 20, 2| thru a high resistance 60, the voltage across the condenser building up at a definite time rate determined by the size of the condenser 59 and the value of the charging resistance 60. Shunting the condenser is an electron discharge tube 53, similar to tube 43, and a relay 62. The tube is normally non-conducting, but when the potential between its anode and cathode rises to the ionizing or critical value, the gas in the tube ionizes and conducts current to energize relay 62 until the energy stored in condenser 59 is no longer sufficient to hold the relay in. Relay 62 when energized, completes over its armature 65 a discharge circuit thru small resistance 61 completely discharge concondenser 59 from current thru resistance 60.

If timing condenser 59 reaches the ionizing potential of tube 53 before relay 42 is operated, (that is, if the trafiic density remains below a predetermined value) the plate current thru the tube 63 operates relay 92 which over its armature 66 completes a discharge thru resistance 6! to reset counting condenser 39. Hence, since its lock-in circuit is not broken at armature 50 relay I4 remains energized to maintain independent operation of the signal controller. The discharge thru the tube 93 reduces the charge on condenser 59 to a negligible value, thus both timing and counting condensers, now reset, recommence operation.

Should the traffic on the main lane increase sufficiently to exceed the predetermined density required to initiate coordination, counting condenser 39 will acquire the potential necessary to operate relay 62 before relay 62 has been operated by the timing condenser in the manner above described. When relay I1 is energized and the circuit thru relay 42 completed over armature 40, relay H2 is energized momentarily as has been noted to break at armature 5!} the locking-in circuit for coordinating relay I i, which assumes its de-energized or coordinating position.

All operating conditions of the system changer have now been described and a condition already explained is now reached again; the counting condenser 39 again counts actuations between successive energizations of cross street green relay Il. Meanwhile since relay I4 is de-energized, the static timing unit including condenser 59 is discharged and kept discharged, as long as relay M is de-energized, by a discharge circuit parallelling the condenser thru resistance 68, contact H and armature HI.

As pointed out above, the apparatus is designed so that one value of trafiic density may be preset for initiating coordination, and a different value may be preset for retaining coordination longer than one signal cycle. These two Values may be established in any of a number of ways.

Accordingly when relay i4 is energized the unit charges are derived from voltage impressed across condenser bank 22 from potentiometer [8 over contact 26, armatures 25, 29, and 32, and contact 33, and when relay i4 is de-energized the unit charges are obtained from potentiometer i 9, contact 24, armatures 25, 29, and 32, contact 3| and condenser bank 23.

Thus the device is arranged so that potentiometer It may be calibrated in number of cars per minute required to initiate coordination, and potentiometer l9 in number of cars per minute required to retain coordination.

It will be appreciated that differing critical trafiic densities might be obtained in other ways than the above wherein the size of the unit charge transferred to the counting condenser is varied. Another method of obtaining difierent adjustable sets of values of critical trafiic densities for initiating or retaining coordination would be by varying the duration of the timing period, for instance by altering the resistance 60 in the timing condenser charging circuit. The system changer may then be built always to count 2. particular number of detector actuations by having the potentiometers l8 and 19 adjusted to the same value and the condensers 22 and 23 adjusted to the same value, for example, and the variations in critical traffic density obtained by regulating the length of the periods for counting the fixed number of actuations under coordinated and independent operation.

It will be understood that the time required for the signal controller to proceed through a complete signal cycle may vary considerably under non-coordinated operation. This type of operation will occur when traffic is relatively light and there may be occasional relatively long periods when the signal controller will continue accord of right of way to one road because of absence of traffic on the other road. These periods might easily be several times the length of the signal cycle when coordinated. On the other hand if traific happened to approach the intersection on the respective roads in relatively small groups of vehicles as might happen occasionally under light trafiic conditions with non-coordinated operation, the signal cycle might be somewhat shorter than the cycle under coordinated operation.

The resistance 60 may be adjusted so that the period of timing condenser 59 under non-coordinated operation will be of the order of one c0- ordinated signal cycle, or it may be adjusted for more or less than this so long as it is long enough to obtain a fair average of the number of vehicles arriving per unit time. In any case a change from non-coordinated to coordinated operation is only possible when the right of way is transferred tothe side road by the signal controller since it is only at this time that the counting condenser is enabled to operate relay 42 to break the lock-in circuit of relay l4. Thus the presence of at least one vehicle on the cross road is necessary to cause the shift from non-coordinated to coordinated operation, and if this vehicle approaches after a relatively prolonged absence of side street trafiic, the timing condenser 59 may have completed its time period several times during the period of absence of traffic, and the effective period for counting the main road traffic in such case will extend from the last completion of its time period by condenser 59 prior to the side road green period to the next completion of the condenser 59 period if the latter occurs during the side road green period. If the count since the last reset by condenser 59 reaches a sufficient level at any time in the side road green period and before the next reset by the condenser 59 the shift to coordinated operation will occur.

It will be noted that in accordance with the invention the trafiic is counted in relation to one signal cycle during coordinated operation, and in relation to a time period which may extend from one signal cycle into another in non-coordinated operation, It will be understood that the signal cycle is not of fixed time length since it depends on the presence of the side road traflic. However, it will be appreciated from the broader aspects of the invention, that in each case the trafiic actuations are counted in relation to time to obtain the number of actuations per unit time, which may be termed the rate of actuations per unit time.

Application of the present invention need not necessarily be restricted to one intersection, at which a system changer is provided to switch over a signal controller between full actuated independent operation and semi-actuated operation under a master timer, but may be extended to embrace control over a number of intersections. Considering for example the system shown in Figure 4, at the intersection II is a signal, signal controller, traiiic detectors in each approach, master timer, and system changer, all of the type explained above and shown in Figure 1. At the other intersections along the main road the signal controllers may be either full actuated or semiactuated. In accordance with the density of main road traffic at intersection II, selected as a key intersection, the system changer will control the several controllers for operation independently or under the supervision of the master timer.

Where a semi-actuated signal controller, as at intersection I of Figure 4, is to be converted from independent operation to operation under the master timer, in conjunction with other controllers governed by one system changer, a relay Z is located at each such intersection and arranged to be connected to lead 6| in the system changer so that it will be energized both when relay I4 is in its energized of non-coordinating position and when contacts 52 are closed by the master timer !5. Relay Z when energized supplies grounded power over its armatures Zl, and Z2 to terminals and Q of the semi-actuated signal controller. This isolates the terminals 0 and Q of the several controllers and prevents feedbacks between them.

If a full actuated signal controller is located at intersection I a form of coordination may be established Without converting the controller to semi-actuated operation by arranging the relay 2 to interrupt at its armature only the circuit from grounded power to terminal Q and connecting terminal 0 directly togrounded power as by closing switch OS. Accordingly the controller may transfer right of way from the main road (vehicle interval, position by operation of the minimum, or condenser QA, timing circuit at any time, but if this transfer of right of way from the main road occurs by operation of the maximum, or condenser QB, timing circuit, grounded power from the master timer must at that time be connected to terminal Q. Under coordinated operation, therefore, when main road traflic at the key intersection is sufiiciently heavy to maintain the coordinated operation but not heavy enough at intersection I to hold main road right of way up to its maximum, transfer of right of way by the controller at intersection I to its cross road under this condition is independent of the master timer (since terminal 0 is connected directly to grounded power), but if right of way is retained on the main road up to a maximum such a transfer will occur at a predetermined time in the master timer cycle.

At intersection III of Figure 4 another system of coordinating a full actuated controller is represented wherein the controller may be made to operate in conjunction with a system changer lo- :ated at a remote key intersection at which critical traffic densities are measured. Such a system is established by allowing the controller to be full actuated when operating independently and converting the controller to semi-actuated use when operating under the coordinating master timer, as is done at the key intersection. Terminals O and Q are again connected to grounded power via armatures of relay Z. A relay M at intersection III is connected to terminal N of the system changer (Figure 2) so that this relay M will be energized whenever coordinating relay I 3 is energized yet is not energized by the periodic closure of contacts 52, as relay Z is. Relay M serves to convert the full actuated controller to semi-actuated operation. Accordingly when relay M is in its non-coordinating or energized position relay M in parallel with relay I4 is also energized and over its armature ml connects the main road detectors DNS at the intersection to terminal G in the controller, rendering the main road detectors operable to modify the signal controller cycle. When the controllers are operating under the coordinated system, relay M will assume its deenergized position where detectors DNS are disconnected from the controller and armature ml completes a circuit from terminal G to L (in the controller of Figure 3) thus shunting switch PNS and providing that under coordination right of way will always revert to the main lane.

Thus it will be seen that one system changer may operate to convert a plurality of individually operating full actuated controllers to synchronized semi-actuated operation, or one system changer and master timer may be used with each individual controller. In the latter case the driving motors of the several master timer units are synchonized so that cam 53 in each operates its contacts 52 simultaneously or in predetermined relation with the others.

It may be desirable in one or another of the above described systems to measure traffic density in the cross road instead of in the main road. Actuation of detector DEW in Figure l, for instance, may be made to energize relay I3 in the system changer by changing the position of double pole switch DS, and operation of this relay repeats or transmits the detector DEW actuation over armature l5 and switch FS in its upper position which under these conditions leads directly to terminal F in the signal controller, armature l6 accordingly being omitted.

It will be understood that a system changer of the type described herein is capable of use in a number of difierent associations and need not be limited to the present embodiment of changing traflic signal controllers from coordinated to noncoordinated operation. For example it may be utilized at intersections which have at certain times a high ratio of left-turning traflic, whereupon it may be desirable to accord a separate period of right of Way to the left turning trafliic. A system changer of the present type may with minor changes apparent to those skilled in the art readily be adapted to change over a suitable controller of well known construction from regular two-phase to three phase control when the density of left turning trafiic attains a certain value.

According to the present invention one plan of operation will be maintained with trafic density below a certain predetermined value and upon the density increasing to the predetermined value this plan will be replaced by a second plan of operation, the second plan being maintained even if the density falls below the said predetermined value, and until such time that the density diminishes to a second and lower predetermined value, whereupon the first plan is restored, even though the said second predetermined density may be considerably less than that required to establish the initial transfer from one plan to the second.

It will be appreciated that numerous changes in the structure or design of the device or rear-. rangements of the parts thereof might be made without departing from the spirit of the invention. For instance, the switch PNS in the signal controller associated with the present apparatus and shown closed in Figure 3 might be placed in its open position and a relay M connected as illustrated by relay M of Figure 4 and arranged so that switch PNS is shunted at the points G and L (Figs. 2 and 4) While the signal controller is operating under the co-ordinated system. Such an arrangement of course permits the signal controller in periods of independent operation to function as a full-actuated controller without any normal preference to one lane or another, the signal periods being initiated in each lane as well as modified by actuation of the respective detector. Other modifications might also be made without departing from the spirit of the invention as'defined by the appended claims.

We claim:

1. In a traffic signal control system for the intersection of a main trafii'c lane with a cross lane having trafi'ic actuated means in the lanes, a.

right of way signal controller connected to the traffic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time periods in accordance with actuations of the respective traffic actuated means, a master control means operatively connected to said controller for periodically determining when efiective when said right of way controller may transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including mechanism for counting the actuations of the trafii'c actuated means in one of the lanes during each cycle of the signal controller and means responsive to the counting of at least a predetermined number of actuations during one cycle of the controller to render said master control means effective.

2. In a traific signal control system for the intersection of a main traffic lane with a cross lane having trafi'ic actuated means in the lanes, a right of way signal controller connected to the traflic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time periods in accordance with actuations of the respective traffic actuated means, a master control means operatively connected to said controller for periodically determining when effective when said right of way controller may transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including switch means for rendering said master control means alternatively effective and ineffective, mechanism for counting the actuations of the traflic actuated means in one of the lanes over a time period during one cycle of the controller, and means responsive to the counting of less than a predetermined number of actuations occurring in said one lane when said master control is effective and during such time period to operate said switch means to render said master control means ineffective for substantially the next cycle of the controller.

3. In a traffic signal control system for the intersection of a main trafiic lane with a cross lane having traffic actuated means in the lanes, a right of way signal controller connected to the traffic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time intervals in accordance with and initiated by actuations of the respective traffic actuated means, a master controlmeans operatively connected to said controller for periodically determining when effective when said right of way controller so initiates its cycle to transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including mechanism for counting the actuations of the traffic actuated means n one of the lanes over a time period at least part of which occurs in one such cycle, and means responsive to the counting of at least a predetermined number of actuations during the time period and operable upon initiation of another such controller cycle during said time period to render said master control means effective at least until any next following initiation of the controller cycle.

4. In a traffic signal control system for the intersection of a main trafiic lane with a cross lane having traffic actuated means in the lanes, a right of way signal controller connected to the traffic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time periods in accordance with actuations of the respective trafiic actuated means, a master control means operatively connected to said controller for periodically determining when effective when said right of way controller may transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including mechanism for counting the actuations of the traffic actuated means in one of the lanes, cyclic tuning means operating to reset said counting mechanism at cyclic time intervals while the master control means is ineffective, means responsive to the counting of at least a predetermined number of actuations during one such cyclic time interval to render said master control means efiective and means operating while the master control means is effective to reset said counting mechanism once in each cycle of the signal controller, means operable immediately prior to the end of said cycle and responsive to the counting of less than a predetermined number of actuations in said one lane during said cycle to render said master control means inefiective again.

5. In a traflic signal control system for the intersection of a main trafiic lane with a cross lane having traific actuated means in the lanes, a right of way signal controller connected to the traffic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time periods in accordance with actuations of the respective traflic actuated means, a master control means operatively connected to said controller for periodically determining when effective when said right of way controller may so transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including switch means for rendering said master control means alternatively effective and ineffective, mechanism for counting the actuations of the traffic actuated means in one of the lanes over a time period, and means responsive to the counting of less than a predetermined number of actuations occurring while said switch means is rendering said master control means ineffective during said time period to maintain said master control means ineffective through said switch means for another cycle of the controller.

6. In a traflic control system for the intersection of a main lane and cross lane having traffic actuated means in both lanes, a right of way controller to accord right of way to one lane and then the other thru a cycle in accordance with actuations of the trafiic actuated means, master control means connected to the right of way controller and operable when efiective for alternately and cyclically permitting and preventing transfer of right of way to the cross lane by the signal controller in response to actuation of the cross lane traffic actuated means, system changing apparatus including a relay having two operative positions one in which said master timer is ineffective, the other in which said master timer is effective, mechanism operating while said relay is in said one position to count actuations of the main lane trafiic actuated means during a cycle of the right of way controller and means responsive to the counting of at least a predetermined number of actuations in one cycle of the controller to shift said relay to said other position.

'7. In a traffic control system for the intersection of a main lane and cross lane having trafiic actuated means in both lanes, a right of way controller to accord right of way to one lane and then the other thru a cycle in accordance with actuations of the trafiic actuated means, master controlmeans connected to the right of way controller and operable when effective for alternately and cyclically permitting and preventing transfer of right of Way to the cross lane by the signal controller in response to actuation of the cross lane traflic actuated means, system changing apparatus including a relay having two operative positions one in which said master timer is ineffective, the other in which said master timer is effective, mechanism operating while said relay is in said one position to count actuations of the main lane traflic actuated means during a cycle of the right of way controller and means responsive to the counting of less than a predetermined number of actuations in one cycle of the controller to retain said relay in said one position. a

8. In a traffic control system for the intersection of a main lane and cross lane having trafiic actuated means in both lanes, a right of way controller toaccord right of way to one lane and then the other thru a cycle in accordance with actuations of the traffic actuated means, master control means connected to the right of way controller and operable when effective for alternately and cyclically permitting and preventing transfer of right of way to the cross lane by the signal controller to initiate such cycle in response to actuation of the cross lane traffic actuated means, system changing apparatus including a relay having two operative positions one in which said master timer is ineffective, the other in which said master timer is effective, mechanism operating while said relay is in said other position to count actuations of the main lane traffic actuated means over a time period during one cycle of said controller and means responsive to the counting of at least a predetermined number of actuations in said period to retain said relay in said other position at the end of said one cycle and substantially throughout the next cycle. 7

9. In a traffic control system for the intersection of a main lane and cross lane having traffic actuated means in both lanes, a right of way controller to accord right of way to one lane and then'the other thru a cycle in accordance with actuations of the trailic actuated means, master control means connected to the right of way controller and operable when effective for alter nately and cyclically permitting and preventing transfer of right of way to the cross lane by the signal controller in response to actuation of the cross lane traffic actuated means, system changing apparatus including a relay having two operative positions one in which said master timer is ineffective, the other in which said master timer is effective, mechanism operating while said relay is in said other position to count actuations of the main lane trafiic actuated means over a time period during one cycle of said controller and means responsive to the counting of less than a predetermined number of actuations in said time period to shift said relay to said one position at the end of said one cycle and retain said relay in said one position during the next following cycle.

10. In a traflic control system for the intersection of a main trafiic lane and a cross lane having traffic actuated means in each lane, a right of way controller connected to the traffic actuated means and operable normally to accord rightof way to the main lane and adapted to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, master timer means when effective operable cyclically and alternately to permit and prevent transfer of right of way to the cross lane in response to actuation therein, means connectible to the main lane traffic actuated means and operable when connected to prolong accord of right of way to the main lane upon actuation while right of way is accorded to the main lane, switchswitching means is in said one position during a cycle of the right of way controller and responsive at the end of such cycle to at least a predetermined number of actuations per unit time to shift said switching means to said second position.

11. In a trafiic control system for the intersection of a main traffic lane and a cross lane having trafiic actuated means in each lane, a right of way controller connected to the traffic actuated means and operable normally to accord right of way to the main lane and adapted upon actuation of the traffic actuated means in the cross lane to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, master timer means when effective operable cyclically and alternately to permit and prevent transfer of right of way to the cross lane in response to actuation therein, means connectible to the main lane trafiic actuated means and operable when connected upon actuation while right of way is accorded to the main lane to prolong accord of right of way to the main lane, switching means having two positions one in which said means for prolonging accord of right of way to the main lane is connected and said master timer means is ineffective, the second in Which the right of way prolonging means is not connected and said master timer means is effective, mechanism connected to the main lane traffic actuated means for determining the number of actuations per unit time, means operating when said switching means is in said one position during a cycle of the right of way controller and responsive at the end of such cycle to less than a predetermined number of actuations per unit time to retain said switching means in said one position.

12. In a traffic" control system for the intersection of a main traffic lane and a cross lane having trafiic actuated means in each lane, a right of way controller connected to the traffic actuated means and operable normally to accord right of way to the main lane and adapted upon actuation of the traffic actuated means in the cross lane to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, master timer means when effective operable cyclically and alternately to permit and prevent transfer of right of way to the cross lane in response to actuation therein, means connectible to the main lane trafiic actuated means and operable when connected upon actuation while right of way is accorded to the main lane to prolong accord of right of way to the main lane, switching means having two positions one in which said means for prolonging accord of right of way to the main lane is connected and said master timer means is ineffective, the second in which the right of way prolonging means is not connected and said master timer means is efiective, mechanism connected to the main lane traffic actuated means for determining the number of actuations per unit time, means operating when said switching means has been in said second position during a cycle of the right of way controller and responsive at the end of such cycle to less than a predetermined number of actuations per unit time to shift said switching means to said one position.

13. In a trafiic control system for the intersection of a main traffic lane and a cross lane having traflic actuated means in each lane, a right of way controller connected to the traffic actuated means and operable normally to accord right of way to the main lane and adapted upon actuation of the traffic actuated means in the cross lane to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, master timer means when effective operable cyclically and alternately to permit and prevent transfer of right of way to the cross lane in response to actuation therein, means connectible to the main lane traffic actuated means and operable when connected upon actuation while right of way is accorded to the main lane to prolong accord of right of way to the main lane, switching means having two positions one in which said means for prolonging accord of right of way to the main lane is connected and said master timer means is ineffective, the second in which the right of way prolonging means is not connected and said master timer means is efiective, mechanism connected to the main lane trafiic actuated means for determining the number of actuations of the latter per unit time, means operating when said switching means has been in said second position during a cycle of the right of way controller and responsive at the end of such cycle to at least a predetermined number of actuations per unit time occurring during such cycle to maintain said switching means in said second position during the next following cycle of the right of way controller.

14. In a traific control system for the intersection of a main trafic lane and a cross lane having traflic actuated means in each lane, a right of way controller connected to the traflic actuated means and operable normally to accord right of way to the main lane and adapted to be initiated into a cycle of operation in. which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, means including a circuit and a circuit closer therein and effective when said circuit closer is operated for initiating such cyclic operation upon actuation of the traffic actuated means in the cross lane, master timer means for cyclically operating the circuit closer, relay means having two positions in one of which said circuit is maintained eifective independent of ope eration of said circuit closer and in the second position said circuit is efiective only when said circuit closer is operated, means operated by said relay means in said one position for measuring the number of actuations per unit time of the main lane traiiic actuated means and means responsive to at least a predetermined number of actuations per unit time to place said relay means in said second position.

15. In a traflic control system for the intersection of a main traific lane and a cross lane having traiiic actuated means in each lane, a right of Way controller connected to the traflic actuated means and operable normally to accord right of way to the main lane and adapted to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again, means including a circuit and a circuit closer therein and effective when said circuit closer is operated for initiating such cyclic operation upon actuation of the traffic actuated means in the cross lane, master timer means for cyclically -perating the circuit closer, relay means having two positions in one of which said circuit is maintained effective independent of operation of said circuit closer and in the second position said circuit is effective only when said circuit closer is operated, means operatedby said relay means in said second position for measuring the number of actuations of the main lane traffic actuated means during a cycle of the signal controller, and means responsive to said means measuring less than a certain number of actuations to place said relay means in said one position. e

16. In a traffic signal control system for the intersection of a main traffic lane with a cross lane having traffic actuated means in the lanes, a right of way signal controller connected to the trafiic actuated means and operable thru a cycle to accord and transfer right of Way between the lanes for time periods in accordance with actuations of the respective traffic actuated means, a master control means operatively connected to said controller for periodically determining when effective when said right of way controller may transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including mechanism for determining the rate of actuations per unit time of the traffic actuated means in the main lane, means operative when said rate of actuations per unit time has been low and rises at least to a predetermined rate to render saidmaster control means efiective at least for substantially one cycle of the controller and means operative when said time rate of actuation has been high and falls at least to a certain rate to render said master control means ineiiective for at least one cycle of thecontroller.

17. In a traffic control system for the intersection of a main trafiic lane and a cross lane having trafiic actuated means in each lane, a right of way controller connected to the trafiic actuated means and operable normally to accord right of way to the main lane and adapted to be initiated into a cycle of operation in which right of way is transferred to the cross lane and subsequently retransferred to the main lane again for at least a minimum period, master control means for generating cyclically spaced impulses, means in the signal controller operable normally only during said impulses occurring after said minimum period to initiate cyclic operation of the controller in response to actuation of said cross lane trafiic actuated means, mechanism for counting actuations of the traffic actuated means in one of the lanes during a cycle of the signal controller, means responsive to said mechanism counting less than a predetermined number of actuations during said last mentioned cycle to transmit continuously an initiating impulse to Elli the signal controller so that cyclic operation of the controller in response to cross lane traffic actuation may occur immediately independently of the master timer at any time after expiration of said minimum right of way period on the main lane.

18. In a traffic signal control system for the intersection of a main trafiic lane with a cross lane having trafiic actuated means'in the lanes, a right of way controller connected to the traffic actuated means and operable thru a cycle to accord and transfer right of way between the lanes for time periods in accordance with actuations of the respective trafiic actuated means, a master control means operatively connected to said controller for periodically determining when effective when said right of way controller may transfer right of way to the cross lane in response to such actuation in the cross lane, system changing apparatus including counting mechanism comprising a unit charge condenser, means for placing a charge on said condenser, a reservoir condenser, means operating upon actuation of the main road trafilc actuated-means to transfer the charge on said unit charge condenser to said reservoir condenser so that the charge on the latter is substantially proportional to the amount of trafiic in said main lane, cyclic timing means operating to discharge said reservoir condenser at periodic time intervals while said master control means is ineffective, and means responsive to at least a predetermined charge on said condenser at a certain point in one controller cycle to render said master control means effective during a following controller cycle.

19. In a traffic control apparatus for a plurality of intersections of a cross lane and a common main lane having at each intersection trafiic actuated means in the cross lane and a right of way controller for normally according right of Way to the main lane and adapted to be initiated into operation thru a cycle to transfer right of way to the cross lane and retransfer right of way to the main lane for at least a minimum period in response to actuation of the actuatable means, the combination of a master timer means for cyclically and alternately providing time periods when the cyclic operation of the controllers may and may not be initiated in response to actuation, at one intersection traffic actuated means in the main in addition to cross lanes, system changing apparatus including mechanism for counting the number of actuations of the main lane traffic actuated means over a time period during one such cycle, means responsive to the counting mechanism counting less than a predetermined number of actuations. during said time period to render the several right of way transferring controllerslso initiatable by actuation independent of said master timer means for at least the next such cycle so that any controller can transfer right of way to the cross lane immediately on actuation occurring at any time after expiration of the minimum right of way period on the main lane and while right of way is accorded to the main lane.

20. In a traflic control apparatus for a plurality of intersections of cross lanes with a common main lane having the combination of traffic actuated means in the cross lane at each intersection and a right of way controller at each intersection for normally according right of way to the main lane and adapted to be initiated into operation thru a cycle to transfer right of way to the cross lane and retransfer right of way to the main lane for at least a minimum period in response to actuation of the trafiic actuated means, relay means at each controller including circuit closers operable when said relay means is energized to cause the associated controller to transfer right of way to the cross lane immediately on actuation occurring at any time after expiration of the minimum right of way period on the cross lane, a master timer means for cyclically providing alternate time periods when said relay means at each controller is respectively energized and deenergized, traffic actuated means in the main and cross lanes at one of the intersections, system changing apparatus at said one intersection and including a switching means having two positions one in which said relay means are constantly energized and the other in which said energization of said relay means occurs only at time periods determined by the master timer, mechanism for measuring the rate of actuations per unit time of the main lane traffic actuated means, and means responsive to said mechanism measuring less than a predetermined rate of actuations to place said switching means in said one position.

21. In a traflic control apparatus'for a plurality of intersections of cross lanes with a com mon main lane the combination of traffic actuated means in both lanes at each intersection and a right of way controller at each intersection operable normally to accord right of way to the main lane and adapted upon actuation of the cross lane actuatable means to be initiated into a cycle of operation in which right of way is transferred to the cross lane and retransferred to the main lane again for at least a minimum period, means in each controller connectible to the main lane traffic actuatable means and operable when connected upon actuation while right of way is accorded to the main lane to prolong accord of right of way to the main lane, relay means at each controller including circuit closers operable when said relay means are energized to cause the associated controller to transfer right of way to the cross lane immediately on actuation occurring at any time after expiration of the minimum period on the cross lane and to connect the main lane right of way prolonging means to the traffic actuated means, a master timer means for cyclically providing alternate time periods when said relay means at each controller is respectively energized and deenergized, system changing apparatus at one of the intersections selected as a key intersection including a switching means having two positions one in which said relay means are constantly energized and the other in which said energization of said relay means occurs only at time periods determined by the master timer, mechanism for measuring the rate of actuations per unit time of the main lane traffic actuated means, means responsive to said mechanism measuring less than a predetermined rate of actuations to place said switching means in said one position.

22. In a traffic control apparatus for the intersection of a cross lane and a main lane, the combination of traffic actuated means in the lanes, a right of way controller adapted normally to accord right of way to one of the lanes in absence of actuation of traffic actuated means in the other lane and adapted to accord right of way alternately to the lanes in response to actuation of the respective traflic actuated means and to prolong right of way in at least said one of the lanes between minimum and maximum time limits in response to successive actuations of the traffic actuated means in said one lane, system changer apparatus connected to said controller and having a plurality of plans of operation for said controller, said apparatus including relay means for shifting from one such plan of operation to another, mechanism for counting actuations and operating said relay to so shift from one plan to another in response to a predetermined number of actuations, a second relay means connected to the traific actuated means in said one of said lanes to be operated by each actuation of the trafiic actuated means therein, said second relay means including circuit closers operated by operation of said second relay means, one of said circuit closers when operated connecting the last mentioned tramc actuated means to the counting mechanism to actuate the latter, and a circuit including another of said circuit closers and also including a circuit closer operated by the first mentioned relay means for connecting said last-mentioned traffic actuated means to the controller whereby the same trafllc actuated means in said one lane serveson both said plans to actuate the system changer for counting traflic and also serves only on one of said plans to actuate the controller to govern such prolongation of accord of right ofway by the controller.

HARRY A. WILCOX.

JOHN L. BARKER.

CERTIFICATE OF CORRECTION.

Patent No. 2, 56,158; April 25, 19 9.

HARRY A. -WILCOX, ET AL.-

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 9, second column, line 8, claim ii, for the word "tuning" read timing; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed and sealed this 21st day of November, A. D. 1959.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.