US2183780A - Traffic actuated control system and apparatus - Google Patents

Description

Dec. 19, 1939. w cox 2,183,780

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15, 1936 5 Sheets-Sheet 1 '1 l 7 F- INVENTOR HAPPY A. W/zcaa A TTOR N E Y5 H. A. WlLCOX Dec. 19, 1939.

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15, 1936 5 Sheets-Sheet 3 A TTORNEYJ H. A. WILCOX Dec. 19, 1939.

TRAFFIC ACTUATED CONTROL SYSTEM 'AND APPARATUS 5 SheetsShee 4 Filed April 15, 1956 WM NMN 3 3 ATTORNEYS 5 SheetsSheet 5 Dec. 19, 1939. H. A. WILCOX TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15, 1936 Patented Dec. 19,1939] um rso STAT Harry A. Wilcox, Bronxvllle, N. Y., asaignor to Automatic Signal Corporation, New York, N. Y.,

a corporation of Delaware Application April 15, 1936, Serial No. 74,422

23 Claims.

This invention relates to a trafllc system capable of use at the intersection of two tramc lanes or streets, and has for its general object to provide an automatic system by means of which traflic will be expeditiously and safely handled. This system is to a large extent controlled by the traffic along the intersecting lanes. Its operation will be responsive not only to the presence of traffic but will be affected also by the density of trailic in each lane. Previous systems to my knowledge have provided for traflic actuation of the signals but have less completely taken into account the element of the relative density of trafflc in the two lanes when traffic is very heavy.

The vehicle actuated traffic control is notin itself ainew invention, such systems having been in general use for some time. Previous systems have served admirably to control traflic at the intersection of two lanes when tramc is light in one lane and heavy in the other, or when traflic is irregularly spaced in one or both of said lanes, but they have not been adapted so well to the most efllcient handling of intersections where traflic is continuously heavy in both lanes. system to be effective under this latter condition must be sensitive to slight difference between two heavy traflicv flows.

The system disclosed herein handles efllcient'ly any type of traffic 'but is especially effective in handling heavy traflic with the utmost efliciency. This system is of the type in which within a maximum limit each vehicle approaching. the intersection on a go signal after an initial interval which is preferably inserted as'described for a time after its approach, such time being designated as a vehicle protection period, right' ES PATENT orrica denser trafiic thereby providing for maximum efficiency in handling heavily travelledintersections where efliciency is of the greatest importance. In effect it provides means whereby waiting traflic is able to exert a forcing eifect to obtain 6 I the right of way sooner in accordance with its demand.

This system, like previous vehicle actuated I trafl'lc control systems, includes stop, and "go signals to be displayed in each traflic' lane enterl0 ing an intersection, a control mechanism to operate the stop and go signals, and trailic detectors located in the aforementioned traffic lanes, which effect the operation of the control mechanism in such a manner as to cause the signal 15' display periods to conform to the requirements of the trafiic approaching the intersection. In this system as in the prior types of vehicle actuated systems the actuation of a traflic detector in a traiilc lane in which. the stop signal is being dis-. 20

I played causes the right of way to be transferred below extends the period of display of such signal interval in this new system is decreased in-ac- .cordance with the number of. vehicles awaiting" on the cross lane. Hence, with a large group of vehicles waitingon the cross lane, each vehicle entering the intersection from the lane in which the go signal is being displayed is allotted a shortened time period for its passage. As a result .of this fact a shorter spacing-between vehicles in the moving line will yield the right of way. Therefore under the system disclosed 50' herein a large number of waiting vehicles is more effective than a small number to cause transfer of the right of way to the lane in which they are waiting. This invention therefore provides a system in which the right of way tends 55- to revert more quickly to the lane having the to that lane at the .flrstsopportunity. If there is no trailic entering the intersection from the lane in which the goflsignal is being displayed a caution signal is usually immediately displayed in said lane and after a short period the right of way is transferred to the lane in which the stop signal was being displayed.

If traflic is moving in the lane wherein the .go signal is being displayed the actuation of 30 the traflic'detector in the lane in which the stop signal is beingdisplayed causes the right of way to be transferred thereto at the first break of a predetermined time in the said moving traffic. If no such break occurs in said movin traffic the right of way will be transferred at the end of a predetermined maximum period usually provided by a different timing element.

' In this system as in previous systems, the actuation of a trafllc detector during the period in which the go signal is being displayed to the lane wherein said traffic detector is located causes such go signal period to be extended under certain conditions. The go period for each traflic lane is divided into two parts. Dur- 5 ing the first part of this period the actuation of the traflic detector in the lane in which the go signal is being displayed is of no effect. This first part of the go period, called the initial interval, is introduced to allow time for standing 5 trafllc to get into motion. While not essential to operation this initial interval is preferably introduced to increase the eiilciency of the system. After the expiration of the initial interval the go signal will continue to be displayed for 5 vehicle to progress from the trafflc detector thru the intersection. This last named interval has been identified above as the "vehicle interval"; During the "vehicle interval" the actuation of a tramc detector in the lane in which the "go" signal is being displayed extends the right of way period therein for a time interval reasonably suiiicient to allow the vehicle which actuated the traiilc detector to progress from said detector thru the intersection.

The system disclosed herein however includes a new and important feature in that the timing of the vehicle interval is affected by the number of waiting vehicles in the cross lane as mentioned before so that as the group of waiting vehicles increases in number the control will take advantage of shorter and shorter breaks in the moving trailic to transfer right of way to these waiting vehicles.

Furthermore this system includes another new feature in that it provides that if desired certain forms of traflic such as trolley cars, fire apparatus, etc., to which it may be advisable to accord preferred treatment can thru actuating special detectors have the same eflect on the timing of the.signals as several ordinary vehicles.

This system, like some previous trai'ilc actuated systems is arranged so that the timing of the "initial interval", the first part of the "go" period, can, before the beginning of said "initial interval, be preadjusted between a predetermined minimum value and a predetermined maximum value, by successive actuations of the traiilc detector in the lane in which the stop" signal is being displayed so that when said lane shall next be given the g0" signal the initial interval" of said go" signal display period will be timed in conformance with the volume of the traillc waiting in said lane, to the end that a large number of waiting vehicles will be granted a longer initial interval than will be granted to a small number. However in the system described herein the variable initial interval is achieved by a method using simpler and more reliable equipment than that used in previous systems, as will be more specifically shown later.

In this system the traflic detectors can be located at a distance from the intersection customary in the prior systems but it is entirely feasible, especially if the variable initial interval is employed, to locate them considerably farther from the intersection (two or three hundred feet or more for example) thereby facilitating the counting of larger numbers of waiting vehicles which will increase the effectiveness of trafllc approaching a stop signal in controlling the signal timing.

With the system adjusted to give a pronounced reduction of the vehicle interval after the accumulation of a certain amount of traflic approaching a stop signal a considerable degree of coordination between adjacent intersections can be obtained solely by the pressure of trafllc itself without any electrical interconnection since the effect of a group of vehicles approaching successive intersections equipped with this system will be to so reduce the vehicle interval for cross traflic at each intersection as at any time subsequent to the cross street initial interval to practically seize the right of way at intersection after intersection thereby favoring uninterrupted progress to a sufliciently large compact group of vehicles.

Cross traflic will however be protected against 9,183,780 an interval of time at least sufficient for a moving unreasonable interruption since 'the cross street initial interval is timed in advance in accordance with the number of vehicles waiting on the cross street and is not reducible by main highway trafflc, and in addition either a maximum limit to right of way on the main highway or a reduction of the main highway vehicle interval by accumulation of waiting cross street traiiic, or both, serve to protect the cross street traffic.

The coordination effect outlined above will be obtained by a compact group oi vehicles whether they move along one street or follow an irregular path through an area which is a considerable advantage over prior non-vehicle actuated coordinated systems in which coordination was necessarily arranged to favor the passage of trafflc along a predetermined route.

Under this system while a compact group of vehicles is crossing its path, scattered traffic is automatically given the opportunity to come into close order through a natural accumulation. Hence when this system is applied to a large area constituting a grid of individually and independently controlled intersections trafflc will form into compact groups at the outlying intersections and then pass thru the grid as favored units thereby causing the controls throughout the whole area to function as a coordinated grid system without the necessity for any electrical interconnection between intersections.

It will be appreciated that traiiic is often heavier inbound toward the central area of a city in the morning and heavier outbound in the afternoon, and that in such cases the automatic natural coordination effect above noted with this invention will be particularly pronounced on the main traffic arteries.

It is an object of this invention to provide an improved traflic control system wherein the functioning of the apparatus will automatically take into account the relative densities of traillc in the two roadways in determining the signal timing.

Another object is to provide an improved sysin which the right of a single vehicle or a scattered group of vehicles to pass the intersection is not by any means permanently withheld. A single waiting vehicle will be given an opportunity to pass within a reasonable period after its approach to the intersection even though moving cross trafllc may be continuous. If there is no cross trafl'ic such a vehicle will be given the right of way immediately upon its approach?- It is another object to provide a system in which vehicles awaiting the right of way in one lane will facilitate yielding the right of way from the other roadway by reducing the time allotted to each vehicle entering the intersection from such other roadway.

It is a further object to provide a system in which vehicles awaiting the right of way in one roadway will reduce substantially in proportion to the number of said waiting vehicles, the time allotted to each vehicle entering the intersection from the other roadway in which the go" signal is being displayed thereby automatically permitting a large amount of waiting traflic to take the right of way more easily than a small amount.

It is also an object of the invention under some conditions to reduce substantially the vehicle protection interval on one street after suiilcient traffic has accumulated on the opposite street.

It'is another object of this invention to pro- -tem in which the denser trafllc is favored, but 5 voiume 'preadiust, by controlling the starting point, the: timing 'of the following. preliminary right of way period. 4 i

It is afurther object 'to provide a system in which waiting traiiic willautomatioally-and substantially in proportion to its'volume preadjust I theduration of the following right of way period by changing the starting point of this timing period in accordance with the number of ve-f I hicles approaching the intersection against the stop signal.

.go" period. 1

1 It is also an obiectiof this invention to provide a system in which the variation of charge in a condenser .is instrumental in timing the goi periods and in which vehicles approaching the .intersection against the stop signal will preadjust the timing of thefollowing "go" period thru varying in accordance with the number of such vehicles the initial charge in said, condenser at the beginning of the said following It is another object to provide an improved system in which the right of way will be automatically returned to a traflic lane later if said right of way was last withdrawn from that lane by the maximum timer less than a predetermined time after the last traffic actuation of a detector in that lane.

It is still another object to provide a system in which the right of way will automatically be returned to a traflic lane at the first reasonable opportunity if, when the right of way is withdrawn, the vehicle interval allotted to vehicles in that lane is thru the action of waiting cross traflic or .otherwisedecreased to less than a predetermined time period.

Another object is to provide a system which can be arranged so thatseveral adjacent intersections under this type of control will operate as a coordinated group or grid so as to facilitate the formation and passage of a large compact group of vehicles thru this group or grid in any path solelythru the pressure of traflic without any electrical interconnection among the intersections. a 1

It is also an object to provide a system in which if desired certain forms of traiilc such as fire apparatus or trolley cars can have a multiple effect in timing the signals so that one actuation by such a vehicle can have the same effect as several actuations by ordinary vehicles -The invention is designed to encourage the closing up of scattered traflic which may wlshto cross the path of dense traflic thereby effecting high emciency in the use of one intersection or a group of intersections. However such scattered trafiic is never forced to come into close order unless the right of heavier cross trafllc requires this procedure. Hence the system operates to procure the greatest good to the greatest number without unduly sacrificing the rig-ht of any.-

The invention is exemplified in and will be particularly described in connection with the accompanying drawings, in which:

Figure 1 is a plan view of an intersection showing the location of traflic detectors, signals and timer housing.

Figure 2 is a plan view of a group of adjacent intersections equipped with this system showing one example of the location of signals, trafllc detectors and timer housings.

Figures 3 and 4 together comprise a circuit diagram of one form of apparatus embodying my invention including apparatus with an- ,nections to and t'railic detectors.

Figures 5 and 6 show a circuit diagram for an alternative and in some respects preferred form of apparatus embodying my invention and. employinga somewhat diiferent form of timing apparatus with its connection to signals and traiiic detectors.

Figure 7 is a schematicdiagram of a form of specialdeteetor equipment by means of which preferred tramc can exert a multiple'ei'fect on the timing apparatus.

' The traillc detectors for'each'intersection in used in this system but the customary red, yellow and green traflic lights are preferable inasmuch as motorists and pedestrians are now generally familiar with the significance of these colored lights. s

'The trafilo detectors may be of any desired form such as a mechanical switch in which the pressure exerted by the weight of a passing vehicle flexes a resilient plate to make a contact, or an energy beam is directed across atraflic lane so as to be interrupted by trailic approaching the intersection. A common form of the latter type is a light beam directed across a trafiic lane with a photoelectric cell arranged as a receiver. .Still another-type of detector isv-an electromagnetic device in which the vehicle disturbs a magnetic field and thereby operates a relay in the control Any of these or other types of traflic detectors such as a push button for use of pedestrians will operate satisfactorily in this system.

The timermechanism shown in Figs. 3 and 4 herein which controls the signals and is responsive to the trailic detectors is of the type in which cams, fixed on a shaft which is revolved in steps by a solenoid with a ratchet and pawl mechanisrn or" other suitable means, operate contacts to control the signal indications and to connect the various timing units in the timer circuit .properly for'th'e particular point in the signal cycle prevailing.

The cam shaft used in this system employs eight steps to complete one revolution which carries the signal indication thru one complete cycle, that is, from a go indication in one lane thru the go indication on the cross lane and thence back to the go indication on the firstlane;

In the embodiment shown in Figs. 3 and 4 the timing of the various intervals is accomplished by means of apparatus including three element thermionic tubes arranged to be influenced by traflic approaching the intersection. A direct current relay is connected in the plate circuit of each tube in such a way that. the plate current passes thru an operating coil of this relay. With A condenser is included in each grid circuit. The voltage of each grid is controlled by the charge on the condenser associated therewith. When a grid condenser is sufliciently charged, the plate current will become great enough to operate the relay thru which it Hence by controlling the starting charge and the rate at which charge is added to or subtracted from the grid condenser, each tube can be made to operate the relay associated with it at the end of a longer or shorter period. I

Figures 3 and 4 are complementary. In both figures the contacts identified by the capital letter C followed by a numeral are operated by cams mounted on a common cam shaft. This shaft is rotated by action of the solenoid 3 shown schematically in Fig. 4. The contacts identified by the letter 8 followed by a numeralare operated directly by the solenoid 8. Each time the solenoid rises in its stroke each of these contacts is changed from its normal condition of closed or open to the opposite condition. As the solenoid returns to its position of rest these contacts return to their normal unoperated conditions. Each cycle of operation of the solenoid including forward stroke on energization and return stroke on de-energization rotates the cam shaft thru degrees.

Eight steps of the shaft complete one revolution during which the signals 4! to ill inclusive in Fig. 3 go thru one complete cycle of changes, i. e., from green in one street thru green in the cross street, back to green in the first street. The table at the bottom of Figure 4 indicates which cam contacts are closed in each of the eight positions. of the cam shaft. An X in a square indicates that the contact whose number is at the top of the particular column including that square is closed when the shaft is in the position identifled by the number at the end of the horizontal row passing thru that square.

The cam shaft positions are numbered from i to 8 as indicated in the table in Figure 4. When the cam shaft is in positions 1, 2 and 3 the green signal 45 is displayed to N-S trafllc, when in position 4 the amber or warning signal 48 is displayed to N-S traillc, and when the cam shaft is in positions 5, 6, 7 and 8 the red signal 41 is displayed to N S trailic. The EW green signal 48 is displayed while the cam shaft occupies positions 5, 6 and 7, the EW amber signal 49 is displayed in cam position 8 and the EW red signal in cam positions 1, 2, 3 and 4. Other signal display sequences can of course be provided by this apparatus but this particular one is cited because it is in quite general use in tramc control systems.

In Figures 3 and 4 negative power is supplied thru the wire designated by a minus sign enclosed in a circle and a square which common grounded negative for both D. C. Positive A. C. is supplied through wires designated by a plus sign in a circle, and positive D. C. thru wires designated by a plus sign in a square.

Referring to Figure 3, the apparatus represented by that part of 'the drawing to the right of the. negative power wire is in general eflective to cooperate with the apparatus of Fig. 4 to call the right-of-way to the EW lane and to hold the right of way thereon. In like manner the apparatus represented by that part of Fig. 3 to the left of the negative power wire is effective to cooperate with the apparatus of Fig. 4 similarly to call or hold the right of way on the N-S lane.

signifies a low and red lights.

At the top of Fig. 3 are shown the two sets of signals representing the customary green, yelnumbers 48 to II being displayed to the EW tramc whereas numbers 4| to 41 are displayed tothe NS traffic.

The traffic detectors located respectively in the N-HS and EW lanes are represented by II and 5!. Relay E is responsive to actuations of detector II and relay 1" operates in response to actuations of detector 52.

The operation of relay F starts a sequential operation which calls the right of way to the E-W lane and when the right of way has been given to the EW lane, operation of this relay tends to hold it there. Similarly relay E operates to call and hold the right of way on the N-S lane.

Relay M cooperates with relays E and F in calling the right of way as mentioned above and is also effective thru cooperation with relay A and a contact of solenoid S to cause right of way to return to a given lane later if, when right of way last left this lane the vehicle protection interval was shorter than a predetermined period, or if a detector was actuated thus initiating a new vehicle interval in this lane within a predetermined time previous to the yielding of the right of way to the cross lane.

Relay C cooperates with tube CT and condenser KC to time all the intervals which remain constant during successive signal cycles such as the amber period for each lane (cam shaft in position 4 or 8) and the maximum period during which trafllc can hold the right of way on either street against a cross lane call (cam shaft in position 3 or 1). In addition if switch 69 is closed relay C, tube CT and condenser KC will cooperate to call the right of way to the E-W lane a predetermined time after said right of way last left the EW lane, and closure ofswitch it will in a like manner cause relay C, tube CT and condenser KC to call the right of way to the N-S trafllc lane a predetermined time after the right of way last left the N-S lane. This effect is termed the periodic call".

By opening or closing switches 68 and 68 the apparatus can be caused to normally operate as a reverting,,arterial or floating system. The closure of both switch 68 and switch 69 will in the absence of traflic cause the right of way to normally revert periodically from lane to lane. This system of operation is commonly called the reverting system.

If switch 68 is closed and switch 89 is open a NS arterial system results in which the right of way will normally remain on the NS lane .until called by trafllc to the EW lane. After the EW trailic has cleared the intersection Q the right f W y will automatically revert to the N-S lane. In the event of continuous EW traflic under the above system the right of way will periodically revert to the NS lane, and remain there as long as N-S traflic may require it up to a predetermined limit.

If switch 59 is closed and switch 68 open the system will operate arterial EW under which system the EW lane instead of the N-S lane will be the artery. The right of way will normally remain on the E-W lane until called by tramc to the NS lane, from which lane it will revert to the EW lane when the N -S traffic has cleared the intersection or has held the right of way on the N-S lane for a predetermined time.

If switches 63 and 69 are both open the apparatus will operate as a floating system under which the right of way will normally remain on the lane to which it was last called until traffic on the cross lane requires it.

Under all of these systems of operation traflic on each lane can hold the right of way up to a predetermined period against waiting traffic in the cross lane and in addition automatically put in a call for the returnof the right of way to the lane from which it is being transferred ii at the time of such transfer a'vehicle interval has been initiated by a detector actuation in said lane within a predetermined time prior to said transfer of the right of way or if the vehicle interval prevailing thereon at the time of such transfer has by waiting cross traffic been reduced to less than a predetermined magnitude.

The cooperative action of relay C, tube CT, and condenser KC which time all intervals which do not vary from cycle to cycle is as follows: Condenser KC during each of these various intervals is being charged thru a fixed resistance, one of the several indicated in the right or left side of Fig. 3. As this charge increases the voltage of the grid ct2 of tube CT to which condenser KC -is connected increases. Hence the plate current of tube CT increases. When this current reaches a suflicient magnitude relay C operates which in turn operates the solenoid S to move the cam shaft into its next position.

In a generally similar manner tubes AT and BT are associated with condensers KD and KB and with relay B, which is a double coil relay, to time the initial and vehicle intervals which vary in their timing from cycle to cycle in accordance with the requirements of traffic. Coil D3 of relay B is its main operating coil. Coil b2, the bucking coil, is connected so that its magneto-motive force opposes that of coil b3 and therefore modifies the effectiveness of coil b3 to operate'relay B. In order to insure that the bucking coil b2 shall under no circumstances operate relay B its magneto-motive force should always be less than that required to operate relay B or as an alternative said relay B might be of the polarized type in which case no limit need be placed on the magneto-motive force of coil b2. Current flows thru coil I)! only when the cam shaft is in position 3 or 1, the NS and EW trafiic timed positions, since in all other positions of the cam shaft the grid of tube ET is biased negative to such a degree that substantially no plate current flows in this tube or in coil b2 of relay B.

With the cam shaft in position 3 or I the current thru the bucking coil D2 is regulated in accordance with previous actuations of the de- 'tector in the lane in which the stop signal is displayed, in such a way that this current is caused to be less than a predetermined maximum by an amount substantially in accordance with the volume of the waiting cross traffic. This effect is the means by which waiting cross traffic decreases substantially in accordance with its volume the timing of the vehicle interval in the lane in which the go" signal is being displayed.

The current thru operating coil 173 when the cam shaft is in position 3 or 1 is affected by actuation of the detector in the lane in which the go" signal is being displayed in such a way that a new vehicle interval is initiated for each actuation of a detector in this lane. Therefore it can be seen that traffic in both lanes affects the operation of relay B to time the vehicle interval for each lane in accordance with the trafto control the effectiveness of tube ZBT in modi-' fying the operation of relay B to the end that waiting cross traflic can be caused to have a greater or less effect on the timing of the vehicle interval. In a network of intersections equipped with this system these by-pass resistances could be adjusted to a high value in order to increase markedly the effect of waiting cross traffic in decreasing the vehicle interval to aid in emphasizing the coordination effect naturally inherent in a group of adjacent intersections equipped with this apparatus.

Tube AT, as mentioned above, also cooperates thru the coil of relay A with coil D3 of relay B, condensers KE and KD, to time the initial intervals, cam shaft position I or 5, substantially in proportion to the number of vehicles waiting in the lane in which the go signal is displayed at the beginning of such interval. During the initial intervals coil D2 of relay B carries no current due to the negative bias of gridbt2 of tube ET. Hence coil b3 alone is effective to control relay B during the initial intervals.

Relay A is effective to cooperate thru solenoid and cam shaft contacts S2, C5, and C6 to operate relay E or relay F which will in turn operate the memory relay M to call the right of way to the lane from which it is being transferred if, at the time of such transfer, the vehicle interval prevailing on said lane is less than a predetermined time or if the right of way is transferred by action of the maximum timer less than a predetermined time after a vehicle interval has been initiated by a detector actuation in said lane from which the right of way is being transferred. If either of these named conditions prevail relay A will be unoperated at the time the cam shaft moves into position 4. Therefore during this movement armature al of relay A thru its back contact and solenoid contact S2 complete a recall circuit to operate the memory relay M and thus cause the right of way to return later to the lane from which it is being transferred just as if a vehicle detector in this lane had been actuated.

To more completely explain this system I shall now described in detail its operation to carry the signals thru one complete cycle.

Relay E is operable in all cam shaft positions upon actuation of the NS vehicle detector 5| which completes a circuit from negative power, thru detector 5| and wire 59 to the coil of relay E thence to positive power. Similarly relay F is operable in all cam shaft positions upon actuation of the EW vehicle detector 52 which completes a circuit from negative power thru detector 52 and wire 60 to the coil of relay F thence to positive power. The effect produced by the operation of these relays is different in different cam shaft positions as will be pointed out in the following description of the operation of the system.

Assume that the cam shaft is in position 2, called the NS rest position. The NS go signal is energized thru wire 53 and cam contact C38. The EW stop signal is energized thru wire 58 and cam contact C39. Condenser KE which cooperates with tube AT and relay B to time the NS vehicle interval is being charged thru the following circuit. Positive power thru resistance R4, contact Cl5, wires 85 and 80 to condenser XE thence to negative power. -While thecamshaftisinposition 2condenserKEis subject to discharge at each vehicle actuation of detector 2i thru the operation of relay 3. The subsequent recharge period of condenser KE constitutes the vehicle interval for the passage thru the intersection of the vehicle in the 21-8 lane which caused the operation of relay E. This discharge circuit for condenser KE goes from negativepower to armature c2 of relay E, wires I2, 2|, contact CI2, wires 22 and 22 thru condenser KE and thence back to negative power.

In this cam shaft position condenser KI: which as before mentioned cooperates with tube AT and relay B to time the NS vehicle interval is connected to the grid at2 of tube AT thru wires 22, 22, contact CI2 and wire I22. Hence the voltage of condenser K1: is effective to control the plate current of tube AT. This plate current passes thru coils of relays A and B thru a circuit starting at negative power, thru potentiometer resistance PI, wire II2, filament MI and plate at2 of tube AT to relay A thence thru wire III to coil b2 of relay 3 to positive power. Coil b2 of relay B carries no current while the cam shaft is in position 2 since the grid N2 of tube BT is biased sufllciently negative with respect tofilament bfI thru wires I2l, I22 and contact CI2 to prevent any plate current from flowing in tube BT. I

When condenser K1: is charged to a sufficient voltage the plate current of tube AT which passes thru coil b2 will be great enough to operate relay 8. When condenser KI: has further charged to a still higher predetermined voltage the plate current of tube AT will further increase thus causing relay A to operate. While the cam shaft remains in position 2 the operation of relay A or relay B is of no effect since their armatures whether operated or not operated do not affect any circuit. Relays A and B will however function when the cam shaft has moved into position 2 as will be explained later.

Movement of the cam shaft into position 2, called the N-S trafllc timed position, is made in response to a cross lane call resulting either from a vehicle actuation of the E-W detector 22, or by action of the E-W periodic call circuit if the system is set to normally revert to the E-W lane, as would for instance be the case if the system were set to revert periodically from street to street or if the i l-W lane were the main highway of an arterial system.

An E-W detector actuation will cause this cam shaft movement as follows: The operation of the E-W detector 22 will complete the circuit of relay F from negative power to positive power thru wire 22. The operation of relay 1'' will energize relay M thru a circuit starting at negative power thru armature 12 of relay F, wires 22, 22, contact CII, wire 22 to coil of relay M thence to positive power. Relay M will thereupon oper-'- ate and lock in thru the circuit starting at negative power thence thru armature ml of relay M, wire 22, contact CI2 and coil of relay M to positive power. Solenoid S will now be energized thru a circuit from negative power thru armature ml of relay M, wire 22, contact CI2, wire I28, armature s2 and coil of solenoid S to positive power, Solenoid S will therefore operate andcause the cam shaft to move into position 2.

With the system set to operate normally as a reverting or EW arterial system switch 62 would be closed so that if no actuation of an E-W vehicle detector takes place the cam shaft, after remaining in position 2 for a predetermined time. will be moved into position 2 by action of the periodic call circuit as was previously mentioned.

The movement of the cam shaft to position 2 by means of the periodic call circuit is accomplished as follows.-

With switch to closed condenser KC is charging while the cam shaft is in positions I or 2 thru the circuit starting from positive power reach a magnitude sumcient to operate relay thru its circuit starting atpositive power thru the coil of relay C and wire I22, plate ct2, and

' filament ctI of tube CT, wire I I2, potentiometer resistance PI to negative power. The operation of relay C will complete the circuit from negative power thru armature cI of relay C, wire I22, 22, contact C22, wire 22, coil of relay F, thence to positive power. Relay F will now operate and cause relay M to operate solenoid S as before explained to move the cam shaft into position 2.

By adjusting the variable resistance R2 the time required to charge condenser KC up to a voltage sufficient to cause the operation of relay C as above described'can be made greater or less. Since condenser KC starts to charge when the cam shaft moves into position I and E--W periodic call can be made to cause the cam shaft to move from position 2 to 2 at any predetermined time after the NS lane is given the go signal unless Iii-W traflic has previously caused said transition. Resistance R2 in a similar manner regulates the timing of the N-S periodic call when the cam shaft is in position 2. It is by closing switches 62 and 69 and properly adlusting variable resistances R2 and R2 that the right of way as before mentioned can be made to normally revert at any desired intervals from street to street in the absence of trafllc.

As the cam shaft moves into position 2 contact CI2 opens thus breaking the lock-in circuit for relay M which thereupon assumes its unoperated condition.

The operation of the solenoid S to move the cam shaft from position 2 to 2 is as follows. When the solenoid S is energized, as explained above, the core moves into the solenoid. The first effect of this movement is to change each of the solenoid contacts SI-SI from its rest position in which some contacts are made and others open to the opposite condition wherein those contacts which were made when the solenoid was at rest are broken and those which were broken are made. As contact S2 opens the solenoid is deenergized but the inertia of the solenoid armsture carries it beyond this point a considerable distance. At the top of the stroke a pawl engages the cam shaft ratchet so that on the down stroke the cam shaft is revolved thru 45 degrees. On the down stroke some cam contacts change before the solenoid contacts return to their .normal positions and others change after in order to secure the proper sequence in the circuit changes occurring during this period of transition from one cam shaft position to another.

While the solenoid is operating to move the cam shaft from position 2 to 2 solenoid contact S2 completes a discharge circuit for condenser KC, which has been timing the periodic call period, to insure that no residual charge remains arcane therein when condenser KC starts to time the maximum period in cam shaft position 3. As the solenoid returns to its unoperated position contact SI opens this discharge circuit which may be traced from negative power thru contact 33, wire I", contact 01, wires Hi2, ill to'con-' denser KC thence back to negative power again.

While the cam shaft is moving into position 8 and while it remains there the circuits thru which relay A and coil M of relay B are energized, which have been previously described, re-

' main as they were when the cam shaft was in position 2. As the cam shaft moves into position 3 relay B will have been operated if more than a predetermined period of time has passed since the last actuation of detector 5| and if relay B remains operated when the cam shaft has,

. coil M as the cam shaft moves into position 3 may, if the current thru coil b8 has at that time reached a magnitude only slightly greater than that required to operate relay B without the opposition of coil b2, be sufficient to cause the armature of relay B to temporarily drop out. However the current thru coil b3 continues to increase if there are no N-S detector actuations. When this last named current reaches a sufiioient magnitude it will overcome the opposition of coil b2 and cause relay B to again operate and move the cam shaft on into position 4.

It is thru the effect of coil b2 on the operation of relay B that waiting EW cross traffic decreases the N-S vehicle interval substantially in accordance with its volume. This is accomplished as follows:

The magnitude of the current thru coil b2 when the cam shaft is in position 3 is regulated in accordance with. the number of actuations of detector 52 since the last display of the go signal in the EW lane, which is substantially a measure of the traffic waiting in the EW lane. This condition is brought about by connecting the grid bt2 of tube BT to condenser KD in cam shaft position 3. As will later be explained in detail the charge on condenser KD at any time .when the cam shaft is in position 8, I, 2, 3 or 4 is a predetermined charge, introduced when the cam shaft last moved from position I to 8, less the several increments removed thereafter in positions 8, I 2, 3 and 4 by small condenser K2 in response to vehicle actuations of EW detector 52. Hence the voltage of condenser KD and therefore the voltage of grid M2 and consequently the plate current of tube BT, i. e., the current flowing thru coil b2 of relay B, will be of a magnitude less than a predetermined value by an amount substantially in proportion to the number of actuations of detector 52 since the go signal was last displayed in the EW lane. As will be later explained in connection with the description of the circuits for reducing the voltage of condenser KD by increments by condenser K2 the amount of this reduction will be independent of the speed of individual E-W vehicles but will depend only upon the number of actuations by such vehicles.

Since a reduction of the current in coil b2 facilitates correspondingly the operation of relay B-by the current in coil his. smaller currentin coil M will be suflicient to operate relay B. A

which controls the current thru coil bl, will be s'ufllcient to'produce this smaller current in coil bl. Since this smaller charge will accumulate in condenser Kit in a proportionately shorter period than would be required for a greater charge the vehicle interval being timed by this relay will. because of the sequential effects described, be decreased in accordance with the reduction of the current in coil 122. Since the reduction of the current in coil b2 is, as above stated, in accordance with the volume of waiting EW cross traflic the reduction of the N-S vehicle interval will consequently also be in accordance with the volume of waiting E'W cross traffic. I

The proportion of the plate current of tube BT passing thru coil D2 of relay B with they cam shaft in position I-is regulated by adjusting resistance Rll in order, as before mentioned, to increase or decrease the effectiveness of waiting EW vehicles to reduce the N--S vehicle interval. circuit including resistance R, wire 81, contact C26, and wire 88 accomplishes this effect by bypassing around coil D2 of relay B a proportion of the plate current of tube BT determined by the value of resistance RI I.

The circuit for the charging of condenser KD during the movement of the cam shaft from position I to 8 as mentioned above will be traced when the transition of the cam shaft from position I to 8 is described. The circuit by which this charge is diminished by vehicle actuation of EW detector 52 occurring while the cam shaft is in positions 8, I, 2, 3 or I is traced as follows.

When relay F is unoperated condenser K2 is charged from condenser KD thru the circuit starting from negative power thru potentiometer resistance P3, wire 16, condenser K2, wire H, ar-

The.

mature fl of relay F, wire 12, contact C25, wire 86, 9|, condenser KD thence back to negative power. An actuation of detector 52 will, as before explained, operate relay F which will break the last described circuit at armature j I of relay F thus disconnecting condenser K2 from condenser KD. Furthermore the operation of relay F will establish a discharge circuit for condenser K2 as follows, condenser K2, wire H, armature f2 of relay F, wire I8, potentiometer resistance P3 and wire 16. As the vehicle releases detector 52, relay F becomes de-energized thereby breaking the discharge circuit for condenser K2 and reconnecting condenser K2 with condenser KD from which it will again be charged thereby removing another increment of charge from condenser KD. As indicated before, condenser K2 is of considerably smaller capacity than condenser KD and therefore each actuation of relay F by an EW vehicle reduces the charge and corresponding voltage of condenser KD by only a small increment. Also such reduction of charge on condenser KD by a series of EW actuations is arranged to take place on a relatively straight portion of the natural discharge-time curve of the condenser KD. Thus successive actuations reduce the charge on condenser KD by substantially the same amount and the total amount cof reduction by a series of actuations is substantially proportionate to the number of actuations in such series. It will be, appreciated that small condenser K2 will be substantially fully charged each time it is connected to large condenser KD by actuation of relay F, and then condenser K2 will be substantially discharged upon de-energization of relay F by cessation of such actuation and therefore the amount of charge removed from condenser KD by each such actuation will be independent of the time relay F is energized bysuch actuation and consequently will be independent of the speed of individual actuating vehicles.

The magneto-motive force of coil M which as before explained opposes that of coil b3 is always considerably less in magnitude than that of coil 123 since it is intended merely to serve to fix the current required in coil hi to operate relay B.

The more vehicles waiting in the EW lane the less will be the current in coil b2 when the cam shaft is in position 3 as previously explained, hence a correspondingly lower current in coil-bl will operate relay B. Since the charge in condenser KE which controls the current thru coil b3 in cam shaft position 3 will be built up more quickly to the lower value required to produce this lower current in coil b3, the vehicle interval being timed thereby is therefore decreased substantially in proportion to the number of vehicles waiting in the EW lane.

The circuit by which condenser KD is connected to grid bt2 is from negative power to condenser KD, wire SI, 93, contact C23, wires I20 and I2l. Contact Cl9 thru which grid M2 is usually biased negative is open when the cam shaft is in position 3.

The circuit by which relay B operates the solenoid S to move the cam shaft to position 4 is from negative power thru contact Ctl, wire I23, armature bl of relay B, wire I26, armature s5 and coil of solenoid S to positive power.

While the cam shaft is in position 3 condenser KE is, as previously mentioned, subject to discharge by actuation of N4 detector M in order that each vehicle entering the intersection from the NS lane may initiate a new vehicle interval to permit its passage thru the intersection. If vehicles in the N-S lane approach at sufficiently short intervals they may by repeatedly discharging condenser KE keep its voltage so low that tube AT will not at any time pass current enough to operate relay B. In order to insure that a continuous line of traflic in the NS lane cannot thus indefinitely hold the right of way another means for moving the cam shaft into position 4 is provided in the maximum timer, the operation of which is not affected by trafllc.

The maximum timer as before mentioned is comprisedof relay C, tube CT, condenser KC and resistance R2. Relay C when operated in cam position 3 is affected to move the cam shaft into position 4 thru the following circuit, negative power, armature cl of relay C, wire I25, contact C30, wires I24, I26, contact s5 and coil of sole-- noid S to positive power. Condenser KC is connected to grid ct! of tube CT by wires I03, Ill and I04, and is charged in cam position 3 thru a circuit from positive power, contact C34, resistance R2 and wire Ill. Resistance R2 is adjusted to charge condenser KC at the proper rate to operate relay C a predetermined time after the cam shaft has moved into position 3 hence this timer circuit will be effective as a maximum timer to move the cam shaft into position 4 at the end of this predetermined period if continuous N-S trafllc has prevented relay B from doing so earlier. I

If relay A is unoperated as the cam shaft moves from position 3 to 4 it will put in a N-S return call by causing operation of relay E, just as if a vehicle were to actuate detector!" at that intransition to position 4 took place.

stant. The circuit by which relay A determines operation of relay E is from negative power to armature al and back contact of relay A, wire Ill, wntact :2 of solenoid 8, wire 63, contact C4, wire II to coil of relay E thence to positive power. Contact C4 is closed only in ,cam position I and contact 82 is closed only while the solenoid is in its operated position, hence this circuit is completed if relay A is unoperated while the solenoid is in its operated pofltion preparatory to moving the cam shaft into position 4 which it will do as it returns to'its unoperated position.

Relay A will be unoperated and will therefore thru the above circuit put in a N-S return call as the cam moves into position 4 ii as before stated the vehicle interval then prevailing has by waiting EW traffic or otherwise been decreased to less than a predetermined time, or if the last N-S vehicle interval was initiated less than a predetermined time before the said cam shaft In the above description of the two conditions under which a return call will be put in, the predetermined time mentioned is fixed by the operating period of relay A. This can be seen to be true because of the following facts.

In cam shaft position 3 the operation of relay B, which times the vehicle interval, or of relay C, the maximum timer, will be effective to move the cam shaft on into position 4 and thus extinguish the NS go signal and illuminate the N-S amber or warning signal. If relay A operates before either relay B or' relay C operates no N-S return call will be put in since contact al will be broken when the solenoid operates but if relay A does not operate before the cam shaft is moved into position 4 by action of either relay B or relay 0 a N-S return call will be put in during this transition. Whether relay A operates before or after relay B or relay C depends upon circumstances involving the following factors.

Relay A always operates when the current thru its coil reaches a predetermined value which, in cam position 3, always occurs a predetermined time after the last vehicle actuation of a N-S detector. Relay B always operates when the difference betwen the current in coils b2 and b3 reaches a predetermined magnitude which condition occurs at a time after the last vehicle actuation of a N-S detector dependent upon the current in coil b2. Hence, although the same current passes thru relay A and thru coil b! of relay B, relay B may operate either before or after relay A dependent upon the effect of the current flowing thru coil M on the operation of relay B. If the operating period of relay B by action of waiting cross traiilc on the current thru coil b! is decreased to less than that of relay A, the return call will be put in. But if the operating period of relay B is not so decreased and is consequently longer than that of relay A no return call will be put in if the cam shaft movement is caused by relay B. Hence the operating period of relay A constitutes the predetermined period below which the vehicle interval must be reduced by waiting crtms traflic in order to put in a return call. If on the other hand the cam shaft is moved into position 4 by action of the maximum timer relay C less than a predetermined time after'the last detector actuation in 7 cam shaft into position 4 condenser KE, preparatory to timing the next N-S initial interval 7 and preparatory to decreasing the E-W vehicle intervals in accordance with the waiting NS cross traiiic, is charged to a predetermined voltage thru a circuit starting at negative power thence to condenser KE, wires 90, 02, contact C4, wire I01, contact sl of solenoid S, wire I09, contact Cl, wire Ill, potentiometer resistance Pl to positive power. The voltage to which condenser KE is charged by this circuit can be reg-'- ulated thru setting the point at which wire Ill makes contact with potentiometer Pl.

While the cam shaft is in position 4, 5, 6, I or 8 the charge put into condenser KE as the cam shaft moved into position 4 is subject to diminution at each vehicle actuation of NS detector by the amount required to charge condenser Kl which is discharged and recharged from condenser KE once for each such actuation. When the cam shaft next reaches position I, the NS initial interval position, the recharging period of condenser KE will time that interval thus causing it to be timed substantially in accordance with the number of vehicles waiting at that time in the N--S lane.

The circuit by which condenser Kl diminishes the charge in condenser KE in response to NS detector actuations is as follows. At each actuation of detector 5i relay E operates as previously explained. While relay E is operated condenser Kl is discharged to a predetermined voltage thru wire 15, condenser Kl, wire 13, contact e2 of relay E and wire 11. The charge left in condenser KI by this circuit is adjustable by setting the points at which wires 15 and 11 make contact with potentiometer resistance P2. Each time relay E returns to its unoperated condition contact e2 breaks after which contact ei makes thus reconnecting condenser K! to condenser KE from which it will recharge thru wire 15, condenser KI, wire 13, contact el, wire H, contact C l4, wires 85, 90, condenser KE thence back to negative power.

During the transition of the cam shaft from position 3 to 4 condenser KC is again discharged thru the circuit previously traced thru contact Cl and solenoid contact 83 preparatory to its use in timing the NS amber period during which period the cam shaft is in position 4. In this cam shaft position the NS go signal circuit is opened by contact C38 and the NS amber or warning signal circuit is completed by contact C40.

While the cam shaft is in position 4, the NS amber position, relays A and B can not operate to move it into position 5 since the grids of tubes AT and BT are biased sufficiently negative thru contacts C20 and C!!! respectively to prevent any ,plate current from flowing in these tubes which control the operation of relays A and B.

The timing of the NS amber period, during which the cam shaft is in position 4, is regulated by the charging period of condenser KC which during this period is charging thru a circuit starting from negative power to condenser KC, wires I03, 10, resistance RI and contact C32 to positive power. The duration of the NS amber period can be adjusted by varying resistance El.

for condenser KC is again completed thru con tact C1 and contact S3 in order to prepare this condenser for timing the next NS periodic call period which it will time while the cam shaft is in positions 5 and 6, if switch 68 is closed as will be the case if the system is operating normally as a reverting system or an arterial system with the NS lane the artery. The charging circuit for condenser KC in cam shaft positions 5 and 6 includes switch 60, contact C36, resistance R3, wires Ill and I03. The charging period for condenser KC in cam shaft positions 5 and 6 can be regulated by varying resistance R3. When this condenser is charged to a predetermined voltage tube CT will operate relay C which will operate relay E thru contact C28 to call the right of way to the NS lane.

In cam shaft position 5 contacts C39 and C40 open the circuit to the E-W stop signal 50 and the NS amber or warning signal 46 respectively. Contacts CH and C42 close to complete the circuits to the E-W go signal 40 and the NS stop signal 41 respectively. Contact C20 is open which disconnects grid at2 of tube AT from negative power and contact C24 is closed to connect grid at2 with condenser KD. Contact 0 is closed in this cam position to complete a charging circuit for condenser KD, thru resistance RID, contact C2! and wires 86, 9|. Thru this circuit condenser KD will be recharged from the voltage to which it had been lowered by vehicle actuations of the E-W detector while the cam shaft was in positions 8, I, 2, 3 and 4. This recharge period will be substantially in accordance with the number of such actuations thereby timing the E-W initial interval in substantial accordance with the number of vehicles waiting in the E--W lane at the beginning of this interval.

When condenser KD is so recharged to a predetermined voltage tube AT will pass a plate current thru coil b3 of relay B suflicient to operate relay B to move the cam shaft into position 6. The operation of relay B is not in this case affected by coil b2 because the grid of tube ET is, as previously stated, biased negative thru contact Clil to prevent the passage of any plate cur rent in tube BT. Because of the small current required in coil D3 to operate relay B in the absence of opposition from coil b2, relay A does not operate. Moreover, if relay A did operate it would have no effect since in cam shaft positions 5 and 6 its connection to relay E and F is broken by contacts C6 and C5 respectively.

As the cam shaft is by action of relay B moved into position 6, condenser K1) is discharged to prepare it for timing the E-W vehicle interval when the cam shaft is in positions 6 or I. This discharge circuit starts at negative power thence to condenser m) then thru wires 9|, 93, contact C3, wire I08, contact SI, wire H0, contact C2, back to negative power.

Position 6 is the E-W rest position just as position 2 is the NS rest position. Movement of the cam shaft from position 6 to I is accomplished, like the movement from position 2 to 3, only thru the operation of relay M. Relay M will have been locked -in its operated position if a vehicle has actuated the NS detector 5i since the go signal in the NS lane was last extinguished or, as previously explained in describing the operation of the apparatuswhenthe cam shaft was in position 3, if either of the following con ditions prevailed when the cam shaft last moved from position 3 to 4:

1. If the right of way was last withdrawn from the 11-8 lane by action of the maximum timer relay C less than a predetermined time after the last actuation of a NS detector, or

2. If at the time of this transfer the N--S vehicle interval had been decreased by waiting EW traflic to less than a predetermined minimum period.

If relay M has been locked as a result of the existence of any of the foregoing conditions it will be effective as soon as the cam shaft reaches position 6 to operate the solenoid to move the cam shaft on into position 1 thru the circuit which included armature ml and contact CI3 previously described in connection with the movement of the cam shaft from position 2 to 3.

If relay M has not been operated when the cam shaft moves into position 8 this last named circuit will be open at armature ml and solenoid S will not be energized until relay M is subsequently operated by action of relay E which can be operated either from an actuation of N-S detector 8| or from the action of the periodic call relay C to cause a normal reversion, the circuit for which has been previously described. Condenser KC which cooperates to time the periodic call is, with the cam shaft in position ,5 or 8, charged thru the circuit including switch 88, contact C38 and resistance R3. The timing of this NS periodic call, as before mentioned, can be adjusted by varying resistance R3.

As the cam shaft moves from position 6 to 1 condenser KC is discharged thru the circuit including contact Cl and armature 83 of solenoid S to prepare it for timing the maximum period in cam shaft position I. The circuit of condenser KC, tube CT and relay C to time this maximum period is identical with that described in connection with the operation of the apparatus when the cam shaft is in position 3 except that the charging circuit for condenser KC includes resistance R1 and contact C35 instead of R2 and C34.

The EW vehicle interval is timed in position I as the N--S vehicle interval was in position 3 except that the grid of tube AT is connected to condenser KD thru contact C24 instead of to condenser KE which makes the operation of the EW detector 52 instead of the NS detector 5| effective to initiate a new vehicle interval. Furthermore the counteracting effect of coil D2 of relay B is controlled by the voltage of condenser KE thru contact CI'I instead of by condenser KD, hence the waiting N-S traffic is effective to decrease the vehicle interval in cam shaft position I just as waiting EW traillc de creased the vehicle interval in cam shaft position 3.

In cam position I resistance RI! thru contact C21 regulates the proportion of the plate current from tube BT flowing thru coil b2 whereby the magnitude of the effect of each, NS vehicle actuation to decrease the EW vehicle interval can be controlled.

As the cam shaft moves into position 8 by action of either relay B or relay C a return call to the EW lane will be put in if relay A is unoperated just as such a call was put in for the N--S lane when the cam shaft left position 3 if relay A was then unoperated. The circumstances under which relay A will be unoperated when the cam shaft moves from position I to 8 are identical with those which would cause it to be unoperated as the cam shaft moves from position I to 4 except that these circumstances perta n to conditions caused by EW tramc instead of N-S traflic.

During the transition of the cam shaft from position I to 8 condenser KD is charged to a predetermined voltage which as before stated will in cam shaft positions 8, I, 2, 3 and 4 be diminished by vehicle actuation of EW detector 52 to prepare this condenser for decreasing the N-S vehicle interval when the cam shaft reaches position 3 and for timing the next E--W initial interval when the cam shaft reaches position 5. The circuit thru which condenser KD is charged as mentioned during the transition position I to 8 is thru wires BI, 93, contact C3, wire I88, armature SI, wire I89, contact CI, wire III to potentiometer resistance PI. The voltage of this charge is regulated by the point at which wire I I I makes contact with PI. The condenser KC is also during this transition discharged thru the circuit including contact C1 and armature S3 in preparation for its use in timing the EW amber period in cam shaft position 8.

In cam shaft position 8, the EW amber signal position, EW go signal 48 is extinguished thru the opening of contact CH and the EW amber or warning signal 49 is illuminated by the closing of contact C43.

Condenser KC, tube CT and relay C co-operate to time the EW amber period as they do to time the N-S amber period which has been previously explained in detail. However, the charging circuit for condenser KC in cam shaft position 8 includes resistance R8 and contact C33 instead of RI and contact C32 which are a part of the corresponding circuit in cam shaft position 4. The duration of the EW amber period can be regulated by adjusting resistance R6.

As the cam shaft moves from position 8 to I, condenser KC is again discharged thru the circuit including contact Cl and armature S3 to prepare it for timing the EW periodic call which it will do in cam positions I and 2 if switch 83 is closed as previously explained.

The NS initial interval, cam shaft position I is timed substantially in accordance with the number of waiting vehicles in the N-S lane by condenser KE cooperating with tube AT and relay 3 exactly as the EW initial interval was timed by the same tube and relay cooperating with condenser KD. Condenser KE, it will be remembered, was charged to a predetermined voltage as the cam shaft moved from position 3 to 4 which charge has in cam shaft positions 4, 5, 6, I and 8 been diminished substantially in accordance with the number of vehicles actuating the N-S detector 5i. Hence, as previously explained, the duration of the N-S initial interval which is governed by the time required to recharge condenser KE will be substantially in accordance with the number of vehicles waiting in the N-S lane at the beginning of this interval.

As the cam shaft moves into position I the EW amber signal 43 is extinguished by the opening of contact C43, and the N--S stop signal 49 is extinguished by the opening of contact C42. The N--S go signal 45 is illuminated by the closing of contact C38, and the EW stop signal 58 is illuminated by the closure of contact C39.

As the cam shaft moves from position I to 2 condenser KE is discharged thru the circuit including contact C4, armature sl and contact C2 to prepare it for timing the N-S vehicle interval in cam positions 2 and 3.

The movement of the cam shaft into position 2 completes the signal cycle.

Stated briefly, intervals are timed by this first embodiment of my invention by charging or discharging condensers KC, KD and KE. Condenser KC times those intervals which are unaffected by traflic and do not vary from cycle to cycle.

The charge in condenser KD is influenced\by E-W traflic actuations and is instrumental in timing the signal display periods in accordance with the requirements of E-W traflic. The charge in condenser KE is similarly influenced by NS trafflc actuations and is instrumental in timing the signal display periods in accordance with the requirements of N--S trafllc.

During the N-S initial interval, cam shaft in position I, condenser KE, which has since the last N-S traflic timed period been subject to the removal of unit charges by each N-S trafllc actuation, is now subject to regular charging action, not reset by actuation, to time the initial interval by recharging from. that point to which it has been discharged by such removal of unit charges.

During the E-W initial interval, cam shaft in position 5, condenser KD functions similarly to time this interval.

During the N-S trafllc timed period of right of way, cam shaft position 3, condenser KE is subject to regular charging action to time this period and is subject to reset discharge by each N-S traillc actuation to extend this period by one vehicle interval. At the same time condensei- KD, which is and has been since the last E-W traflic timed period subject to the removal of unit charges by each E-W traffic actuation, serves to govern the length of such N-S vehicle interval.

During the E-W traffic timed period, cam shaft in position I, condensers KD and KE perform similarly except that their functions are interchanged.

Another and in some respects a preferred embodiment of this invention is shown in Figs. 5 and 6. This second embodiment employs a rotary line switch instead of a cam shaft, and grid controlled discharge tubes instead of the amplifier type three element thermionic tubes. The use of the grid controlled discharge tubes makes it uhnecessary to employ a double coil relay to permit waiting cross trafllc to decrease the vehicle interval as will subsequently be explained. Furthermore because of the sharply defined "breakdown voltage of this type of tube great accuracy is possible in timing the various intervals. Moreover since their grid potential determines their breakdown voltage the circuits involving these tubes can be adjusted to compensate for variations in tube characteristics by connecting the grid to an appropriate potentiometer tap when tubes are replaced. Thus the accuracy of the timing of the various intervals can be maintained independent of variation of tube characteristics in different replacement tubes.

The stepping switch shown in Fig. 5 has eight positions just as did the cam shaft of Figs. 3 and 4. A stepping switch of more than eight positions can be used as an eight position switch if desired by providing rapid stepping thru the extra positions in accordance with well known methods.

The various time intervals correspond substantially in both embodiments. In this second embodiment as in the first the initial interval is timed substantially in accordance with the number of waiting vehicles by charging a condenser during that interval from an initial voltage predetermined by the amount of said waiting tramc.

When the stepping switch is in its traflic timed positions 3 or 1, three timers run concurrently.

One of these, the maximum timer, is not subject to vehicle control. The other two. the variable vehicle interval timer and the normal vehicle interval timer, are both subject to reset thru plate condenser discharge by traflic actuations in the lane in which the go signal is being displayed. Hence their periods start simultaneously after each such reset. The variable vehicle interval timer is subject also to partial control by waiting cross trafilc which decreases its operating period. The normal vehicle interval timer on the other hand is not affected by cross traffic.

The variable vehicle interval timer period is decreased by waiting cross traflic thru having the grid potential of the tube timing this period rendered less negative by waiting cross trafilc thus causing said tube to become conducting at a lower plate voltage which correspondingly decreases the period required for charging the plate condenser to this lower voltage and so decreases correspondingly the variable vehicle interval. Hence the larger the amount of waiting cross traflic the shorter the variable vehicle interval will be. From the above description it can be seen that the variable vehicle interval timer in eifect balances the increasing pressure to take the right of way exerted by accumulating waitting traffic on one street against the right of way retaining effect exerted by moving traffic on the other street. The latter efiect may be termed the holding power and is proportionate to the frequency with which said moving traflic resets the variable vehicle interval timer, since moving trafiic having the right of way will reset this timer at a higher time frequency as the time spacing between actuated vehicles is reduced in "the moving stream of trailic, or in other words as the vehicles become more closely spaced. The closer the spacing of vehicles is in the stream of traffic moving with the right of way the shorter is the time interval between vehicles in which condenser KVV is allowed to charge, and the lower is the maximum voltage condenser KVV is allowed to reach, so that such traffic tends to hold the condenser voltage below the break down of tube VVT and thus to hold the right of way. This holding power is opposed by the action of trafiic approaching at a distance on the opposite street, which does not have the right of way and on which approaching trafiic stops as it reaches the intersection. Each actuation by vehicles of the latter traffic reduces the negative grid bias on tube VVT and thus reduces its break down voltage, so that condenser KVV voltage does not have to rise so high to operate tube VVT and cause release of right of way.

If the variable vehicle interval is decreased to less than the normal vehicle interval right of way will be yielded by action of the variable vehicle interval timer when ti'affic ceases to approach the intersection from the lane in which the go signal is being displayed. The variable vehicle interval timer is arranged to automatically put in a return right of way call whenever it operates to yield right of way. If there is little waiting cross traffic and consequently the variable vehicle interval is not reduced to less than the normal vehicle interval, the normal vehicle interval timer will operate first to yield the right of way. The operation of this timer does not put in a return right of way call. Hence in the second embodiment of my invention as in the first, a right of way recall will be automatically put in if the vehicle interval at the time of right of way transfer has been reduced by waiting cross traflic to less than a predetermined period. In this second embodiment shown in Figs. 5 and 6 the fpredetermined period" referred to is the normal vehicle interval timer period whereas in the first embodiment shown in Figs. 3 and 4 the corresponding predetermined period is the normal period for charging the timing condenser to the voltage necessary to operate period of relay A. This charging period will be greater than that for operation of relay B in the presence of any considerable amount of waiting cross trafllc.

If repeated traflic actuations in the lane in which the go signal is being displayed continually reset both of the vehicle interval timers thus preventing either of them from operating the right of way will be transferred by action of the maximum timer, which is effective in the traffic timed stepping switch positions 3 or 1. A return call for the right of way is automatically put in by this timer whenever it operates.

The fact that the maximum timer operates and the normal vehicle interval timer does not operate indicates that the normal vehicle interval timer was reset by a traflic actuation less than the time period of said normal vehicle interval timer, i. e., less than a predetermined time before the transfer of the right of way.

It will be remembered that this is one of the conditions under which the embodiment of Figs. 3 and 4 also is arranged to automaticaly put in a. return right of way call, the predetermined time in that apparatus being the time period of relay A. Hence both embodiments fulfill this condition.

The stepping switch, like the cam shaft of the first embodiment, will remain in either of its two rest positions 2 or 6 unless the system is set for normally arterial or reverting operation or unless a cross traffic call is put in by a cross lane detector actuation.

Referring to Figs. 5 and 6 the following points will be noted. Those elements in Figs. 5 and 6 which correspond closely with specific parts shown in Figs. 3 and 4 are designated in Figs. 5 and 6 by the same number or letter used in Figs. 3 or 4 with the letter Z added, as for example the signals in Fig. 3 are numbered to inclusive and in Fig. 5 are designated as Z45 to Z50 inclusive.

The stepping switch contact banks, designated as SBI to $36 inclusive, are shown in Figs. 5 and 6 to the right of the grounded power wire which extends from the bottom to the top of both figures just to the left of the center. The

stepping switch driving magnet, designated as DM, is shown in the lower left corner of Fig. 6. This magnet DM drives the wipers WI to W8 in unison over-the banks SBI to SE8 respectively. Beside it is a rectifier used to supply D. C. for the driving magnet coil.

The signals shown at the top of Fig. 5 are controlled by relays ALR and BLR. The apparatus to the left of the grounded power wire in Fig. 5 is in general effective to co-operate with the apparatus of Fig. 6 to call and hold the right of way on the NS lane whereas that to the right of the grounded power wire similarly cooperates with the apparatus of Fig. 6 to call and hold the right of way on the EW lane.

Relay AM is energized thru contacts in step ping switch bank SB! when the stepping switch is in positions 2 and 3, the N-S rest position and the N-S traflic timed positions respectively. Right of way can be called to the N-S lane by the de-energization of relay AM which can occur in response to a N4 trafllc actuation when the right of way is not on the NS lane. Furthermore if the right of way leaves the NS lane thru action of the maximum timer relay MXR or the variable vehicle interval timer relay VVR the relay AM will be de-energized thus putting in a call for the return of the right of way to the lane from it is being withdrawn, in this instance the N-S lane. It will be remembered that the placing of a return call has been mentioned as a function of both the maximum timer and the variable vehicle interval timer.

If on the other hand the right of way is transferred from the N--'S lane by action of the normal vehicle interval timer relay YR, relay AM will not be de-energized but will remain locked in thru subsequent stepping switch positions unless it is de-energized by the actuation of a N-S vehicle detector in order to call the right of way to the N-S lane.

Relay-BM performs similarly with respect to the E-W lane, being operated thru contacts of stepping switch bank SBI when the stepping switch is in position 6 or I, the EW rest and traffic timed positions respectively. It is deenergized to put in an E--W return call as the right of way is withdrawn from the E--W lane if said withdrawal is caused by the maximum timer relay MXR or the variable vehicle interval timer relay VVR but remains locked in if said withdrawal of the right of way is caused by the operation of the normal vehicle interval timer relay YR. Relay BM in subsequent stepping switch positions can be de-energized by action of relay FZ in response to an actuation of EW detector Z52 in order to call the right of way to the E-W lane.

Relay AR which is energized by stepping switch contacts of bank SBI in stepping switch positions I, 2, 3 and 4, the NS right of way and amber positions, energizes signal relay ALR and completes certain of the timing condenser circuits as will later be explained in detail.

Relay BR is energized in stepping switch positions 4, 5, 6 and l to similarly energize signal relay BLR and connect other timing condenser circuits.

The maximum timer, effective in the N% and E--W traffic timed stepping switch positions 3 and 1 to limit the time during which moving trailic can hold the right of way against waiting cross traffic, includes relay MXR, plate condenser KMX and tube MXT.

The variable vehicle interval timer includes relay VVR, tube VVT, plate condenser KVV and grid condensers KGNS and KGEW. It times the variable vehicle intervals in stepping switch positions 3 and I, the charge in condensers KGNS and KGEW being affected respectively by EW and N--S trafflc so as to decrease the variable vehicle interval in the N-Sfand E-W lanes respectively in accordance with the amount of waiting cross traflic as previously mentioned.

Relay YR, tube YT and condenser KV cooperate to' time the normal vehicle interval, with the ,stepping switch in position 3 or 1, which interval starts simultaneously with the variable vehicle interval after each vehicle actuation in the lane having the go signal. The timing of the normal vehicle interval it will be remembered is not affected by waiting cross traihc whereas the timingof the variable vehicle interval is affected stop signal in order to time the NS initial interval in accordance with the amount of NS traflic waiting at the beginning of the NS go signal display period.

Relay YR and tube YT cooperate similarly with condenser KIEW to time the E--W initial interval, stepping switch in position 5, in accordance with the amount of E-W trafllc waiting at the beginning of the E-W go signal display period, the starting charge in condenser KIEW being predetermined in accordance with the amount of said waiting E-W traflic.

The same relay and tube cooperate with condenser- KY to time a minimum period during which the stepping switch remains in its rest positions 2 and 6 in order to ensure that when the go signal is given to alane it will remain there for a reasonable minimum period. At the expiration of said minimum period the right of way will be transferred to the other lane only' times the NS and E--W amber or warning periods, stepping switch in position 4 f and 8 respectively.

To more completely descibe the features of the embodiment of my invention shown in Figs. and 6 I shall now explain its operation thru a complete signal and stepping switch cycle beginning in the NS initial interval when the right of way has just been given to the N--S lane, stepping switch in position I. r

In this stepping switch 'position relay AR is operated, current being supplied thru the circuit starting at grounded power thence thru position I of stepping switch bank SBI to relay AR to A. C. plus power. Relay AR when operated causes signal relay ALR to be energized thru the circuit starting at A. C. plus, thru relay ALR, wire 202 to contact arl of relay AR thence to grounded power. Relay BB is de-energized in stepping switch position I, its circuit being open at stepping switch bank SE2. Hence signal relay BLR is de-energized since its operating circuit includes contact brl of relay BR.

Wipers WI and W2 are of the bridging type so that the relays energized thru them at their respective contact banks SBI and SB2 will not be de-energized as the stepping switch moves from one position to the next.

With relay ALR operated and relay BLR unoperated the NS go signal Z45 will be illuminated thru the circuit beginning at grounded power, thru signal Z45 thence to contact blrl of relay BLR thenceto connect alr4 of relay ALR and to A. C. plus power. The E-W stop signal Z50 is illuminated thru the circuit from grounded power to A. C. plus power including signal Z50 and contact alr2 of relay ALR. The circuits to the other four signals are incomplete in stepping switch position I.

Explanation of the relay AM coil circuit will be helpful at this point as an aid in following this Relay AM has an operating circuit from grounded power thru wiper'W2, stepping switch bank SE2 positions 2 and 3, wire 206, .205, coil of relay AM, wires 204, 216, 2'", 221, contact dm2 to A. C. plus. It has in addition a holding circuit from grounded power thru contact ezl of relay EZ, contact aml of relay AM, wire 205, coil of relay AM, wires 204, 216, 211 to contact am2 of relay AM, wire 219, contact marl of maximum timer relay MXR, contact curl of variable vehicle interval timer relay VVR, thence to A. 0. Plus power.

In stepping switch position 2 relay AM is energized thru the operating circuit described above. That part of the operating circuit supplying current to the left side of the coil remains complete from the time the stepping, switch enters position 2 until it leaves position 3 after which it is broken at bank SE2. Wiper W2 is of the bridging type to insure continuity of the above circuit as the stepping switch moves from position 2 to 3.

That part of the operating circuit energizing the right side of the coil of relay AM will be opened at contact dm2 as the stepping switch moves from position 2 to 3. However that portion of the holding circuit parallelling the last named part of the operating circuit remains intact to supply relay AM with A. C. plus power while contact dmZ is open during the stepping switch movement. From the above description it can be seen that relay AM is always energized when the stepping switch is in position 2 or 3 and when it is moving from position 2 to position 3.

The functioning of relay AM in subsequent stepping switch positions will be explained as the circuit operation in each position is considered.

The NS initial interval is timed by relay YR, tube YT and condenser KINS. During this interval condenser KINS is connected to relay YR and to the plate of tube YT thru the circuit going from grounded power to condenser KINS to wires 282, 290, 284 to stepping switch bank SB3 position I to wiper W3, wires 224, 225 to coil of relay YR, wire 26!] to plate of tube YT. During the NS initial interval condenser KINS is charged thru the circuit starting at grounded power, to condenser KINS, wires 282, 290, 284, to stepping switch bank SE3 position I to wiper W3, wires 224, 223 to timing resistance RZ5, wire 2, to stepping switch bank SB4 position I, to wiper W4, wire 226 to stepping switch driving magnet contact dml to D. C. plus power. When condenser KINS is charged to a predetermined voltage the tube YT will break down, i. e., become conducting, thereby connecting relay YR to ground and allowing condenser KINS to discharge thru relay YR which will therefore operate and thru contact yrl connect the rectifier associated with the driving magnet DM to power thus energizing the stepping switch driving magnet DM which will thereupon move the stepping switch into its next position. To vary the duration of the NS initial interval the rate at which condenser KINS is charged in stepping switch position I can be adjusted by regulating the variable charging resistance RZ5.

It has previously been stated that the initial interval is by the apparatus of Figs. 5 and 6 as well as by that of Figs. 3 and 4 timed substantially in accordance with the amount of waiting cross trafiic thru having the charge in the initial interval timing condenser at the beginning of the initial interval predetermined by such waiting cross trailic. In this connection consider specifically the NS initial interval during which the stepping switch is in position I.

While the stepping switch was last in positions 2 and I relay AM was energized as has been previously explained. Therefore in these twoistepping switch positions condenser KENS was charged thru the circuit from grounded power to condenser KINS, wires III. III, contact and of relay AM, to resistance RZIS, wire 22. to pctentiometer resistance PZ I. The maximum voltage to which condenserKINS can be charged by this circuit is predetermined by the point on the potentiometer PZ'I to which wire 228 is attached. The rate at which condenser KINB is so charged can be regulated by the adjustment of variabl resistance RZII.

While condenser ms was being charged in.

stepping switch positions 2 and 8 as explained above andduring succeeding intervals up .to the I EW amber period immediately preceding the next NS initial interval, i. e., while the stepping switch was in positions 2, I, l, 6, 6 and I, the charge of condenser KINS was subject to the removal of an increment of charge by action of condenser KZI at each actuation of NS detector ZSI just as, in the embodiment shown in Figs. 3 and 4 the charge in condenser KE was removed in increments by action of condenser Kl.

The fact that increments of charge are removed from condenser ms in response to NS actuations even during the NS go signal display period provides a means whereby those NS vehicles which, under heavy tramc conditions, are stopped by loss of right of way after having actuated the NS detector make their presence effective to increase the next NS initial interval.

The removal of increments of charge from condenser KINS is accomplished thru the following circuit including contacts of relay EZ. Con denser KINS is connected to contact es! of relay EZ thru contact am3 of relay AM in stepping switch positions 2 and 3 and thru contact bi"! of relay BR in stepping switch positions 4, 6, 6 and 1. Hence in all of these named stepping switch positions actuations of NS detector Z5I which operates relay EZ will cause contact es! and cs3 to cooperate to remove an increment of charge from condenser KINS just as contacts el and c2 did in the embodiment of my invention shown in Figs. 3 and 4.

The charge so removed from condenser KINS by waiting NS trafflc is replaced thru resistance RZS during the initial interval thus timing said initial interval in accordance with the amount of such waiting NS trafllc. When; condenser KINS is so recharged, i. e., when the NS initial interval is over, tube YT becomes conductive and condenser KINS discharges thru relay YR which thereupon operates. The stepping switch, as previously explained, thereupon moves on into position 2, the NS rest position. During the movement of the stepping switch from position I to 2 condenser KY is discharged thru driving magnet contact dmi in preparation for its use as a timing condenser in stepping switch position 2.

If the system is not set for normal reversion to the E--W lane and there is no waiting EW traffic the stepping switch will remain in this NS rest position and the NS lane will be continuously accorded the go signal until an EW traihc actuation shall occur.

In stepping switch position 2, the NS go signal rest position, relay YR, tube YT and condmser KY time a ed minimum period attheendofwhichthestepping switch can be moved on into position I either by an EW traiiic actuation or by normal reversion.

The circuit connectingrelayYR, tuheYTand .condmserKYinsteppingswitchpositionlisss follows. Relay YR thru wires 226, I24, wiper WIandpositionlofbankBBIisconnectedto 'condmser KY thru wires 226 and 266. In addias the stepping switch moves from one position to the next there will be no interconnection of condenser circuits. Contact dml is included in the charging circuit described above to prevent the plate or tube YT from being charged to flashover voltage during the instant that condenser KY is disconnected therefrom as wiper W1 moves from one stepping switch position to another.

The timing of the NS minimum rest position period can be adjusted by regulating resistance RZII to control the charging rate of condenser KY in stepp n switch position 2.

The grid circuit of tubeYT in stepping switch position 2 is connected thru wire 26!, wiper W6 and position 2 of bank 836, wire "I to potentiometer PZS. Wiper W6 is of the bridging type to prevent fluctuations in grid potential as the stepping switch moves from one position to the next.

It will be noted that the resistance PZl and PZ6 are arranged in series across the D. .C. plus and minus power terminals, and that the Junction point of PZ'I and PZ6 is-connected to the central vertical ground wire, thus providing a potentiometer arrangement in which ground potential and the left end of P26 are more positive than the right end, and various points on PZI may be tapped for different negative voltages with respect to ground. PM and PZS are adapted to be individually connected between D. C. minus and ground, and when either is so connected it provides a potentiometer across the resistance PZ6. The negative end of potentiometer PZE is permanently connected to D. C. minus but the positive end of PZS is connected to ground thru a circuit including wire 254 and contact bm6 of relay BM or EW arterial switch Z66. Hence if both switch Z69 and contact bm6 are open the potential of the grid of tube YT will be biased negative to such a degree that said tube .will not break down even though plate condenser KY be charged to its maximum positive voltage. Therefore with contact bm6 and switch Z69 open the stepping switch will remain at rest in position 2 even after condenser KY has become fully charged.

The above condition prevails if the system is not set for normal reversion to the EW lane and there is no waiting EW traflic. Under these conditions the stepping switch remains in position 2, its NS rest position, and the go signal continues to be displayed in said NS lane until the next EW traflic actuation occurs.

If normal reversion to the EW lane is desired switch Z69 is closed which will make the grid potential of tube YT less negative so that the tube will breakdown" and operate relay YR causing the stepping switch to move from posinal and the EW stopsignal remain displayed,

detector Z52 which will de-energize relay BM by opening its holding circuit at contact 12! of relay F2. The de-energization of relay BM causes contact bmG to complete a circuit connecting potentiometer PZ5 to ground thus making the grid potential of tube YT much'less negative so as to cause the tube to break-down and relay YR: to operate, causing thestepping switch to move from position 2 to 3. If an actuation of detector Z52 takes place before the expiration of the re t position minimum period said stepping switq movement will take place at the end of this minimum period.

In stepping switch position 3 the NS go sigand three timers, the normal vehicle interval timer, the variable vehicle interval timer and the maximum timer run concurrently. The first two of these timers are subject to reset by N-S detector actuations and the timing period of the variable vehicle interval timer is in addition shortened by waiting EW traflic in accordance with the amount of such waitingEW trafiic. The maximum timer is not affected by trailic in either lane and sets a maximum limit beyond which N-S traflic cannot continue to hold the right of way against the cross lane.

The normal vehicle interval timer'includes relay YR, tube YT and condenser KV. The ,grid of tube YT is in stepping switch position 3 connected to potentiometer PZ6 thru position 3 of bank 835. The circuit from relay YR to .wiper W3 of bank SE3 has been traced. Thru this bank, in position 3, condenser KV is connected to relay YR by wires 23, 232, 233 and 234.

Condenser KV, while the stepping switch was in positions I and 2, was being charged thru a circuit including grounded power to condenser KV, wires 234, 233, 232 and 230 to variable resistance RZII, wire 238 contact ar4 of relay AR. to positive D. C. power. In stepping switch' positions I and 2 condenser KVwas also subject to discharge by N'--S detector actuations thru contact e24 of relay EZ, wire 231, contact ar2 of relay AR to ground. If, when the stepping switch enters position 3, the trailic in the N--S lane has'cleared the intersection condenser KV will have had sufficient time since the last N-S detector actuation to become fully charged. In stepping switch position 3 condenser KV is connected to the plate of tube YT. Hence if this condenser is fully charged when the stepping switch moves into position 3 tube YT will immediately breakdown and operate relay YR to move the stepping switch on into position 4 with no appreciable stop in position 3. If on the other hand N-S detector actuations have recently discharged condenser KV the normal vehicle interval timer will continue its timing as long as the stepping switch remains in position 3.

The variable vehicle interval timer includes relay VVR, tube VVT, plate condenser KVV and, in stepping switch position 3, gridcondenser KGNS. In stepping switch position 3 plate condenser KVV is charged thru a circuit from grounded power to condenser KVV, wire 263, 26!, 222, Hi, 220, variable resistance RZ4, wire 212 to position 3 of bank SB4, wiper W4, wire 226, contact dml to D. 0. plus power. Wiper W4 is or the non-bridging type to prevent interconnection of charging circuits during stepping switch movement. Contact dml is included in this circuit to prevent tube fiashover during the'stepping switch movement as has been explained before.

Condenser KVVis subjecttojdischarge upon actuation of N-S detector Z51 thru the circuit from grounded powerto contact arG of "relayAR to contact 625 of relay EZ thru' wire 240 which ties into the condenser KVV charging circuit at wire 222 The grid of tube W1 is connected to condenser KGNS thru the circuit including wire 249, contact br5 of relay BR and wire 245 to condenser KGNS, thence to ground. The charge of condenser KGNS has in previous stepping switch positions been made less negative by the introduction of increments of charge by .con-

denser KBNS, one increment of charge being added for each actuation of EW detector Z52, so that the charge on condenser KGNS when the stepping switch is in position 3 is in accordance with the amount of waiting EW traflic.

, The circuits which accomplish the above results are as follows: In stepping switch positions 6 and I condenser KGNS is charged negatively thru the circuit from grounded power to con denser KGNS, wires 246, 241, contact bm5, variable resistor RZ20, wire 255 topotentiometer P26. The point at which wire 255 makes contact with potentiometer PZS fixes the maximum negative potential to which condenser KGNS can be pmiged"by this circuit. The rate at which this charge takes place can be regulated by adjusting resistance RZ20.

The introduction of increments of charge into condenser KGNS is accomplished as follows. In

all stepping switch positions condenser KBNS is charged to a. predetermined potential and then discharged into condenser KGNS once for each actuation of EW detector Z52. This detector operates relay FZ whose contacts fzG and f2! are effective to accomplish the above as follows. With contact is! closed condenser KBNS is charged to a predetermined voltage thru the circuit including grounded power, condenser KBNS, wire 248, contact ,fz'7 wire 250 to potentiometer F26. The voltage to which condenser KBNS is so charged is regulated by setting the point at which wire 250 contacts potentiometer PZG. A vehicle actuation of'E--W detector Z52 opens this charging circuit at contact I21 and connects condenser KBNS to condenser KGNS thru the direct circuit including contact 126. The charge in condenser KBNS, which was regulated to be less negative than that of condenser KGNS, will therefore cause the voltage on condenser KGNS to become less negative. Hence, when the stepping switch reaches position 3 the charge in condenser KGNS will be in accordance with the total of all the increments introduced by condenser KBNS in response to EW trafiic actuations and will be substantially in accordance with the number of such EW actuations since the right of way last left the EW lane.

The fact that increments of charge are introduced into condenser KGNS in response to EW traflic actuations even during the E--W go signal display period provides a means whereby those EW vehicles which, under heavy traffic conditions, are stopped by loss of the right of way after having actuated the EW detector make their presence felt in decreasing the next N--S

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