US3333240A

US3333240A - Intersection traffic controller

Info

Publication number: US3333240A
Application number: US360270A
Authority: US
Inventors: Daniel L Gerlough; James B Rudden
Original assignee: Bunker Ramo Corp
Current assignee: Bunker Ramo Corp; Eaton Corp
Priority date: 1964-04-16
Filing date: 1964-04-16
Publication date: 1967-07-25
Anticipated expiration: 1984-07-25

Description

5 Sheets-Sheet l Filed April 16, 1964 DAN/EL 65mm/6H JAMES .5. @apoE/v BY Y A v70/ems V5 July 25, 1967 D. L.. GERLOUGH ETAL 3,333,240

INTERSECTION TRAFFIC CONTROLLER 3 Sheets-Sheet 2 Filed April 16, 1964 1 w. l: wwi i: SMN ZMS? lh. RU M y h uw 1imom E QZ i Nm@ 7M ww E www m 'lvl oa vw. H B A L5 zozu, AO :E w O@. llkfmj w Mm s 5% B v f w MS l N@ -NI N |.NN o@ Emmkw r 1 l @2Q/H@ lvllll 1| EN SNN @da :i: 023cm mm3 .NN ..523 J ZWAOWC|ZOU DZO IFQOZ Q NF d3ou 20mn, wm .pu @n A wmmww a a 4 a 1 J m .W1 bm W W @umm M M @M wwwwwwwww m a a 1 ozsomjom mv m-\ @m Nv n m Z A ozsom S 3 Sheets-Sheet 5 July 25, 1967 D. l.. GERLOUGH ETAL INTERSECTION TRAFFIC CONTROLLER Filed April I 16, 1964 A WOR/vf vs United States Patent O 3,333,240 INTERSECTION TRAFFIC CONTROLLER Daniel L. Gerlough, Pacific Palisades, and James B. Rudden, Canoga Park, Calif., assignors to The Bunker- Ramo Corporation, Canoga Park, Calif., a corporation of Maryland Filed Apr. 16, 1964, Ser. No. 360,270 14 Claims. (Cl. 340-36) This invention relates to a signal system for controlling tratlc ow at an intersection, and more particularly, to a system for automatically controlling traic flow through an intersection in accordance with the demands of traffic volume.

Achieving eilicient traic ilow at an intersection is difcult since vehicular flow moving in one direction through the intersection .intereferes with that moving in other directions. Without effective control, the vehicles using the intersection may Ibe subjected to unnecessary delays and hazards.

Traffic control at an intersection may be provided by stop signs, simple traftlc signals with a xed cycle, or very complex signal systems responsive to the volume of traiiic How in the diierent directions. The etliciency of any such control system may be measured by considering the average delay of all vehicles passing through the intersection. Accordingly, a system is improved if made responsive to the volume of traic approaching from each direction so that fewer vehicles are delayed. For this purpose, present automatic control systems frequently make use of predictive information based upon analyses of the daily tratiic ow at the intersection. Unfortunately, the traic actually present at a certain time or any given day may frequently vary considerably from that predicted.

In particular, traiiic responsive control systems are commonly used to control four-way trac at major intersections along a primary street, the intersecting street being termed a secondary street. The control system primarily operates periodically to interrupt the flow of traffic along the primary street to permit those vehicles approaching on the secondary street to pass through the intersection.

In addition, some of the vehicles approaching the intersection on the primary street may want to turn across the oncoming trac onto the secondary street. In places such as the United States, where vehicles drive to the righthand side of the road, this would vbe a left turn maneuver. Systems operating to permit such left turns may actually speed traffic ilow through the intersection under some light traflic conditions. Left turns should, however, be prohibited in most instances by the control system Whenever the oncoming trac ow is heavy. Because both oncoming and secondary street traffic must be stopped for left turns, the system efliciency is substantially decreased should left turns be permitted during periods of heavy traflic flow.

Therefore, it is an object of the present invention to provide an improved traflc control system for regulating vehicular flow at intersections.

Another object of the present invention is to provide an intersection tratlic control system responsive to the actual dow of trac in the different directions.

A further object of the invention is to provide an improved trac control system for intersections which is responsive to the delay of approaching trac.

Yet another object of the present invention is to provide an improved tratic control system, which is responsive to the flow of traiiic for etiiciently controlling left turn maneuvers.

These and other objects are accomplished in accordance with the invention by comparing the time average of the number of vehicles approaching the intersection in a given direction with given standards to determine the ICC most efficient manner of operating the intersection control system. The intersection control system then automatically responds to the results of the comparisons to eliiciently control the ow of vehicular trailic.

In accordance with particular aspects of the invention as shown by the embodiment described herein, the trafc control system in accordance with the invention efiiciently controls vehicles approaching the intersection from one direction on the primary street and desiring to turn lefit onto the secondary street. A time average of the number of Vehicles approaching the intersection from the oncoming direction is first compared with a preset standard to establish whether left turns should be allowed or not. If the time average exceeds the preset standard, left turns are forbidden under all conditions; if the time average does not exceed the preset standard, left turns are allowed conditionally.

The time average of the number of vehicles approaching the intersection from the oncoming direction is also compared with a time average of the number of vehicles waiting to make a left turn. Whenever the time average of the number of left turning vehicles exceeds that of the oncoming vehicles during a time at which left turns are permitted conditionally, the signal system operates to stop both the oncoming traiic and traiiic on the secondary street to permit the left turn.

A better understanding of the present invention may be had by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplied block diagram illustration of an intersection tratiic control system in accordance with the invention;

FIG. 2 is a detailed circuit diagram illustrating vehicle detection circuits, comparison circuitry, and a relay-operated left turn control signal in accordance with one particular embodiment of the invention; and,

FIG. 3 is a detailed circuit diagram of a four-way trafc control signal, which is interconnected with the circuitry of FIG. 2 to form a particular embodiment of an intersection tratiic control system in accordance with the invention.

It should be understood that the general principles described herein are applicable to various intersecting trafic situations. For example, the primary and secondary directions need not actually be different directions, but may be deemed to apply to any two interfering trafc ows. Thus, if two parallel lanes of traflc, both traveling in the same direction, converge or interefere, the point at Which they merge is deemed an intersection within the meaning of this general description.

Referring now to FIG. l, which illustrates in simplified block diagram form the function or units of a trafic control system 'm accordance with the invention, the iiow of vehicles through an intersection from a primary direction and from a secondary direction is regulated by the traic control signal circuit 10. Stop, go and caution light displays are mounted at appropriate locations in the vicinity yof the intersection so as to be visible to the vehicles approaching from the diiferent directions. Each light display is operated selectively by the control circuit 10 to permit the trafc -to flow in either the primary or the seconda-ry direction. In certain instances, the control circuit 10 may be used to control the operation of additional signals 11, such as turn signals, or may be made responsive to signals from an external control unit 12, such as either a central computing system for controlling traic in a network of intersecting streets or a local program unit for operating the particular control unit according to estimated conditions.

A vehicle sensing unit 14 is provided to sense the number of vehicles approaching the intersection from the primaryrdirection, while a similar vehicle sensing unit 16 determines the number of vehicles approaching the intersection from the secondary direction. The approaching vehicles should be understood to include not only those moving towards the intersection, but those that are stopped awaiting a change of signal. In other words, the

sensing units

14 and 16 measure the total number of vehicles in a selected portion of the respective street adjacent the intersection, and provide the outputs NP and NS which are proportional to the number measured. These outputs NP and NS are applied to the inputs of respective time averaging circuits 18 and 2 0, which produce output levels Ep and ES lrepresenting a time average of the number of vehicles approaching the intersection from the primary and secondary directions.

A preset output level EL of constant magnitude is obtained from a preset level source 22 to be compared with the primary direction time average output EP in a comparator 24. When the level of the time average output EP is greater than the preset level EL, the signal level comparator 24 produces a first comparator output EP EL to actuate a forbidden secondary signal 26. The forbidden secondary signal 26 is a visual device for indicating to motorists approaching the intersection in the seconda-ry direction that they will not be allowed to pass through the intersection under present conditions. For convenience, the signal should be displayed toV provide a timely warning to the approaching motorists, thereby permitting them to choose an alternative route avoiding Vthe intersection. Such a device might, for example, take the form of a No Left Turn sign in some instance or a Do Not Enter sign in others.

A second comparator output EL E1.1 is obtained from the comparator 24 whenever the time average output level EP is smaller than the present level EL. This com pa-rator output EL EP may be coupled to actuate a permissive secondary signal 28 and enable an AND gate circuit 30.

The time average output level EP is also applied to a second signal level comparator 32 to be compared with the other time average output level Es from the time averaging circuit 20. Whenever the time average output level is greater than Ep, a comparator output ES EP is generated to be applied to the other input terminal of the AND gate 30. If the AND gate is enabled by the EL EP comparator output from the comparator 24, then the ES EP 4comparator output is delivered through t-he AND gate 30 to the traiiic signal control circuit 10. After a proper delay interval provided by the control circuit 10, the ES EP comparator output actuates a go secondary signal 34 while at the same time operating the various signal displays under the control of the control circuit to stop traic flow in the primary direction so as to permit the uninterrupted ow of vehicles through the intersection in the secondary direction.

Referring now to PIG. 2, a detailed circuit diagram is shown illustrating a particular embodiment of an intersection tratiic control system in accordance with the invention. The intersection, which is shown generally to Y aid in the following description, is of the type yfrequently found, having a primary and a secondary street intersecting one another at right angles. The primary street has separate lanes for both northbound and southbound vehicles, which travel in opposite directions separated by a center divider or a Icenter marker 36,'The secondary street likewise carries separate lanes of eastbound and westbound traic on opposite sides. A righthand drive convention is assumed, and the direction of traic flow is shown by the directional arrows 38.

Northbound traic approaching the intersection may be separated into a plurality of lanes, of which the far left lane nearest the center divider 36 is used by those vehicles desiring to turn left at the intersection. In order to simplify the illustration, southbound traffic is assumed to move in only a'single lane. Also, it is assumed that southbound at other times it is comparatively light. When southbound Y traffic is light, permitting left turns from the extreme left northbound lane to the secondary street speeds the ow of traflic through the intersection, whereas during periods of heavy southbound traic such left turns should not be permitted.

A bank of relays 42, operated by vehicle presence kdetectors (not shown), is arranged to provide an output voltage directly proportional to the number of southbound vehicles approaching the intersection. Each relay consists of movable contact 44 for contacting either of two xed contacts, one upper contact and one lower contact as 4shown in the drawing of FIG. 2. Each of the upper contacts is connected through a like resistor 45 to a source of positive potential, and thelower contacts are connected through equal individual resistors 46.to

, ground potential. The vehicle presence detectors are of the well konwn magnetometer variety or may be of any other conventional construction, and are accordingly not shown in detail herein. The Yvehicle presence detectors are spaced apart by approximately one vehicle length starting at the iirst vehicle position adjacent the intersection and extending northward along the southbound lane. Each vehicle presence detector operates its respective movable contact 44 to engage the lower fixed contact when no vehicle is present and to engage the upper fixed contact during the time that a vehicle is present. A center conductor 48 connects all of the movable contacts together, so that the voltage appearing on the center conductor 48 is in direct proportion to the number of southbound vehicles approaching.

Another bank of relays 50 is -used with another set of vehicle presence detectors disposed in the far left northbound lane. A number of movable contacts 52 are each operated -by an associated vehicle presence detector to move between upper and lower tixed contacts, as shown in the drawing. The upper fixed contacts are connected through like resistors 54 to another source 'of positive potential, and the lower fixed contacts are connected through equal resistors 56 to ground potential. The vehicle presence detectors (not shown) are disposed in the northbound lefthand lane, and are spaced apart by one vehicle length beginning at the rst vehicle position adjacent the intersection. When the presence of a vehicle lis sensed by one of the vehicle presence detectors, the associated movable contact 52 is moved to the upperV fixed contact to connect a central conductor 58 to the source of positive potential through one of the resistors 54. Accordingly, the voltage appearing on the center conductor 58 is directly proportional to the number 'of the northbound vehicles approaching the intersection or waiting in the far Vleft lane.

The two voltage levels on the

center conductors

48 and 58 are coupled to a time averaging and comparing circuit 60. The voltage level 'on the center conductor 58 is coupled through 4a variable resistor -62 to charge an integrating capacitor 64. The setting of the variable resistor 62 determines the time constant of the time averaging circuit, since the current flow through the resistor 62 is directly proportional both to its resistance value and to the voltage difference between the charge on the capacitor 64 and the voltage level on the center conductor 58. The voltage on the capacitor 64 is coupled to the control grid of a triode elect-ron tube 66 connected in conventional cathode follower fashion. Y

In similar fashion, the voltage level on the center conductor 48 is coupled through a variable resistor 68 to charge an integrating capacitor 70', the time constant of the charging circuit Ibeing determined by the setting of the resistor 68. The voltage on the capacitor 70 is coupled to the control grid of another triode vacuum tube 72, also connected in cathode follower fashion. Y

The outputs from the cathode followers are connected together through the actuating coil of a 4relay 74 and .a`

series-connected diode 76. The diode 76 is poled to conduct in the forward direction only when the voltage at the cathode of the tube 66 exceeds the voltage at the cathode of the tube 72. When current does How through the diode 76, the relay 74 is actuated to close a normally-open relay switch 78.

The voltage produced at the cathode of the tube 72 is also coupled through another diode 79 and an actuating coil of a relay 80 to be compared with a preset voltage level. This preset voltage level is determined by the setting of a movable contact arm on a potentiometer 82, which has its end terminals connected between a source of positive potential and ground. The diode 79 is poled to permit current flow in the forward direction only when the voltage from the cathode of the tube 72 exceeds the preset voltage level, so that then the relay 80 is actuated to swich a movable contact 84 from its normal engagement with an upper contact to engage a lower contact. Thus, the positive voltage applied to the movable contact 84 is applied to either the upper or lower xed contact, depending upon whether or not the relay 80 is actuated.

The operation of the time averaging and comparing circuit 60 is as follows: Voltage levels equal to the number of northbound vehicles in the left lane and to the number of southbound vehicles are applied via the

center conductors

58 and 48 to the circuit 60. The voltage level on the center conductor 58 is time averaged =by the integrating action of the resistor 68 and the capacitor 70 to produce a voltage signal at the control electrode of the tube 72, which voltage signal is an accurate measure of the current volume of southbound traffic ow. The voltage level produced on the center conductor 58 for northbound traffic is time averaged in a similar manner by the variable resistor 62 and its associated integrating capacitor 64, so that a voltage signal is applied to the control electrode of the tube 66, which signal is representative 'of the volume of traic ow in the northbound lane intending to turn left.

The cathode follower circuits including the tubes 72 and 66 exhibit a high input impedance and a low output impedance, so that the load exhibited by the succeeding cornparison and switching circuitry does not affect the charge on the associated capacitors 64 and 70.

The -voltage produced at the cathode of the tube 72 represents a time average of the southbound ilow of traic, which is compared with the preset level by means of the diode 79. Thus, whenever the southbound trailic ow is sufficiently heavy, current ows through the diode 79 to actuate the relay 80, thereby applying a positive signal through the lower xed contact to indicate a no left turn condition. During periods of light southbound traic flow, however, the positive voltage is applied to the upper iixed contact through the movable contact 84 to indicate a condition in which left turns are permitted.

The voltage levels at the cathodes of the tubes 72 and 66 are also compared to each other through the diode 76. Accordingly, whenever the time average voltage level representing northbound traffic Waiting to turn left exceeds the time average voltage level produced by the southbound traic, the current owing through the diode 76 actuates the relay 74 to close the associated normally open relay contact 78. The upper fixed contact for the movable relay contact 84 is coupled to the xed contact for the movable relay contact 78. Therefore, if the relay 80 has not been actuated by heavy southbound trac, the positive voltage is applied through the movable contacts 84 and 78 to indicate that a left turn operation should begin.

A left turn signal unit 86 receives the positive voltage indications from the time averaging and comparing circuit 60. A positive voltage applied to the lower xed contact of the movable contact 84 is applied directly as a no left turn indication to actuate a no left turn signal display 88. On the other hand, if the movable contact 84 is against the upper xed contact, the no left turn signal display 88 is no longer actuated and the positive voltage is now applied directly to actuate a left turn on arrow only signal display 90 to indicate that left turns are permitted. If the relay 74 should then be actuated, the positive signal would also be applied as a turn left indication to initiate a sequence of events for actuating the turn left .arrow signal display 92. A positive turn left indication actuates a -relay 94 to move two

movable contacts

96 and 98 to their lower positions. In the normal upper position, the movable relay contact 96 is connected to ground potential through the upper fixed contact, whereas the other movable relay contact 98 connects its upper fixed contact to ground. When the relay 94 is actuated, the movable contact 98 removes the ground potential from its upper fixed contact and the movable contact 96 is disconnected from ground .and coupled to receive a positive current flow through a diode 102.

The positive turn left indication is also applied through a variable resistor 104 to gradually charge a capacitor 106. Alternatively, the capacitor 106 may be quickly charged by a current through small resistor 108, the movable relay contact 96 and the diode 102.

The voltage on the capacitor 106 is coupled to the control grid of `a triode gating tube 110, which has its cathode connected in series with the actuating coil of a relay 112. A pair of resistors 114 and 116 form a voltage divider circuit between the ground potential and the positive plate supply for tube 110, and the cathode of the tube 110 is connected to the junction between the two resistors. Thus, the tube 110 remains non-conductive until the capacitor 106 attains a charge in excess of the cathode voltage, at which time it becomes conductive to actuate relay 112. The relay 112 controls the position of two

movable relay contacts

118 and 120, the movable contact 120 normally applying a ground potential to its upper contact and the movable Contact 118 normally being disconnected from its lower iixed contact. Upon actuation, the relay 112 disconnects the movable contact 120 to remove the ground potential from its upper xed contact and connects the movable contact 118 to the left turn arrow signal display 92 through its lower xed contact.

The entire operation of the left turn signal unit 86 may best be understood by rst referring to the details of the four-way traffic control signal unit 122, as illustrated in FIG. 3. The four-way signal unit 122 contains four separate red, yellow and green signal light displays 124, 125, 126 and 127. These signal displays may be mounted in conventional fashion to provide stop, caution and go visual commands to motorists approaching the intersection from each of the four directions. As indicated in the drawing, the signal display 124 is for eastbound (E.B.) traic, signal display 125 for westbound (W.B.), signal display 126 for northbound (N.B.), and signal display 127 for southbound (S.B.) traic. Each of the lighting displays 124-127 is provided with a separate relay circuit for supplying a positive illuminating voltage to selectively display one of the three lights. The relay circuits are operated under the control of a pair of flipop circuits 128 .and 130 and a pair of

relay circuits

132 and 134. The details of the four-way traffic control signal unit may thus be understood by reference to a typical operating sequence.

The ilip-op 128 consists of two

triode tubes

136 and 137 connected in a conventional ilip-tlop arrangement, and the tlip-op consists of the

triode tubes

138 and 139 connected in like manner. The actuating coil of a relay 140 is -coupled in the anode circuit through the tube 137, and the actuating coil of a relay 141 is connected in the anode circuit of the tube 139.

Initially assume that the relays 140 and 141 are not energized, since the

tubes

137 and 139 of the flip-

hops

128 and 130 are not conducting. Two

movable contacts

143 and 144, which are operated by the relay 140, and

the

movable contacts

146 and 147, which are operated by the relay 141, are all in their normal upper positions engaging the upper fixed contacts. The movable contact 143 applies a positive voltage to a pair of

relays

149 and 151 associated with the eastbound and

westboundvsignal displays

124 and 125, respectively. The

relays

149 and 151 are energized to connect their associated

movable contacts

153 and 155, respectively, to the green signals of the signal displays 124 and 125.

In a similar-fashion, the positive voltage is also applied through the movable contact V147 to energize a pair of

relays

157 and 159. Energizing the relay 157 causes a positive voltage to be applied through an associated movable contact 161 to the movable contact 153 to light the green signal of the eastbound display 124. Similarly, the energized relay 159 switches an associated movable contact 163 to its lower fixed contact to apply the positive illuminating voltage through the movable contact 155 to the green signal light on the westbound display 125.

While in this initial condition, no signal is being applied to energize

relays

165 and 167 associated with the northbound display 126 or to

relays

169 and 171 associated with the southboundrdisplay 127. Accordingly, a movable contact 173 operated by the relay 165 remains in its upper position to apply the positive illuminating voltage to the red signal light of the northbound display 126, while a movable contact 175 operated by the relay 169 applies the positive illuminating voltage to the red signal light of the southbound display 127.

The illuminating voltage applied to the green signal on the westbound display 125 causes a current fiow through a variable resistor 173 and a series connected diode 174 to begin charging a capacitor 176. At the end of a given timing interval, determined by the setting of the variable resistor 173, the voltage across the capacitor 176 becomes sufiicient to cause a gating tube 178, normally cutotr', to conduct. The actuating coil of a relay 180 is coupled in the anode circuit of the tube 178 to be actuated upon conduction to switch a pair of

movable contacts

181 and 182. The movable contact 182 is switched to apply a ground potential to discharge a capacitor 176. The movable contact 181 is switched to apply a positive pulse through the movable contact 146 to the control grid of the tube 137, thereby causing the tube 137 of the fiipflop 128 to conduct and the tube 136 to cutoff. The relay 140 is actuated by the current ow through the tube 137 to switch the movable -

contacts

143 and 144 to their lower fixed contacts.

Switching of the movable contact 143 causes the

relays

149 and 151 to be deenergized so that the eastbound and westbound green signals are extinguished so that the illuminating voltage is applied to the yellow signals. At lthe same time, the positive voltage is applied by the movable contact 143 to energize the

relays

167 and 171 to connect a movable contact 184 through its lower fixed contact to the green signal of the northbound display 126 and to connect a movable contact 186 through its lower fixed contact to the green signal of the southbound display 127.

The illuminating voltage applied to the westbound yellow signal is also applied through a variable resistor When the tube 139 conducts, the relay 141 is energized -to switch the position of the

movable contacts

146 and 147. The positive voltage on the movable contact 147 is removed from the

relays

157 and 159, which are then deenergized. When the associated relays 157 and 159 deenergize, the

movable contacts

161 and 163 return to their upper fixed contacts to apply the illuminating voltage to the eastbound and westbound red signals, while also extinguishing the eastbound and westbound yellow signals. The positive voltage now applied to the lower fixed -contact by the movable contact 147 energizes the

relays

165 and 169 so that the illuminating voltage is removed from the northbound and southbound red signals and applied to the

movable contacts

184 and 186, which have been previously switched into engagement with their lower fixed contacts, to illuminate the northbound and southbound green signals.

The voltage illuminating the southbound green signal is also applied through a variable resistor 198 and a Y Y applied to energize the

relays

149 and 151, while the 187 and a series connected diode 188 to begin charging a capacitor 190 in the timing circuit 132. After a chosen timing interval determined by the setting of the variable resistor 187, the voltage across the capacitor causes a gating tube 192 to conduct. A relay 194 connected in the anode circuit of the tube 192 operates a pair of

movable contacts

196 and 197. With the relay 194 energized a ground potential is applied through the movable contact 196 to discharge the capacitor 190, while a positive pulse is applied by the movable contact 197 through the movable contact 194 to the control grid of the tube 139 in the fiip-op 130. The positive pulse causes the tube 139 to conduct and the tube 138 to cutoff.

relays 167 and 171 are deenergized. The

movable contacts

184 and 186 move upward to remove the illuminating voltage from the northbound and southbound green signals and apply it to the northbound and southbound yellow signals. The

movable contacts

153 and 155 nowv contact their lower fixed contacts to prepare for the next eastbound and westbound green indication due to the reenergization of the associated relays 149 and 151.

The voltage illuminating the northbound yellow signal is also applied through a variable resistor 201 and a series connected diode 202 to again charge the capacitor 190. After the interval determined by the setting of the variable resistor 201, the relay 194 is energized by conkduction of the tube 192. The energized relay 194 Ycloses the

movable contacts

196 and 197 to discharge the capacitor 190 and apply a positive pulse through themovable contact 144, now in the upper position, to cause the tube 138 to become conductive and the tube 139 to cutoff. The relay 141 is deenergized so that the positive voltage is applied through the movable -contact 147 to energize the

relays

157 and 159. With the

relays

157 and 159 energized, the positive illuminating signal is applied through the

movable contact

161 and 153 to the eastbound green and through the movable contacts 163 andY 155 to the Westbound green. At this point a completeV cycle of operation has been completed.

Where the primary street carries northbound and southbound traic, as illustrated herein, the

variable resistors

173, 187, 198 and 201 are given different settings to permit the north-south green signals to remain illuminated for a greater portion of each cycle than the east-West green signals. To illustrate, the timing circuit 132 determines the interval during which a yellow signal is displayed for all four directions, so that the resistors 187 Y and 201 are set with low resistance values to provide comparatively short intervals. Both of the

resistors

173 and 198 of the timing circuit 134 are set to comparatively large resistance values, which are capable of producing substantially longer charging intervals than in the other timing circuit 132. However, the resistance value of the resistor.173 may be made somewhat smaller than the resistance value for the resistor 198, since the resistor 173 controls the interval during which an eastbound and westbound green signal remains.

In order to provide the proper interrelation between the operations of the left turn signal unit 86 and the four-way traffic control unit 122, interconnections are provided between the two units on the four conductors 211, 212, 213 and 214. The purpose of these interconnections is best understood by considering the operation of the left tum signal unit 86 upon receipt of a turn left indication from the time averaging and comparing circuit 60.

The turn left indication is applied as a positive voltage to energize the relay 94 and gradually charge the capacitor 106 through the variable resistor 104. The energized relay 94 disconnects the movable contact 96 from the ground potential at its upper xed contact and connects it through the diode 102 to the conductor 211. The conductor 211 is directly connected to the southbound red signal of the display 127. Therefore, if the southbound red signal is receiving an illuminating voltage, the same voltage is applied through the conductor 211, diode 102, the movable contact 96 and the small resistor 10S to quickly charge the capacitor 106, which otherwise would be more gradually charged through the resistor 104.

In addition, energizing of the relay 94 removes the ground potential from the conductor 214, thus preventing any current ow through the relay 171. Therefore, if the southbound display 127 previously displayed a green signal, then a yellow signal now results.

When the capacitor 106 is charged sufiiciently, the resulting conduction of the tube 110 energizes the relay 112 to disconnect the ground potential from the conductor 213. 1f previously energized, the relay 169 is now deenergized so that the movable contact 175 applies an illuminating signal to the southbound red signal. Also the illuminating voltage to the northbound green signal is applied through the conductor 212 and the movable contact 118 to illuminate the turn left arrow 92. Thus, the interconnecting conductors 211-214 permit operation of the left turn signal unit 86 only when the proper signals have been displayed on the four-way signal unit 122.

For example, assuming that a turn left indication is produced by the demand of left turning ve-hicles during an interval in which northbound and southbound trafiic is owing, the capacitor 106 begins to gradually charge while the southbound display 127 changes from green to yellow When capacitor 106 has charged suiciently, the relay 112 is energized to apply an illuminating signal to the left turn arrow 92 and to insure the display of a southbound red signal through deenergization of the relay 169. If on the other hand, the turn left indication results when northbound and southbound traffic is stopped by a red signal, the relay 112 is almost immediately energized along with the relay 94 to prevent the occurrence of a southbound green signal and to connect the northbound green signal to the left turn signal 92. Accordingly, as the four-Way signal unit 122 advances through its normal cycle to display an eastbound and westbound red signal, the southbound signal remains red while an illuminating voltage is applied to the northbound green signal and through the conductor 212 to the left turn arrow 92. Thus, in both cases, eastbound, westbound and southbound trafiic is stopped to permit northbound vehicles to turn left.

Although a preferred embodiment of the invention has been illustrated and described herein, by way of example, it 'will be appreciated that the system and its parts may be adapted, modified or changed without departing from the invention as set forth in the appended claims.

What is claimed is:

1. A traiiic control device for regulating vehicular flow in a primary and secondary direction at an intersection, the vehicular flow in each direction -interfering with traffic flow in the other direction, comprising:

first and second detecting means for sensing the presence of vehicles and for providing separate first and second output signal levels indicative of the number of vehicles approaching the intersection in said primary and secondary directions, respectively;

rst and second time averaging .circuits coupled to receive the rst and second output signal levels and for providing separate first and second averaged voltage levels proportional to a time average of the number of vehicles approaching in either direction;

a preset voltage level source;

rst signal comparing means coupled to receive the preset voltage level from said source and the Iaveraged voltage level from said first time averaging circuit;

a first trafiic control signal for forbidding traiiic iiow in the secondary direction coupled to said first comparing means to be `actuated whenever the first averaged voltage level from said first time averaging circuit exceeds said preset level;

second signal comparing means coupled to receive the averaged Voltage levels from the rst and second time averaging circuits and for providing an actuating signal whenever the output voltage level from said second time averaging circuit is greater than the output voltage level from said iirst time averaging circuit;

gating means responsive to an enabling signal for passing the actuating signal from the second comparing means, said first comparing means providing an enabling signal to said gating means whenever the rst Vaveraged voltage level is less than the preset voltage level; and

a second traffic control signal coupled to the output of said gating means and responsive to the actuating signal passed by the gating means to stop traffic in the said primary direction and permit trafiic flow in said secondary direction.

2. An intersection traflic control system for regulating the ow of vehicular traflic at an intersection in a primary and secondary direction comprising:

first detector means for sensing the presence of vehicles approaching said intersection from said primary direction and providing a first output signal representing a time average of the number of vehicles sensed;

second detector means for sensing the presence of vehicles approaching said intersection from said secondary direction and providing a second output signal which is a time average of the number of vehicles sensed;

a voltage source for providing ya third output signal at a preset level;

first signal comparing means for comparing the levels of the first output signal with the preset level of the third output signal from the voltage source;

second signal comparing means for comparing the levels of the first and second output signals; and

a traffic signal control means responsive to the first and second signal comparing means, said traffic signal control means operating to forbid the vehicular flow in said secondary direction whenever the level of the first output signal is above the preset level of said third output signal, and to permit the vehicular flow in said secondary direction whenever the level of the iirst output signal is below the preset level and the level of the second output signal is `above the level of the first output signal.

3. A traic signal device for controlling the turning of veh-icles from =a first direction across the path of oncoming vehicles from the opposite direction comprising:

first means for deriving a iirst signal level indicative of the traic flow in the oncoming direction;

second means for deriving a second signal level indicative of the number of vehicles waiting to turn;

a -traflic control signal means responsive to command signals and including fa first visual signal for forbidding turns, a second visual signal for permitting waiting vehicles to turn, and a third signal indicating said turns will be permitted upon the occurrence of the second signal;

1 1 1 2 iirst comparison means for comparing the iirst signal 6. The device of claim 5 wherein .said traflic signal level from said first means with a predetermined control means further includes level -to provide a first command signalV to actuate 'means responsive to the opening of said second switch said first visual signal whenever said iirst signal level for forbidding the ow of turning vehicles across from said first means exceeds a predetermined level 5 oncoming trafic from the opposite direction; and and to provide a second command signal to actuate means responsive to the closure of said second switch said third visual signal whenever said first signal and the opening of said first switch for conditionally level does not exceed said predetermined level; permitting the ilow of turning vehicles across oncomsecond comparison means for comparing the first yand ing trafiic when said iirst switch is also closed.

second signal levels to provide a third command sig- 7. The device of claim 6 wherein said trafiic control nal for actuating said second visual signal; and signal means includes gating means coupled between said second comparison a cyclically operated stop-go trafiic light arrangement,

means and said second signal for -passing said third and command signal to actuate said second signal only means interconnecting said cyclically operated traffic when the gating means is enabled by the second control arrangement to operate in synchronism with command signal from said first comparison means. the signal for permitting the l'low of turning vehicles 4. A trafiic control device for -controlling the turning across oncoming traiiic. of vehicles across oncoming trafiic -from the opposite 8. The traic Control device of claim 7 further indirection comprising: n cluding first detection means for measuring the now of oncoma cyclically operated four-way traffic control signal for ing traffic in said opposite direction and providing starting and stopping the ow of vehicles on the two a first output signal indicative thereof; streets; and rst comparing means for comparing said first output means interconnecting said comparing means with said signal from said first detection means with a precyclically operated four-way traic control signal determined signal level; for stopping said trafc in the oncoming lanes and second detection means for providing a second output permitting the ow of turning vehicles.

signal indicative of a time `average of the number of 9, A traffic control device for controlling the flow of vehicles waiting to turn; vehicles at an intersection of a main street and a cross second comparing means for comparing the first and street comprising:

second output signals from said first and second a four-way traffic control signal cyclically operated to detection means; and permit the flow of traf'lic on the main street through a turn control signal for Stopping the ow of oncomthe intersection during a first portion of a cycle and ing trafiic to allow the waiting cars to turn, said turn to Permit trame to lloW through the interSeCtion control signal being operated by circuit means, said from the cross Street during a second portion of the circuit means being responsive to command signals Cycle; from said first and second comparison means indicati lirSt detectlng means reSPonSiVe to the number of oni ing that the first output Signal .is less than Said precoming vehicles present in a given area adjacent said determined level and Said Second output signal is intersection for producing a firist signal level indicagreater than Said rst output signal, tive of the time average of the number of vehicles 5. A traic control device for controlling vehicles 40 detected; t turning across oncoming trafiic approaching an intersec- Second detecting meanS reSPonSiVe to the number of tion from an opposite direction comprising: vehicles that approach the intersection from the a plurality of vehicle detectors vfor providing a first opposite direction Which are Within another area signal level indicative of the number of oncoming adlacent Seid interSection intending to turn aCroSS vehicles in a given area adjacent the intersection; the oncoming tronic, .Salvo Second means Providing' a second plurality of vehicle detectors for providing a a Second Signal level mdlcatlVe of the tlme aVerage ofthe number of turning vehicles present;

means for comparing said first and second signal levels for prohibiting the vehicles within said another area from turning unless said second signal level exceeds said first signal level; and Y means interconnecting said comparing means with said four-way traffic control signal to cause said fourway trafiic control signal to display a stop signal to the oncoming traiiic and to the cross street traffic to second signal level indicative of the number of turning vehicles in a given area adjacent the intersection;

first means for integrating said first output signal to provide a time :average of the number of oncoming vehicles detected;

second integra-ting means for providing a time average of the number of turning vehicles detected;

means providing a predetermined signal level for comparison with said first time average signal;

a unidirectional diode coupled between said predetermined signal level means and said rst and second integrating means in a direction to conduct current only when the level of said first time average ex ceeds said predetermined level; Y 6

a second unidirectional diode coupled between said first and said second time average signal means in a direction to conduct only when the level of s-aid second time average signal exceeds the level of said first time average signal;

first relay means responsive to the conduction of current through said first unidirectional diode -for `closing a first switch;

second relay means responsive to the conduction of mined portion of each said cycle.

10. The device of claim 9 further including another traine control signal for forbidding the vehicles in said another area from turning whenever said first signal exceeds a predetermined level.

11. A trafiic control device for regulating the ilow of traffic in two directions through an intersection comprising:

a first vehicle detection means for providing a first output signal proportional to the number of vehicles approaching the intersection traveling from a first of the two different directions;

a second vehicle detection means for providing a seccurrent through said second unidirectional diode to 0nd Output Signal Proportional t0 the number of close second Switch; and vehicles approaching the intersection from the second a traiiic signal responsive to the closure of both said ofthe tWo different directionS;

lirst `and second switches to permit the turning of the e irSt integrating circuit including a lirSt integrating vehicles across oncoming traffic from the opposite capacitor and a first resistor for limiting the flow of direction. charging current to the capacitor;

permit the turning of vehicles during a predetera second time averaging circuit including a second integrating capacitor and a second resistor for limiting the fioW of charging current to the capacitor;

a first diode, means connecting the first diode to conduct current to a first terminal when the voltage level on said rirst integrating capacitor exceeds the voltage level on said second integrating capacitor;

a second diode, means connecting the second diode to conduct current to a second terminal when the voltage level on said second integrating capacitor exceeds a predetermined level;

first circuit means including said first and second terminals;

a first trafiic control signal means controlled by said first circuit means for forbidding the fiow of traffic in the first direction when the second diode conducts current to the second terminal;

a second traic control signal means controlled by said first circuit means for indicating that trafiic Will be permitted to flow in the first direction when no current is conducted by the second diode to the second terminal; and

a third trafiic control signal means controlled by said first circuit means for stopping trafiic in the second direction and permitting the fiow of trafiic in the first direction through the intersection when no current is conducted by the second diode to the second terminal and the lirst diode conducts current to the first terminal.

12. The traic control system of claim 11 further comprising:

cyclic trafiic control means associated with said first circuit means for intermittently permitting traic in the second direction, and wherein said first, second and third trafiic control signals control vehicles approaching the intersection from the first direction and turning across oncoming traiic from the second direction; and

second circuit means associated with said third trafiic control signal and coupled to said first circuit means for synchronizing the actuation of the first, second and third trafiic control signals with the operation of the cyclic traliic control means.

13. A trafiic control device for regulating the flow of 'trafiic through an intersection of a primary street with a secondary street comprising:

trafiic control signal means for alternatively displaying go and stop signals to traic approaching the intersection on the primary and secondary streets, the .tratc control signal means having means for automatically controlling the display of a stop signal to approaching trafiic on the secondary street during a first portion of a cycle interval and displaying a stop signal to trafic approaching on the primary street during a second portion of -a cycle interval;

a first vehicle presence detector means responsive to the number of vehicles approaching the intersection from a first direction on the primary street for providing a time average of the number of vehicles desiring to turn left across oncoming traffic;

a second vehicle presence detector means responsive to the number of vehicles approaching the intersection from the oncoming direction on the primary street for providing a time average of the traffic ow in the oncoming direction;

turn signal means including circuit means coupled to the first and second vehicle presence detector means, said turn signal means being `operative to display a signal forbidding turns of traffic from said first direction across the oncoming direction Whenever the time average of the oncoming traic is above a predetermined level, said turn signal means being further operative to display a signal conditionally permitting said turn when the time average of the oncoming traliic is below a predetermined level, and said turn signal means being still further operative to display a signal permitting said turns whenever the time average of the number of vehicles Waiting to turn exceeds the time average of the oncoming traffic and the time average of the oncoming trafiic is below the predetermined level; and

means interconnecting the turn signal means With the intersection traic control signal means for coordinating the operation of both signal means so that the signal permitting left turns is displayed only during the second portion of the cycle interval and assuring that a stop signal is displayed to the approaching trafiic on the secondary street and the oncoming tratiic on the primary street.

14. A traffic control device for regulating vehicular flow in a primary and secondary direction at an intersecv tion, the vehicular flow in each direction interfering with trafiic liow in the other direction, comprising:

first detection means for measuring the flow of traiiic approaching the intersection in said primary direction and providing a first output signal indicative thereof;

first comparing means for comparing said output signal from said first detection means with a predetermined signal level;

second detection means for measuring the flow of traffic approaching the intersection in said secondary direction and providing a second output signal indicative thereof;

second comparing means for comparing the first and second output signal from said first and second detection means; and

a traffic lcontrol signal to stop traffic in the said primary direction and permit traffic How in said secondary direction, said traflie control signal being operated by circuit means, and said circuit means being responsive to command signals from said first and second comparison means indicating that the first output signal is less than said predetermined level and said second output signal is greater than said rst output signal.

References Cited UNITED STATES PATENTS 2,542,978 2/1951 Barker 340-35 2,750,576 6/1956 Beaubien 340-35 2,883,644 4/1959 Barker 340-36 3,208,038 9/ 1965 Jeffers 340-35 FOREIGN PATENTS 992,198 10/1951 France.

NE1L C. READ, Primary Examiner.

THOMAS B. HABECKER, Examiner.

Claims

1. A TRAFFIC CONTROL DEVICE FOR REGULATING VEHICULAR FLOW IN A PRIMARY AND SECONDARY DIRECTION AT AN INTERSECTION, THE VEHICULAR FLOW IN EACH DIRECTION INTERFERING WITH TRAFFIC FLOW IN THE OTHER DIRECTION, COMPRISING: FIRST AND SECOND DETECTING MEANS FOR SENSING THE PRESENCE OF VEHICLES AND FOR PROVIDING SEPARATE FIRST AND SECOND OUTPUT SIGNAL LEVELS INDICATIVE OF THE NUMBER OF VEHICLES APPROACHING THE INTERSECTION IN SAID PRIMARY AND SECONDARY DIRECTIONS, RESPECTIVELY; FIRST AND SECOND TIME AVERAGING CIRCUITS COUPLED TO RECEIVE THE FIRST AND SECOND OUTPUT SIGNALS LEVELS AND FOR PROVIDING SEPARATE FIRST AND SECOND AVERAGED VOLTAGE LEVELS PROPORTIONAL TO A TIME AVERAGE OF THE NUMBER OF VEHICLE APPROACHING IN EITHER DIRECTION; A PRESET VOLTAGE LEVEL SOURCE; FIRST SIGNAL COMPARING MEANS COUPLED TO RECEIVE THE PRESET VOLTAGE LEVEL FROM SAID SOURCE AND THE AVERAGED VOLTAGE LEVEL FROM SAID FIRST TIME AVERAGING CIRCUIT; A FIRST TRAFFIC CONTROL SIGNAL FOR FORBIDDING TRAFFIC FLOW IN THE SECONDARY DIRECTION COUPLED TO SAID FIRST COMPARING MEANS TO BE ACTUATED WHENEVER THE FIRST AVERAGED VOLTAGE LEVEL FROM SAID FIRST TIME AVERAGING CIRCUIT EXCEEDS SAID PRESET LEVEL; SECOND SIGNAL COMPARING MEANS COUPLED TO RECEIVE THE AVERAGE VOLTAGE LEVELS FROM THE FIRST AND SECOND TIME AVERAGING CIRCUITS AND FOR PROVIDING AN ACTUATING SIGNAL WHENEVER THE OUTPUT VOLTAGE LEVEL FROM SAID SECOND TIME AVERAGING CIRCUIT IS GREATER THAN THE OUTPUT VOLTAGE LEVEL FROM SAID FIRST TIME AVERAGING CIRCUIT; GATING MEANS RESPONSIVE TO AN ENABLING SIGNAL FOR PASSING THE ACTUATING SIGNAL FROM THE SECOND COMPARING MEANS, SAID FIRST COMPARING MEANS PROVIDING AN ENABLING SIGNAL TO SAID GATING MEANS WHENEVER THE FIRST AVERAGED VOLTAGE LEVEL IS LESS THAN THE PRESET VOLTAGE LEVEL; AND A SECOND TRAFFIC CONTROL SIGNAL COUPLED TO THE OUTPUT OF SAID GATING MEANS AND RESPONSIVE TO THE ACTUATING SIGNAL PASSED BY THE GATING MEANS TO STOP TRAFFIC IN THE SAID PRIMARY DIRECTION AND PERMIT TRAFFIC FLOW IN SAID SECONDARY DIRECTION.