US3582876A

US3582876A - Traffic responsive control system

Info

Publication number: US3582876A
Application number: US713831A
Authority: US
Inventors: Richard Urbaniak; Howard Carmack
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-03-18
Filing date: 1968-03-18
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01

Abstract

In order to provide efficient and safe traffic control at a signal intersection, a system is shown for operating the signal sequence according to detection of the approach, presence and passage of vehicles relative to the intersection. Each approach lane to the intersection is provided with traffic detector, such as an induction loop detector for sensing the presence of an automobile within a circumscribed area. Utilizing this detection feature to its fullest extent, logic circuitry is described responsive to the information generated by the loop detectors and operating the signals, for providing directional traffic flow primarily in accordance with the instantaneous, clear space available within the intersection and protection against conflicting signal indications. Additionally, the circuitry in its preferred form is modulized to provide a separate control unit for each direction of traffic, which units may be conveniently interconnected for providing a wide variety of intersection control functions.

Description

United States Patent [72] Inventors Howard Carmack 17034 Via Margarita, San Lorenzo, Calif.

94580; Richard Urbaniak, 3265 Primrose Lane, Walnut Creek, Calif. 94598 [21] Appl. No. 713,831

[22] Filed Mar. 18, 1968 [45] Patented June 1,1971

[54] TRAFFIC RESPONSIVE CONTROL SYSTEM 12 Claims, 8 Drawing Figs.

52 us. Cl 340/37, 340/ 3 8 [51] Int. Cl G08g1/01, 608g 1/02 [50] Field otSearch 340/37, 38

[56] References Cited UNITED STATES PATENTS 3,430,221 2/1969 Barringer et al. 340/38X 3,464,059 8/1969 Brockett 340/ 3 7 3,473,147 10/1969 Hill 340/37 ACH Primary Examiner-Donald .l. Yusko Auomeywarren, Rubin, Brucker and Chickering ABSTRACT: In order to provide efficient and safe traffic control at a signal intersection, a system is shown for operating the signal sequence according to detection of the approach, presence and passage of vehicles relative to the intersection. Each approach lane to the intersection is provided with trafi'ic detector, such as an induction loop detector for sensing the presence of an automobile within a circumscribed area. Utilizing this detection feature to its fullest extent, logic circuitry is described responsive to the information generated by the loop detectors and operating the signals, for providing directional traffic flow primarily in accordance with the instantaneous, clear space available within the intersection and protection against conflicting signal indications. Additionally, the circuitry in its preferred form is modulized to provide a separate control unit for each direction of traffic, which units may be conveniently interconnected for providing a wide variety of intersection control functions.

VEHICLE CONYROL UNIT REST 95 FIG. 1

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2 4 8 3 M W 3 M L E A 6 3 w 9 i 6 u e m R R wR Eh ML mm l l T T e W R w a m 4 M N T L M. v m v W a I 2 l K m w/ m R N 0 E I T CT TP VP Em DW D A REST INVENTORS HOWARD CARMACK RICHARD URBANIAK BYzflm/rzafm,

C E ;ATTORNEZ$S PATENIEUJUN H971 3 5 2 7 SHEET 8 [IF 6 CONTROL VEHICLE CONTROL VEHICLE CONTROL CONTROL VEHICLE INVENTORS HOWARD CARMACK RICHARD URBANIAK BY Mew/we, WM

Mm j ATTORNE 8 FIG. 8

TRAFFIC RESPONSIVE CONTROL SYSTEM The present invention relates to traffic control systems and more particularly to an improved traffic control system which operates on a principle of space allocation rather than conventional time allocation.

To provide a background for appreciating the contribution made by the present invention to the art, several widely used traffic control techniques will be considered. The most common type of controller is the fixed time device, wherein traffic lights are set according to a semipermanent time cycle. That is, the time sequence may be adjusted during the day at the signal station to compensate for variable traffic conditions. in locations where highly varying traffic conditions exist, this is the most inefficient of all the devices.

Another type of system is the semitraffic actuated controller wherein, approaching cross-street traffic is sensed by a vehicle detector, such as a pressure detector. In the absence of cross street traffic, the main street is provided with a continuous green light. Upon detection of an approaching cross-street vehicle by the detector, which commonly is placed about 80 feet from the intersection, the main street green light is changed through yellow to red and the cross-street signal receives a green indication. The green proceed indication is maintained for at least a preselected initial fixed interval sufficient to allow the maximum possible number of cars waiting between the intersection and the vehicle detector, e.g. 80 feet, to pass through the intersection regardless of the actual number of cars waiting, and for a longer time interval if vehicles continue to approach and pass over the detector in close order. This second, vehicle responsive time interval will terminate upon occurrence of a sufficient gap in the flow of cars, in this instance 80 feet, or otherwise upon elapse of a preset maximum time interval. After such termination, the main street traffic will obtain a green signal, for an assured preset duration independent of traffic requirements.

Additionally, there is in use a system characterized as a volume density controller, modifying the above semitraffic actuated controller, in which both the initial time interval and the vehicle responsive interval are varied by the density of traffic flow. That is, the controller counts cars approaching the intersection during a stop indication and attempts to provide an average initial green interval of sufficient duration to allow the average number of waiting cars to pass through the intersection. Subsequently arriving vehicles in close order extend the green light into the vehicle responsive interval as above, however, in the volume density system the permissible gaps between cars decreases with time according to detected and computed average trafiic density, again independently of the instant traffic needs. For example, at first substantial gaps between cars may occur without inducing a red indication, however, as time elapses the permissible gap distance decreases rapidly when a large number of cars are waiting in the other approaches to the intersection arid more slowly when the heavier traffic is in the moving stream.

It will be apparent that all of the above described traffic actuated systems attempt to construct a time model of the average traffic at the intersection and control the signal lights according to the model conditions. Accordingly, such systems, while offering some improvement over entirely fixed time devices, neglect the instantaneous traffic requirements and make signal control decisions which are to a large degree arbitrary and inefficient. Moreover, and with particular reference to the volume density system, complex and expensive circuitry is required to achieve the described control functions, wherein the incurred substantial cost of construction and maintenance prohibits widespread applications of the system.

Accordingly, it is an object of the present invention to provide a traffic responsive control apparatus which is to a large degree more efficient, more reliable and safer in regulating the movement of traffic through an intersection.

It is a still further object of the present invention to provide a versatile traffic control system for performing allocation of available intersection space, and which is capable of handling a plurality of traffic phases, i.e. lanes of traffic flow through an intersection allowing non conflicting concurrent moves safely and efficiently.

A feature and advantage of the instant invention is that pedestrian traffic control may be achieved in combination with vehicle control utilizing the same basic circuit for both traffic components.

A further feature and advantage of the instant invention is that pedestrian travel may occur during a slack in the vehicle traffic so as to avoid pedestrian dominance of the intersection.

A still further feature and advantage of the invention is that the system may be arranged for concurrent movement of several nonconflicting lanes of traffic. in this same regard, the system may be conveniently adapted to provide for movement of one lane of traffic during separate movements of several other traffic lanes, that is, allowing for overlapping signal controls. Additionally, the system is particularly adaptable for providing preempter operations, desirable in emergency traffic situations such as preempting normal traffic flow to allow fire vehicles and the like, clear passage.

The present invention possesses other objects, features and advantages, some of which of the foregoing will be set forth in the following description of the preferred form of the invention which is illustrated in the drawings accompanying and forming part of this specification. It is to be understood, however, that variations in the drawings and description may be,

adopted within the scope of the invention as set forth in the claims.

Referring to the d4awings:

FIG. 1 depicts, in block diagram form, the traffic control system operating in conjunction with the basic two-way intersection.

FIG. 2 shows a schematic diagram of the control circuitry indicated in FIG. 1.

FIG. 3 is a schematic diagram of a solid-state signal light switching circuit utilized in the invention.

FIGS. 4 and 5 are detailed schematic diagrams of electronic timers used in the various circuits of the invention.

H6. 6 shows a schematic diagram of a more sophisticated control unit including the features of advanced vehicle detection and mandatory timed stop intervals between each conflicting traffic movement.

FIG. 7 is a further schematic diagram illustrating a pedestrian signal control unit ofthe present invention.

FIG. 8 shows a typical intersection situation utilizing the system of the present invention.

The control system of the present invention to allocate available space within an intersection to approaching traffic. Pursuant to this end, the control apparatus, for most purposes, is solely responsive to vehicle or pedestrian traffic.

Referring to FIG. 1, the invention here includes at least two detectors l0 and 12 arranged within a preselected area of the approach lanes to an intersection, in this case intersection 14 of two one-way street approaches, A and B. Detectors l0 and 12, in this instance, are of the type which provide for opening and closing of a switch in response to the presence of a vehicle within the areas bounded by each of the respective loops.

Connected to each of detectors l0 and 12 are vehicle controlunits A and B, 15 and 16, having letters corresponding to approaches A and B, which are in turn interconnected with one another to insure mutually exclusive operation of green or proceed traffic directory conditions for the intersecting traffic.

Signal lights

18 and 19, each having red (stop), yellow (caution), and green (proceed) indicator lights, are connected respectively to control

units

16 and 15 for supervising vehicle traffic along the respective directions of B and A approaches.

in practice, when both of area detectors l0 and 12 are free of vehicles, indicating no traffic in either the A or B approaches, both of

signal lights

18 and 19 are in the red or stop condition. Now, as a car enters the area of one of the detectors, for example, car 11 shown entering the area of detector 10, the corresponding vehicle control'unit, in this instance, unit 15, receives an impetus from the detector which causes the associated signal, signal light 19, to switch from the red to the green condition. As car 11 passes into the intersection proper thus leaving the boundaries of area detector 10, control unit 15, receives another impetus which responsively causes signal light 19 to cycle through a yellow indication to a red indication. Should a vehicle enter area detector 12, approaching the intersection in direction B, during the time period in which car 11 is receiving a green signal, vehicle control unit 16, is prevented from switching light 18 to the green condition until car 11 has left the boundaries of detector 11 and entered the intersection. That is, control unit 16 is disabled during the actuation of control unit 15. Of course, as soon as car 11 leaves the area of detector 10, which eventually changes signal light 19 to a red or stop indication, then unit 16, is again operative such that the detection of a car by area detector 12, causes signal light 18 to switch from its normally red or stop indication to the green or proceed indication.

Additionally, several advantageous and preferred features may be added to this basic operation as discussed more fully hereinafter. Among such features are a means for detecting a vehicle approach in advance of area detectors 11 and 12, wherein additional similar detectors are disposed upstreet from area detectors and 12 to allow early switching of the signal lights to the proceed condition, during light traffic, so that approaching cars need not slow down.

Furthermore, circuitry is shown for providing a pedestrian control unit which operates in conjunction with the vehicle control unit such as those shown in FIG. 1, to permit pedestrian traffic to pass during periods of nonconflicting vehicular movement.

Referring now to both FIGS. 1 and 2, wherein FIG. 2 schematically illustrates the control circuitry for

vehicle control units

15 and 16, and the interconnections therebetween as partially shown in FIG. 1. Each of the

control units

15 and 16 are oflike circuitry such that any number of such units may be cascaded for controlling a corresponding number oftraffic approaches or phases. This is to be considered an important advantage of the invention due to the present day usage of multiple traffic lanes at busy intersections, e.g. rightand left-hand turn lanes. Only the circuitry of vehicle control unit 16, will be described in detail due to such universalness between the units and reference will be made to unit 16 only to describe the interconnection and cooperation between the circuits.

Unit 15 is provided with inputs of detector input 21 and alternating current (AC+) power input 22. Detector input 22 also shown in FIG. 1, is connected to terminal 23 of detector switch 24 of area detector 10. Connected to the remaining terminal, terminal 25 of switch 24 is an alternating current source (AC+) which for the present purposes will be denoted as the side of such source.

Detectors

10 and 12 are means which detect the presence of a vehicle in a defined area. In the instant case, induction loop detectors are utilized for detectors l0 and 12 which operate on a radiant electromagnetic field principle, wherein a loop conductor 26 connected to switch 24 is supplied with a given frequency of alternating electrical energy. As a vehicle enters the area defined by loop conductor 26, the electromagnetic field is altered by the Ferromagnetic or magnetizable mass of the vehicle, thereby changing the frequency of the field and of the alternating electrical signal appearing on conductors 27 connected to switch 24. Switch 24, responds thereto and closes a contact connected between

terminals

23 and 25. Accordingly,

terminals

23 and 25 in a rest or open condition are insulated From one another, in the absence of vehicles within loop conductor 26 while the same terminals are in an activated or closed condition, shorted together when an automobile is present within the detector area.

Thus,

detectors

10 and 12 provide a means for detecting the presence of traffic within the approaches proximate the controlled intersection, and provide information for operating the switching circuitry of the instant invention. If desired, other types of detection means may be utilized, however, it has been found that the type of induction detectors described herein are very reliable and best suited for use in the present inventlon.

Considering now the operation of

area detectors

10 and 12 with

control units

15 and 16, as a car for example, car 11, enters induction loop 26, switch 24

shorts terminals

23 and 25 and applies AC(+) to detector input 21 of control unit 15. Now as best shown in FIG. 2, AC current flowing between terminal 25 of detector switch 24, see FIG. 1, and terminal 29 connected to AC(-), see FIG. 2, activates an M relay coil through normally closed

contacts

30 and 31 of an R relay. The M relay and its associated contacts thus provide a detector controlled switching means operating between first and second modes in response to the presence or absence of traffic in the associated approach. In its second or in this cast activated mode AC(+) applied to input 22 passes through normally open contacts 32 and 33 (now closed) of the M relay, energizing a delay network comprising diode 35,

resistors

36, 37 and 38, and capacitor 39. After a preselected delay, which may typically vary between 10 and 20 milliseconds, the green light of signal lights 19 is turned on by means of a solid-state switching circuit 41, see FIGS. 1 and 3, in response to a signal appearing at terminal 40. The operation of this delay network is provided by the rectification of the AC current by diode 35 and the eventual charging of capacitor 39 through resistor 36 providing a unidirectional voltage across resistors 37 and 38 a portion of which is applied to terminal 40 via line 42. The purpose and advantage of this delay is to permit contacts 43 and 44 (previously opened) of a P relay to close securing firm electrical connection therebetween such that AC power may be supplied to signal light switching circuits 41 through terminal 81 and the above-mentioned

contacts

43 and 44. It will be noted that the P relay coil is in an energized state during the operation of vehicle control unit 16. This is, the normally open contacts of the P relay, for example,

contacts

43 and 45 are closed during time periods in which unit 16 was in operation passing traffic appearing in the B approach through the intersection.

During the operation discussed above, as the M relay coil is energized, M relay normally closed

contact

32 and 34 are open preventing energization of the P relay coil and thereby disabling unit 16 as discussed more fully hereinafter.

Upon the activation of the M relay in response to vehicle detection, power is supplied to the coil of an N relay from power input 22, through line 46, normally closed

P relay contacts

43 and 44, line 47, normally opened

M relay contacts

48 and 49, and

terminals

52 and 53 of primer 51, and through the end relay coil to AC(-). As the N relay is energized, normally

open contacts

57 and 58 thereof close, latching the N relay in its energized state and normally closed

contacts

61 and 62 thereof open interrupting AC power applied to terminal 64 through

contacts

61 and 62 and resistor 63 and thereby extinguishing the red or stop light of signal lights 19 controlled by solid-state switching circuit 41.

As soon as car 11, shown in FIG. 1, passes over and leaves loop conductor 26 of detector 10,

terminals

23 and 25 of detector switch 24 open and consequently removes power from the coil of the M relay. As soon as this occurs, and the M relay is deenergized, the normally

open contacts

32 and 33 thereof open and thereby terminate the proceed or green light of signal light 19. Additionally, normally closed

contacts

32 and 34 of the M relay close at this point applying AC power through normally open contacts 71 and 72 (now closed) of the N relay through resistor 76 to terminal 75 actuating the caution or yellow light indication of signal lights 19. It will be appreciated that the N relay is still in its energized state due to the latching thereof on its own normally

open contacts

57 and 58, and thereby remains energized even though the M relay has deenergized.

At the same time that the caution indication is given at signal lights 19, the coil of an R relay is energized through diode 78 and resistor 79 which causes normally closed

R relay contacts

30 and 31 to open thereby preventing actuation of the M relay by detector 10 during clearance of the intersection, that is during the caution light signal. The R relay coil is operated by a rectified and filtered AC signal provided respectively by diode 78 and shunt capacitor 80 and thus provides a prevent switching means disabling operation the M relay upon actuation thereof,

Concurrently with the caution indication, as the M relay is deenergized, normally closed

contacts

49 and 50 thereof close supplying AC(+) power from input 22 through terminal 54 of timer 51 through line 46, normally closed

P relay contacts

43 and 44, line 47, normally open

N relay contacts

57 and 58, and

M relay contacts

49 and 50. This connection, starts timer 51 which after a preselected interval deenergizes the N relay coil by shorting terminal 53 to terminal 55 as discussed herein. Terminal 55 of timer 51 is connected to AC().

As the N relay is deenergized, normally

open contacts

71 and 72 thereof are opened removing the signal to terminal 75 and thereby extinguishing the yellow or caution light of signal lights 19. In effect the N relay and timer 51 operate as a caution timer switching means for activating the caution condition of signal lights 19 for a preselected interval after the M relay resumes its first or nonactuated mode.

Additionally, normally closed

contacts

61 and 62 of the N relay again close and thereby actuate the red or stop light signal at signal lights 19.

In summary of the forgoing, a system is provided for controlling traffic flow along approaches to a region of conflicting movement, including detector means for detecting the presence of traffic in each ofa number of approaches, means for signalling stop and proceed conditions for each of the several approaches, a switching means (M relays) for responding to such detection of traffic and switching the signal means from a normal stop condition to a proceed condition for each approach in which traffic is detected and means for preventing the signals from displaying a proceed indication for one approach during a proceed indication for the other approach. Particularly, vehicle control unit 15, responds to an approaching vehicle by means of detector and switches signal lights 19 from a red to a green condition. As the vehicle passes into the intersection, thus leaving the boundaries of area detector 10, unit causes signal lights 19 to cycle from a proceed indication through a timed interval of the caution indication and finally back to the normally stop indication.

Similarly, vehicle control unit 16, operates in response to detection of the presence or approach of a vehicle in approach B by means of area detector 12 and causes a green or proceed signal to appear at lights 18 which eventually cycles through caution to a stop indication as the vehicle proceeds through the intersection.

As an important aspect of the present invention,

control unit

15 and 16 are connected together as shown in FIGS. 1 and 2 to provide for instantaneous sharing of the intersection proper according to the immediate traffic demands. ln other words, the particular cooperation of

control units

15 and 16 permits allocation of nonconflicting intersection space in response to approaching or awaiting vehicles. Specifically, as illustrated in FIGS. 1 and 2, an output terminal 83 of control unit 15 is connected to an input terminal 22 of unit 16 while a release terminal 93 of unit 15 is connected to a rest terminal 95 of unit 16. As most clearly shown in FIG. 2, connection between

terminals

83 and 22 supplies AC power to unit 16 only when the P relay of control unit A is energized and

contacts

43 and 45 thereof are closed. Furthermore, connecting line 94joining unit 15 release terminal 93 with unit 16 rest terminal 95 provides power to energize the P relay coil of unit 15 only when the M or N relays of unit 16 are in an energized state. In other words, the P relay coil of unit 15 will be cnergized through input 22, normally closed

contacts

32 and 34 of the M relay of unit 15, normally closed

contacts

71 and 73 of the N relay of unit 15, through the P relay coil of unit 15 to release terminal 93 thereof and through line 94 to unit 16 rest terminal 95 and through either the unit 16 M or N relay contacts 68-65 or 8990 to AC().

The cooperation between

units

15 and 16 will be described by .means of several examples. First, consider the case where approach A is absent of vehicles and approach B by means of detector 12 senses an oncoming car. Vehicle control unit 16 responds thereto causing the M relay thereof to close, thus closing normally open

M relay contacts

86 and 85. This connection places rest terminal of unit 16 at AC() and thereby energizes P relay of unit 15. Normally open

P relay contacts

43 and 45 of unit 15 accordingly close connecting AC(+) power from input terminal 22 of unit 15 to input terminal 22 of unit 16. Unit 16 is now in condition to switch signal lights 18 from a red to a green state and accordingly does so in the manner described in reference to unit 15 above. it will be noted that the P relay of unit 15 remains energized through release terminal 93 of unit 15 and rest terminal 95 of unit 16 throughout the green and yellow light condition of signal lights 18 and the P relay of unit 15 opens only after unit 16 has cycled signal lights 18 back to the stop or red condition.

Now consider a second situation where a steady stream of 1 cars traveling over detector 10 in approach A is operating control unit 15 providing a continuous green or proceed indication of signal lights 19. In this state, unit 15, M and N relays are energized connecting normally open

M relay contacts

32 and 33 are accordingly applying AC(+) power to terminal of timer 67. Now at this point with a green light indication on signal lights 19, a car enters loop conductor 28 of detector 12 and thereby closes the M relay of unit 16. The P relay coil of unit 15 cannot close due to open

M relay contacts

32 and 34 and accordingly power cannot be supplied to unit 16 rendering this unit disabled for operation so long as unit 15 remains in operation passing approach A traffic. However, with AC(+) applied to terminal 66 of timer 67 and AC() applied to terminal 69 of timer 67 to the R relay coil and release terminal 73 and timer through the R relay coil and release terminal 73 timer 67 is actuated. After a preselected interval, timer 67 connects terminal 66 with terminal 69 thereof and thereby energizes the R relay. Normally closed

R relay contacts

30 and 31 accordingly open deenergizing the M relay, which in turn closes normally closed

M relay contacts

32 and 34 and starts timer 51 for cycling through the yellow light interval. Upon termination of the yellow light interval, the N relay is deenergized closing normally closed

N relay contacts

71 and 73, supplying power through the P relay coil which in response thereto closes normally open

P relay contacts

43 and 45 delivering AC power to input 22 of unit 16.

Additionally, upon closure of normally open P relay contacts 43 and 45 a rectified alternating current signal is applied through diode 84 of unit 15 to the R relay coil thereby maintaining the R relay in an energized state such that

R relay contacts

30 and 31 are maintained open preventing unit 15 from being actuated during operation of control unit 16.

Since AC power is now supplied to unit 16, its operation may proceed as normal, switching signal light 18 from a red to a green state and eventually back through yellow to red again. This immediately above described sequence allows vehicles waiting in the B approach to interrupt a steady stream of traffic flowing in the A approach after a given substantial time period, fixed by a timer 67 of unit 15.

Now consider the reverse of the above situation, wherein approach B is undergoing a steady stream of traffic with a green light indication on signal light 18 and a car approaches the intersection from Direction A. At variance with the con nections for unit 15, unit 16 release terminal 93 is connected directly to AC(). Accordingly, with B unit in a green light condition, timer 67 thereof starts immediately without waiting for a response from unit 15, and fixes the maximum time duration at which unit 16 will remain in the green light state.

As an example of the versatility of the present system, unit- 15 may be easily modified to operate as a preempter control unit. Particularly, by removing the connection of the R relay coil of unit 15 to release terminal 93 of the same unit the M' relay of unit 16 will be conditioned to response to detector 10 even during continuous traffic in approach B. Upon such an occurrence the M relay of unit A will immediately return the P relay of unit A to its unactivated state, disabling unit 16. Such an arrangement is desirable in the case of emergency traffic such as fire equipment, where detector 10 would be arranged to respond only to the emergency vehicles for immediately returning a proceed condition therefor.

Also, it will be appreciated that from the foregoing described operation, that any number of control units such as and 16 may be cascaded to provide allocation of available intersection space for a multiplicity of approach lanes. Additionally, while the embodiment of the invention described in FIGS. 1 and 2 provides for maximum time intervals for which any one approach lane can receive a green light condition, it has been found in practical applications that substantial gaps between vehicles, even in heavy traffic, occur such that awaiting vehicles on a cross street approach may efficiently share the available intersection space without inducing the operation oftimers 67 of

units

15 and 16. Also, in view of this fact, it has been possible to extend the portion of loop conducters 26 and 28 distal theintersection, back as far as I00 feet from the intersection to provide for early green light indication and thus reducing traffic slow down to a minimum.

To enhance the multilane traffic control capabilities of the instant system, a pair of

auxiliary terminals

183 and 184 are provided for each

unit

15 and 16, to be shorted by normally

open contacts

185 and 186 of the P relays.

Terminals

183 and 184 may then be connected as shown in FIG. 8, to control AC power supplied to another unit, in a manner similar to normally closed

P relay contacts

43 and 44,

Up to this point, the actual switching of

signal lights

18 and 19 has not been discussed. For this purpose a pair of

solidstate switching circuits

41 and 42 shown in FIG. 1 are employed to respond to the control signals provided by control units A and B and in accordance therewith switch the light lamps of signals lights 18 and 19. While

circuits

41 and 42 are shown separately in this instance, it will be appreciated that they form a portion of each control units and may if desired be incorporated in the circuitry thereof. Particularly, FIG. 3 shows the schematic diagram for solid-

state switching circuits

41 and 42, each of which include a set of three solid-

state switching devices

98, 99 and 100, known in the art as triacs, a set of

input terminals

40, 75, 64, 81 and 107, and a set of

output lines

108, 109 and 110 connected to the signal lights 18 and 19. Each set of the input terminals to

circuit

41 and 42 are connected to the output terminals of like reference numerals of

units

15 and 16. Briefly, the operation of each of switching

devices

98, 99 and 100 provide for example, connection of AC power between input 102 and output 103 of device 98 in response to a gating signal applied to gate terminal 104 of device 98. Accordingly, as power is supplied to the input of

devices

98 and 99 through terminal 81 from vehicle control unit 15, each such device will allow power to flow into green lamp 105 and yellow lamp 106 in response solely to the presence of separate gating signals at

terminals

40 and 75, respectively.

Somewhat at variance with the operation of

devices

98 and 99, a permanently connected AC(+) supply is provided to terminal 107 and thus to the input of device 100, for energizing red lamp 111 solely in response to the presence of a gating signal at terminal 64. The purpose of supplying power to

devices

98 and 99 through terminal 81 which is controlled by normally closed

P relay contacts

43 and 44 of

units

15 and 16 is to prevent spurious and erroneous green or yellow light indications for one approach during a green or yellow light indication in the remaining direction thereby to a large degree eliminating the possibility of conflicting traffic movement. On the other hand, red lamp 111 is normally lit in the absence of approaching traffic in either direction and, therefore, receives a permanent supply of power controlled only by a red gating signal appearing at terminal 64 of

units

15 and 16. Thus

circuits

41 and 42 cooperate with the P relays of the control units to provide supervisory circuit means to insure consistent operation of the approach signal lights 18 and 19.

The combination of solid-state switching devices for controlling the power supply to the lamp loads together with electromagnetic relays for performing various logical functions, takes advantage of the most useful characteristics of each class of device. Particularly, relay contacts tend to disintegrate after periods of constant high current load switching, yet operate very efficiently for switching low current such as found in the logic circuit. The solid-state switching devices, particularly triacs, on the other hand perform most advantageously under high current load switching conditions such as in the case ofincandescent lamp loads.

Timers 67 and timer 51 of

unit

15 and 16 are shown in detail by FIGS. 4 and 5. Timer 67 having

terminal

66, 69 and 68 corresponding with like reference numerals in FIGS. 2, 6 and 7 provide for allowing a rectified alternating current signal to pass through

resistors

124, 119 and 118 charging capacitor 122 upon application of AC across

terminals

66 and 69. Diode 113 together with capacitor 114, the latter of which is connected to AC() at terminal 68 provides rectification and filtering of the AC source such as to present a relatively unidirectional voltage atjunction 115 with respect to terminal 69. In the presence of such voltage capacitor 122 begins to charge through resistor 119 and variable resistor I18 and upon reaching a preselected voltage value switches unijunction transistor 116 to a low impedance state. Upon reaching such a low impedance state, the potential at control electrode of silicon controlled rectifier (SCR) 112 changes rapidly and thereby switches SCR 112 to a low impedance mode. Zener diode 117 maintains a constant charging voltage across capacitor 122 to insure uniformity of timing.

Resistors

124, 123, 120 and 121 are biasing resistors which maintain SCR 112 and unijunction transistor 116 in a quiescent condition suitable for switching thereof. Accordingly, timer 67 provides for the passage of generally unidirectional current between

terminals

66 and 67 after a preselected time interval, which may be adjusted by variable resistor 118, of AC power connected across

terminal

66 and 69. Thus, timer 67 provides a means for energizing the R relay coil shown in FIG. 2 so as to provide a maximum time interval during which a single approach may dominate the intersection.

Timer 51 illustrated in detail in FIG. 5, includes

terminals

52, 53, 54 and 55 corresponding to like reference terminal numbers in FIG. 2. Timer 51 is particularly advantageous, in that it operates with a relatively high power current sufficient for directly energizing and deenergizing a relay coil. That is, most timers are low power devices, which are not capable of supplying sufficient current to operate a relay coil directly and must use intermediate switching means connected between the timer and the relay coil for supplying operational current thereto. On the other hand, a timer 51 operating on an AC power source, is capable of directly energizing and deenergizing the N relay coil as in FIG. 2 thereby eliminating an additional switching component. Specifically, referring to FIG. 2 and 5, upon application of AC to terminal 52, timer 51 operates to energize the N relay coil through terminal 53 and AC(). This condition of the timer will continue until AC(+) is applied to terminal 54 which in combination with AC() connected to terminal 55 initiates charging of capacitor 126. After a preselected interval determined by the rate of charging capacitor 126, which may be controlled by variable resistor 136, unijunction transistor 127 is switched to a low impedance state, which in turn rapidly changes the voltage applied to gate 129 of silicon controlled rectifier 128. In response thereto, SCR 128 switches to a low impedance state thereby effectively shorting

terminals

53 and 55 together deenergizing the N relay coil. Diode 131 together with

resistors

132 and 133 and capacitor 140 provide for rectifying and filtering the AC signal applied across

terminals

52 and 53 and as mentioned above, provide for passing current energizing the N relay coil. Diode 137 together with

resistors

134 and 135 and variable resistor 126 provide for introducing current for charging capacitor 126 upon application of AC across

terminals

54 and 55. Zener diode 138 and capacitor 139 stabilize the charging current for capacitor 126 thereby insuring uniformity of timing intervals. Resistor provides for biasing transistor 127 and SCR 129.

Referring now to FIG. 6, a schematic diagram is shown ofa vehicle control unit similar to that ofunits 1S and 16, shown in FIG. 2, but further including the features of advancing called detection and all red overlap. The operation of this unit is the same as the basic control unit, units and 16, with the exception that provision is made for advance detection of vehicles approaching the intersection. The purpose of the advance calling detection feature is to permit an on-coming vehicle to obtain a green light signal at a greater distance from the intersection during light traffic for efficient flow thereof. Additionally, the control unit shown in FIG. 6 allows for greater gaps to occur between the approaching vehicles during the first part of the green interval without inducing a reversion of the signal light to its red condition.

For this purpose, an additional or advance detector would be attached to advance detector input 41, which in turn con nected to detector input 21 through normally closed

L relay contacts

142 and 143. In this configuration, the M relay coil can be energized by a signal from either detector. The advanced calling detector would be an area type detector similar to those described in FIG. 1 arranged proximate the principal detector upstreet from the intersection. As a car proceeds toward the intersection, the advance detector input 141 would first respond, energizing the M relay through the normally closed contacts of the L and R relays, respectively 142 and 143 and 30-31. With M relay energized, timer 67a starts timing a preselected interval due to the application of AC(+) power to terminal 66a through normally open M relay contacts 32 and 34 (now closed). Upon termination of the timing sequence, the L relay coil is energized via a connection'may be timer 67a between

terminals

66a and 69a thereof. At this point normally closed

L relay contacts

142 and 143 open thereby leaving only the principal detector connected to detector input 21 to respond to vehicle movement or presence. In effect, the L relay and timer 67a functions as an advance timing means for conditioning the M relay to respond to the advance detector only for a preselected time interval if the M relay is thereafter continuously maintained in its activated condition. Subsequent action of the vehicle control unit illustrated in FIG. 6 is the same as described above, in reference to FIG. 2 except for the all-red overlap feature.

The all-red overlap provides for separating otherwise adjacent yellow light and green light indications by a preselected red light time interval. For this feature, relay K and timer 510 are included in the circuit of FIG. 6. Particularly when M relay energizes, normally

open contacts

48 and 49 close, energizing the N relay coil through timer 51. In response thereto, N normally

open relay contacts

145 and 146 energizes the K relay coil through timer 51a through terminals 52a and 53a, thereupon the K relay locks on its own normally

open contacts

147 and 148. Therefore, relays M, N and K are all energized during the green light condition. As discussed in reference to FIG. 2, a yellow light condition is timed by timer 51. Additionally by means of closing of normally closed

N relay contacts

149 and 146 and opening of the normally open N relay contacts 145 and 146 a timing sequence at timer 51a is initiated. Also, normally closed

N relay contacts

61 and 62 close completing the circuit to the red light gate, terminal 64. When timer 51a times out, the K relay coil is deenergized and closes normally closed

K relay contacts

150 and 151 completing normally closed

K relay contacts

150 and 151 completing the circuit to the P relay coil so as to allow other cascaded vehicle control units to respond to a vehicle demand. The K relay when energized additionally provides power, through normally

open contacts

151 and 152 thereof, to the R relay coil via diodes 92 and resistor 79 so as to maintain the R relay energized during the red light overlap period. Also, it is noted that K relay contacts I53 and 154 provide for connecting rest terminal 95 to AC() during this period. The result of this arrangement is to disable other cascaded control units for a certain time period determined by timer 51a immediately after the control unit reverts to its red light condition. The advantage gained is to allow additional time for the intersection to clear before vehicles are permitted to proceed from the remaining approaches.

The circuit of FIG. 6 may be connected in cascade with a like or similar unit in the manner as described in conjunction with FIGS. 1 and 2 for

vehicle control units

15 and 16.

Up to this point in the description, no provision has been made for controlling pedestrian traffic. However, the method and apparatus of the present invention is readily adapted for such purpose. Specifically, FIG. 7 illustrates a schematic diagram of a pedestrian control unit especially adapted for cooperating with vehicle control units such as those shown in FIG. 2 and FIG. 6. Pursuant to the invention, the principle or basic operation of the pedestrian control unit is the same as that of the vehicular control units. Exceptions are a provision for limiting the maximum walk" interval (corresponding to green light or proceed interval) and a provision for delaying the walk indications independently of reoccurring demands until a certain time interval has elapsed. This latter feature is particularly advantageous in cooperation with the vehicular control unit for the following reason. If the vehicular movement is light in both directions of travel, the green light intervals presented in response thereto are very short, in the range of 2 seconds allowing efficient use of the intersection. However, minimum pedestrian walk" intervals are much longer, on the order of 15 seconds. If pedestrians are permitted to move each time a vehicle is given a green indication, pedestrian traffic will accordingly determine the timing of the intersection, greatly reducing the efficiency of vehicular control. For this reason, the features of the present invention provide for collecting of pedestrians for selected time intervals, typically in the range of 30 seconds. After such collection, the pedestrians are allowed to cross the street with the next nonconflicting vehicular interval. In the meantime, several cycles of vehicular intersection transversals, in both directions, may take place.

Referring now to FIG. 7, a pedestrian calling detector, pushbutton switch 160, is serially arranged between an AC(+) power source and detector input 21 and substitutes for the function of vehicle detectors l0 and 12 shown in FIG. 1. Output terminals 161 for a walk signal; terminal 162, for a flashing dont walk" signal; 163, for a constant dont walk signal and 164 for AC power corresponding to

output terminals

40, 75, 64 and 81 in FIG. 2 provide for the control of the pedestrian signal lights.

As in the case of the embodiment described in FIGS. 1, 2 and 3, it is preferred that outputs at terminals 16l165 operate the corresponding lamp loads through a solid-state switching circuit so as to avoid deterioration of the relay contacts with the control unit itself.

Output terminals

93, 83, and 95, are respectively the release output and rest terminals of control unit A shown in FIG. 2. Similarly, AC(+) power input 22 of FIG. 6 corresponds to inputs 22 in FIG. 2.

In operation, as pushbutton switch is momentarily depressed in response to a pedestrian call, a circuit is completed from AC(+) through switch I60, through normally closed G relay contacts and 176, through

terminals

52 and 53 of timer 51 completing the circuit through the E relay coil and locking the E relay on normally open

E relay contacts

166 and 167. Timers 61b and 51c are ofthe same type of timer as illustrated in FIG. 4. As the E relay closes, power supplied to the M relay coil through normally open

E relay contacts

169 and 170, and normally close

F relay contacts

171 and 172. Particularly, the E relay and timer 51b function as a pedestrian timer switching means for controlling the mode of the M relay in response to actuation of the pedestrian calling detector.

When AC power is applied to input 22 from another cascaded control unit, for example

vehicular control units

15 or 16 of FIG. 2, a walk indication is given in response to AC power being applied to walk" terminal 161 through now closed

M relay contacts

32 and 33. At the same time, AC power will be delivered 54b of timer 51b commencing its timing operation. Upon termination of this timing operation, relay E will deenergize opening the circuit to the M relay by opening

E relay contacts

169 and 170. As the M relay drops out, the walk" light indicating signal is extinguished and the flashing dont walk" signal is actuated at terminal 162 through previously closed

N relay contacts

71 and 72.

The remainder of the operating characteristics of this pedestrian control unit are the same as that of the above described vehicular unit A except for the provision of lock out timer, timer 51d. The purpose of timer 51d is to prevent the immediate reoccurrence of a walk" light indication after a previous pedestrian crossing. As mentioned above, this feature avoids pedestrian domination of the signal controlled in tersection. In operation, relays N and M energize at the same time in the normal manner.

Relay N contacts

181 and 182 close energizing the G relay coil through

terminals

52d and 53d of timer 51d whereupon the G relay locks upon its own normally

open contacts

178 and 179.

Upon termination of the flashing "don't walk" interval (which correspond to the yellow or caution signal in the vehicle control units) the N relay deenergizes and the normally closed

contacts

180 and 181 thereof close the circuit to terminal 54d of timer 51d thus initiating its timing cycle. On the terminal of this cycle, the G relay is deenergized by the shorting of

timer terminals

53d and 55d. The object of this action is to disable switch 160 from activating the E relay, after an immediately proceeding pedestrian crossing by means of the open

G relay contacts

175 and 176 until timer 51d marks offa preselected interval thus the G relay together with timer 51c provide a prevent timer switching means so as to avoid pedestrian dominance of the intersection. As discussed above, this timed interval which may be in the range of 30 seconds, allows efflcient vehicular traffic movement while pedestrians are collected for eventual crossing.

it is noted that in the pedestrian control unit shown in FIG, 6, the F relay provides a similar prevent function to that of the R relay described in previous embodiments of the invention. Particularly, normally closed

F relay contacts

171 and 172 open the circuit to the M relay coil in response to energization of the relay coil which occurs upon demand by another control unit through release terminal 93. At variance with the circuits shown in FlGS. 3 and 6, however, the actuation of the F relay is not delayed through a timer but occurs promptly upon demand, opening

contacts

171 and 172 so as to prevent further pedestrian control of the M relay.

it will be apparent that each of the circuits shown in FIGS. 2, 6 and 7 have a common basis of operation, this is evidenced by the reoccurrence of the M relay which is responsive to the vehicle or pedestrian traffic and provides for displaying proceed indications in accordance therewith, and the reoccurrence of the P relay in each of the units, which provides with switching

circuits

41 and 42 for disabling the operation of one of the units during conflicting operation of the other and insuring against erroneous conflicting signal indications. It is this common basis of operation which provides for the extreme versatility and flexibility of the invention. For example, as shown in FIG. 8 a three-phase vehicular and pedestrian control system is readily assembled through the use of three

vehicle control'units

200, 201 and 203, each identical to control unit 15 shown in FIG. 2 and a pedestrian control unit 205 identical to the pedestrian control unit shown in H0. 7. in a manner similar to that described in conjunction with FIG. 1, control unit 200 provides for switching signal lights 219 for A approaches, unit 201 provides for switching signal lights 218 for B approaches, unit 202 switches signal lights 220 for a lefthand turn approach C and pedestrian control unit 205 operates signal lights 22] for controlling pedestrian traffic along the B direction. Only the output terminals of the control units are shown for convenience, each having a reference numeral corresponding to the terminal numbers shown and described in detail hereinabove. For example, unit A has a detector input terminal 21 connected to detector switches 24 for the A approaches, control unit 201 has a detector input 21 connected to detector switches 24 for the B vehicle approaches, control unit 202 similarly has a detector input 21 connected to detector switch 24 for the left-hand turn C approach while pedestrian control unit 205 has a detector input 21 connected to pedestrian detector switches 160 for the B direction.

Each of control units 200-202 have signal

control output terminals

40, 75, 64 and 81 connected to solid-

state switching devices

98, 99 and 100 in the manner described for switching each of

signal lights

219, 218 and 222. Pedestrian control unit, 205, similarly has

output terminals

161, 162 163 and 164, a pair of solid-

state switching devices

208 and 209 for switching pedestrian signal lights between walk and don't walk" indications. It is noted in this regard, that terminal 162 of pedestrian control unit 205 which provides for the dont walk signal indication is not used in this instance.

Now in regard to the connections of each of the units for providing the sequential operation thereof in accordance with instantaneous traffic demands, vehicle control unit 200 has released terminal 93 thereof connected to rest terminals 95 for each of

control units

201, 202 and 205 for preventing operation ofunit 200 during proceed and walk indications and caution indications for

units

201, 202 and 205. Additionally, vehicle control unit 200 has power output terminal 83 connected to AC power input terminals 22 of vehicle control unit 201 and pedestrian control unit 205 for preventing operation of these latter two units during a proceed or caution operation of unit 200 for the A approaches.

Control unit 202, providing for left-hand turns from the C approach receives power to input terminal 22 thereof, from output 83 of control unit 200 through

auxiliary terminals

183 and 184 of pedestrian control unit 205, so as to disable control unit 202 for the C approach not only when control unit 200 is operating to pass traffic from the A approaches but also during passage of pedestrians in the C direction. That is, during operation of unit 200 passing vehicles in the A direction, power is interrupted at output terminal 83 of unit 200 preventing power from reaching input terminal 22 via

unit

201 and 205. During operation of unit 201, power is interrupted at output terminal 83 thereof again preventing unit 202 from receiving power at input terminal 22 thereof through pedestrian unit 205. During operation of pedestrian control unit 205, power is interrupted at auxiliary terminal 184 again preventing operation of unit 202.

Additionally, in this example, each of release terminals 93 for units 101, 102 and are connected to AC() so as to provide a maximum time out interval during which each of control units 101, 102 and 105 may maintain a proceed indication. At variance with this operation, unit 200 having release terminal 93 connected to the rest terminals 95 of each of

units

201, 202 and 205 providing such a maximum time out interval for unit 200 only in the event vehicle or pedestrian traffic is waiting in the B approaches or if vehicle traffic is waiting in the left hand turn C approach. Accordingly, in the instant case, it is anticipated that the A approaches are oriented along the direction of the main street traffic, so as to allow a continuous stream of traffic therealong to maintain a continuous proceed indication until the traffic approaches the intersection along one of the other directions.

It is noted that several of the terminals for each of the control units remain unconnected, for example rest terminal 95 of unit 200. As indicated above, due to the universal characteristics of each of the units, allowing for mass production and modular assembly, it is not always necessary or desirable to utilize each and every function of the units. However, by providing identical and universal units which may be sold separately and assembled into a system according to the requirements of a particular intersection or traffic control problem, extreme versatility is obtained together with economy in manufacturing the circuits.

As an example of this versatility, it will be appreciated that concurrent movements of trafflc may be provided if desired for certain intersections, such as concurrent left-hand turns from the C approach together with nonconflicting movement of trafiic from the right-hand side A approach. Additionally, overlapping movements may be provided for, wherein a first approach to an intersection is allowed to proceed concurrently with adjacent but separate movements of traffic from two or more approaches. That is, movement in the first direction overlaps the movement in the remaining several directions. Further still, preemptor traffic operations are readily adapted to the instant system as discussed above, allowing for emergency traffic situations at intersections for example near a fire station. ln this situation, separate detection of the emergency traffic by a separate control unit, would immediately interrupt operation of each of the remaining control units so as to allow preemption thereof.

We claim:

1. A system for controlling traffic through an intersection having at least first and second approaches thereto, wherein the traffic in said first approach is characterized by vehicles exhibiting a substantial magnetizable mass, comprising in combination:

first detector means associated with the first approach characterized by an electromagnetic sensor productive of an electromagnetic field within a region of the first approach proximate the intersection and being responsive to such vehicles within said field to assume its actuated condition, and having a rest condition and an actuated condition and being responsive to the presence of traffic in the first approach to assume its actuated condition;

second detector means associated with the second approach characterized by having a rest condition and an actuated condition and being responsive to the presence of traffic in the second approach to assume its actuated condition;

first detector controlled switching means operatively connected to said first detector means and having first and second modes, said first switching means being responsive to said first detector means in its rest condition to assume its first mode and being responsive to said first detector means in its actuated condition to assume its second mode;

second detector controlled switching means operatively connected to said second detector means and having first and second modes, said second switching means being responsive to said second detector means in its rest condition to assume its first mode and being responsive to said second detector means in its actuated condition to assume its second mode;

supervisory circuit means operatively connected to said first and second switching means and having first and second states, said supervisory circuit means being responsive to said first switching means in its second mode to assume its first state and being responsive to said second switching means in its second mode and said first switching means in its first mode to assume its second state;

first traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the first approach, said first signal means operatively connected to said supervisory circuit means together with said first switching means and being responsive to said supervisory switching means in its first state and said first switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its second state to assume its stop condition;

second traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the second approach, said second signal means operatively connected to said supervisory circuit means together with said second switching means and being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its first state to assume its stop condition;

first prevent switching means operatively connected to said first and second switching means and said supervisory circuit means and having a normal mode and a disabling mode, said first switching means responsive to said prevent switching means in its disabling mode to assume and remain in its first mode, said prevent switching means being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its disabling mode;

first time out switching means operatively connected to said first and prevent switching means, said time out switching means responsive to said first switching means in its second mode to actuate said prevent switching means to its disabling mode after a preselected time interval with said supervisory circuit means in its first state and said second switching means in its second mode;

second prevent switching means and second time out switching means operatively connected to said second switching means and said supervisory circuit means, said second prevent switching means having a normal mode and a disabling mode, said second switching means responsive to said second prevent switching means in its disabling mode to assume and remain in its first mode, said second prevent switching means responsive to said second time out switching means to assume its disabling mode after a preselected time interval with said supervisory circuit means in its second state and said second switching means in its second mode;

advance detector means having a rest condition and an actuated condition and being characterized by an electromagnetic sensor productive of an electromagnetic field and responsive to the presence of such vehicles within said field to assume its actuated condition, said advance detector means positioned to arrange its field within said approach adjacent the field of said first detector on the side thereof opposite the intersection to respond to such vehicles approaching the intersection prior to the response of said first detector means; and advance timer switching means operatively connected to aforesaid first switching means and said advance detector means and having a normal state and a disabling state, said first switching means being responsive to said advance detector means in its actuated condition and said advance timer switching means in its normal state to assume its second mode, said advance timer switching means being responsive to said first switching means in its first mode to assume its normal state and responsive to said first switching means being in its second mode for a preselected time interval to assume its disabling state. 2. A system for controlling traffic through an intersection having at least first and second approaches thereto, wherein the traffic in the second approach is composed of pedestrians, comprising in combination:

first detector means associated with the first approach characterized by having a rest condition and an actuated condition and being responsive to the presence of traffic in the first approach to assume its actuated condition;

second detector means associated with the second approach characterized by a manually operated switch disposed for operation by the pedestrians and responsive to such operation to momentarily assume its activated condition and having a rest condition and an actuated condition and being responsive to the presence of traffic in the second approach to assume its actuated condition;

first detector controlled switching means operatively connected to said first detector means hand having first and second modes, said first switching means being responsive to said first detector means in its rest condition to assume its first mode and being responsive to said first detector means in its actuated condition to assume its second mode;

second detector controlled switching means operatively connected to said second detector means and having first and second modes, said second switching means being responsive to said second detector means in its rest condition to assume its first mode and being responsive to said second detector means in its actuated condition to assume its second mode; supervisory circuit means operatively connected to said first and second switching means and having first and second states, said supervisory circuit means being responsive to said first switching means in its second mode to assume its first state and being responsive to said second switching means in its second mode and said first switching means in its first mode to assume its second state; first traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the first approach, said first signal means operatively connected to said supervisory circuit means together with said first switching means and being responsive to said supervisory switching means in its first state and said first switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its second state to assume its stop condition;

first time out switching means operatively connected to said first and prevent switching means, said time out switching means responsive to said first switching means in its second mode to actuate said prevent switching means to its disabling mode after a preselected time interval with said supervisory circuit means in its first state and said second switching means in its second mode; and

a pedestrian timer switching means operatively connected between said second detector means and second switching means and having a normal state and an actuated state, said pedestrian timer switching means operative in its normal state to maintain said second switching means in its first mode and operative in its timing state to activate said second switching means to its second mode for a preselected time interval, said pedestrian timer switching means responsive to said second detector means being momentarily in its activated condition to assume its timing state until termination of said interval.

3. A system as defined in claim 2, further comprising prevent timer switching means operatively connected between said second detector means and said pedestrian timer switching means and having a normal mode and a disabling mode, said prevent timer switching means operative in said normal mode to permit said pedestrian timer switching means to assume its normal and timing states in aforesaid response to said second detector means and operative in its disabling mode to render said pedestrian timer switching means nonresponsive to said second detector means.

4. A control unit for use in a traffic control system having a traffic detector associated with one approach to an intersection and productive ofan electrical signal in response to tral'fic therein and an electrically operated traffic signal having separate proceed, caution and stop conditions also associated with such approach and electrical control means for regulating traffic associated with another approach to the intersection productive of an electrical signal indicating its instant mode of operation and reception of a source of operating power, wherein the control unit comprises;

a detector input adapted to be connected to the detector for receiving the electrical signal therefrom,

a first electrical power input adapted to receive a controlled source of electrical power;

a second electrical power input adapted to receive a continuous source of electrical power;

a release input adapted to be connected to the control means for receiving the electrical signal indicative of the instant operational mode thereof;

an electrical power output adapted to be connected to the control means unit for providing the controlled source of power therefor;

traffic signal proceed, caution and stop outputs adapted to be connected to the traffic signals for providing electrical signals separately actuating its proceed, caution and stop conditions;

detector controlled switching means having first and second modes and being connected to said detector input, and said first power input, said detector controlled switching means being responsive to said detector input to assume its first or second modes in response to the electrical signal appearing thereat;

supervisory circuit means having first and second states and being connected to said detector controlled switching means, said first electrical power input, said release input, said electrical power output and said traffic signal proceed and caution outputs, said supervisory circuit means being responsive to said detector controlled switching means in its second mode to assume its first state and being responsive to said detector controlled switching means in its first mode and the controlled source of power appearing at said first power input and the electrical signal appearing at said release input to assume its second state, said electrical power output being responsive to said supervisory circuit means in its second mode and the controlled source of power appearing at said first power input to provide the controlled source of power for the control means, said traffic signal proceed output being responsive to said supervisory circuit means in its first state and said detector controlled switching means in its second mode, and the controlled source of power appearing at the said first power input to provide the electrical signal for actuating the traffic signal to its proceed condition; and

caution timer switching means having a normal and an actuated state and being connected to said supervisory circuit means, said detector controlled switching means, said second power input, said traffic signal caution output and stop output, said caution timer switching means being responsive to said supervisory circuit means in its first state and said detector controlled switching means in its second mode and the controlled source of power appearing at said first power input to assume its actuated state being responsive to said detector controlled switching means resuming its first mode to assume its normal state after a preselected interval, said traffic signal caution output being responsive to said caution timer switching means in its normal state to provide the electrical signal for actuating the traffic signal to its stop condition.

5. in a system as defined in claim 4, wherein the control means is receptive to an electrical signal indicating the instant operational mode of the control unit and the control unit further comprises;

a rest output adapted to be connected to the control means,

said rest output being connected to said detector controlled switching means and said caution timer switching means and being responsive to said detector controlled switching means in its second mode or said caution timer switching means in its actuated state to provide the electrical signal at said rest output indicating the mode of the control unit.

6. In a system as defined in claim 4, the control unit further comprising;

a prevent switching means connected to said detector controlled switching means, said supervisory circuit means and said release input and having a normal mode and a disabling mode, said detector controlled switching means being responsive to said prevent switching means in its disabling mode to assume and remain in its first mode, said prevent switching means responsive to said supervisory circuit means in its second state and the electrical signal appearing at said release input to assume its actuated mode.

7. in a system as defined in claim 4, the control unit further comprising;

time out switching means connected to said detector controlled switching means and said prevent switching means, said prevent switching means being responsive to said time out switching means and said detector controlled switching means in its second mode and said supervisory circuit means in its first state and the presence of the electrical signal at said release input for a preselected time interval to assume its disabling mode.

8. In a system as defined in claim 4, wherein said supervisory circuit means is responsive to said caution time switching means being in its actuated state to remain in its first state.

9. In a system as defined in claim 6, the control unit as defined, wherein said prevent switching means is responsive to said caution timer switching means in its actuated state and said detector controlled switching means in its first mode to assume its disabling mode.

10. in a system as defined in claim 4, further characterized by an additional traffic detector associated with the first named approach and productive of an electrical signal indicative of traffic conditions therein in advance of the first named detector, and the control unit further comprising;

an advance detector input adapted to be connected to the addition detector for receiving the electrical signal therefrom; and

advance timer switching means having a normal state and a disabling state and being connected to said advance detector input and said detector controlled switching means, said detector controlled switching means being responsive to the electrical signal appearing at said advance detector input when said advance timer switching means is in its normal state to assume its first and second modes, said advance timer switching means being responsive to said detector controlled switching means being in its second mode for a preselected time interval to assume its disabling state and being responsive to said detector controlled switching means in its first mode to assume its normal state.

11. In a system as defined in claim 5, further characterized by the traffic in the first named approach being composed of pedestrians and the detector being a manually operated switch providing the electrical signal therefor,

pedestrian timer switching means connected to said detector input and said detector controlled switching means and having a normal state and an actuated state, said detector controlled switching means being responsive to said pedestrian timer switching means in its actuated state to assume its second mode for a preselected time interval, said pedestrian timer switching means being responsive to the electrical signal appearing at said detector input and the source of power at said second power input to assume and remain in its actuated state and being responsive to said supervisory circuit means being in its first state and said detector controlled switching means being in its second mode for said interval to assume its normal state.

12. In a system as defined in claim 11, the control unit further comprising;

prevent timer switching means connected between said detector input and said pedestrian timer switching means and having a normal mode and a disabling mode, said pedestrian timer switching means being responsive to said detector input, said prevent timer switching means further being connected to said second power input and said caution timer switching means and being responsive to said second power input and said caution timer switching means in its actuated state to assume its disabling mode for a preselected interval.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 582,876 Dated June 1 1971 Inventor) Howard Carmack et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 2, "non conflicting" should read Column 3 line 66 "From" should read from Column 6 line 26, "155" should read 66

lines

35 and 36, cancel "to the R relay coil and release terminal 73 and timer". Column 10, line 72, after "delivered" insert to terminal Column 16, line 62, after "switching means" insert in its actuated state and said detector controlled switching means in its first mode to provide the electrical signal for actuating the traffic signal to its caution condition, said traffic signal stop output being responsive to said caution timer switching means Signed and sealed this 18th day of January 1972.

(SEAL) Attest EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents non-conflicting line 30, "d4awings" should read drawings FORM F'O-1 (10-69) USCOMM-DC 603764 69 9 U S. GOVERNMENT PRINTING OFFICE I969 D365'334

Claims

1. A system for controlling traffic through an intersection having at least first and second approaches thereto, wherein the traffic in said first approach is characterized by vehicles exhibiting a substantial magnetizable mass, comprising in combination: first detector means associated with the first approach characterized by an electromagnetic sensor productive of an electromagnetic field within a region of the first approach proximate the intersection and being responsive to such vehicles within said field to assume its actuated condition, and having a rest condition and an actuated condition and being responsive to the presence of traffic in the first approach to assume its actuated condition; second detector means associated with the second approach characterized by having a rest condition and an actuated Condition and being responsive to the presence of traffic in the second approach to assume its actuated condition; first detector controlled switching means operatively connected to said first detector means and having first and second modes, said first switching means being responsive to said first detector means in its rest condition to assume its first mode and being responsive to said first detector means in its actuated condition to assume its second mode; second detector controlled switching means operatively connected to said second detector means and having first and second modes, said second switching means being responsive to said second detector means in its rest condition to assume its first mode and being responsive to said second detector means in its actuated condition to assume its second mode; supervisory circuit means operatively connected to said first and second switching means and having first and second states, said supervisory circuit means being responsive to said first switching means in its second mode to assume its first state and being responsive to said second switching means in its second mode and said first switching means in its first mode to assume its second state; first traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the first approach, said first signal means operatively connected to said supervisory circuit means together with said first switching means and being responsive to said supervisory switching means in its first state and said first switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its second state to assume its stop condition; second traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the second approach, said second signal means operatively connected to said supervisory circuit means together with said second switching means and being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its first state to assume its stop condition; first prevent switching means operatively connected to said first and second switching means and said supervisory circuit means and having a normal mode and a disabling mode, said first switching means responsive to said prevent switching means in its disabling mode to assume and remain in its first mode, said prevent switching means being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its disabling mode; first time out switching means operatively connected to said first and prevent switching means, said time out switching means responsive to said first switching means in its second mode to actuate said prevent switching means to its disabling mode after a preselected time interval with said supervisory circuit means in its first state and said second switching means in its second mode; second prevent switching means and second time out switching means operatively connected to said second switching means and said supervisory circuit means, said second prevent switching means having a normal mode and a disabling mode, said second switching means responsive to said second prevent switching means in its disabling mode to assume and remain in its first mode, said second prevent switching means responsive to said second time out switching means to assume its disabling mode after a preselected time interval with said supervisory circuit means in its second state and said second switching means in its second mode; advance detector means having a rest condition and an actuated condition and being characterized by an electromagnetic sensor productivE of an electromagnetic field and responsive to the presence of such vehicles within said field to assume its actuated condition, said advance detector means positioned to arrange its field within said approach adjacent the field of said first detector on the side thereof opposite the intersection to respond to such vehicles approaching the intersection prior to the response of said first detector means; and advance timer switching means operatively connected to aforesaid first switching means and said advance detector means and having a normal state and a disabling state, said first switching means being responsive to said advance detector means in its actuated condition and said advance timer switching means in its normal state to assume its second mode, said advance timer switching means being responsive to said first switching means in its first mode to assume its normal state and responsive to said first switching means being in its second mode for a preselected time interval to assume its disabling state.

2. A system for controlling traffic through an intersection having at least first and second approaches thereto, wherein the traffic in the second approach is composed of pedestrians, comprising in combination: first detector means associated with the first approach characterized by having a rest condition and an actuated condition and being responsive to the presence of traffic in the first approach to assume its actuated condition; second detector means associated with the second approach characterized by a manually operated switch disposed for operation by the pedestrians and responsive to such operation to momentarily assume its activated condition and having a rest condition and an actuated condition and being responsive to the presence of traffic in the second approach to assume its actuated condition; first detector controlled switching means operatively connected to said first detector means hand having first and second modes, said first switching means being responsive to said first detector means in its rest condition to assume its first mode and being responsive to said first detector means in its actuated condition to assume its second mode; second detector controlled switching means operatively connected to said second detector means and having first and second modes, said second switching means being responsive to said second detector means in its rest condition to assume its first mode and being responsive to said second detector means in its actuated condition to assume its second mode; supervisory circuit means operatively connected to said first and second switching means and having first and second states, said supervisory circuit means being responsive to said first switching means in its second mode to assume its first state and being responsive to said second switching means in its second mode and said first switching means in its first mode to assume its second state; first traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the first approach, said first signal means operatively connected to said supervisory circuit means together with said first switching means and being responsive to said supervisory switching means in its first state and said first switching means in its second mode to assume its proceed condition and responsive to said supervisory circuit means in its second state to assume its stop condition; second traffic signal means characterized by having mutually exclusive stop and proceed traffic directory conditions and positioned to indicate its condition to traffic in the second approach, said second signal means operatively connected to said supervisory circuit means together with said second switching means and being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its proceed condition and responsive to sAid supervisory circuit means in its first state to assume its stop condition; first prevent switching means operatively connected to said first and second switching means and said supervisory circuit means and having a normal mode and a disabling mode, said first switching means responsive to said prevent switching means in its disabling mode to assume and remain in its first mode, said prevent switching means being responsive to said supervisory circuit means in its second state and said second switching means in its second mode to assume its disabling mode; first time out switching means operatively connected to said first and prevent switching means, said time out switching means responsive to said first switching means in its second mode to actuate said prevent switching means to its disabling mode after a preselected time interval with said supervisory circuit means in its first state and said second switching means in its second mode; and a pedestrian timer switching means operatively connected between said second detector means and second switching means and having a normal state and an actuated state, said pedestrian timer switching means operative in its normal state to maintain said second switching means in its first mode and operative in its timing state to activate said second switching means to its second mode for a preselected time interval, said pedestrian timer switching means responsive to said second detector means being momentarily in its activated condition to assume its timing state until termination of said interval.

4. A control unit for use in a traffic control system having a traffic detector associated with one approach to an intersection and productive of an electrical signal in response to traffic therein and an electrically operated traffic signal having separate proceed, caution and stop conditions also associated with such approach and electrical control means for regulating traffic associated with another approach to the intersection productive of an electrical signal indicating its instant mode of operation and reception of a source of operating power, wherein the control unit comprises; a detector input adapted to be connected to the detector for receiving the electrical signal therefrom, a first electrical power input adapted to receive a controlled source of electrical power; a second electrical power input adapted to receive a continuous source of electrical power; a release input adapted to be connected to the control means for receiving the electrical signal indicative of the instant operational mode thereof; an electrical power output adapted to be connected to the control means unit for providing the controlled source of power therefor; traffic signal proceed, caution and stop outputs adapted to be connected to the traffic signals for providing electrical signals separately actuating its proceed, caution and stop conditions; detector controlled switching means having first and second modes and being connected to said detector input, and said first power input, said detector controlled switching means being responsive to said detector input to assume its first or second modes in response to the electrical signal appearing thereat; supervisory circuit means having first and second states and being connected to said detector controlled switching means, said first electrical power input, said release input, said eleCtrical power output and said traffic signal proceed and caution outputs, said supervisory circuit means being responsive to said detector controlled switching means in its second mode to assume its first state and being responsive to said detector controlled switching means in its first mode and the controlled source of power appearing at said first power input and the electrical signal appearing at said release input to assume its second state, said electrical power output being responsive to said supervisory circuit means in its second mode and the controlled source of power appearing at said first power input to provide the controlled source of power for the control means, said traffic signal proceed output being responsive to said supervisory circuit means in its first state and said detector controlled switching means in its second mode, and the controlled source of power appearing at the said first power input to provide the electrical signal for actuating the traffic signal to its proceed condition; and caution timer switching means having a normal and an actuated state and being connected to said supervisory circuit means, said detector controlled switching means, said second power input, said traffic signal caution output and stop output, said caution timer switching means being responsive to said supervisory circuit means in its first state and said detector controlled switching means in its second mode and the controlled source of power appearing at said first power input to assume its actuated state being responsive to said detector controlled switching means resuming its first mode to assume its normal state after a preselected interval, said traffic signal caution output being responsive to said caution timer switching means in its normal state to provide the electrical signal for actuating the traffic signal to its stop condition.

5. In a system as defined in claim 4, wherein the control means is receptive to an electrical signal indicating the instant operational mode of the control unit and the control unit further comprises; a rest output adapted to be connected to the control means, said rest output being connected to said detector controlled switching means and said caution timer switching means and being responsive to said detector controlled switching means in its second mode or said caution timer switching means in its actuated state to provide the electrical signal at said rest output indicating the mode of the control unit.

6. In a system as defined in claim 4, the control unit further comprising; a prevent switching means connected to said detector controlled switching means, said supervisory circuit means and said release input and having a normal mode and a disabling mode, said detector controlled switching means being responsive to said prevent switching means in its disabling mode to assume and remain in its first mode, said prevent switching means responsive to said supervisory circuit means in its second state and the electrical signal appearing at said release input to assume its actuated mode.

7. In a system as defined in claim 4, the control unit further comprising; time out switching means connected to said detector controlled switching means and said prevent switching means, said prevent switching means being responsive to said time out switching means and said detector controlled switching means in its second mode and said supervisory circuit means in its first state and the presence of the electrical signal at said release input for a preselected time interval to assume its disabling mode.

10. In a system as defined in claim 4, further characterized by an additional traffic detector associated with the first named approach and productive of an electrical signal indicative of traffic conditions therein in advance of the first named detector, and the control unit further comprising; an advance detector input adapted to be connected to the addition detector for receiving the electrical signal therefrom; and advance timer switching means having a normal state and a disabling state and being connected to said advance detector input and said detector controlled switching means, said detector controlled switching means being responsive to the electrical signal appearing at said advance detector input when said advance timer switching means is in its normal state to assume its first and second modes, said advance timer switching means being responsive to said detector controlled switching means being in its second mode for a preselected time interval to assume its disabling state and being responsive to said detector controlled switching means in its first mode to assume its normal state.

11. In a system as defined in claim 5, further characterized by the traffic in the first named approach being composed of pedestrians and the detector being a manually operated switch providing the electrical signal therefor, pedestrian timer switching means connected to said detector input and said detector controlled switching means and having a normal state and an actuated state, said detector controlled switching means being responsive to said pedestrian timer switching means in its actuated state to assume its second mode for a preselected time interval, said pedestrian timer switching means being responsive to the electrical signal appearing at said detector input and the source of power at said second power input to assume and remain in its actuated state and being responsive to said supervisory circuit means being in its first state and said detector controlled switching means being in its second mode for said interval to assume its normal state.

12. In a system as defined in claim 11, the control unit further comprising; prevent timer switching means connected between said detector input and said pedestrian timer switching means and having a normal mode and a disabling mode, said pedestrian timer switching means being responsive to said detector input, said prevent timer switching means further being connected to said second power input and said caution timer switching means and being responsive to said second power input and said caution timer switching means in its actuated state to assume its disabling mode for a preselected interval.