Street traffic signalling system

Abstract

A street traffic signalling system for automatically effecting respective selectable signalling conditions or phases at an intersection in correspondence to a mutually independent selection with predetermined protective delay periods between predetermined changes in signalling conditions and in which a plurality of traffic signal means or units are employed at a street intersection with a plurality of logical linkages for controlling the individual conditions or phases, each of the latter having a pair of phase responsive switches cooperable with the associated logical linkage and with timing means for controlling such linkage and an associated signal unit, with one of each pair of switches being operative to effect initiation of a signalling condition or phase and operative to effect termination of a then existing signalling condition or phase and the other switch of a pair being operative to determine protective periods of other signal phases in the event of a transition thereto, with the timing means and each pair of switches being operatively connected to the logical linkages associated therewith by respective shunting fields.

Description

BACKGROUND OF THE INVENTION

The invention is directed generally to a street traffic signalling system utilizing timing means which automatically controls various selectable signalling conditions or phases at a street intersection, according to an arbitrary selection, preferably a traffic dependent selection.

The various signalling connditions which are possible at an intersection may in some instances always succeed one another in the same periodic sequence. This is particularly true when the intersection is controlled in dependence upon time according to a predetermined program. However, many rapid changes in signalling conditions can be involved in the traffic-dependent control of an intersection and it thus should be possible to adjust, in dependence upon the traffic load, the signalling conditions to meet the then existing traffic conditions. To assure a safe operation, it is necessary that minimum protective periods of time be provided between phase changes, and while this may be readily accomplished where the operation is controlled in a set pattern or program, arbitrary phase changes usually will require different minimum periods between the various phase change relationships. It will be apparent that to most effectively utilize the available time, it is desirable that the protective periods be limited to the respective minimum safe periods.

In order to maintain established minimum requirements in connection with arbitrary phase changes, the necessity of providing shunting means and logical linkages to meet such requirements involves a considerable expense which, in the past, has not been economically feasible as, in addition to the physical structure, the necessary shunting and connecting operations involved presented too great an expenditure. As a result technical disadvantages were necessarily tolerated, necessitating increases over the minimum protective periods which might otherwise be required and with corresponding loss in effective utilizable time.

The present invention is therefore directed to a system enabling exceedingly simple connecting arrangements, and providing a very flexible adjustment to achieve minimum protective periods with traffic-dependently controllable signalling systems, eliminating the above disadvantages, at the same time permitting full freedom to meet varying geographical conditions and independently of the different signalling conditions of each signal system.

BRIEF SUMMARY OF THE INVENTION

The desired results are achieved with the present invention by utilizing suitable timing means which automatically determines one of several selectable signalling conditions at an intersection, according to a mutually independent selection, in which the signal means or units, i.e. light signals, at the cross point can be controlled by a plurality of logical linkages corresponding to the number of signal conditions or phases, preferably utilizing AND-gates, and that each of such logical linkages can be controlled by the timer and by two phase-responsive switches, one of which is utilized for determination of the signalling condition or phase which is to be initiated, and the termination of an existing signalling condition or phase and the other determines protective periods required in the next phase transition. With this arrangement all of the various timing periods which are required in connection with the various changes in signalling conditions can be readily determined and each of such phase-responsive switches can be readily circuited, for the desired timing required for each condition change of the respective signal units, in a very simple manner and with relatively simple circuitry.

In a further development of the invention, respective pairs of AND gates are provided for each signal unit, one of which is utilized to initiate actuation of the "stop" or "red" light of such signal unit and the other gate of such pair for initiating actuation of the "go" or "green" light of the associated signal unit with the gates and other logical linkages associated with a respective signal unit having their inputs operatively connected to the respective phase-responsive switches and the timing means through respective shunting fields. The timing means is adapted to provide all necessary timing periods and in some cases it may be possible to actuate the stop lights of all signal units by only the first timing step of the timing counter (output 0), and to actuate only the go lights over the corresponding AND gates. It is particularly advantageous to utilize the present invention in connection with traffic-dependently controllable program-selection apparatus, for example, a traffic computer, by means of which the respective condition-selecting switches can be controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings wherein like reference characters indicate like or corresponding parts:

FIGS. 1a-1d are respective figures illustrating four different traffic conditions or phases for a side road intersection, respectively designated conditions or phases Ph1 through Ph4;

FIG. 2 is a matrix chart illustrating the protective periods involved for the respective four traffic conditions;

FIG. 3 is a diagram showing the relation of FIGS. 3a and 3b;

FIGS. 3a and 3b, collectively is a schematic figure of a circuit arrangement for practicing the invention;

FIG. 4 illustrates a suitable timing generator, counter and delay member which could be employed in the circuit of FIGS. 3a and 3b; and

FIG. 5 is a schematic figure corresponding to a portion of FIG. 3b and illustrating the use of 3-input AND gates.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated an intersection comprising a main or through road having respective traffic flows a and b in opposite directions, and a side road intersecting the through road at one side thereof and having traffic flows c and d. In addition, pedestrian flow is indicated by the double headed arrow e. Respective signal means for example, respective signal units, SgA through SgE are disposed at the indicated points of the intersection for controlling the respective traffic flows a through e and corresponding to the respective traffic conditions or phases Ph1 through Ph4 illustrated.

As will be apparent from reference to FIG. 2 that there exists three possible transitions or changes from one phase to any of the remaining three phases and in which different protective delay periods might be required for a transition from one phase condition to another. For example, from condition Ph3 there exists three possible transitions to other phases, mainly to phase Ph1, phase Ph2 or condition Ph4, and let it be assumed that a protective period of, for example, nine seconds is required for the signal means SgA. This protective period, thus, in this case, is equal for all three phase changes due to traffictechnical reasons, further explanation of which is not necessary. In order to avoid traffic danger, existing traffic flows must initially be stopped by the stop lights before the go lights are actuated to initiate othher traffic flows. It might be mentioned that while additional transition signal lights such as a "yellow" or a "red/yellow" will normally be provided, they have not been illustrated in the present disclosure as they can be readily coupled with the stop or go lights over suitable timing means or the like.

For example, if a transition is to be made from phase Ph3 to phase Ph1, the signal means SgD and SgE must actuate their stop lights at the time 0 according to FIG. 2, phase Ph3, column 1, following which the signal units SgA and SgB can actuate their go lights after a protective delay period of 9 and 10 seconds respectively.

The switchover from phase Ph3 to phase Ph1 will be further explained for the signal units SgA and SgE with the aid of FIGS. 3a and 3b and this figure thus illustrates the circuitry primarily for these two signal units, however, analogous considerations are valid for the signal units SgB through SgD which have been omitted in the circuit of FIG. 3.

A plurality of condition-determining switches, designated by the reference character prefix Sb are provided, in which reference characters Sb1 through Sb4 designate respective first bistable phase -responsive switches, while reference characters Sb11-Sb14 designate respective second phase-responsive switches, with the first phase-responsive switches being under the control of respective second switches T1 through T4, illustrated, as being pushbutton switches by means of which phase changes may be initiated. While the switches T1-T4 illustrated as being, for example, manually operated switches and thus theoretically could be controlled by a policeman or other operator, the phase selection would in almost all cases be effected through suitable known program-selecting devices, either time or traffic dependent, as for example, a computer or similar device.

The signal unit SgA is adapted to be controlled by a relay A having contact a which is the rest position illustrated actuate the stop light, and in like manner the signal unit SgE is adapted to be controlled by the relay E having contact e with each relay being under the control of respective bistable switches Sba and Sbe. The circuit for each respective signal phase includes a plurality of logical linkages in the form of AND gates, gates Ga1-Ga6 being associated with signal unit SgA and gates Ge1 through Ge6 being associated with the signal unit SgE.

The duration of respective protective delay periods is determined by suitable timing means such as a timer Z, which may be in the form of a counting circuit adapted to count one second pulses, at one second intervals, received over an AND gate Gu2 from a pulse generator Tg. The respective phase-responsive switches, as well as the counter Z are operatively connected with the respective logical linkages and associated with a signal unit over respective connecting fields. The shunting fields Rf11 through Rf15 (only 11 and 15 being illustrated), and fields Rf21 through Rf25 (only 21 and 25 being illustrated) respectively operatively connect the two switches for each signal phase in preselected arrangement to selected inputs of the respective gates associated with a signal unit, while connecting fields Rf31 through Rf35 (only 31 and 35 being illustrated) operatively connect the counter Z to selected gate inputs of the associated linkages.

Considering the transition from phase Ph3 to phase Ph1, during condition Ph3, the counter Z will be in its last step (output 15) and the bistable switches S.sub.b 13 and S.sub.b e will be actuated while all remaining switches will be in a rest condition. The stop light of signal unit SgA will therefore be actuated over the contact a of the unactuated relay A and the go light of signal unit SgE will be actuated over the contact e of energized relay E. At the same time the connection between the output of switch Sb3 and input of switch Sb13, over connecting fields Rf15 will produce a preparing signal at the gate Ge5.

Simultaneously therewith, the output at terminal 15 of the counter Z is applied over a delay member V to the associated input of the gate Gu1 with the other input of such gate being supplied with pulses at one second intervals from the timing generator Tg. Gate Gu2 over which timing pulses from the generator Tg are to be supplied to the counter Z, is blocked. At the same time the output of switch Sb13 applies a preparatory signal on one input of the gate Ga2.

With the circuit in such condition, upon closure, for example, of the switch T1 followed by receipt of the next one second pulse from the timing generator Tg over the gate Gu1, bistable switch Sb1 will be actuated to provide an enabling voltage on its output which is conducted through OR gate Go1 to the monostable switch Sm1 which momentarily flips to produce a starting pulse at the counter Z, switching the latter from output 15 to output 0, thus removing blocking voltage from gate Gu2 to open the same to input timing pulses from the generator Tg and at the same time applying blocking voltage over the delay member V to the associated input of the gate Gu1, blocking the latter to any subsequent pulses from the generator Tg and thus preventing any interference in the event one of the other switches T2-T4 were inadvertently actuated. Simultaneously, the output from the switch Sb1 is conducted over shunting field Rf11 to the associated input of gate Ga6.

As soon as a pulse is received at the output of position O, a pulse is conducted over Rf35 to the other input of gate Ge5, with the output voltage of such gate flipping the bistable switch Sbe to deenergize relay E and immediately actuate the stop light of signal unit SgE. As will be apparent from a reference to the chart of FIG. 2 the go light of signal unit SgA is adapted to be actuated following a protective delay of nine seconds. Consequently, when a pulse appears at position 9 of the counter, it will be conducted over the connecting field Rf31 to the other input of gate Ga2 with the output thereof being conducted over OR gate Ga4 to the other input of gate Ga6 resulting in the appearance of a signal at the output of such gate operative to flip the bistable switch Sba, energizing relay A and actuating the go light of signal unit SgA. The counter Z will continue to count until position 15 is again reached, at which point blocking voltage will again be placed on the corresponding input of gate Gu12, stopping the counter Z, and over delay member V to the gate Gu1, opening the latter to the timing pulses from the generator Tg and the pulses with the output voltage of such gate thereby resetting switch Sb1 to its original rest position. However, prior to the opening of the gate Gu1, the monostable switch Sm.sup.2 will be momentarily actuated to reset the bistable switch Sb13 to its rest position and actuate the switch Sb11, thus preparing gate Ge1. Thus, the delay member V ensures actuation of the switch Sb11 before switch Sb1 is returned to its rest position. The circuit thus is prepared for the next condition change.

FIG. 4 illustrates, by way of example, the details of a timing generator Tg, a counter Z and delay member V.

Thus, the timing generator Tg could be a suitable device, such as a clock, or as illustrated switch contacts tg adapted to be periodically closed by a plunger st, actuated by a rotary cam N driven by a synchronous motor Sy, thereby supplying pulses of potential Pot. of suitable polarity.

The counter Z, for example, may comprise a rotary stepping switch dr driven by a cooperable solenoid winding Z.sub.d whereby voltage from the source Pot. may be sequentially supplied to its respective outputs.

The delay member V likewise may comprise a relay of the delay type having a winding V.sub.d adapted to close its contacts v only after a predetermined delay.

It will be appreciated that by appropriate connection in the respective connecting fields any arbitrary combination or sequence of changes may be effected with any desired protective delay time between the actuation of a stop light and subsequent actuation of a go light being effected by suitable simple connections in the shunting fields Rf31-Rf35.

As previously mentioned normally the switches T1-T4 would be automatically actuated by operation of a suitable program selection device which may be either time or traffic dependent.

Likewise, in some cases it may be desirable to use AND gates having three inputs, instead of the dual input gates illustrated.

FIG. 5 corresponds to the lower portion of the circuitry illustrated in FIG. 3b, relating to the actuating circuit for the relay E, utilizing 3-input AND gates instead of 2-input gates as illustrated in FIG. 3b. It will be noted that with the three-input gates, each gate has one input connected to the appropriate output of the counter Z, one to the appropriate first phase-responsive switch and the third to the appropriate second phase-responsive switch. The outputs of the respective gates may be operatively connected to the appropriate signal light, i.e. operating relay thereof, by suitable means such as the OR gate Ge4 illustrated.

Having thus described my invention, it will be obvious that various minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such embodiments as reasonably and properly come within the scope of my contribution to the art.

Claims

I claim:

1. A street traffic signalling system having a plurality of mutually independently selectable signal phases for traffic control at an intersection, particularly a traffic-dependent selection, comprising a plurality of traffic signal units, each for a respective traffic direction, means for each signal unit for actuating respective signal lights thereof to provide the respective desired phases therefor, timing means having a plurality of timing outputs, a plurality of logical linkages for each selectable signal phase, operatively connecting predetermined timing outputs of said timing means with the cooperable actuating means for such signal phase, for providing respective protective periods prior to actuation of the go light associated therewith, phase-responsive switch means for each respective selectable phase, operative upon selection of such phase to determine the go light thereof to be actuated, and to initiate termination of the signal phase immediately preceding such new phase, and second phase responsive switch means for each respective selectable phase, operatively connected to logical linkages of other signal phases for effecting a selection of the timing outputs and connecting linkages therefor associated with such other signal phases, in the event of a transition from the associated phase to a new phase, whereby a predetermined time period is provided between termination of such immediately preceding signal phase and actuation of the selected go light of the new phase, in dependence upon the said immediately preceding phase so terminated.

2. A system according to claim 1, comprising in further combination, a plurality of connecting fields, the logical linkages associated with a respective signal phase having a connecting field operatively connecting the same with the cooperable first phase-responsive switch means associated therewith, a connecting field connecting such linkages with cooperable second phase-responsive switch means of the signal phases, and a connecting field connecting such linkages with said timing means, whereby operational and timing variations may be effected by changes in connections within the respective connecting fields.

3. A system according to claim 1, wherein the group of logical linkages for a respective signal phase comprises AND gates, with each independent signal unit having a pair of such gates, with one gate of such a pair being operative to effect actuation of the stop lights, and the other gate of such a pair being operative to effect actuation of the go lights of the associated signal unit.

4. A system according to claim 3, wherein said timing means and said gates are so connected that initiation of actuation of the stop lights of all signal units is effected by means of an output step of the timing means, and initiation of actuation of the go lights is effected by means of corresponding AND gates.

5. A system according to claim 3, wherein the stop lights of all signal units are actuated by respective AND gates, which in turn are placed in nonblocking condition by an impulse from an output step of the timing means, and actuated to blocking condition in response to actuation of a first phase-responsive switch means.

6. A system according to claim 3, wherein at least some of the AND gates forming logical linkages are three input gates.

7. A system according to claim 3, wherein at least some of the AND gates forming logical linkages are two input gates.

8. A system according to claim 3, wherein the phase-responsive switch means are bistable switches, the first phase-responsive switches being so arranged that all but an initially actuated switch are blocked during a transition change, and the second phase-responsive switches are controlled by the first phase-responsive switches and the last output step of the timing means.

9. A system according to claim 8, comprising in further combination, a plurality of connecting fields, the logical linkages associated with a respective signal phase having a connecting field operatively connecting the same with cooperable first phase-responsive switches, a connecting field connecting such linkages with cooperable second phase-responsive switches, and a connecting field connecting such linkages with said timing means, whereby operational and timing variations may be effected by changes in connections within the respective connecting fields.

10. A system according to claim 1, wherein said first and second phase-responsive switch means are bistable switches, each having a preparing input, a triggering and resetting input, and an output, the outputs of respective first phase-responsive switches being connected to respective preparing inputs of the second phase-responsive switches, and the logical linkages for each signal phase comprise a group of two-input AND gates and an OR gate with each signal unit having a pair of such AND gates, one gate of such pair being operative to effect actuation of the stop light of such unit, and the other gate of such pair being operative to effect actuation of the go light of such unit, such group having an operational and timing variations may be effected by changes in connections within the respective shunting fields.

11. A system according to claim 10, wherein said timing means comprises a timing generator and a counter therefor, the latter having a plurality of outputs representing respective time intervals, an AND gate, one input of which is operatively connected to the output of the timing generator and the other input thereof being connected over a delay member to an output of the counter representing the last counting output, operative to block such gate when such last counting output is reached, said counter having a start input operatively connected to the outputs of the respective first phase-responsive switches over an OR gate and a monostable switch.

12. A system according to claim 11, wherein each preparing input of the first phase-responsive switches is connectible to receive preparing voltage for effecting a phase selection, and each triggering input is connected over an AND gate having an input connected to the timing generator, and another input connected to the last counting output of the counter over a delay member, said last counting output being connected to the triggering input of the second phase-responsive switches over a monostable switch.

13. A system according to claim 1, wherein said first phase-responsive switch means are adapted to be selectively actuated in response to the operation of a usual traffic system timer.

14. A system according to claim 1, wherein said first phase-responsive switch means are adapted to be selectively actuated in response to the operation of a program selection device in time or traffic dependence, for example, a computer.

15. A system according to claim 1, wherein such logical linkages for a respective signal phase each comprise a plurality of AND gates, equal in number to the number of different protective periods required for the go light associated with a signal phase, each of such AND gates linking a respective timing output of said timing means with a respective second phase-responsive switch means, and a further AND gate controllable by said first-mentioned AND gates and an associated first phase-responsive switch means, said last-mentioned gate being operatively connected to the go light associated with such signal phase.

16. A system according to claim 1, wherein such logical linkages for each respective signal phase comprise a plurality of three-input AND gates, each having one input connected to a selected output of the timing means, a second input connected to a selected second phase-responsive switch means, and a third input connected to a selected first phase-responsive switch means, and means for operatively connecting each of the outputs of said AND gates to the go light associated with such signal phase.