US2761120A - Traffic control system - Google Patents

Description

Aug. 28, 1956 H. A. WILCOX TRAFFIC CONTROL SYSTEM 2 Sheets-Sheet 2 Filed Nov. 50, 1953 VFL VFR/

' FIGS.

FIG.4.

INVENTOR.

HARRY A. WILCOX ATTORNEY United States Patent 2,761,120 TRAFFIC CONTROL SYSTEM Harry A. Wilcox, Westport, tionm, assignor to Eastern Industries, Incorporated, East Norwalk, Colin, a corporation of Delaware This invention relates to traffic control systems and a control apparatus for tr'afiic signals in such systems, and relates more particularly to electrical apparatus for remote control of the total lengthof the traflic signal cycle over a wide range, While retaining a substantially constant length for apart of the cycle such 'as the trafric clearance intervals, following the respective traffic g'o intervals in the signal cycle.

The invention further relates to an improved masterlocal control system and apparatus for the control of one or more of a series of intersection traflic signals in which a master controller provides a variable frequency power to the one or more local controllers to drive the local controllers at a faster or slower rate as desired, during one part of the local traffic signal control cycle, as during the green signal periods for the respective intersecting streets controlled by the signal, to thus control the length of the green period and total cycle remotely, but in which the local controller is operated on fixed frequency power during another part of the cycle, as for example during the yellow signal periods ordinarily provided for traflic clearance following the green period's, where it is desired to have this latter part of the cycle of substantially constant length while varying the first mentioned part of the cycle over a wide range. h M

Various systems for coordinating the trafiic signals at a series of intersections alohg a common street or highway are already well known, including systems by which a maser controller provides a' common cycle length for a series of local signal controllers, and the local controllers may be individually adjusted to time the beginning or the end of the common street green signal period with respect to a common reference point in the cycle usually referred to as the zero offset point, and the local controllers can also be individually adjusted to determine the relative lengths of the green signal periods for the respective streets and the following yellow signal periods, the proportioning of the green signal periods of the signal cycle being usuallyrefe'rred to as the split" of the signal cycle.

Such proportioning of the local signal cycle is quite commonly done by means of a rotary dial unit on which pins or keys may be located in desired angular relation ship, the dial being rotated so that the pins engage contacts to actuate a step-by-step rotary switch unit whose several positions operate the desired green, red and yellow signals. The local rotary dial unit is ordinarily resynchronized once per cycle with the master controller cycle unit. y m

It is already also well-known to employlv arious means of lengthening the total cycle of the local controller by remote control from the master controller. One of the most effective of such remote control means has been the operation of a synchronous motor unit in the local controller from a variable frequency power supplied by the master controller as disclosed in S. Patent 2,542,978, granted February 27, 1951, to John L. Barker "ice for example. Such systems are most flexible in providing a wide range of adjustment of the total time cycle, in

which the longest time cycle may be two or three or more times the length of the shortest time cycle. Where said systems have such a Wide range of adjustment it has been found to be a disadvantage for certain parts of the signal time cycle, as for example the yellow clearance signal periods, to be lengthened and shortened along with the total cycle, as is the case where the variable frequency control is, applied directly to the local rotary dial unit for example. 1

Therefore, in accordance with one aspect of the present invention, means is provided in connection with the local controller to provide the remotely controlled variable frequency power to drive the local rotary dial unit during one part of the cycle, as for example the green periods, and to apply a local fixed frequency power to drive the local rotary dial unit during another part of the cycle as for example during the yellow periods, thus permitting the total cycle to be widely varied along with the green periods but to retain substantially constant yellow periods.

1 In accordance with a further aspect of the invention the master controller is provided with a total cycle determining unit which is driven from the common variable frequency power over the major part of its cycle but is driven by a substantially constant frequency power corresponding substantially with the local fixed frequency power during another part of its cycle to provide a total cycle for its resynchronization unit comparable to the total cycle of the local controllers, the resynchronization unit assuring that the local controllers will be restarted in synchronism once per cycle for example, and the master control cycle unit having a slightly longericycle than the local controllers over the entire range of adjustment.

It is a general object of the invention to provide an improved traflic control system for varying by remote control over a wide range the length of the total cycle of one or more traflicsignals while maintaining apart of such cycle. substantially constant.

It is a more specific object of the invention to provide an improved traflic control system in which the relative proportion of the respective green signal periods forthe intersecting roads at individual trafiic signals is locally determined by individual controllers and. in which the total signal cycle of such controllers is varied from a. com;

mon master controller While maintaining substantially constant the individuahproportioning of the green or go periods, and in which the yellow or clearance periods ,are a nt in d at a sub al ons ant v l 9Y a wid range of adjustment of the total cycle by such remote control from the mastereontroller j i It is a further object of the invention to provide proved means for operating a local traflic signal corn troller through a variable total time cycle and variable length of greener go periods While maintaining substantially constant yellow or clearance periods and a substan-- tially constant ratio between the respective green or go peiifodsof the signal cycle. I p

is so an bje of e in e n t r de a traf ic control system in which one ormor e individual traiiic controllers are operated at varying time rates to control the total cycle length over a wide range by variable frequency IlljlVlllgjPQWfll supplied to the local controllers from a single master controller, and in which means are provided in connection With the local controller to make such variable frequency driving power ineffective on the local controller during a part of the signal cycle providing the yellow or the clearance signal periods for example and supplanting such variable frequency power by a substantially fixed frequency local power drive during such yellow or clearance periods.

It is a still further object of the invention to provide a master-local control system for traflic signals employing variable frequency power for the local controllers supplied by the master controller for varying the total signal control cycle and employing means at the local controller for supplanting the variable frequency power drive at the local controller during the yellow or clearance signal parts of the cycle to provide a substantially constant period for such parts of the cycle, and means at the master controller for operating a master cycle resynchronization unit from the variable frequency power during one part of its cycle and from a fixed frequency drive during another part of its cycle, with the latter part of its cycle corresponding to the time length of the local yellow or clear-- ance periods approximately, said resynchronization unit serving to resynchronize the local controller with the master controller.

Other objects of the invention will appear from the accompanying claims and from the following description with respect to the drawings in which:

Fig. 1 illustrates in schematic form the master control apparatus for a traffic control system according to one embodiment of the invention, and providing output master control lines for control of local signal controllers.

Fig. 2 similarly illustrates a set of trafiic signals and associated local control apparatus in schematic form for one intersection, and in block diagram form for a second intersection along a highway or roadway, and the connections with the master control apparatus of Fig. l for a trafiio control system.

Fig. 3 illustrates in schematic form the local signal control apparatus for conection to the master control lines according to another embodiment of the invention, in which relays are employed for the respective individual green signal circuits for control of the connection and disconnection of the master variable frequency power and local fixed frequency power for operation of the local controller. I

Fig. 4 illustrates a schematic diagram of the local control apparatus as in Fig. 3 but according to another embodiment of the invention in which a relay is controlled by or operated in both of the yellow signal periods to control the connection and disconnection of master variable frequency power and local fixed frequency power for the local controller.

Fig. 5 illustrates a schematic diagram similar to Fig. 4 but according to another embodiment of the invention in which a relay controlled by or operated during both green signal periods serves to connect and disconnect master variable frequency power and local fixed frequency power for the local controller.

Fig. 6 illustrates still another chematic diagram in which direct circuits from cam operated contacts for Referring now to Fig. 1 in more detail the master control apparatus is illustrated as comprising two principal components shown in the broken line blocks VFG and MCU representing the variable frequency generator and the master cycle unit respectively, together with the several output lines or circuits VFL and VFR representing the variable frequency line and return respectively, and RSL and RSR respresenting the resynchronization line and return respectively.

A schematic circuit of one form of variable frequency generator is shown in the lefthand broken line block designated VFG, employing a series A. C. motor designated MM and an associated A. C. generator driven by the motor MM. The speed of the motor MM and the generator GN is varied by moving the top PV along the potentiometer PR. This variable potentiometer thus provides an adjustable controlling resistance in series with the motor circuit via the motor coil MM23, to vary 4 the speed of the motor and consequently the frequency of the output of SN from the brushes 1ll2 and along the variable frequency lines VFL and VFR. The fixed resistance FR is preferably included in series with PR and the motor circuit as a protective minimum res-istancef The adjustment of the potentiometer PV-PR may be made by moving the tap PV manually or by means of a time clock or other timing device, or by means of a trafiic actuated cycle selector or offset selector as in thc Patent 2,542,978 referred to above, either smoothly or by steps to one of several tap positions along the potentiometer PR, to vary the output frequency on the lines VFL and VFR.

It will be appreciated that while the motor-generator form of variable frequency generation is illustrated for simplicity an electronic variable frequency generator may be used if desired, such as the familiar audiofrequency generator employed in electric laboratories, in place of the motor-generator type of variable frequency generator shown.

The master cycle unit MCU includes an amplifier MA operated from the variable frequency line to repeat and amplify the variable frequency power to drive the master synchronous motor MSM to rotate the cams MCY and MCR. The cam MCY controls the switch MSCMSK- MSV to connect the motor MSM between variable frequency and fixed frequency power during different parts of the cycle, and the cam MGR controls the switch MSR to provide a cyclic resynchronization pulse over the lines RSL and RSR.

The amplifier MA has its input side connected via wires 13 and 14 to the variable frequency lines VFR and VFL respectively and has its output represented by the Wires 15 and 16. The wire 15 thus connects one side of the output of the amplifier to one terminal MSM3 of the operating coil of the motor MSM. The wire 16 on the other side of the output of the amplifier is connected to the switch contact MSV. The other side of the motor coil MSM2 is connected via wire 19 to the movable switch contact MSC, and the other switch contact MSK is connected to a fixed frequency power source indicated by the plus in a circle, which may for example be ordinary 60 cycle alternating current power.

As the motor MSM rotates, the corresponding rotation of cam MCY will connect the movable switch contact MSC to the contact MSK to apply the fixed frequency power to the motor coil MSM2 during a relatively small part of the total cycle of cam MCY. The cam and switch contacts are shown in Fig. l in this position, in which the contact MSV is separated from contact MSC to discon nect the motor MSM from the amplifier MA output at wire 16.

As indicated in Fig. 1 these circuits are maintained in this position for only a small part of the cycle corresponding approximately to the time of two yellow signal periods of the order of about 6 seconds total for example in one preferred embodiment of the invention. However, during the remainder of the cycle of cam MCY the movable contact MSC will be disconnected from contact MSK and connected to contact MSV, thus connecting the motor coil at MSM2 via MSV-MSC to the amplifier output line 16, to operate the motor MSM from the variable frequency power output of the amplifier repeating in amplified power form the frequency from the lines VFL and VFR, the motor MSM operating fast or slow in accordance with the frequency of the applied power. The cam MCR preferably closes the contacts MSR throughout all but avery small part of the total cycle. and opens the contacts MSR during this small part of the cycle, for example one or two seconds in length, so that power from one side of the power supply line indicated by the plus in a circle is connected to the resynchronization output line RSL during most of the cycle but is disconnected momentarily once per cycle for example. The return resynchronization line RSR is illustrated as connected to the oppositeside' of thepower supply as indicated by ther'ninus sign 'in a circle, whioh' also may be grounded as shown for example.

Referring now to Fig. 2 illustrating one form of'local control apparatus and associated traffic signal, the lines extending across the lower 'part of'this Fig. 2 and designated VFL, VFR, RSL, RSR are extensions of the correspondingly designated output lines to the rightdf Fig. 1, so that if the left side of Fig. 2 is connec'tedtothe right side of Fig. 1 a Complete master localcdhtrol system is illustrated. These master control lines at the bottomof Fig. 2 can beconsi'deredas extending along a highway or roadway for example common to several intersections having individual l-ocal control units and associated traffic signals. One local control unit, and includingo'ne set of ttaific'signals S for one atlic intersection, is illustrated schematically within the broken litre bloc'kdesignated LOU-1, and is shown connected to the master control lines way 'of the wires 21, 22, 23, and 2 A similar but smaller broken line biock'desigriated. LCUZ represents a second local control unit for a second intersection along the common roadway or highway, and including its traffic control signals, this second "unit 'LCU2 being similarly connected to the several master control lines as indicated.

' It will be appreciated that the general construction of thelocal control units LCUI and LCUZ may be the same but these units maybe adjusted for aditlerent proportioningof the green signal periods for the respective streets or in other words a dilferent distribution of the signal cycle for example as will be more fully explained below. The local control units may also "be adjusted for different relation of their'respectiv'e signal cycles to theresynchronization point controlled by the master cam MCR of Fig. l as more fully explained below.

The signal S in the upper part of Fig. 2 illustrates schematically the two sets of signals for a common form of trafic right-of-way signal for intersecting streets A and B torexample (not shown), including thered, yellow and :green signals AR, AY and AG respectively for street A and the red, yellow and green signals 1BR, BY and 'BG for street B. One side of all of these signals is connected to one side of an ordinary power supply as indicated by the minus sign in a circle, and the other side of the signals are connected respectively v by individual lines LAR, LAY and LAG and by lines LBR, L'BY and LBG to a local drum controller represented. by the solid block LDC. This local drum controller any be one of several well known types of which the most coinrnon is a set of cam operated switches an opening and closing the respective signal circuits as the cams are retated by a motor drive which may preferably be of the step=by-step type widely used in traffic signal controllers. One 'form of such step-bystep local drtim controller is illustrated in part in Fig. 3 for example. i

The power supply for the local drum controller and associated other apparatus is indicated schematically at the left of Fig. 2 with the power side of the line indicated by a plus in a circle and the grounded side of the line indicated by minus in a circle for example, which may represent an ordinary local 60 cycle alternating current power supply for example. The lead 20 at the lower side of the block LDC'indicates an actuating line for operating the drum controller {from one step to the next in its cycle under the control of the local dial switch unit LDl- LDSE operated by the local synchronous motor unit LSM. The same local synchronous motor LSM also drives the dial switch unit LDRLDS34 indicated below it in Fig. 2, which serves to resynchroniae the local dial switch assembly with the master cycle unit once per cycle.

In the form illustrated the dial switch unit LDS3- i is normally closed throughout most of the cyele of the rotary dial .LDR and associated rotary dial LD1, but the switch LDS3-4 is opened by the resynchronization pin RP illustrated in the lower leftquadrant of medial LDR, the pin RP deflecting the movable contact LDS3 as the dial LDR rotates through its cycle. This momentaryinterruption of the contacts LDS34 opens the circuit of the motor coil LM2LM3 of the local synchronous motor LSM via wire 27, thus stopping the motor LSM and its associated rotary dials LD1 and LDR until the resynchronizing release pulse is received via relay LRS from the master resynchronizing lines RSLRSR from the master controller.

If as is normally the case the local rotary dial assembly is substanti'allyin synchronism with'the master cycle unit MCU of Fig. 1 then the'local rotary dial assembly will be stopped only momentarily at this resynchronizing point since the cam MCR in the mastercontrol unit shown in Fig. 1 will then open the contacts MSR and thus cut olt power from theresynchronization line RSL, thus releasing momentarily the relay LRS which is connected across the lines RSL and 'RSR via wires 22 and 21. This momentary release of relay LRS causes its movable contact LRS3 to fallback so as to close with contact LRS4 to provide a shunt circuit around the open contact LDS3-LDS4, thus reclosing the circuit for the motorcoil LM2-LIVES to restart the motor LSM and the associated rotary dials in synchronism with the master'control unit.

As the local rotary dials then resume rotation the passage of the pin RP causes the reclosure of the contacts EDSZ'si so that as the master resynchronizingcontacts MSR are again closed by the continued rotation of h .ECR, and relay LRS is consequently again reenergized to reopen its contacts LRS34, the dial control contacts 'LDS3--4 maintain the dial motor circuit closed through the balance of the cycle. Although the circuit includes contacts of relays REY and RAY, the operation of the resynchronizing circuit as described, above is not appreciably affected by the position of either of these relays.

it .will be understood by those skilled in the art that braking means may be employed to stop the rotary dial motor LSM quickly so as to avoid coasting throughthe resynchronization position, and it will be also understood that the arrangement of the contacts LDS3-4 and LRS3-4 could readily be reversed so vthatthepin RP would close the dial switch contacts LDS3A--4, to close a motor brake coil circuit to stop the motor in opposition to a normal continuously energized driving coil,-in which case the relay contacts corresponding to 'LRS3-4 would then be arranged in series with LDS3-4 and the brake coil to be closed through most of the cycle. and opened only momentarily by the release of relayLRS to reopen the brake coil circuit to permit the rotary dial motor to proceed from the resynchronization position. In this latter alternative arrangement, the driving coil terminal LM2 would be directly connected to wire 29 and thus to RBY6 for example. i

The rotary dial LD1 in Fig. 2 is provided with several pins DP spaced in desired angular relation around the rotary dial to close the contacts LDS'l momentarily several times during each revolution of the rotary dial so as to operate the step-by-step controller LDC one step at a time for switching the signal circuits. These signal circuits are switched by the, drum controller through successive positions to providothe greenand the following yellowperiods for street A and then the green and following yellows signal periods for street B and to provide a red signal period for street olvefrlapping the A green and yellow periods and to ,provide a red signal period for streetA overlapping the B green and yellow periods respectively for example. i i

n win be appreciated that the dial LDl is sh wn its simplest form with four pins DP to providethe basic four steps of the cyclecomp'rising the two green lsig nal periods and the two yellow signal periods but mor pins could be provided in the rotary dial and more steps in the cycle of the drum controller so that each green signal period could overlap more than one position for example, as is well known in the art.

The angular distribution of the pins DP around the rotary dial determines the distribution of the total cycle among the green periods and yellow periods for any given constant speed of rotation of the dial, and determines the length of the green periods for any given setting of the frequency of the variable frequency power. Thus the pins DP may be set for a 60%40% split of the green periods at one local controller LCUl and may be set for a 50%50% split at another local controller LCU2, and these respective splits will be maintained at the respective controllers with a short cycle and short green periods of the variable frequency is set at a relatively high level and with a longer cycle and longer green periods if the variable frequency is set at a relatively low level, for example.

It will be appreciated that the starting point of the main street or A green signal for example in relation to the resynchronization point and the other signal controllers along the main street can be determined by the relative positions of the resynchronization pin RP and the pins DP determining the start of the main street or A green in cooperation with the drum controller. The length of time that the rotary dial unit travels from the resynchronization point controlled by pin RP to the beginning of the next following main street green is usually referred to as the offset for that controller or signal, and the pin RP is ordinarily located in one or the other of the green signal parts of the cycle to avoid having the rotary dial unit dwell in a yellow position until resynchronized if it should be out of step. The corresponding pin RP (not shown) in the other local controller unit LCUZ may be set the same as the pin RP in the unit LCUl to maintain the two controller units in synchronism, or the pins RP in the respective controller units may be set in different relative positions to the pins DP controlling the beginning of the main street or A green for example to maintain a predetermined desired phase relation between the controllers so that the beginning of the green at one will lag behind the beginning of the green at the other to allow for travel time along the main street between the controllers and associated signals for example.

The block indicating the drum controller LDC and its rotary dial assembly for operating and resynchronizing the drum controller as just described are shown enclosed in a broken line block designated LC since these components may be identified conveniently as an ordinary local signal controller for operating the signals S. However, outside of the broken line block LC representing the ordinary local controller and within the outer broken line block LCUl representing one complete local control unit, the relays RBY and RAY are added in accordance with one embodiment of the invention to control the operation of the local synchronous motor LSM of the rotary dial assembly to permit the rotary dial cycle to be lengthened or shortened, along with the respective green periods for the respective streets A and B, by remote control from the master controller over the lines VFL and VFR, while keeping the yellow signal periods substantially constant.

This is accomplished in the embodiment of the invention illustrated in Fig. 2 by interposing contacts of the relays RBY and RAY in the circuits of the coil LM2 LM3 of the roary dial motor LSM, these relays being operated in the respective yellow signal periods of the controller to connect the LM motor coil to local fixed frequency, such as for example the ordinary 6O cycle alternating current local power supply represented by the plus and the minus in circles. When neither of these relays RBY and RAY are operated, as for example in either of the green signal periods of the signal cycle, the contacts of these relays connect the motor coil LM2LM3 via wires 25 and 26 to the output side of the local amplifier LA, the input side of which is connected via wires 23 and 24 to the variable frequency lines VFLVFR to provide variable control of these green signal periods.

Considering these relays and their control circuits more specifically the relay RBY has its coil connected between the yellow signal power output wire LBY and the negative power terminal, and the relay RAY has its coil connected between the yellow signal power output wire LAY and the negative power terminal, the wires LAY and LBY serving to operate the respective signals AY and BY when power is applied in the respective yellow sig* nal of the drum controller LDC. The coil of the relay RBY controls the movable contacts RBY3 and RBY6 and the coil of the relay RAY controls the movable contacts RAYS and RAYG. These movable contacts are shown in their normal rest positions with the relays deenergized in Fig. 2.

With these relays RBY and RAY both deenergized as shown in Fig. 2, and also assuming that the pin RP is in the position shown in Fig. 2, the LSM motor coil LM2 will be connected via wire 27, LDS3-4, wire 29, normally closed contacts RBY6RBYS, normally closed contacts RAY6--RAY 8, and wire 25 to the output of the amplifier LA, and the other terminal LM3 of the motor coil will be connected via Wire 28, the normally closed contacts RBY3RBY5, the normally closed contacts RAY3-RAY5, and wire 26 to the other side of the output of the local amplifier LA. This local amplifier is a form of repeater amplifier for repeating and amplifying the variable frequency from the master control lines VFL-VFR to operate the local synchronous motor LSM of the rotary dial assembly.

It will be appreciated by those skilled in the art that although it would be possible to drive the several local controllers directly from variable frequency power supplied by the master controller, this would involve the transmission over the variable frequency lines of considerable amounts of current and would be inefficient from the view point of the size of the wires required to avoid excessive line losses. Thus in the preferred embodiment of the invention the variable frequency power supplied by the master controller on the lines VFL-VFR is of relatively low voltage and very small current, and the several amplifiers MA and LA serve to repeat and amplify the low power variable frequency to a substantial power variable frequency for operation of the several synchronous motors in the respective controllers. The output of the amplifiers is of suflicient voltage and current capacity to operate an ordinary small size synchronous motor of the type already familiar in rotary dial type traffic signal controllers, for example.

It is now assumed that the rotary dial assembly has rotated so that the local drum controller LDC is in the AY signal position. Power from LDC on wire LAY will operate the signal AY and also operate the relay RAY to open its normally closed contacts RAY3RAY5 and RAY6-RAY8 and to close its normally open contacts RAY3RAY4 and RAYd-RAYT Since the relay RBY is deenergized at this time, the only change in the circuit from that just described above, is that the motor terminal LM3 is now connected via wire 28 and RBY3RBY5 and RAY3RAY4 to the positive power terminal, and the wire 29 controlling the other motor coil terminal LM2 is connected via RBY6RBY8 and RAY6-RAY7 to the negative power terminal, these power terminals representing for example a fixed frequency local power supply such as 60 cycle alternating current.

Similarly if it is assumed that the rotary dial assembly is in another part of its cycle to operate the B yellow signal BY, the relay RBY will be operated from power on the line LBY which also operates the signal BY, and the relay contacts BY6 and RBY3 will be moved to interrupt the variable frequency connection for the motor coil LM2-LM3 and to close the fixed frequency connection signal circuits.

for this coil. These connections can be traced from the control wire 28 or" the coil terminal LM3 via the now closed contacts RBY3-RBY 4 to positive power, and from the wire 29 controlling the coil terminal LMZ as above described via the new closed contacts RBY6-RBY7 to the negative power terminal. It will be noted that in the respective yellow signal periods the operation of the respective relays RA Y and RBY interrupts the connection of the variable frequency power output of amplifier LA, by opening the contacts RAYS-RAYS and RAY6-RAY8 in the case of the relay RAY, and by the opening of the contacts RBYS-RBYS and RBY6RBY8 in the case of relay RBY.

Reviewing briefly the operation of the local controller under control of the master controller the local synchronous motor LSM, which controls the local signal cycle through theassociated rotary dial assembly and in turn through the local drum controller, is operated through the A green period and B green period of the local controller from the variable frequency power from the master control so that these two green signal periods can be shortenedor lengthened remotely from the master control, and this local synchronous motor LSM is operated from local fixed frequency power during the two yellow signal periods so that these periods may remain constant despite the wide variation in the cycle of the rotary dial as controlled by the master control.

The master control motor MSM is designed to beslightly slower than the local control motor LSM and thus to have the master controller complete its cycle on a slightly longer time period than the local controller, so that l the local controller will remain in synchronisrn by reaching its resynchronization point normally slightly before the master cam MCR reaches its resynchronization point, and the local controller will thus rest momentarily each cycle for the resynchronization pulse from the master controller. In order to assure that the master control cycle will approximate the local controlcycle however, although being slightly longer, over the entire range of the variable frequency power which may be of the order of cycles to 120 cycles for example, the cam MC Y in the master controller is set to open its contacts MSC-MSV and close its contacts MSC-MSK for a period of time approximating the total of the two yellow signal periods normally provided at the several local signal controllers, this period being ordinarily of the order of a total of 6 or 7 seconds for example, thus operating the master cycle motor MSM through a small part of its cycle on fixed frequency and through the remainder of its cycle on the same variable frequency power supplied to the local control motors.

Referring now to Fig. 3 another embodiment of the invention is illustrated schematically in which relays RAG and REG are provided, controlled by the respective green signal circuits to control the connection of the coil LM2-LM3 of the local synchronous motor LSM to the output of the local amplifier LA or to the fixed frequency local power. In Fig. 3 the local amplifier LA and the local synchronous motor LSM, the local resynchronization relay LRS and the local rotary dials LDR and LDl and their associated contacts are the same as inFig. 2 but with the rotary dials and associated contacts and the relay LSR slightly rearranged in position for convenience of illustration of the step-by-step ratchet drive for. the cams of the drum controller for operating the it is assumed that the upper orinput side of the local amplifier LA is connected to the variable frequency power line VFL and VFR as in Fig. 2 and that the coil of the relay LRS is similarly connected by leads shown in part in Fig. 3, to the resynchronization lines RSL and RSR as shown in Fig. 2.

In Fig. 3 the cams CAG, CAY, CBG and CBY are indicated schematically for the control of the respective signal contacts and signals AG, AY, BG, and BY, these cams being indicated by the horizontal Broken line as rotated by the ratchet wheel DWR, which -'in aim is rotated by the live pawl Ll under control of the solenoid DS, the dead pawl FP serving to prevent reverse rotation of the ratchet wheel and cam shaft. The solenoid DS is controlled by the wire 20 and rotary dial switch contact LDSl corresponding to those shown in Fig. 2, the solenoid DS being energized momentarily and then deenergized as each 'pin 'DP engages the contacts LDSl and passes by the contact. At each momentary energization and deenergizatio-n of solenoid DS for example the live pawl LP is pulled away from and reengages the ratchet wheel DRW, the return stroke by spring action moving the ratchet wheel one tooth or one step and thus rotating the cainsas shown.

Cams controlling the red signals AR and BR are not shown in Fig. 3 for simplicity of illustration, but it will be appreciated that the cam controlling the red signal BR would have periods overlapping the periods of cams CAG and CAY and close an associated pair of contacts for the signal BR throughout the periods of the signal AG and the following signal AY, and the cam for the signal AR would also correspondingly have a period overlapping the periods of the cams CBG and CAY to close an associated set of contacts throughout the periods of the signals BG and BY.

It will be noted in Fig. 3 that the relay RAG has an associated movable contact RAG3 and fixed contacts RAG4- and RAGS. Relay RBG has associated movable contacts RBG3 and RBG6 with an associated normally open contact RBG3 and a normally closed contact RBG7. As indicated from the position of the rotary dial H31 and the respective cams the cam shaftof the drum controller in Fig. 3 is illustrated in the A green signal period, in which the signal AG is operated, along with the signal BR (not shown in Fig. 3). Consequen tly the relay RAG is shown energized and the relay RBG shown deenergizedin Fig. 3. Thus the normally closed contacts RAG3-RAG5 are shown open and the normally open contacts RAG3'-RAG4 are shown closed in Fig. 3. The relay RBG is shown in its normal deenergized position. The coil of the relay RAG is operated from the line LAG energized from the now closed contact SAG connecting positive power to this line, the other side of the relay being connected to the return side of the power line or ground. The other cam controlled contacts illustrated for the signals AY, BG, and BY are shown open in the condition of operation of the signal AG assumed and illustrated.

Considering the control of the motor circuit by the contacts of the relays RAG and RBG in more detail it will be observed that in the embodiment of the invention in Fig. 3, the contact arrangement is somewhat different from that of Fig. 2, thus illustrating another possible circuit arrangement. output of the local amplifier LA at line 35 is connected via either the contacts LDSS-LDS l or the contacts LRS3-LRS4 as previously described in connection with the resynchronization, and via wire 3'7 directly to one: terminal LM2 of the motor coil of the motor LSM. The control of the motor by relays RAG, RBG is entire ly on the other side LMS of the motor coil. Thus terminal LM3 of the motor coil is connected via wire 38 and the now closed contact RAGS-RAG4 and wire as to the other side of the input of the amplifier LA. In the circuit as shown it is assumed that during the A green signal period the motor LSM is connected to be operated by the output of the amplifier LA, which is. the variable frequency power output.

If it is now assumed in connection with Fig. 3 that: the local controller has rotated to the B green signal position the cams will be rotated so that the contact SAG will be open and relay RAG deenergized and the contact SBG will be closedand the relay RBG consequently energized along with the signal BG (and the In Fig. 3 one side of thesignal AR not shown in Fig. 3). It will be noted that the signals AY and BY will not be energized by their associated cams and cam operated contacts in this now assumed condition of BG signal period. Thus with re lay RAG deenergized and relay RBG energized the motor coil terminal LM3 will be connected via wire 38 and the now closed contact RBG3-RBG4 to the wire 36 and the output of amplifier LA. It will be observed that although with the deenergization of relay RAG the contacts RAG3-RAG5 will be closed the contacts RBG6RBG7 will also be open so that the positive power of contact RBG7 is not connected to the motor coil LM at this time.

If it is now assumed that the controller has rotated to either one of the two yellow signal positions then neither of the green signal circuits will be operated by their associated cams and both relays RAG and RBG will consequently be deenergized. Under these conditions it will be observed that the motor coil terminal LM3 is connected via wire 38 the now closed contacts RAG3RAG5 and the now closed contacts RBG6 RBG7 to the positive terminal of the local fixed frequency power supply, the circuits via the other relay contacts and amplifier LA now being open. The left side of the output of amplifier LA is connected to the negative terminal of the local fixed frequency power, which is thus applied to motor coil terminal LM2 via wires 35, 37 and the resynchron-izing contacts. Thus in either of the yellow signal positions of the local signal controller the fixed frequency power supply will be connected to the motor circuit.

The rotary dial and ratchet drive assembly along with the resynchronization relay LRS are shown enclosed in a broken line block designated DD in Fig. 3, the motor LSM comprising its rotary element LM and the operating coil LM2LM3 being shown as outside of this block for convenience of illustration, the block DD be ing repeated in outline form only in the remaining Figs. 4, 5, and 6. in these remaining figures it will be understood that the internal components of the block DD may be as illustrated in Fig. 3 which can be conveniently referred to on the same sheet of drawings.

Referring now to Fig. 4 only one of the cams of the drum controller is shown in this figure as reference may readily be had to the signal cams and associated contacts and circuits for the signals AG, AY, BG, and BY in Fig. 3. Fig. 4 shows another embodiment of the invention in which the motor circuit of the motor LSM is controlled by a relay RY operated in common in the respective two yellow signal periods. In the embodiment of the invention an additional cam CY is provided on the drum controller with an associated cam operated switch which is closed in both of the yellow signal periods but open in the remaining signal periods of the cycle. The contacts SCY when closed connect positive power to the coil of the relay RY, the other side of this coil being connected to the negative or grounded side of the power line. It is assumed that in Fig. 4 the drum controller cam shaft is in the A green signal position and as illustrated therefore the contacts SCY are open and the relay RY deenergized so that its normally closed contacts RY3-RY5 are shown closed and its contacts RY3-RY4 are open. In this position, which is also representative of the B green position of the cycle, the motor coil at terminal LM3 is connected via wire 48, RY3-RY5 and wire 46 to the output of the local ampli fier LA, the other side of the output of the local amplifier being connected to the other side of motor LM2 via the wire 35, DD and wire 37, as illustrated in Fig. 3.

It will be appreciated in Fig. 4 that if the controller is in either of the yellow periods of its cycle however the cam CY would be turned so as to close the contacts SCY and consequently energize the relay RY. This will interrupt the circuit from amplifier LA to the motor coil by the opening of contacts RY3-RY5 and will close 12 the fixed frequency power supply circuit to the motor coil via the contact RY3-RY4 and wire 48 as will be obvious from the drawing.

Referring now to Fig. 5 another embodiment of the invention is illustrated showing the use of a relay RG common to both of the green signal periods to control the operation of the motor circuit of motor LSM, the latter motor circuit being connected to the output of the amplifier LA during the green periods connected to the 10- cal fixed frequency power supply during the remainder of the cycle, that is during the yellow signal periods. In Fig. 5 the cam CG is shown in one of the green signal periods with its associated contacts SCG closed to energize the coil of the relay RG. Thus normally closed contacts RG3RG5 are shown open in Fig. 5 and the normally open contacts RG3RG4 are shown closed. Thus during the green signal periods the output of the amplifier LA is connected via wire 56 and the closed contacts RG4RG3 to the wire 58 and the motor coil terminal LM3, the other side of the motor coil LM2 being connected via wire 37 and the block DD and wire 35 to the opposite side of the output of the amplifier LA.

It will be obvious in Fig. 5 that during both of the yellow signal periods the contact SCG will be open as the cam CG is turned for these periods and the relay RG will consequently be deenergized so that the motor coil will be disconnected at the open contact RG3-RG4 from the output of the amplifier LA and will be connected via the closed contact of RG3RG5 to the positive terminal of the local fixed frequency power supply.

Fig. 6 illustrates still another embodiment of the invention in which the connections between the motor coil and the local amplifier or the local fixed frequency power supply are controlled directly by cam operated contacts in the local controller. In Fig. 6 the cams CY and CG are illustrated as operated by the rotary dial and ratchet assembly DD with the contact SCY associated with CY open and the contact SCG associated with CG closed, illustrating the position of the local controller in one of the green signal periods. Thus in the position illustrated as shown in Fig. 6 the motor coil terminal LM3 is connected via wire 68 and closed contact SCG and wire 66 to the output of the local amplifier, the other side of the motor coil being connected directly to the amplifier via DD as described above in connection with Fig. 3. At this time the motor coil is disconnected from the local power supply by the open contact SCY. It will be observed however that as the cams CY and CG rotate to either of the two yellow positions the contact SCG will be opened and the contact SCY will be closed in both of the yellow positions so as to open the connection between the motor and the local amplifier and close the circuit from the motor direct to the positive terminal of the local fixed frequency power supply.

It will be appreciated that in Figs. 3, 4, 5 and 6 the lefthand side of the output of the amplifier is connected at all times to the negative terminal of the local power in the form of the circuits illustrated in these figures, for providing a return circuit for the fixed frequency power connection. However, it will be appreciated that the connection between this side of the local amplifier output and the terminal LM2 of the motor may also be interrupted and separated from the local power supply and negative terminal by additional relay or cam operated contacts, along the lines of the interruption of both sides of the motor circuit as illustrated in Fig. 2, in which case the connection of wire 35 to negative power is unnecessary.

It will also be appreciated that the two contacts SCY and SCG could be combined into a single set of con tacts with the outer contact SCY combined with the inner contact of SCG and connected to wire 68 as shown in Fig. 6, the outer contacts remaining connected as shown in Fig. 6 but the combined inner contact being operated by cam CY to switch the motor terminal LM3 and wire 68 between wire 66 and positive power of fixed frequency in lieu of the separate contacts and the associated cams CY and CG as shown in Fig. 6. Thus this alternative arrangement would comprise the substitution of a single pole double throw switch for the two alternately operated single pole single throw switches SCY and SCG of Fig. 6. Another way of considering this alternative arrangement would be the direct operation of the movable contact RY3 to control its associated contacts KY4 and KY5 of Fig. 4 directly by the cam CY instead of through the intermediate relay RY and contacts SGY.

It will be understood that the drum unit DD may be resynchronized cyclically with therotary dial unit LD1 LDR by means of cooperating additional drum and dial pin control contacts as is well known in the art.

For simplicity of illustration in Figs. 2 and 3 for example the normal drum advance contacts LDSil and the resynchronization contacts LDS2i-4 are shown operated by separate rotary dials LDl and LDR respectively rotatedin synchronism by the synchronous motor LSM. it will be understood however that these two rotary dial units may be combined. into one rotary dial unit, if desired, with the pin RP longer than the pins DP and with the dial contacts arranged so that LDSl is operated by the pins DP only and LDS3 is operated by the pin RP only, as is common practice in well known types of rotary dial traffic signal controllers.

It will be appreciated that the green signal display period may overlap the yellow signal display period in some traflic control systems by overlapping cam arrangements as is well known .in the art, but the green and yellow overlap period then would be considered the clearance period and the green alone would be considered the go or true green period.

It will beappreciated also by those skilled in the art that the switching between variable frequency and fixed frequency power in accordance with the invention may be on the input side of the amplifier LA or MA for example instead of on the .output side as shown in the several figures of the drawings but with similar circuits and with a voltage matching transformer interposed where the voltage of the variable frequency power is different from that of the fixed frequency power.

It will be understood that the frequency of the variable frequency power as the term is used herein is variable in the sense that it may .be adjusted as desired for remote control of the green signal parts of the cycle or total cycle for example but such frequency may remain at some desired constant value for a considerable period of time, such as for one or several signal cycles for example and may then be changed to another constant value for a further period of time, but the frequency of the variable frequency power may also be changed if desired at any time during the cycle.

As previously pointed out the master cycle unit preferably has a slightly longer time cycle than the local rotary dial cycle control units for cyclic resynchronization. This may be accomplished by the employment of a slightly larger gear reduction for the master cycle unit than for the local dial units, where these units are driven conventionally by the respective synchronous motors through gearing, for example. As an alternative arrangement however, it will be appreciated that the fixed frequency supply of the master control unit MCU connected by MSK may have a lower frequency than the local fixed frequency to insure a slightly longer master cycle.

Although a number of alternate forms or arrangements of apparatus according to the invention have been pointed out above, it will be obvious to those skilled in the art that other modifications of the apparatus or of the arrangement or character of its parts may be made without departing from the spirit of the invention within the scope of the claims.

I claim:

1. A trafiic control system for interfering trafiic lanes including right-of-way signals for the respective lanes, clearance signals for the respective lanes, cyclicswitch means for operating the respective right-of-way signals in succession and for operating the respective clearance signals between the respective successive right-of-way signal operations, synchronous motor drive means for operating said cyclic switch means through its cycle, a remotely controlled variable frequency circuit means for operating said synchronous motor at varying speeds in accordance with varying frequency on said circuit means when connected, a fixed frequency circuit means, and further switch means cooperating with said cyclic switch means for connecting said variable frequency circuit means to operate said synchronous motor driving means during the right-of-way signal operating parts of such cycle and for connecting said fixed frequency circuit means to operate said synchronous motor during the clearance signal operating parts of such cycle.

2. A trafi'ic signal controller including two sets of signal circuits for go signals and clearance signals for two interfering traflic lanes, a cyclic switch unit having a cycle of operation for the go and clearance signal circuits for one set followed by the go and clearance signal circuits for the other set of signals, a frequency responsive driving means for said cyclic switch for operating the latter at variable time rates in response to variations in frequency, a variable frequency source for said driving means, a fixed frequency source for said driving means, and switch means controlled by said cyclic switch for operatively connecting said driving means to said variable frequency source during a part of its cycle and to the fixed frequency source during another part of its cycle.

3. Atraific signal controller including two sets of signal circuits for go signals and clearance signals for two interfering traffic lanes, a cyclic switch unit having a cycle of operation forthe go and clearance signal circuits for one set followed by the go and clearance signal circuits for the other set, when operating, a frequency responsive driving means for said cyclic switch for operating the latter at variable time rates in response to variations in frequency, a variable frequency source for said driving means, a fixed frequency source for said driving means, and switch means controlled by said cyclic switch means for operatively connecting said driving means to said variable frequency source during the go signal parts of the cycle and to said fixed frequency source during the clearance signal parts of the cycle.

4. in .a traffic signal control system, a. signal circuit controller having a cycle of operation, a frequency re sponsive driving means including a syncl'ironons motor for operating said controller at variable speed in accordance with variable frequency, a variable frequency alternating current power circuit, a fixed frequency alternating current power source, and switch means operated by said controller in its cycle to operatively connect said variable frequency power circuit to said synchronous motor driving means during a part of the cycle and to connect said fixed frequency power source to said driving means during another part of the cycle and remote control means for varying the frequency of said variable frequency circuit.

5. in a traffic signal control system, a signal circuit controller having a cycle of operation, a frequency responsive driving means for operating said controller at variable time rates in accordance with variable frequency, a variable frequency power circuit, a fixed frequency power source, switch means operated by said controller in its cycle to operatively connect said variable frequency power circuit to said driving means during a part of the cycle and to connect said fixed frequency power source to said driving means during another part of the cycle, and remote control means for varying the frequency of said variable frequency power circuit.

6. In a traffic control system, a fixed frequency power supply, a variable frequency power supply, a traflic signal controller having a cycle of positions through which it is adapted to be operated for control of a traffic signal at variable time rates in accordance with variable frequency input to the controller; said cycle including a position for operating a first go signal, a following position for operating a first clearance signal, a following position for operating a second go signal and a following position for operating a second clearance signal, and means controlled by said controller in its cycle of operation to connect said variable frequency power supply as input to said controller during the go signal operating positions of said cycle and to connect said fixed frequency power supply as input to said controller during the clearance signal operating positions of said cycle.

7. In a tratfic control. system, a master control unit having a variable frequency power generator, means for varying the frequency output of said generator, a fixed frequency power source, a cyclic controller operable at variable time rates through its cycle in accordance with variations of 'requency applied to operate it, and switch means controlled by said cyclic controller in its cycle to apply the variable frequency output of said generator to operate said controller during a major part of its cycle and to apply said fixed frequency power from said power source to operate said controller through a minor part of its cycle; a local signal controller having a cycle of operation for traffic signal control, a frequency responsive driving means for said local controller, and switch means operated by said local controller in its cycle to operativcly connect the variable frequency power from said master control unit to said driving means during the major part of said last named cycle and to operatively connect a corresponding fixed frequency source to said driving means during a corresponding minor part of said last named cycle, and means for cyclically resynchronizing the local controller cycle with the master controller cycle.

8. In a trafic control system, a master control unit having a variable frequency power generator, means for varying the frequency output of said generator, a fixed frequency power source, a cyclic controller operable at variable time rates through its cycle in accordance with variations of frequency applied to operate it, and switch means controlled by said cyclic controller in its cycle to apply the variable frequency output of said generator to operate said controller during the major part of its cycle and to apply said fixed frequency power from said power source to operate said controller through a minor part of its cycle; a local signal controller having a cycle of operation for traffic signal control, a frequency responsive driving means for said local controller, and switch means operated by said local controller in its cycle to operatively connect the variable frequency power from said master control unit to said driving means during the major part of said last named cycle and to operatively connect a corresponding fixed frequency source to said driving means during a corresponding minor part of said last named cycle, said local controller being operated by its frequency responsive driving means through its cycle in a slightly shorter time than said master cyclic controller and means controlled cooperatively by said master controller and said local controller for cyclically resynchronizing the local controller cycle with the master controller cycle by causing the local controller to dwell in part of each cycle until the master controller reaches the corresponding point in. its cycle.

9. in a trafiic control system of the master-local type, a master control unit having a variable frequency power generator, means for varying the frequency output of said generator, 21 fixed frequency power source, a cyclic controller operable at variable time rates through its cycle in accordance with variations of frequency applied to operate it, and switch means controlled by said cyclic controller in its cycle to apply the variable frequency output of said generator to operate said controller dur ing a major part of its cycle and to apply the fixed frequency power from said power source to operate said controller through a minor part of its cycle; a local signal controller having a cycle of operation for traffic signal control including a phase for traffic right-of-way followed by traffic clearance and a second phase for other traffic right-of-way followed by other traffic clearance, a frequency responsive driving means for said local controller, and switch means operated by said local controller in its cycle to connect the variable frequency power from said master control unit to said driving means during the said right-of-way parts of said last named cycle and to connect a fixed frequency source corresponding to the first mentioned fixed frequency source to said driving means during the traffic clearance parts of said last named cycle, said major part of the first named cyclic controller cycle corresponding with the right-of-way parts of the local controller cycle and the minor part of the first named cyclic controller cycle corresponding with the traflic clearance parts of the local controller cycle, means including other switch means controlled by the first named cyclic controller in the master control unit and further switch means operated by said local con troller in the cycle of the latter and interconnecting circuit means cooperating to interrupt temporarily the operation of the local controller once per cycle until the master controller arrives at a corresponding predetermined point in the master control cycle for cyclically resynchronizing the local controller cycle with the master controller cycle.

10. A traffic signal controller including output circuits for a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cyclic switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, and relay means operated by said clearance signal circuits to connect said fixed frequency circuit to said driving means during operation of said clearance signal circuits and to connect said variable frequency circuit to said driving means during operation of said go signal circuits during said cycle of operation.

11. A traffic signal controller including output circuits for a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cyclic switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, and relay means controlled by said go signal circuits to connect said variable frequency circuit to and disconnect said fixed frequency circuit from said driving means during operation of said go signal circuits and to connect said fixed frequency circuit to and disconnect said variable frequency circuit from said driving means during operation of said clearance signal circuits.

12. A traffic signal controller including output circuits for a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cyclic switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, switch means operated by said cyclic switch unit in both of the clearance signal circuit operating periods only in said cycle, and relay means operated by such operation of said switch means to connect said fixed frequency circuit to and disconnect said variable frequency circuit from said driving means during said clearance periods and to connect said variable frequency circuit to and disconnect said fixed frequency circuit from said driving means during the remaining signal operating periods in said cycle.

13. A traffic signal controller including output circuits for a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cyclic switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, switch means operated by said cyclic switch unit in both of the go signal circuit operating periods only in said cycle, and relay means operated by such operation of said switch means to connect said variable frequency circuit to and disconnect said fixed frequency circuit from said driving means during said go periods and to connect said fixed frequency circuit to and disconnect said variable frequency circuit from said driving means during the remaining clearance signal operating periods in said cycle.

14. A trafiic signal controller including output circuits for a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cycle switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, switch means operated by said cyclic switch unit in both of the go signal circuit operating periods only in said cycle for connecting said variable frequency circuit to said driving means during said go periods only, and additional switch means operated by said cyclic switch unit in both of the clearance signal periods only in said cycle to connect said fixed frequency circuit to said driving means only in said clearance periods.

15. A trafiic signal controller including output circuitsfor a first go signal, a first clearance signal, a second go signal and a second clearance signal, a cyclic switch unit having a cycle of operation for the several signal circuits in sequence respectively when operating, a frequency responsive driving means for operating said cyclic switch unit at variable time rates in response to variations in frequency respectively, a variable frequency input circuit for said driving means, a fixed frequency input circuit for said driving means, and relay means controlled by said signal circuits to connect said fixed frequency circuit to said driving means during operation of the respective clearance signal circuits and to connect said variable frequency circuit to said driving means during operation of the respective go signal circuits.

16. In a trafiic control system, a first frequency source, a second frequency source, a signal circuit controller having a cycle of operating positions including a plurality of right-of-way signal circuit positions and following clearance signal circuit positions, a rotary dial cycle distribution unit for operating said signal circuit controller through its cycle of positions and having actuating elements therefor arranged in adjustable angular relationship for determining the proportions of its total cycle allocated to the respective right-of-way periods and respective clearance periods for any predetermined speed of rotation of said rotary dial unit, a synchronous motor for driving said rotary dial unit at a speed substantially proportional to the frequency input thereto, switch means controlled by said signal circuit controller for connecting said first frequency source to said synchronous motor in said rightof-way signal positions and for connecting said second frequency source to said synchronous motor in said clearance positions, and remote controlmeans for varying the frequency of said first frequency source to vary the speed of said synchronous motor to vary the length of the rightof-way periods while the relative proportions of the respective right-of-way signal periods to each other is maintained as determined by said relationship of said actuating elements on said rotary dial unit and the length of the clearance periods is independently maintained by said second frequency source and the relationship of the actuating elements of said rotary dial unit.

17. In a traffic control system of the master-local control type, a first frequency supply circuit; a second frequency supply circuit; a plurality of local signal circuit controllers each having a cycle of operating positions including a plurality of right-of-way signal circuit positions and following clearance circuit positions, a rotary dial cycle distribution unit having actuating elements arranged in adjustable angular relationship for operating said signal circuit controller through its cycle of positions and determining the proportions of its total cycle allocated to the respective right-of-way periods and clearance periods for any predetermined speed of rotation of said rotary dial unit, a synchronous motor for driving said rotary dial unit at a speed substantially proportional to the frequency input thereto, switching means controlled by said signal circuit controller for connecting said firstfrequency supply circuit to said synchronous motor in said right-of-way signal positions and for connecting said second frequency supply circuit to said synchronous motor in said clearance positions, and a further actuating element and associated switch means in said rotary dial unit for interrupting the rotation thereof at any desired part of its cycle of operation in desired relationship to one of the respective right-ofiway periods, all associated With and individual to each local signal circuit controller; a master controller including means for varying the frequency of the first frequency supply circuit, a master cyclic switch unit operable through its cycle at a speed substantially proportional to frequency input thereto and having switch means for connecting the input of the cyclic switch unit to a frequency source of substantially the same frequency as said second frequency supply circuit for a part of its cycle approximating the total time of the said clearance periods and for connecting the input of the cyclic switch unit to said first frequency supply circuit during substantially the remainder of its cycle, and further switch means operated by said cyclic switch unit in a predetermined part of the cycle of the latter for restarting rotation of the several local rotary dial units in synchronism cyclically with the cyclic switch unit in the master controller.

References Cited in the file of this patent UNITED STATES PATENTS

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