Patent GB-450602-A (GB)
Title: Improvements in road traffic control systems
IPC: G08G1/082
Filed: 1935-01-16
Abstract: 450,602. Road signals for controlling traffic. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO., Ltd., Caxton House, Tothill Street, DOWNES, F. A., Central House, Kingsway, MARTIN, N. H., 3, Fairfax Road, Hampstead, RIDDLE, H. J. N., Central House, Kingsway, and TYACK, F. G., 21, King William Street, Greenwich, all in London. Jan. 16, 1935, No. 1496. [Class 118 (ii)] In a vehicle-controlled road traffic control system in which " green-wave " working along a highway is provided, a master controller transmits pulses to each slave controller to ensure right-of-way is available for the main road when required, the arrival of the pulses preceding the arrival of " green-wave " traffic by a period of time equal to or greater than the minimum green period, demands for transfer of the right-of-way to the cross-road being ineffective for a predetermined time after the receipt of the pulse. A second pulse may be transmitted to ensure transfer of right-of-way to the cross-road at least once during each cycle, whilst if more than two roads meet at an intersection three or more pulses may be transmitted to ensure all roads having a rightof-way period. The system provides for " greenwave " working in both directions and on both main and cross streets. The master controller is arranged to adjust cycle time with traffic flow. Specification 408,706 is referred to. Fig. 1 indicates a time and distance diagram for progressively controlled traffic passing in both directions along the main street which is shown on the left of the Figure. The bands 1 represent groups of traffic passing up and down the main road and at each intersection the main road " green " and " red " periods are indicated by strips 2 and 3 respectively. In the first diagram the cycle time is 50 seconds and the speed 15 miles per hour, whilst the second diagram indicates a 75 second cycle with a 10 m.p.h. speed. Part of the apparatus provided at Eagle St., which is progressively controlled in both directions, is shown in Fig. 3, whilst an operating cycle of the relays is indicated by Fig. 2. Right-of-way is required on the main road right-of-way from time 4 to 5, Fig. 2, and to ensure this a pulse is transmitted at time 6. This pulse initiates timing of a prevent period 6-4 and a privilege period 4-5. At time 7 a second pulse is received which initiates transfer of right-of-way from the main road. If the cross-road traffic is progressively controlled the " B " pulse is followed by " prevent " and " privilege " periods for the cross-road. Otherwise this pulse is used only to ensure transfer of right-of-way once in a cycle, the prevent and privilege periods being abbreviated to values of less than a second. Under normal conditions the pads " A " and " B " which are in the " main " and " cross " roads respectively are connected to relays RW and DE. When the first or " A " pulse is received relay PA, which operates only when its two windings are energized in opposition, pulls up. Whilst PA is energized condensers QK and QND are charged to an extent dependent on the period of operation of the relay and consequently on the length of the " A " pulse. Relays PE, PJ and PK pull up. When the pulse ends relay PA falls away and relays PF and PG energize. If, as shown, right-of-way is with the main road, the road pad B is disconnected from the demand relay DE and connected to storage relay PL which locks up if the pad B is operated. Pad A is still connected to the right-of-way relay RW. If right-of-way is with the cross-road, contacts RC are reversed and vehicles on the cross-street can hold right-of-way by continued depression of pad B whilst demands on the main road energize relay DE to initiate transfer if a break in the cross-road traffic should occur. Condenser QND is now connected in a discharge circuit and begins to measure off the " prevent " period. When this period has elapsed, condenser QND is sufficiently discharged to allow lamp FP to strike and relay PC to operate. Relay PD pulls up and opens the circuit of relays PE and PF. Relay PE drops at once, but relay PF, by means of its slow-release lug, holds up until relay PD falls away so that the circuit of relay PG is not broken. If right-of-way is with the main road at this stage no transfer is made, but if it is with the cross-road, relay DE is energized at once if contacts 12 are closed or if the contacts 12 are open when the pad A is next operated and the maximum green timer (not shown), is operated so that right - of - way is transferred to the main road. Condenser QK is now connected to lamp FP and to the discharge circuit and the privilege period, during which rightof-way is held on the main road, is timed. At the end of this period relays PC and PD are again energized and relay PG releases. As the initial charges on both condensers QND and QK are dependent on the length of the " A " pulse, the length of this pulse determines the length of both the " prevent " and " privilege " periods. The release of relay PG reconnects pad B to demand relay DE and disconnects relay PL, but if this relay has been energized by a demand on the cross-road during the prevent or privilege periods, relay DE is energized from PL1 during the slow period of relay PL. The apparatus is now in condition for the first vehicle controlled period so that the crossroad can obtain right-of-way if a gap occurs in the main road traffic or if the maximum green period expires. As relay PK is still energized, the direction of current flow in the polar winding of relay PA is reversed so that when the " B " pulse, which is in the opposite direction to the " A" pulse, is received relay PA is again energized. Condensers QK and QND are again energized and the cycle detailed above is repeated except that the periods are for the cross, and not the main, road. If the crossroad is progressively controlled the prevent and privilege periods are such as to ensure normal progression of the cross-road traffic. Otherwise these periods are abbreviated to values of less than one second by discharging the condensers through very small resistances. A master controller is indicated in Fig. 4. Twenty-five keys 13 and 14 are provided for each intersection and these control the points in the cycle at which " A " and " B " pulses are respectively transmitted. One key in each of groups 13 and 14 is operated for each intersection. The cycle is divided into twenty-five periods each of which is measured by the pulse space timer comprising condenser QNA, lamp P and relay P. The condenser is charged over PA2 and then discharged slowly over lead 15 until the lamp strikes and the relay P energizes to operate relay PA. Relay PA pulls up and falls away slowly, condenser QNA being charged whilst relay PA is up so that the cycle is repeated indefinitely. The resistance over which QNA discharges is varied, as described later, with traffic flow to adjust the cycle time. The units and multiplying relay chains SE-SDA, SJA-SK count the operations of relay PA and contacts of these relays mark the leads 24-48 in turn so that the relays such as AP1, BP1 are energized at those times in the cycle determined by the operated keys 13 and 14. Relay PQ is energized when relay PA operated and relay PMR pulls up when relay PA falls away. Relay PMR connects negative and positive to any outgoing pulse wires, the positive being connected by means of a condenser, which have been connected up by the operation of their BP1 or AP1 relays. Relay PMR also allows the pulse timer comprising condenser QNB, lamp P1 and relay P1 to start functioning. When the relay P1 energizes, relay PQ falls away and relay PMR releases to remove the pulse from the line. The time of operation of the pulse timer is controlled by a resistance connected over lead 16 which is adjusted in accordance with traffic flow, as will be described later, so that the pulse length, and consequently the prevent and privilege periods of the slave controllers, can be adjusted. The apparatus for adjusting the timer resistances with traffic flow is indicated in Fig. 5. The adjustment is made in accordance with traffic flowing during five-minute periods, the periods being marked off by a one-minute pulse generator TP, QNE and a relay counter circuit CA-CD, the relay CX being operated at the end of each five-minute period. During these periods vehicles operating road pads A and B at a selected intersection energize relays AT and BT so that relays CR and CS are energized for each axle passing over either pad. Contacts of relay CR energize relay BR whilst those of relay CS close the charge circuit of condenser QND which circuit is opened when relay BR pulls up. Relay BR is arranged to operate with a slight lag so that the charge on condenser QND is the same for each pad operation. When a predetermined number of vehicles have passed condenser QND is sufficiently charged to allow relay TC to operate and counting switch C is stepped once. Condenser QND is discharged and the count of the pad operations continues. At the expiration of a five-minute period relay CX is operated as mentioned above and switch C is in a position corresponding to the traffic flow. If switch S is in a position other than that marked by switch C or one contact below this position, relay DS is energized and switch S is stepped. If switch S is set below switch C, wiper S6 reaches a contact marked by wiper C4 and relay T operates to release relay DS and stop the switch. If the setting of switch C is below switch S, the switch S must be stepped through its positions 23 and 24. In these positions relay SP is energized to transfer control from wiper S6 to wiper S4, stepping being stopped when wipers S4 finds the marked contact. The contacts wiped by wiper S6 are connected to the contacts next below that of those wiped by wiper C4 and the contacts associated with wiper S4 are connected to those next above, so that switch S is set to the position next to the