Patent GB-1039534-A (GB)
Title: Improvements in and relating to traffic control systems
IPC: G08G1/07
Filed: 1963-05-24
Abstract: 1,039,534. Road traffic signalling apparatus; electric analogue calculating. GENERAL SIGNAL CORPORATION. May 24, 1963 [July 5, 1962], No. 20819/63. Headings G4G and G4Q. Access to a freeway from a ramp, Fig. 1, is controlled by vehicle detectors A, B, C, in association with signals 10, and signs 11, 12, the timing of the signals being in accordance with the occupancy of the freeway as determined by detector A. With occupancy greater than 30%, the signals 10 show a continuous red, and further entry of vehicles into the ramp is prevented by the illuminations of " no entry " signs 11, 12. These signs are only extinguished when the occupancy falls below 25% and detector C records no vehicle. The detector B prevents a continuous red signal from being given as long as vehicles are present in the access road. The output from detector A is fed to a number of switching circuits 22 ... 25, Fig. 2, each of which operates at a predetermined lane occupancy to control, via the dial unit 29 and cam unit 34, the relative red and green signal periods presented to traffic in the approach road. Further switching circuits 37, 38 associated with detectors B, C respectively are interlocked with the gates 24, 25 so that once lit by detector C or A the no entry signs 11, 12 remain lit as long as switches 37 or 34 are actuated. In a first modification, Fig. 3 (not shown), a separate detector A, A<1>, A<11>, Fig. 1, is associated with each lane of the freeway and the resulting outputs are summed before application to the switching circuits 22 . . . 25. In a second modification, Fig. 5 (not shown), the speed of traffic is measured instead of lane occupancy. In a further modification, Fig. 6 (not shown), individual occupancy detectors A, A<1>, A<11> (Fig. 1) are associated with each lane of the freeway, and their outputs summed before being fed to the switching circuits. Alternatively parameters other than occupancy or speed can be used for ramp control. For example, the regularity of vehicle spacing may be computed to produce an analogue signal which varies from a first limit with random spacing to a second limit with uniform spacing. Control system. Figs. 4A, 4B, 4C, 4D (not shown). With the output from detector A indicating less than 15% occupancy relays 76, 77, 78, 79 are all energized, so that closure of one of the continually driven cam switches 30, 31 or 32 will operate solenoid 123 to switch the lights to a green phase. As occupancy rises to 15À20% relay 76 releases and the next closure of cam contact 28 energized 123 to switch lights to yellow. Cam switch 33 closes 3 seconds later to switch to red and the next closure of cam switch 30 switches back to green, the cycle repeating with a 15-second red and a 42-second green sequence. A rise in occupancy to 20-25% releases relay 77 as well and the red phase persists until cam switch 31 closes, giving a longer red phase. Similarly with 25-30% occupancy relay 78 also releases and the red phase is terminated by cam switch 32. If the occupancy increases above 30% relay 79 also releases and a continuous red signal is given unless a vehicle is detected by detector B, in this case relay 110 operates, giving an alternative supply path to cam switch 32 to ensure a 12-second green period. Relay 79 releasing energizes relay 89 to light the ramp closed signs 11, 12. If the ramp fills, detector C release relay 120 also energizing relay 89, lighting the ramp full signs 11, 12. Once energized, relay 89 locks in until relay 110 releases and the occupancy detected by detector A is less than 25%. Gap regularity computer, Fig. 7. Relay SR is a slow-release repeater relay for detection relay D. During a gap between vehicles, relays D and SR are both released, and amplifier 130 integrates, the charge rate for capacitor 131 depending on the output V3 from amplifier 133. During the time period between relay D releasing and relay SR releasing, the output V1 from amplifier 130 is an analogue of the preceding time gap, and is fed to averaging amplifier 135 the output from which is substantially constant and is an analogue of the average gap duration. This average is compared with a reference voltage in summing amplifier 133 and the difference fed back to control the charge time of capacitor 131. Output V1 is also fed to a further summing amplifier 142, the output V4 from which is an analogue of the deviation of the gap duration from average. V4 is fed to amplifier 14 to produce an inverted signal VS and whichever of the two signals V4, V5 is negative is fed through diode 151 or 152 to averaging amplifier 154 to produce an output V7, which varies from zero volts with randoms gap to 100V. with regular gaps.