Patent GB-1375813-A (GB)
IPC: G08G1/08
Filed: 1973-03-21
Abstract: 1375813 Traffic signal control systems IBM UNITED KINGDOM Ltd 21 March 1973 13480/73 Heading G4Q A traffic control system (Fig. 1) comprises a central control unit 15 connected to control traffic signals 1-3 in accordance with stored data representing a model of the road network, said model comprising data representing predicted vehicle arrivals at the intersections and data representing traffic signal timings calculated in accordance with the predicted arrivals, the system also including vehicle sensors 7-12 coupled to the control unit 15 to provide data to update continuously the predicted arrival data in accordance with the number of vehicles sensed, the control unit 15 being operable in response to the updated data to re-calculate the timing data and thereby to modify the timing of the phases of the traffic signals. As shown, the signals 1-3 are controlled by local controllers 4-6 each of which operates from a time clock wheel to control signal timing in a fixed pattern. The controllers 4-6 receive command signals from the central control unit 15 to modify the patterns as required by sensed traffic conditions. The local controllers 4-6 provide output signals to the control unit 15 to indicate the phases of their associated signals 1-3. Each sensor 7-12, positioned at the inlet to a section of road leading to a signal 1-3, may be loop or ultrasonic type which indicates vehicle passage and area occupancy to give data on queue formation. The sensors may be coupled to the control unit 15 via telephone line pairs, multiplex line links or radio links and the input and output units of the control unit 15 will be appropriately constructed to handle the data. The stored traffic model is similar to the TRANSYT model described in Road Research Report LR253 prepared by the Road Research Laboratory. On the basis of the model, the central control unit 15 calculates and stores the expected vehicle arrivals at a traffic signal set, while counts effected by the sensors 7-12 replace the predicted data to continuously update the latter to improve the model by matching it more nearly to actual traffic patterns. The optimizer unit of the central control unit 15 operates on the model data until minimum traffic delays are obtained and applies new timing data to a signal setting control unit. The latter supplies feedback to up-date the signal timing data of the model. The number of vehicles in a queue and the waiting time can be calculated to determine the alteration of light timings subject to certain restraints such as minimum green periods or priority for particular lanes, e.g. public transport or emergency service lanes. Preferential treatment for a particular traffic flow can be given by weighting the appropriate data before optimization. The process of optimization includes adjustments of splits, offsets and cycle times until queues and delays are optimized. A full description of this process is given. The central control unit (Fig. 6) comprises input unit 31 which includes a plurality of accumulators connected, to the sensors 7-12, the outputs thereof being transferred to a store 35 each time the accumulators are sequentially reset from a program unit 32. The model is inserted in store 35 in a plurality of areas thereof which also store predicted signal timings. Program unit 32 addresses the store 35 area-by-area so as to replace data in the areas by counts from unit 31. Signal changes are controlled by an output unit 40 comprising a respective shift register for each traffic signal set. Optimization occurs in arithmetic and logic unit 36 coupled to three input registers 37-39.