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A simple adaptive signal control algorithm for isolated intersections using time-space diagrams

Traffic signals are the main devices for controlling traffic to guarantee the safe crossing of opposing streams of vehicles and pedestrians. In this study, a simple cycle and split optimization method is developed for isolated intersections. The split optimization is based on the notion of minimizing delay per cycle while cycle length is adjusted according to the residual queues at the end of the cycle. Traffic dynamics at signalized intersections are represented on time-space diagrams using the shockwave theory and information from detectors installed upstream of intersections. Splits are incrementally adjusted so that the delay per cycle is gradually diminished. Cycles are modified to have an efficient use of the provided green times without causing the residual queues. Unlike most algorithms, the proposed method can manage traffic even when queues extend beyond detector locations. Simulation experiments on a two-one-way intersection with different demand scenarios are performed to demonstrate efficiency of the developed algorithm. Hypothesis tests are conducted to statistically verify the efficient comparison between the proposed method and the Webster formula. It is found that in case of fixed demand the proposed method can optimize splits and cycle lengths with no worse performance measures than the optimal fixed-time signal settings according to the Webster formula. For the variable demand case, the result indicates that the algorithm can adjust splits and cycle lengths in response to the change of demand and provides better performance measures than the Webster formula.