Signal Coordination for a Two-way Street Network with Oversaturated Intersections

This paper presents an algorithm to solve signal coordination problem on two-way arterial networks with oversaturated intersections. A discrete-time signal coordination model is formulated as a dynamic optimization problem and solved using Genetic Algorithms (GA). The concept of ideal offsets to dissipate queue for the primary and opposing directions and the relationship between the two offsets are developed. When queue in the primary direction is dissipated and, thus offsets can be positive and can potentially provide forward traffic progression, the processes of queue dissipation can be made for the opposing traffic. Thus, releasing queue in the opposing direction is made provided that the process of queue dissipation in the primary direction has been made. A hypothetical arterial network with 10 signals is used for model validation and to demonstrate the implementation of signal coordination with various queue dissipation schemes. The microscopic simulation software, CORSIM, is used to validate the signal coordination model. Some features of the model must be relaxed for the validation since CORSIM cannot simulate traffic-responsive signal timings. The outcome of validation is desirable. Depending on the scheme of queue dissipation process (one or two ways) and the position of critical signals, the algorithm intelligently generates optimal signal timing. The critical signals are those serving two or more competing coordinated movements. For a scheme with one-way directional traffic progression and with balanced flows, the algorithm confirms the notion that traffic progression should start from the critical intersection and move in the direction of coordinated movements. For a scheme with two-way directional progression and with unbalanced flows, the algorithm also confirms that queue can be dissipated in both directions with ideal offsets attained earlier in the primary direction and later in the opposing direction.