Signal Timing and Coordination Strategies Under Varying Traffic Demands
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Signal Timing and Coordination Strategies Under Varying Traffic Demands

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English

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  • TRIS Online Accession Number:
    01651578
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    Final Report
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  • Abstract:
    Current practice for signal timing and signal coordination is to develop and operate a limited number of predetermined time-of-day plans. Coordination plans are commonly developed for and based on weekday morning, mid-day, evening, and weekend peak periods. During the remaining time periods signals are operating either in fully/semi-actuated modes or fixed modes. Engineers often face a dilemma to decide when signals should be coordinated. Numerous studies have been conducted to develop practical guidelines by considering volume, signal spacing, platoon dispersion, and signal timing parameters. Although some guidelines recognize the need of coordination when traffic demand is high, none of them explicitly quantifies the term “high”. Therefore, most decisions are still made based on engineering judgment. This project aims at developing more quantitative guidelines. One of the most significant benefits of signal coordination is the reduction of number of stops which has received less attention in previous studies. For instance, none of the developed guidelines define stop thresholds when determining signal coordination. This research specifically focuses on this aspect. First, a probabilistic model that predicts the expected number of stops on non-coordinated arterials was developed. The model is a function of the effective green to the cycle length (??/??) ratio that considers the effect of traffic demand and capacity indirectly. It is also assumed that vehicle arrival is random which deems reasonable when demand is low in actuated operational mode. The model was validated through VISSIM simulation of a real signalized arterial, Sparks Blvd. in Sparks, Nevada. The results confirmed that the model was highly reliable in estimating the number of stops. Based on the probabilistic model, a practical signal timing guideline was developed according to the percentage of stops on non-coordinated arterials. The guideline states that: 1) If the percentage of stops along a non-coordinated arterial exceeds 50, coordination is recommended for the arterial; 2) If the percentage of stops along a non-coordinated arterial is 20 or lower, an actuated operation is recommended for the arterial; and 3) If the percentage of stops falls between 20 and 50, an engineering judgment should be applied to decide whether to coordination is necessary. Finally, a case study was conducted to demonstrate the application of the guideline. The same Sparks Blvd. arterial was used in the case study but with various traffic demand conditions. The case study confirmed the practicality of the guideline.
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