KENTİÇİ KARAYOLU AĞLARINDA IŞIK SÜRELERİ DİKKATE ALINARAK YEDEK KAPASİTENİN ENİYİLENMESİ OPTIMIZATION OF RESERVE CAPACITY IN URBAN ROAD NETWORKS BASED ON TRAFFIC SIGNAL TIMINGS

BAŞKAN, Özgür; OZAN, Cenk; CEYLAN, Hüseyin · 2019 · Crossref

DOI: 10.21923/jesd.459055

archive: archived pipeline: cataloged verified

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Summary

This study addresses the problem of maximizing reserve capacity in urban road networks to mitigate traffic congestion without requiring expensive infrastructure investments such as road widening or lane additions. The authors argue that local governments can alleviate economic, social, and environmental issues associated with congestion by optimizing traffic signal timings. The core research question involves determining the maximum Origin-Destination (O-D) demand multiplier that a network can support without exceeding link capacities, thereby identifying unused "reserve" capacity caused by suboptimal signal settings. To solve this non-convex optimization problem, the researchers developed a bi-level programming model. At the upper level, the model maximizes the O-D demand multiplier. At the lower level, it solves the traffic assignment problem using Stochastic User Equilibrium (SUE) to represent driver behavior. The solution algorithm utilizes the Harmony Search (HS) optimization method for the upper-level decisions, specifically optimizing signal timings and the demand multiplier. For the lower-level traffic assignment, the Route Choice Algorithm (RAT) is employed, which is based on a logit route choice model and avoids the need for explicit route enumeration. A penalty function is incorporated into the objective function to ensure that equilibrium link flows do not exceed their respective capacities. The proposed model was tested on the Allsop & Charlesworth test network, a standard benchmark in transportation literature consisting of six signalized intersections, 23 links, and 14 green time variables. The baseline total hourly travel demand was 4,920 vehicles. The analysis used specific parameters, including a minimum phase green time of 7 seconds, cycle lengths between 36 and 120 seconds, and an inter-green time of 5 seconds. The results demonstrated that by optimizing signal timings, the O-D matrix could be increased by approximately 16% without exceeding the capacity of any link in the network. Table 4 in the paper details the resulting link flows and saturation degrees, showing that several links reached high saturation levels (e.g., Link 21 at 98% and Link 20 at 97%) under the optimized conditions, confirming the network was pushed to its maximum reserve capacity. The significance of this work lies in providing a computationally efficient method for urban planners to identify and utilize existing reserve capacity through signal optimization rather than costly physical infrastructure changes. By integrating Harmony Search with SUE traffic assignment via the RAT algorithm, the study offers a robust tool for enhancing network reliability against demand fluctuations. The findings suggest that proper signal timing can significantly increase the throughput of urban road networks, offering a cost-effective strategy for managing traffic congestion and improving overall transportation system performance.

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• traffic density