Study on Saturation Flow Rate and its Influencing Factors at Signalized Intersections Under Hetrogenous Traffic Condition (The Case of Addis Ababa)

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Addis Ababa University


In Addis Ababa signalized intersections are the most important and common bottleneck locations because the functional traffic signals are inadequate to the job of handling current traffic levels and poor traffic management strategies. To mitigate capacity-related problems at signalized intersections appropriate allocation of traffic signal timing and providing effective management of signalized intersections have great importance. The saturation flow is the most important design parameter for traffic signal timing and performance evaluation of signalized intersections. In different cities, various studies have been done to evaluate the saturation flow rate under homogeneous traffic conditions and estimate it only for through movements. However, until now no sufficient study has been conducted on the saturation flow rate at signalized intersections in the case of Addis Ababa for different lane groups under heterogeneous traffic conditions. Therefore the major objective of this research was to determine prevailing Saturation Flow Rate for specific lane groups at signalized intersections during peak hours the case of Addis Ababa, Ethiopia. The lane groups considered were an exclusive left lane, shared left and through lanes, through only lane, and shared through plus right lanes. Using video recording technique data were collected from 24 approaches of six signalized intersections and HCM 2010 standard procedure was followed in the data collection, extraction, and analysis processes. The results of the study indicate that both in the morning and afternoon peak hours the highest mean prevailing saturation flow rate was found for the through lane group, while the lowest was to be determined for the exclusive left lane. Generally, the overall mean prevailing saturation flow rate appropriate for Addis Ababa signalized intersections are 1462 vehicles per hour per lane for exclusive left lane, 1446 vehicles per hour per lane for shared left and through lane, 1542 vehicles per hour per lane for through lane movement and 1492 vehicles per hour per lane for through plus right lane. Those prevailing SFRs can be used as input for planning, design, operation, and analyses of signalized intersections in Addis Ababa. It was determined from ANOVA analysis there was a significant statistical difference between four types of lanes in the morning and afternoon peak hour at 5% significance level. Independent sample t-test shows that there is a statistically significant difference between saturation flow rate values of the lane groups considered in this research.



Saturation Flow Rate, Hetrogenous Traffic Condition, Signalized Intersections, Addis Ababa