Comparison of Delay Time Models for Over-Saturated Traffic Flow Conditions at Signalized Intersections

Ghasemlou, Kiarash; Aydın, Metin Mutlu; Yıldırım, Mehmet Sinan · 2015 · Crossref

DOI: 10.14257/ijast.2015.84.02

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Summary

This paper addresses the challenge of accurately estimating vehicle delay at signalized intersections operating under over-saturated traffic conditions, where traffic demand exceeds road capacity. Delay is a critical parameter for determining Level of Service (LOS) and optimizing signal timing to improve fuel economy and travel time. The authors note that existing deterministic and steady-state models are inadequate for over-saturated conditions, as they either predict infinite delay or zero delay at saturation points. Consequently, the study focuses on comparing various time-dependent analytical models and empirical models to evaluate their usability and effectiveness, with a specific interest in comparing performance between models developed in Turkey and Iran to account for potential differences in driver behavior and modal approaches. The methodology involves a comparative analysis of five distinct delay models: the Highway Capacity Manual (HCM) model, models by Akçelik, Akgöngör and Bullen, Akgöngör, and an empirical model by Nassiri and Nadernejad. The authors detail the mathematical structures of these models, which generally decompose total delay into uniform delay, over-saturated flow delay (comprising random and continuous components), and initial delay. The empirical model by Nassiri and Nadernejad was derived from regression analysis of video-recorded data from intersections with saturation degrees greater than one. The comparison utilized specific input parameters, including a 0.25-hour analysis duration, 500 veh/hr capacity, 1500 veh/hr saturated flow, and a degree of saturation of 1.7, to generate delay estimates for evaluation. The results indicate that the empirical model proposed by Nassiri and Nadernejad yields delay estimates similar to those produced by the HCM and Akçelik models. The analysis revealed that the coefficient 'a' in the Nassiri and Nadernejad model approximates the duration coefficient found in time-dependent models, suggesting it accurately describes continuous saturated delay. However, the study found that the Nassiri and Nadernejad model failed to calculate delays for saturation degrees exceeding 1.7. Furthermore, the comparison showed that performance properties and resulting delay times were nearly identical across the different models, despite variations in driver characteristics and regional contexts between Iran and Turkey. The significance of this study lies in its conclusion that signal duration and the similarity of traffic control systems are more influential factors in delay estimation than driver behavior or regional differences. The findings suggest that existing time-dependent models, particularly those aligned with HCM and Akçelik, are robust for estimating delays in over-saturated conditions across different regions. This implies that transportation engineers can rely on these established analytical frameworks for signal timing optimization and LOS estimation without needing region-specific adjustments for driver behavior, provided the signal timing parameters are accurately accounted for.

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