A NEW DELAY PARAMETER DEPENDENT ON VARIABLE ANALYSIS PERIODS AT SIGNALIZED INTERSECTIONS. PART 2: VALIDATION AND APPLICATION

Akgüngör, Ali Payidar · 2008 · Crossref

DOI: 10.3846/1648-4142.2008.23.91-94

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Summary

This study validates a new delay parameter model for signalized intersections, specifically addressing variable demand, time periods, and oversaturated traffic conditions. The research aims to test the performance of the analytical model proposed in Part 1 of this series, which utilizes a time-dependent variable delay parameter rather than a constant one. The motivation stems from the need to evaluate complex traffic strategies and validate analytical models against microscopic simulation data, as obtaining comprehensive field validation for numerous scenarios is often impractical. The validation was conducted using the TRAF-NETSIM microscopic simulation program, part of the TSIS suite. The experimental design involved a simulated intersection with one lane per approach, major approach link lengths of 4000 feet, and minor approach lengths of 3000 feet. The simulation utilized a 90-second cycle length with a green time ratio of 30/50 for minor and major approaches, respectively. To reflect real-world variability, the 60-minute simulation period was divided into three phases: a 5-minute initialization period (degree of saturation 0.7), an analysis period with oversaturated conditions (degrees of saturation ranging from 1.1 to 1.4) and varying durations (5 to 30 minutes), and a dissipation period (degrees of saturation 0.5 or 0.7). This design created 48 distinct scenarios, each replicated 10 times with different random seeds to account for stochastic traffic arrivals, resulting in 480 simulation runs and 960 data points. The results demonstrated a strong correlation between the delays estimated by the proposed model and those generated by the simulation. Linear regression analysis yielded a coefficient of determination ($R^2$) of 0.989 at a 95% confidence level after excluding outliers associated with extreme oversaturation (30-minute analysis period with a degree of saturation of 1.4). The proposed model’s delay estimates ranged from 47 to 388 seconds per vehicle, closely matching the simulated delays, which ranged from 45 to 348 seconds per vehicle. The study found that changes in the degree of saturation during the dissipation period had no significant effect on average delay, provided the arrival flow remained below capacity. The significance of this work lies in confirming the proposed model as a reliable tool for estimating delays at signalized intersections under varying flow and time conditions. The findings suggest that using a time-dependent variable delay parameter provides more realistic estimations than constant parameters, particularly as analysis periods lengthen. While the study validates the model for oversaturated conditions, it notes that future research should incorporate field data and investigate unsaturated conditions and vehicle-actuated signal controls to fully assess the model's effectiveness.

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