Various control algorithms process vehicle detector on / off times with the objective ofquantifying split performance. Two such metrics are: Green Occupancy Ratio (GOR)and Volume to Capacity (v/c) ratio, both of which can be used to estimate the efficiencyof a split as well as estimate oversaturated conditions. The GOR metric is attractivebecause of its simplicity of implementation, whereas the v/c ratio is based upon wellestablished traffic flow concepts and is independent of detector geometry, though itrequires additional processing to develop the metric. Characterizing the impact ofdetection zone length and vehicle speed on the GOR as well as comparing itsperformance with another metric is important to understanding the robustness of GORas a surrogate performance metric. This paper analyzes the difference betweencalculated GOR and V/C ratios over different detection zone lengths and differingvehicle speeds, compares these values to a calculated delay metric, and observes theeffectiveness of GOR as an indicator of oversaturation. Based upon the analysis, thepaper documents the influence of approach speed and detection zone length on thecalculated GOR metric. The paper concludes that the GOR values tend to reach asaturated value of 1.0 more rapidly than v/c, making it challenging for the analyst toidentify oversaturated conditions by the metric alone. For practitioners using the GORmetric, it is critical that the system be calibrated properly due to the sensitivity of GOR tothe detection zone length and vehicle speed. However, since direct measurement of v/cis difficult to obtain, GOR may still be a reasonable surrogate in real-time performanceassessment of traffic signal systems.
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