Determining effects on saturation flow rate during longer cycle lengths.

摘要

Traffic signal timing is one of the most important tasks being faced by traffic engineers in the United States. Saturation flow is a key input for optimal signal timing. A small variation in saturation flow values could affect changes in cycle length and duration of green time for a particular phase. This could have an impact on the efficiency of an intersection thereby affecting operations on an urban street system. A great deal of research has been done on estimating saturation values, taking into account prevailing conditions at signalized intersections. Various methods exist for determining saturation flow by observing queues of vehicles at the intersection and determining their respective headways, but little research has been carried out to evaluate the impact of longer green periods on saturation flow. A couple of studies have suggested that there is a decrease in saturation flow after about 30 to 40 seconds of green. This thesis examines the impact on saturation flow at signalized intersection approaches in the Dallas/Fort Worth metropolitan area with longer greens, and its potential significance to the concept of saturation flow at signalized intersections.; Five signalized intersection approaches in the Dallas/Fort Worth metropolitan area were studied to determine the impact of longer greens on saturation headway and flow. A comprehensive data analysis estimated the saturation headway and flow values. Headways were observed for different queue positions including and excluding the impact of heavy vehicles. Analysis of the data did not indicate a significant impact of longer green time when compared to the expected values. One signalized intersection approach showed an increase in headway after about 60 seconds of green time. But, this result was not significant in concluding the impact of longer green times on vehicle headways.