INVESTIGATION OF SATURATION FLOW RATES IN NEBRASKA. FINAL REPORT

Saturation flow rate at signalized intersections is defined as the rate of flow that can pass through a given intersection approach or lane group under prevailing traffic and roadway conditions, assuming that the approach or lane group had 100% of real time available as effective green time. The saturation flow rate is an important parameter in the capacity analyses and signal timing of at-grade intersections. The main purpose of this study was to investigate the validity and adaptability of the base saturation flow rate of 1800 passenger cars per hour of green per lane (pcphgpl), that is suggested by the 1985 Highway Capacity Manual, in the state of Nebraska. The results of the study showed that there is a high degree of variability among the saturation flow rates that were obtained from six cities in the state of Nebraska. This finding is consistent with other research results that were reported in the literature. Because of the high degree of variability of saturation flow rates, the study concluded that the direct measurement of this parameter is necessary in order to assure the accuracy of the capacity analyses and signal timing at certain intersections. However, under budgetary and time constraints, the base saturation flow rates of 1939 pcphgpl for straight through, 2146 pcphgpl for exclusive left turn, and 1964 pcphgpl for exclusive right turn lanes, which were obtained in this study, can be used as a substitute for directly-measured values in the state of Nebraska. All these values are higher than the base saturation flow rate of 1800 pcphgpl which was recommended by the 1985 Highway Capacity Manual.