Establishment of Ideal Saturation Flow Rate for Intersection Level of Service Analysis for Washington DC

Saturation flow rate (SFR) measures the maximum rate of flow of traffic in specific lane groups on the approach to signalized intersections. SFR is used extensively in the analysis and design of signalized intersections, and is a factor in the level of service analyses for signalized intersections. SFR depends on several roadway and traffic conditions (parking, lane configuration, lane width, presence of heavy vehicles, traffic behavior, number of lanes, traffic volumes, approach grade, etc.). Most jurisdictions use default values for SFR, built into traffic operations software programs and often do not provide guidelines for selecting SFR for specific conditions at intersections. However, the use of inappropriate SFR values leads to poor estimation of the average vehicle delays, thereby leading to erroneous level of service (LOS) reporting. Due to the sensitivity of the effect on the LOS of a signalized intersection with modest changes in the value of the SFR, a number of jurisdictions (Pennsylvania, Delaware, and others) have conducted studies to determine an "average" or representative SFR value for their respective areas. This research is intended to establish an appropriate SFR for use by traffic operations engineers at the District Department of Transportation (and consultants) in the conduct of LOS analysis for all signalized intersections in Washington, DC.