Saturation flow rate is defined as the maximum flow rate assuming that the green phase is always available to the approach. This is the basis for analyzing the capacity of signalized inter sections, the traffic signal timings, evaluation of intersection performance. Accordingly, the saturation flow rate has to be preceded before planning, designing, operating the signalized intersections. U.S. Highway Capacity Manual, Canadian Capacity Guide for Signalized Intersections and Australian Road Research Board propose various methods for measuring the saturation flow rate. However, these existing approaches define the saturation ambiguously and have difficulties in putting into practice. The purpose of this study is to solve the problems of defining and measuring the saturation flow rate by using cumulative throughput and to propose a simple method for measuring the saturation flow rate by lane operating which could reasonably account for reality.