Abstract: The purpose of this paper is to study the saturation flow rate and its adjustment factors which is the basis of estimating the signalized intersection capacity.Based on the field data,the passenger car equivalences are calculated using the time headway method,which is adopted to analyze the effect of different type vehicles on the saturation flow rates.In order to determine the effect of lane width on the saturation flow rate,a regression model is developed and the adjustment factor for lane width is obtained.The approach grade effect on the saturation flow rate is studied and the adjustment factor for approach grade is provided.The multiple regression method is used to analyze the right-turn vehicle effect on the through-turn shared lane saturation flow rate and the adjustment factor for right turn is suggested.