Dynamic extraction method of saturation flow rate at signalized intersection

The dynamic extraction method of saturation flow rate by using induction coil detector was proposed. Taking the time difference of the front vehicle and the following vehicle when departing from an induction coil detector as headway, the average saturation headway from the fourth vehicle to the last vehicle in saturation state was calculated. The average saturation headways of history and current cycle were dealt with exponential smoothing method. Thresholds for judging vehicle type and saturation headway were determined. When the occupation time of a vehicle was more than twice of the average occupation time of small vehicle, the vehicle was judged as large vehicle. The threshold of saturation headway for small vehicle was historical average saturation headway adding 1 s, and that of large vehicle was historical average saturation headway adding 5 s. The validity of the proposed method was testified by using software VISSIM. Simulation result indicates that the dynamic extraction method can reduce the sudden change influence of saturation headway. When the saturation headway suddenly decreases by 31.3% in current cycle, the saturation flow rate only increases by 5.6%, and the saturation flow rates in 5 cycles are 1 782, 1 682, 1 600, 1 690, 1 773 veh·h^-1 respectively, nevertheless, the rate of HCM model is 1 680 veh·h^-1. Compared with the traditional methods, the method meets the demand of dynamic extraction, and the implementation of the method is low-cost.