Estimating saturation flow rates at signalized intersections in Japan

The capacity calculations for signalized intersections have not been reexamined in Japan for a long time. The base value and adjustment factors are out of date, but these are still used nowadays. However, in the United States, these values have been reconsidered with each revision of the Highway Capacity Manual. Through comparisons of actual observations with studies conducted in Japan and internationally, this study identified problems in the Japanese method for calculating the saturation flow rate. As a result, the base value of through lanes in Japan is higher than that in the USA, while the measured value tended to decrease over the years. Therefore, the base value must be reconsidered. In addition, we use recent observational data in Japan to examine the adjustment factors for the influence of heavy vehicles and the probability of a right turn. Finally, we propose future research subjects.