Modelling the saturation flow rate for continuous flow intersections based on field collected data

The continuous flow intersection [CFI) is an unconventional intersection design which has been used in many cities all over the world. However, as an important parameter for the geometric design, signal timing, and operation evaluation, the saturation flow rate at CFI has not been carefully examined. In this paper, a saturation flow rate adjustment model for CFI intersections is established based on field data under the calculation framework of the HCM2016. Four movements related with CFI, namely the left-turn at the CFI approach, through movement at the CFI approach, left-turn at the pre-signal, and exit movement at the pre-signal, are discussed. The proposed model is validated and the relative error is less than 10%. The treatments to mitigate the negative impact on the saturation flow rate at the CFI are also recommended. The results show the saturation flow rate of the first three movements are decreased due to the CFI control. For the left-turn, through movement, and left-turn at the pre-signal, the degree of the reduction of the saturation flow rate are mainly related to the heavy vehicle ratio, the proportion of lane changing vehicles, and the length of displaced left-turn lanes, respectively.