Effect of Bicycles on the Saturation Flow Rate of Turning Vehicles at Signalized Intersections

This paper studies the effect of bicycles on intersection operations for those intersections where bicycle traffic causes the most disturbances to vehicular traffic. By studying different states of bicycles crossing a signalized intersection, this paper divides the conflicts between bicycles and turning vehicles into multiple stages and models the saturation flow rate of turning vehicles under the bicycles’ influence for each stage. For right-turn vehicles, in the first stage, previously queued turning vehicles and bicycles are released at the onset of green, and right-turn vehicles are blocked by through bicycles; in the second stage, bicycles arriving at the intersection randomly after initial queues are discharged, and gap acceptance consideration is used to analyze the conflict between the right-turn vehicles and bicycles to obtain the saturation flow reduction factor for right-turn vehicles. In the first stage, left-turn vehicles wait while the opposing through vehicles discharge from the queue; in the second-stage, the left-turn vehicles cross opposing randomly arriving vehicular flow and may be blocked by the bicycles in queue discharge mode and in the third stage, left-turn vehicles cross randomly arriving opposing through bicycles. The saturation flow rates of right-turn and left-turn vehicles under the bicycles’ influence are modeled considering differences in these stages. The model results are compared with real-world observations and show a better match than those from the Highway Capacity Manual (HCM) model. The results of this study can supplement the content of the signalized intersection capacity analysis method in the HCM and provide the basis for design of intersection signal timing and capacity calculation under mixed traffic conditions at signalized intersections.