Saturation Flow and Capacity of Shared Permissive Left‐Turn Lane

Abstract

Capacity analysis is an essential task in the planning and design of signalized intersections. This task becomes difficult to perform satisfactorily when shared permissive left‐turn lanes are present. A shared permissive left‐turn lane allows opposed left‐turn vehicles and vehicles of other directional movements to proceed into the intersection when signal operation enters a permissive left‐turn phase. Because the vehicular movement in such a lane during a green interval may not be continuous, modeling the saturation flow and capacity of a shared left‐turn lane is a complex matter. Existing models are inadequate. To address this problem, an improved model is developed. This model provides logical explanations of the causal relationships between the capactiy, as well as ther saturation flow, of a shared left‐turn lane and a number of governing variables. The governing variables include number of opposing lanes, opposing flow rate, proportion of left turns in opposing lanes, proportion of left turns in shared lane, flow rate in the lane adjacent to the shared lane, proportion of opposing vehicles arriving in red interval, cycle length, green interval, and signal change interval.