Saturation Flow Models of Exit Lanes for Left-Turn Intersections

Abstract

A newly proposed unconventional intersection design, exit lanes for left-turn (EFL) intersections, has been demonstrated to be very promising for capacity improvement. However, the difference in saturation flow rates at EFL intersections compared with conventional intersections and the influencing factors remain unknown. In this paper, a saturation flow rate adjustment model for EFL control is developed and calibrated based on field data. Five influencing factors, namely the median opening blockage, demand starvation, multilane interference, conflict with opposing vehicles, and lane changing, are considered. The accuracy of the model is validated using nonparametric tests. Results show that the reduction in saturation flow rate for the normal approach left-turn lanes, the left-turn lanes in the mixed-use area, and the left-turn lane at the prestop line caused by EFL control are 6%, 31%, and 19%, respectively. The key impact factors for the saturation flow rate at the main-stop line and the prestop line are the demand starvation (16% reduction) and lane changing (16% reduction), respectively. This research provides guidelines for planning, design, and operation of EFL intersections to prevent negative effects while retaining their efficiency.