Geometric Models to Calculate Left-Turn Sight Distance for Signalized Intersections on Horizontal Curves

Abstract

At signalized intersections where protected left turn signals are not provided, simultaneous opposing left-turn vehicles may cause insufficient sight distance for each other. There is a lack of literature presenting left-turn sight distance analysis at intersections located on curved highways. In this paper, sight distance calculation models focusing on curved-approach intersections were developed for left-turn maneuvers toward the outside of the curve and toward the inside of the curve, separately. Using those models, it was found that, for left-turn maneuvers toward the outside of the curve, opposing left-turn vehicles might cause serious sight distance problems even for a 3.7-m median. However, for a left-turn maneuver toward the inside of the curve, the curve may mitigate the sight distance problem and the median width plays a more important role in the available sight distance, especially when the curve radius is relatively large. The models and related analyses can be used to lay out intersection design or evaluate the sight distance problem of an existing intersection located on the horizontal curve to ensure safe left-turn maneuvers by drivers.