Modeling for Left-Lane Line Extensions at Signalized Intersections with Permitted Left-Turning Phase

Abstract

At a signalized intersection with a permitted left-turning phase, left-turning and opposing through vehicles always compete for priority according to actual traffic conditions instead of following strict priority rules. It is a critical cause of safety challenges. To alleviate the problem, this article develops a working model to determine the form of left-lane line extensions. In the proposed model, left-lane line extensions were approximated as a combination of (1) straight lines, and (2) circular curves and straight lines. In addition, they were constrained by the entering point, exiting point, and controlling point. As a result, a left-turning vehicle traveling along left-lane line extensions would be forced to yield the right-of-way to opposing through streams. Additionally, the location of the left-lane stop line was also optimized to meet the demand of left-lane line extensions. On this basis, a recommended application procedure was further introduced to make it easy for traffic engineers to use. Finally, three case studies with different intersection geometries were conducted in Changchun, China, to demonstrate the effectiveness of the proposed model. The proposed models are valuable because they could provide a guideline on designing left-lane line extensions and also help to make intersections safer.