Operational evaluation of partial crossover displaced left-turn (XDL) versus full XDL intersections

With increasing traffic and limited resources, the Florida Department of Transportation (FDOT) moves forward with a vision of optimizing intersection control using innovative intersection designs through the Transportation Systems Management & Operations (TSM&O) program. These alternative designs successfully eliminate the left-turn phase, which otherwise reduces the conventional intersection’s (CI) efficiency considerably. This paper focused on the Crossover Displaced Left-turn intersections (XDL), also known as Continuous Flow Intersections (CFI). The XDL concept is best suited for intersections with heavy or unbalanced traffic volumes. There is little guidance on determining whether partial XDL intersections are adequate to mitigate the overall intersection condition or full XDL is always required. The primary objective of this paper was to evaluate the overall intersection performance in the case of different partial XDL designs compared to a full XDL. The study intersection in Orlando, Florida, is experiencing two heavy conflicting movements operating near capacity. The XDL alternative was investigated for 4 different designs. Also, the impact of increasing volume on the intersection performance was considered by modeling the unbalanced volumes with 10% increment resulting in 5 different traffic scenarios. The results showed that a partial XDL alternative proved to be effective and compared favorably to a full XDL. Significant throughput improvements were observed in the XDL scenarios at the higher volume level with increase in capacity of 25%, 30-45% reduction in delay for the critical movements, and 25-40% reduction in queue lengths. The analysis revealed how partial XDL design can improve the overall intersection performance at various demands, reduce the costs associated with full XDL and proved to outperform the conventional intersection. However, partial XDL serving low volumes or only one of the critical movements while other critical movements are operating near or above capacity do not provide significant benefits when compared to the conventional intersection.