Evaluation of displaced left-turn intersections

Abstract

Displaced left-turn intersections (DLTs) are designed to enhance the operational performance of conventional intersections that are congested due to heavy left-turn traffic volumes by excluding the left-turn movements at the main intersection. This results in reducing the number of potential conflict points and increasing the intersection capacity. However, since drivers are not familiar with DLTs’ operation, there is a need to assess the safety and operational efficiency of this type of intersections. This paper evaluates the safety performance of DLTs using two common methods, which are a before-and-after study with comparison group and cross-sectional analysis. Furthermore, it investigates the operational performance of DLTs using a general linear model describing the relationship between a selected measure of performance and other operational and geometric characteristics based on high-resolution traffic data. The safety analysis indicates that DLTs can increase crash frequency in comparison to conventional intersections. In addition, the operational analysis implies that DLTs have the potential to reduce the delay at intersections. Consequently, evaluation of the different aspects of costs and benefits were conducted to decide if this alternative design is appropriate for implementation. The study concludes that DLTs have negative safety impacts in comparison to conventional intersections for many crash types, but it might be more efficient for operational performance. It is recommended that appropriate safety countermeasures should be developed and implemented to enhance traffic safety at DLTs.